From 474cd6b1c7dc7b8f338d914ec89bc79f0fbe9361 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Mon, 21 Dec 2020 20:58:11 +0100
Subject: [PATCH 01/21] Improve Qt handling in CMake

Support 3 options:

	* VIRCADIA_USE_SYSTEM_QT is set -- use system's Qt
	* VIRCADIA_QT_PATH is set -- use Qt found in that dir
	* Otherwise -- use downloaded Qt package

This removes these variables:
	* VIRCADIA_USE_QT_VERSION
	* VIRCADIA_USE_PREBUILT_QT
	* HIFI_QT_BASE
---
 cmake/macros/SetupQt.cmake                    |  14 +++
 hifi_qt.py                                    | 100 +++++++++++++++---
 interface/CMakeLists.txt                      |  32 +++---
 .../src/controllers/UserInputMapper.cpp       |   4 +
 tools/nitpick/CMakeLists.txt                  |   2 +-
 tools/skeleton-dump/src/SkeletonDumpApp.cpp   |   5 +
 6 files changed, 126 insertions(+), 31 deletions(-)

diff --git a/cmake/macros/SetupQt.cmake b/cmake/macros/SetupQt.cmake
index 6f31a3994c..35a22ecb4d 100644
--- a/cmake/macros/SetupQt.cmake
+++ b/cmake/macros/SetupQt.cmake
@@ -25,6 +25,9 @@ function(calculate_qt5_version result _QT_DIR)
     set(_QT_CORE_DIR "${_QT_DIR}/lib/QtCore.framework/Versions/5/Headers")
   else()
     set(_QT_CORE_DIR "${_QT_DIR}/include/QtCore")
+    if(NOT EXISTS "${_QT_CORE_DIR}")
+      set(_QT_CORE_DIR "${_QT_DIR}/include/qt5/QtCore")
+    endif()
   endif()
   if(NOT EXISTS "${_QT_CORE_DIR}")
       message(FATAL_ERROR "Could not find 'include/QtCore' in '${_QT_DIR}'")
@@ -78,6 +81,17 @@ macro(setup_qt)
         message(FATAL_ERROR "Unable to locate Qt5CoreConfig.cmake in '${QT_CMAKE_PREFIX_PATH}'")
     endif()
 
+    set(RCC_BINARY "${QT_DIR}/bin/rcc")
+
+    if(NOT EXISTS "${RCC_BINARY}")
+    set(RCC_BINARY "${QT_DIR}/bin/rcc-qt5")
+    endif()
+
+    if(NOT EXISTS "${RCC_BINARY}")
+    message(FATAL_ERROR "Unable to locate rcc '${QT_DIR}'")
+    endif()
+
+
     message(STATUS "Using Qt build in : '${QT_DIR}' with version ${QT_VERSION}")
 
     # Instruct CMake to run moc automatically when needed.
diff --git a/hifi_qt.py b/hifi_qt.py
index 7ee8a787b5..dbff6319ff 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -28,18 +28,83 @@ endif()
         self.args = args
         self.configFilePath = os.path.join(args.build_root, 'qt.cmake')
         self.version = os.getenv('VIRCADIA_USE_QT_VERSION', '5.15.2')
-
         self.assets_url = hifi_utils.readEnviromentVariableFromFile(args.build_root, 'EXTERNAL_BUILD_ASSETS')
 
-        defaultBasePath = os.path.expanduser('~/hifi/qt')
-        self.basePath = os.getenv('HIFI_QT_BASE', defaultBasePath)
-        if (not os.path.isdir(self.basePath)):
-            os.makedirs(self.basePath)
-        self.path = os.path.join(self.basePath, self.version)
-        self.fullPath = os.path.join(self.path, 'qt5-install')
-        self.cmakePath = os.path.join(self.fullPath, 'lib/cmake')
+        # OS dependent information
+        system = platform.system()
 
-        print("Using qt path {}".format(self.path))
+        qt_found = False
+
+        # Here we handle the 3 possible cases of dealing with Qt:
+        if os.getenv('VIRCADIA_USE_SYSTEM_QT'):
+            # 1. Using the system provided Qt. This is only recommended for Qt 5.15.0 and above,
+            # as it includes a required fix on Linux.
+            #
+            # This path only works on Linux as neither Windows nor OSX ship Qt.
+
+            if system != "Linux":
+                raise Exception("Using the system Qt is only supported on Linux")
+
+            cmake_paths = [ "lib64/cmake", "lib/cmake" ]
+            cmake_path_ok = False
+
+            # This makes the lockFile stuff happy. Needs to be writable.
+            self.path = tempfile.mkdtemp()
+
+            self.fullPath = '/usr'
+
+            # Find the cmake directory
+            for cp in cmake_paths:
+                self.cmakePath = os.path.join(self.fullPath, cp)
+                if os.path.isdir(self.cmakePath):
+                    cmake_path_ok = True
+                    break
+
+            if not cmake_path_ok:
+                raise Exception("Failed to find cmake directory. Looked under " + self.fullPath + " in " + (', '.join(cmake_paths)))
+
+            qt_found = True
+            print("Using system Qt")
+
+        elif os.getenv('VIRCADIA_QT_PATH'):
+            # 2. Using an user-provided directory.
+            # VIRCADIA_QT_PATH must point to a directory with a Qt install in it.
+
+            self.path = os.getenv('VIRCADIA_QT_PATH')
+            self.fullPath = self.path
+            self.cmakePath = os.path.join(self.fullPath, 'lib/cmake')
+
+            qt_found = True
+            print("Using Qt from " + self.fullPath)
+
+        else:
+            # 3. Using a pre-built Qt.
+            #
+            # This works somewhat differently from above, notice how path and fullPath are
+            # used differently in this case.
+            #
+            # In the case of an user-provided directory, we just use the user-supplied directory.
+            #
+            # For a pre-built qt, however, we have to unpack it. The archive is required to contain
+            # a qt5-install directory in it.
+
+            self.path = os.path.expanduser("~/vircadia-files/qt")
+            self.fullPath = os.path.join(self.path, 'qt5-install')
+            self.cmakePath = os.path.join(self.fullPath, 'lib/cmake')
+
+            if (not os.path.isdir(self.path)):
+                os.makedirs(self.path)
+
+            qt_found = os.path.isdir(self.fullPath)
+            print("Using a packaged Qt")
+
+        if qt_found:
+            # Sanity check, ensure we have a good cmake directory
+            if not os.path.isdir(os.path.join(self.cmakePath, "Qt5")):
+                raise Exception("Failed to find Qt5 directory under " + self.cmakePath)
+
+        # I'm not sure why this is needed. It's used by hifi_singleton.
+        # Perhaps it stops multiple build processes from interferring?
         lockDir, lockName = os.path.split(self.path)
         lockName += '.lock'
         if not os.path.isdir(lockDir):
@@ -47,21 +112,16 @@ endif()
 
         self.lockFile = os.path.join(lockDir, lockName)
 
-        if (os.getenv('VIRCADIA_USE_PREBUILT_QT')):
-            print("Using pre-built Qt5")
+        if qt_found:
+            print("Found pre-built Qt5")
             return
 
-        # OS dependent information
-        system = platform.system()
-        cpu_architecture = platform.machine()
-
         if 'Windows' == system:
             self.qtUrl = self.assets_url + '/dependencies/vcpkg/qt5-install-5.15.2-windows.tar.gz'
         elif 'Darwin' == system:
             self.qtUrl = self.assets_url + '/dependencies/vcpkg/qt5-install-5.15.2-macos.tar.gz'
         elif 'Linux' == system:
             import distro
-            dist = distro.linux_distribution()
 
             if 'x86_64' == cpu_architecture:
                 if distro.id() == 'ubuntu':
@@ -124,6 +184,14 @@ endif()
             print("Machine     : " + platform.machine())
             raise Exception('UNKNOWN OPERATING SYSTEM!!!')
 
+    def showQtBuildInfo(self):
+        print("")
+        print("It's also possible to build Qt for your distribution, please see the documentation at:")
+        print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
+        print("")
+        print("Alternatively, you can try building against the system Qt by setting the VIRCADIA_USE_SYSTEM_QT environment variable.")
+        print("You'll need to install the development packages, and to have Qt 5.15.0 or newer. ")
+
     def writeConfig(self):
         print("Writing cmake config to {}".format(self.configFilePath))
         # Write out the configuration for use by CMake
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index c307c63142..142fda15ce 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -34,14 +34,14 @@ if (ANDROID)
   add_custom_command(
     OUTPUT ${RESOURCES_RCC}
     DEPENDS ${RESOURCES_QRC} ${GENERATE_QRC_DEPENDS}
-    COMMAND "${QT_DIR}/bin/rcc"
+    COMMAND "${RCC_BINARY}"
     ARGS ${RESOURCES_QRC} -no-compress -binary -o ${RESOURCES_RCC}
   )
 else ()
   add_custom_command(
     OUTPUT ${RESOURCES_RCC}
     DEPENDS ${RESOURCES_QRC} ${GENERATE_QRC_DEPENDS}
-    COMMAND "${QT_DIR}/bin/rcc"
+    COMMAND "${RCC_BINARY}"
     ARGS ${RESOURCES_QRC} -binary -o ${RESOURCES_RCC}
   )
 endif()
@@ -199,6 +199,8 @@ endif()
 
 if (WIN32 OR APPLE)
   add_dependencies(${TARGET_NAME} resources)
+if (WIN32 OR APPLE OR UNIX)
+    add_dependencies(${TARGET_NAME} resources screenshare)
 endif()
 
 if (SCREENSHARE)
@@ -435,18 +437,20 @@ else()
   endif()
 endif()
 
-if (DEV_BUILD AND (APPLE OR UNIX))
-  # create a qt.conf file to override hard-coded search paths in Qt libs
-  set(QT_LIB_PATH "${QT_CMAKE_PREFIX_PATH}/../..")
-  if (APPLE)
-    set(QT_CONF_FILE "${RESOURCES_DEV_DIR}/../Resources/qt.conf")
-  else ()
-    set(QT_CONF_FILE "${INTERFACE_EXEC_DIR}/qt.conf")
-  endif ()
-  file(GENERATE
-    OUTPUT "${QT_CONF_FILE}"
-    CONTENT "[Paths]\nPrefix=${QT_LIB_PATH}\n"
-  )
+if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+  if (DEV_BUILD AND (APPLE OR UNIX))
+    # create a qt.conf file to override hard-coded search paths in Qt libs
+    set(QT_LIB_PATH "${QT_CMAKE_PREFIX_PATH}/../..")
+    if (APPLE)
+      set(QT_CONF_FILE "${RESOURCES_DEV_DIR}/../Resources/qt.conf")
+    else ()
+      set(QT_CONF_FILE "${INTERFACE_EXEC_DIR}/qt.conf")
+    endif ()
+    file(GENERATE
+      OUTPUT "${QT_CONF_FILE}"
+      CONTENT "[Paths]\nPrefix=${QT_LIB_PATH}\n"
+    )
+  endif()
 endif()
 
 if (SCRIPTS_INSTALL_DIR)
diff --git a/libraries/controllers/src/controllers/UserInputMapper.cpp b/libraries/controllers/src/controllers/UserInputMapper.cpp
index 6333792b3f..b5e07d5691 100755
--- a/libraries/controllers/src/controllers/UserInputMapper.cpp
+++ b/libraries/controllers/src/controllers/UserInputMapper.cpp
@@ -44,6 +44,10 @@
 #include "impl/Route.h"
 #include "impl/Mapping.h"
 
+#if QT_VERSION > QT_VERSION_CHECK(5, 13, 0)
+// FIXME: Remove this after Qt 5.15 upgrade
+#define endl Qt::endl
+#endif
 
 namespace controller {
     const uint16_t UserInputMapper::STANDARD_DEVICE = 0;
diff --git a/tools/nitpick/CMakeLists.txt b/tools/nitpick/CMakeLists.txt
index 8b4a5d03df..18ee84c0e5 100644
--- a/tools/nitpick/CMakeLists.txt
+++ b/tools/nitpick/CMakeLists.txt
@@ -12,7 +12,7 @@ generate_qrc(OUTPUT ${RESOURCES_QRC} PATH ${CMAKE_CURRENT_SOURCE_DIR}/resources
 add_custom_command(
     OUTPUT ${RESOURCES_RCC}
     DEPENDS ${RESOURCES_QRC} ${GENERATE_QRC_DEPENDS}
-    COMMAND "${QT_DIR}/bin/rcc"
+    COMMAND "${RCC_BINARY}"
     ARGS ${RESOURCES_QRC} -binary -o ${RESOURCES_RCC}
 )
 
diff --git a/tools/skeleton-dump/src/SkeletonDumpApp.cpp b/tools/skeleton-dump/src/SkeletonDumpApp.cpp
index 42a1c78090..e3169098d6 100644
--- a/tools/skeleton-dump/src/SkeletonDumpApp.cpp
+++ b/tools/skeleton-dump/src/SkeletonDumpApp.cpp
@@ -15,6 +15,11 @@
 #include <FBXSerializer.h>
 #include <AnimSkeleton.h>
 
+#if QT_VERSION > QT_VERSION_CHECK(5, 13, 0)
+// FIXME: Remove this after Qt 5.15 upgrade
+#define endl Qt::endl
+#endif
+
 SkeletonDumpApp::SkeletonDumpApp(int argc, char* argv[]) : QCoreApplication(argc, argv) {
 
     // parse command-line

From b88f380c87b2c0865da3a28952b8c0a3702faf03 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sun, 27 Dec 2020 22:08:45 +0100
Subject: [PATCH 02/21] Update documentation on Qt in Linux

---
 BUILD_LINUX.md | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/BUILD_LINUX.md b/BUILD_LINUX.md
index e9c5047e38..3bae13df9e 100644
--- a/BUILD_LINUX.md
+++ b/BUILD_LINUX.md
@@ -93,15 +93,16 @@ git checkout master
 
 ### Using a custom Qt build
 
-Qt binaries are only provided for Ubuntu. In order to build on other distributions, a Qt5 install needs to be provided as follows:
+Qt binaries are only provided for Ubuntu. In order to build on other distributions, a Qt5 install
+ needs to be provided by setting the `VIRCADIA_QT_PATH` environment variable to a directory containing
+ a Qt install.
 
-* Set `VIRCADIA_USE_PREBUILT_QT=1`
-* Set `VIRCADIA_USE_QT_VERSION` to the Qt version (defaults to `5.12.3`)
-* Set `HIFI_QT_BASE=/path/to/qt`
+ ### Using the system's Qt
 
-Qt must be installed in `$HIFI_QT_BASE/$VIRCADIA_USE_QT_VERSION/qt5-install`.
+ The system's Qt can be used, if the development packages are installed, by setting the
+ `VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.0.
 
-### Compiling
+ ### Compiling
 
 Create the build directory:
 ```bash

From efd15dc43a09d29244edbd1c27c33a6cebe3e0f7 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Wed, 6 Jan 2021 20:51:17 +0100
Subject: [PATCH 03/21] Make hifi_vcpkg.py use ~/vircadia-files too

Makes it consistent with the change made for Qt
---
 hifi_vcpkg.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hifi_vcpkg.py b/hifi_vcpkg.py
index fb77fd2507..642ed1253e 100644
--- a/hifi_vcpkg.py
+++ b/hifi_vcpkg.py
@@ -60,7 +60,7 @@ endif()
             self.path = args.vcpkg_root
             self.noClean = True
         else:
-            defaultBasePath = os.path.expanduser('~/hifi/vcpkg')
+            defaultBasePath = os.path.expanduser('~/vircadia-files/vcpkg')
             self.basePath = os.getenv('HIFI_VCPKG_BASE', defaultBasePath)
             if self.args.android:
                 self.basePath = os.path.join(self.basePath, 'android')

From 6cd8eca159ab32d1e49921309cde21ff15998d7f Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sat, 30 Jan 2021 19:54:33 +0100
Subject: [PATCH 04/21] Take into account that Windows executables have an
 extension

---
 cmake/macros/SetupQt.cmake | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/cmake/macros/SetupQt.cmake b/cmake/macros/SetupQt.cmake
index 35a22ecb4d..b39c423a05 100644
--- a/cmake/macros/SetupQt.cmake
+++ b/cmake/macros/SetupQt.cmake
@@ -81,14 +81,14 @@ macro(setup_qt)
         message(FATAL_ERROR "Unable to locate Qt5CoreConfig.cmake in '${QT_CMAKE_PREFIX_PATH}'")
     endif()
 
-    set(RCC_BINARY "${QT_DIR}/bin/rcc")
+    set(RCC_BINARY "${QT_DIR}/bin/rcc${CMAKE_EXECUTABLE_SUFFIX}")
 
     if(NOT EXISTS "${RCC_BINARY}")
-    set(RCC_BINARY "${QT_DIR}/bin/rcc-qt5")
+    set(RCC_BINARY "${QT_DIR}/bin/rcc-qt5${CMAKE_EXECUTABLE_SUFFIX}")
     endif()
 
     if(NOT EXISTS "${RCC_BINARY}")
-    message(FATAL_ERROR "Unable to locate rcc '${QT_DIR}'")
+    message(FATAL_ERROR "Unable to locate rcc. Last looked in '${RCC_BINARY}'")
     endif()
 
 

From 2b05c324368c9a244a7805421942c7e98b0209aa Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sat, 30 Jan 2021 22:56:29 +0100
Subject: [PATCH 05/21] Don't depend on screenshare on Android

---
 interface/CMakeLists.txt | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index 142fda15ce..9710aa53e8 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -197,9 +197,7 @@ if (BUILD_TOOLS AND NPM_EXECUTABLE)
   add_dependencies(resources jsdoc)
 endif()
 
-if (WIN32 OR APPLE)
-  add_dependencies(${TARGET_NAME} resources)
-if (WIN32 OR APPLE OR UNIX)
+if ((WIN32 OR APPLE OR UNIX) AND NOT ANDROID)
     add_dependencies(${TARGET_NAME} resources screenshare)
 endif()
 

From 1e63916940e5f805f5502a32ce867c2269bf7df4 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Mon, 15 Feb 2021 23:58:20 +0100
Subject: [PATCH 06/21] Disable almost all the code in SetupQt.cmake for system
 qt

We're already using the standard find_package method to setup Qt
for the most part, so none of the manipulations of SetupQt should
be needed for system Qt.
---
 CMakeLists.txt             |   5 +-
 cmake/macros/SetupQt.cmake | 100 +++++++++++++++++++------------------
 2 files changed, 56 insertions(+), 49 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 77d0413690..5993ab8764 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -290,7 +290,10 @@ set_packaging_parameters()
 
 # Locate the required Qt build on the filesystem
 setup_qt()
-list(APPEND CMAKE_PREFIX_PATH "${QT_CMAKE_PREFIX_PATH}")
+
+if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+  list(APPEND CMAKE_PREFIX_PATH "${QT_CMAKE_PREFIX_PATH}")
+endif()
 
 find_package( Threads )
 
diff --git a/cmake/macros/SetupQt.cmake b/cmake/macros/SetupQt.cmake
index b39c423a05..4676a00e97 100644
--- a/cmake/macros/SetupQt.cmake
+++ b/cmake/macros/SetupQt.cmake
@@ -48,51 +48,59 @@ endfunction()
 # Sets the QT_CMAKE_PREFIX_PATH and QT_DIR variables
 # Also enables CMAKE_AUTOMOC and CMAKE_AUTORCC
 macro(setup_qt)
-    # if we are in a development build and QT_CMAKE_PREFIX_PATH is specified
-    # then use it,
-    # otherwise, use the vcpkg'ed version
-    if(NOT DEFINED QT_CMAKE_PREFIX_PATH)
-        message(FATAL_ERROR "QT_CMAKE_PREFIX_PATH should have been set by hifi_qt.py")
+    if ($ENV{VIRCADIA_USE_SYSTEM_QT})
+        message(STATUS "Using system Qt")
+    else()
+        # if we are in a development build and QT_CMAKE_PREFIX_PATH is specified
+        # then use it,
+        # otherwise, use the vcpkg'ed version
+        if(NOT DEFINED QT_CMAKE_PREFIX_PATH)
+            message(FATAL_ERROR "QT_CMAKE_PREFIX_PATH should have been set by hifi_qt.py")
+        endif()
+        if (DEV_BUILD)
+          if (DEFINED ENV{QT_CMAKE_PREFIX_PATH})
+            set(QT_CMAKE_PREFIX_PATH $ENV{QT_CMAKE_PREFIX_PATH})
+          endif()
+        endif()
+
+        message("QT_CMAKE_PREFIX_PATH = " ${QT_CMAKE_PREFIX_PATH})
+
+        # figure out where the qt dir is
+        get_filename_component(QT_DIR "${QT_CMAKE_PREFIX_PATH}/../../" ABSOLUTE)
+        set(QT_VERSION "unknown")
+        calculate_qt5_version(QT_VERSION "${QT_DIR}")
+        if (QT_VERSION STREQUAL "unknown")
+            message(FATAL_ERROR "Could not determine QT_VERSION")
+        endif()
+
+        if(WIN32)
+            # windows shell does not like backslashes expanded on the command line,
+            # so convert all backslashes in the QT path to forward slashes
+            string(REPLACE \\ / QT_CMAKE_PREFIX_PATH ${QT_CMAKE_PREFIX_PATH})
+            string(REPLACE \\ / QT_DIR ${QT_DIR})
+        endif()
+
+        if(NOT EXISTS "${QT_CMAKE_PREFIX_PATH}/Qt5Core/Qt5CoreConfig.cmake")
+            message(FATAL_ERROR "Unable to locate Qt5CoreConfig.cmake in '${QT_CMAKE_PREFIX_PATH}'")
+        endif()
+
+        set(RCC_BINARY "${QT_DIR}/bin/rcc${CMAKE_EXECUTABLE_SUFFIX}")
+
+        if(NOT EXISTS "${RCC_BINARY}")
+            set(RCC_BINARY "${QT_DIR}/bin/rcc-qt5${CMAKE_EXECUTABLE_SUFFIX}")
+        endif()
+
+        if(NOT EXISTS "${RCC_BINARY}")
+            message(FATAL_ERROR "Unable to locate rcc. Last looked in '${RCC_BINARY}'")
+        endif()
+
+
+        message(STATUS "Using Qt build in : '${QT_DIR}' with version ${QT_VERSION}")
+        if (WIN32)
+          add_paths_to_fixup_libs("${QT_DIR}/bin")
+        endif ()
+
     endif()
-    if (DEV_BUILD)
-      if (DEFINED ENV{QT_CMAKE_PREFIX_PATH})
-        set(QT_CMAKE_PREFIX_PATH $ENV{QT_CMAKE_PREFIX_PATH})
-      endif()
-    endif()
-
-    message("QT_CMAKE_PREFIX_PATH = " ${QT_CMAKE_PREFIX_PATH})
-
-    # figure out where the qt dir is
-    get_filename_component(QT_DIR "${QT_CMAKE_PREFIX_PATH}/../../" ABSOLUTE)
-    set(QT_VERSION "unknown")
-    calculate_qt5_version(QT_VERSION "${QT_DIR}")
-    if (QT_VERSION STREQUAL "unknown")
-      message(FATAL_ERROR "Could not determine QT_VERSION")
-    endif()
-
-    if(WIN32)
-        # windows shell does not like backslashes expanded on the command line,
-        # so convert all backslashes in the QT path to forward slashes
-        string(REPLACE \\ / QT_CMAKE_PREFIX_PATH ${QT_CMAKE_PREFIX_PATH})
-        string(REPLACE \\ / QT_DIR ${QT_DIR})
-    endif()
-
-    if(NOT EXISTS "${QT_CMAKE_PREFIX_PATH}/Qt5Core/Qt5CoreConfig.cmake")
-        message(FATAL_ERROR "Unable to locate Qt5CoreConfig.cmake in '${QT_CMAKE_PREFIX_PATH}'")
-    endif()
-
-    set(RCC_BINARY "${QT_DIR}/bin/rcc${CMAKE_EXECUTABLE_SUFFIX}")
-
-    if(NOT EXISTS "${RCC_BINARY}")
-    set(RCC_BINARY "${QT_DIR}/bin/rcc-qt5${CMAKE_EXECUTABLE_SUFFIX}")
-    endif()
-
-    if(NOT EXISTS "${RCC_BINARY}")
-    message(FATAL_ERROR "Unable to locate rcc. Last looked in '${RCC_BINARY}'")
-    endif()
-
-
-    message(STATUS "Using Qt build in : '${QT_DIR}' with version ${QT_VERSION}")
 
     # Instruct CMake to run moc automatically when needed.
     set(CMAKE_AUTOMOC ON)
@@ -100,8 +108,4 @@ macro(setup_qt)
     # Instruct CMake to run rcc automatically when needed
     set(CMAKE_AUTORCC ON)
 
-    if (WIN32)
-        add_paths_to_fixup_libs("${QT_DIR}/bin")
-    endif ()
-
 endmacro()

From ca489bd4208e4a2d44b9f1d2624304b43f371c0a Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Tue, 16 Feb 2021 11:46:22 +0100
Subject: [PATCH 07/21] Simplify system Qt path

---
 CMakeLists.txt | 10 ++++++----
 hifi_qt.py     | 45 +++++++++++++++++----------------------------
 prebuild.py    | 17 ++++++++++-------
 3 files changed, 33 insertions(+), 39 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5993ab8764..cf82dfdfc6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -101,11 +101,13 @@ include("${CMAKE_BINARY_DIR}/vcpkg.cmake")
 
 if (HIFI_ANDROID)
   set(QT_CMAKE_PREFIX_PATH "$ENV{HIFI_ANDROID_PRECOMPILED}/qt/lib/cmake")
-else() 
-  if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
-      message(FATAL_ERROR "qt configuration missing.")
+else()
+  if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+    if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
+        message(FATAL_ERROR "qt configuration missing.")
+    endif()
+    include("${CMAKE_BINARY_DIR}/qt.cmake")
   endif()
-  include("${CMAKE_BINARY_DIR}/qt.cmake")
 endif()
 
 option(VCPKG_APPLOCAL_DEPS OFF)
diff --git a/hifi_qt.py b/hifi_qt.py
index dbff6319ff..d11988ed2e 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -34,6 +34,7 @@ endif()
         system = platform.system()
 
         qt_found = False
+        system_qt = False
 
         # Here we handle the 3 possible cases of dealing with Qt:
         if os.getenv('VIRCADIA_USE_SYSTEM_QT'):
@@ -45,25 +46,11 @@ endif()
             if system != "Linux":
                 raise Exception("Using the system Qt is only supported on Linux")
 
-            cmake_paths = [ "lib64/cmake", "lib/cmake" ]
-            cmake_path_ok = False
-
-            # This makes the lockFile stuff happy. Needs to be writable.
-            self.path = tempfile.mkdtemp()
-
-            self.fullPath = '/usr'
-
-            # Find the cmake directory
-            for cp in cmake_paths:
-                self.cmakePath = os.path.join(self.fullPath, cp)
-                if os.path.isdir(self.cmakePath):
-                    cmake_path_ok = True
-                    break
-
-            if not cmake_path_ok:
-                raise Exception("Failed to find cmake directory. Looked under " + self.fullPath + " in " + (', '.join(cmake_paths)))
+            self.path = None
+            self.cmakePath = None
 
             qt_found = True
+            system_qt = True
             print("Using system Qt")
 
         elif os.getenv('VIRCADIA_QT_PATH'):
@@ -98,19 +85,21 @@ endif()
             qt_found = os.path.isdir(self.fullPath)
             print("Using a packaged Qt")
 
-        if qt_found:
-            # Sanity check, ensure we have a good cmake directory
-            if not os.path.isdir(os.path.join(self.cmakePath, "Qt5")):
-                raise Exception("Failed to find Qt5 directory under " + self.cmakePath)
 
-        # I'm not sure why this is needed. It's used by hifi_singleton.
-        # Perhaps it stops multiple build processes from interferring?
-        lockDir, lockName = os.path.split(self.path)
-        lockName += '.lock'
-        if not os.path.isdir(lockDir):
-            os.makedirs(lockDir)
+        if not system_qt:
+            if qt_found:
+                # Sanity check, ensure we have a good cmake directory
+                if not os.path.isdir(os.path.join(self.cmakePath, "Qt5")):
+                    raise Exception("Failed to find Qt5 directory under " + self.cmakePath)
 
-        self.lockFile = os.path.join(lockDir, lockName)
+            # I'm not sure why this is needed. It's used by hifi_singleton.
+            # Perhaps it stops multiple build processes from interferring?
+            lockDir, lockName = os.path.split(self.path)
+            lockName += '.lock'
+            if not os.path.isdir(lockDir):
+                os.makedirs(lockDir)
+
+            self.lockFile = os.path.join(lockDir, lockName)
 
         if qt_found:
             print("Found pre-built Qt5")
diff --git a/prebuild.py b/prebuild.py
index d5bed2d813..47ec01f8cc 100644
--- a/prebuild.py
+++ b/prebuild.py
@@ -130,23 +130,26 @@ def main():
         with timer('NSIS'):
             hifi_utils.downloadAndExtract(assets_url + '/dependencies/NSIS-hifi-plugins-1.0.tgz', "C:/Program Files (x86)")
 
-    qtInstallPath = ''
+    qtInstallPath = None
     # If not android, install our Qt build
     if not args.android:
         qt = hifi_qt.QtDownloader(args)
         qtInstallPath = qt.cmakePath
-        with hifi_singleton.Singleton(qt.lockFile) as lock:
-            with timer('Qt'):
-                qt.installQt()
-                qt.writeConfig()
+
+        if qtInstallPath is not None:
+            # qtInstallPath is None when we're doing a system Qt build
+            with hifi_singleton.Singleton(qt.lockFile) as lock:
+                with timer('Qt'):
+                    qt.installQt()
+                    qt.writeConfig()
 
     pm = hifi_vcpkg.VcpkgRepo(args)
-    if qtInstallPath != '':
+    if qtInstallPath is not None:
         pm.writeVar('QT_CMAKE_PREFIX_PATH', qtInstallPath)
 
     # Only allow one instance of the program to run at a time
 
-    if qtInstallPath != '':
+    if qtInstallPath is not None:
         pm.writeVar('QT_CMAKE_PREFIX_PATH', qtInstallPath)
 
     # Only allow one instance of the program to run at a time

From 758ebd7f9d212281e16299f94eb2d237574132e1 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Tue, 16 Feb 2021 12:46:30 +0100
Subject: [PATCH 08/21] Fix environment variable cmake syntax

---
 CMakeLists.txt           | 4 ++--
 interface/CMakeLists.txt | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cf82dfdfc6..cbde769d3f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -102,7 +102,7 @@ include("${CMAKE_BINARY_DIR}/vcpkg.cmake")
 if (HIFI_ANDROID)
   set(QT_CMAKE_PREFIX_PATH "$ENV{HIFI_ANDROID_PRECOMPILED}/qt/lib/cmake")
 else()
-  if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+  if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
     if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
         message(FATAL_ERROR "qt configuration missing.")
     endif()
@@ -293,7 +293,7 @@ set_packaging_parameters()
 # Locate the required Qt build on the filesystem
 setup_qt()
 
-if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
   list(APPEND CMAKE_PREFIX_PATH "${QT_CMAKE_PREFIX_PATH}")
 endif()
 
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index 9710aa53e8..267f996535 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -435,7 +435,7 @@ else()
   endif()
 endif()
 
-if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
   if (DEV_BUILD AND (APPLE OR UNIX))
     # create a qt.conf file to override hard-coded search paths in Qt libs
     set(QT_LIB_PATH "${QT_CMAKE_PREFIX_PATH}/../..")

From 6611d6ef5b9c40f99a9d925604cd1cb7a8245bbd Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Wed, 17 Feb 2021 20:59:28 +0100
Subject: [PATCH 09/21] Fix quazip cmake portfile to work with system Qt

---
 cmake/ports/quazip/portfile.cmake | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/cmake/ports/quazip/portfile.cmake b/cmake/ports/quazip/portfile.cmake
index 0789062892..3f5703dcf4 100644
--- a/cmake/ports/quazip/portfile.cmake
+++ b/cmake/ports/quazip/portfile.cmake
@@ -1,6 +1,15 @@
 include(vcpkg_common_functions)
 
-file(READ "${VCPKG_ROOT_DIR}/_env/QT_CMAKE_PREFIX_PATH.txt" QT_CMAKE_PREFIX_PATH)
+if(EXISTS "${VCPKG_ROOT_DIR}/_env/QT_CMAKE_PREFIX_PATH.txt")
+    # This environment var file only exists if we're overridding the default Qt location,
+    # which happens when using Qt from vcpkg, or using Qt from custom location
+    file(READ "${VCPKG_ROOT_DIR}/_env/QT_CMAKE_PREFIX_PATH.txt" QT_CMAKE_PREFIX_PATH)
+    set(QUAZIP_EXTRA_OPTS "-DCMAKE_PREFIX_PATH=${QT_CMAKE_PREFIX_PATH}")
+else()
+    # In the case of using system Qt, don't pass anything.
+    set(QUAZIP_EXTRA_OPTS "")
+endif()
+
 file(READ "${VCPKG_ROOT_DIR}/_env/EXTERNAL_BUILD_ASSETS.txt" EXTERNAL_BUILD_ASSETS)
 
 vcpkg_download_distfile(
@@ -19,7 +28,7 @@ vcpkg_extract_source_archive_ex(
 vcpkg_configure_cmake(
   SOURCE_PATH ${SOURCE_PATH}
   PREFER_NINJA
-  OPTIONS -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DCMAKE_PREFIX_PATH=${QT_CMAKE_PREFIX_PATH} -DBUILD_WITH_QT4=OFF
+  OPTIONS -DCMAKE_POSITION_INDEPENDENT_CODE=ON ${QUAZIP_EXTRA_OPTS} -DBUILD_WITH_QT4=OFF
 )
 
 vcpkg_install_cmake()

From 50dfa73244045d667f5ae991e09b4a81d2167113 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sat, 27 Feb 2021 14:47:17 +0100
Subject: [PATCH 10/21] Concatenate Windows paths correctly

---
 hifi_qt.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hifi_qt.py b/hifi_qt.py
index d11988ed2e..df84c45ddd 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -59,7 +59,7 @@ endif()
 
             self.path = os.getenv('VIRCADIA_QT_PATH')
             self.fullPath = self.path
-            self.cmakePath = os.path.join(self.fullPath, 'lib/cmake')
+            self.cmakePath = os.path.join(self.fullPath, 'lib', 'cmake')
 
             qt_found = True
             print("Using Qt from " + self.fullPath)
@@ -77,7 +77,7 @@ endif()
 
             self.path = os.path.expanduser("~/vircadia-files/qt")
             self.fullPath = os.path.join(self.path, 'qt5-install')
-            self.cmakePath = os.path.join(self.fullPath, 'lib/cmake')
+            self.cmakePath = os.path.join(self.fullPath, 'lib', 'cmake')
 
             if (not os.path.isdir(self.path)):
                 os.makedirs(self.path)

From 2a8278f5222b4bb442308f094f3f1d4ff5de24cd Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sat, 13 Mar 2021 23:17:15 +0100
Subject: [PATCH 11/21] Temp changes

---
 hifi_qt.py  | 9 ++++++---
 prebuild.py | 7 +++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/hifi_qt.py b/hifi_qt.py
index df84c45ddd..e5f54ea545 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -89,9 +89,12 @@ endif()
         if not system_qt:
             if qt_found:
                 # Sanity check, ensure we have a good cmake directory
-                if not os.path.isdir(os.path.join(self.cmakePath, "Qt5")):
-                    raise Exception("Failed to find Qt5 directory under " + self.cmakePath)
-
+                qt5_dir = os.path.join(self.cmakePath, "Qt5")
+                if not os.path.isdir(qt5_dir):
+                    raise Exception("Failed to find Qt5 directory under " + self.cmakePath + ". There should be a " + qt5_dir)
+                else:
+                    print("Qt5 check passed, found " + qt5_dir)
+                    
             # I'm not sure why this is needed. It's used by hifi_singleton.
             # Perhaps it stops multiple build processes from interferring?
             lockDir, lockName = os.path.split(self.path)
diff --git a/prebuild.py b/prebuild.py
index 47ec01f8cc..34549b038c 100644
--- a/prebuild.py
+++ b/prebuild.py
@@ -138,10 +138,17 @@ def main():
 
         if qtInstallPath is not None:
             # qtInstallPath is None when we're doing a system Qt build
+            print("cmake path: " + qtInstallPath)
+            
             with hifi_singleton.Singleton(qt.lockFile) as lock:
                 with timer('Qt'):
                     qt.installQt()
                     qt.writeConfig()
+        else:
+            if (os.environ["VIRCADIA_USE_SYSTEM_QT"]):
+                print("System Qt selected")
+            else:
+                raise Exception("Internal error: System Qt not selected, but hifi_qt.py failed to return a cmake path")
 
     pm = hifi_vcpkg.VcpkgRepo(args)
     if qtInstallPath is not None:

From 506fd9563ae55550963f91023cc163dd0d6b746f Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Wed, 24 Mar 2021 22:15:47 +0100
Subject: [PATCH 12/21] Handle empty environment variables as false

---
 CMakeLists.txt           | 9 ++++++---
 hifi_qt.py               | 4 ++--
 interface/CMakeLists.txt | 2 +-
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cbde769d3f..bbeb92ca4c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -102,11 +102,14 @@ include("${CMAKE_BINARY_DIR}/vcpkg.cmake")
 if (HIFI_ANDROID)
   set(QT_CMAKE_PREFIX_PATH "$ENV{HIFI_ANDROID_PRECOMPILED}/qt/lib/cmake")
 else()
-  if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
-    if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
+  if ("$ENV{VIRCADIA_USE_SYSTEM_QT}" STREQUAL "")
+     if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
         message(FATAL_ERROR "qt configuration missing.")
     endif()
     include("${CMAKE_BINARY_DIR}/qt.cmake")
+    message(STATUS "${CMAKE_BINARY_DIR}/qt.cmake included!")
+  else()
+    message(STATUS "System Qt in use, not including qt.cmake!")
   endif()
 endif()
 
@@ -293,7 +296,7 @@ set_packaging_parameters()
 # Locate the required Qt build on the filesystem
 setup_qt()
 
-if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
+if ("$ENV{VIRCADIA_USE_SYSTEM_QT}" STREQUAL "")
   list(APPEND CMAKE_PREFIX_PATH "${QT_CMAKE_PREFIX_PATH}")
 endif()
 
diff --git a/hifi_qt.py b/hifi_qt.py
index e5f54ea545..530aaff8ec 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -37,7 +37,7 @@ endif()
         system_qt = False
 
         # Here we handle the 3 possible cases of dealing with Qt:
-        if os.getenv('VIRCADIA_USE_SYSTEM_QT'):
+        if os.getenv('VIRCADIA_USE_SYSTEM_QT', "") != "":
             # 1. Using the system provided Qt. This is only recommended for Qt 5.15.0 and above,
             # as it includes a required fix on Linux.
             #
@@ -53,7 +53,7 @@ endif()
             system_qt = True
             print("Using system Qt")
 
-        elif os.getenv('VIRCADIA_QT_PATH'):
+        elif os.getenv('VIRCADIA_QT_PATH', "") != "":
             # 2. Using an user-provided directory.
             # VIRCADIA_QT_PATH must point to a directory with a Qt install in it.
 
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index 267f996535..f6d84e4e4b 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -435,7 +435,7 @@ else()
   endif()
 endif()
 
-if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
+if ("$ENV{VIRCADIA_USE_SYSTEM_QT}" STREQUAL "")
   if (DEV_BUILD AND (APPLE OR UNIX))
     # create a qt.conf file to override hard-coded search paths in Qt libs
     set(QT_LIB_PATH "${QT_CMAKE_PREFIX_PATH}/../..")

From 1b999acb2fd5e44ec115d5b30c70b326a397a76e Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Wed, 24 Mar 2021 22:16:42 +0100
Subject: [PATCH 13/21] Add more explanatory comments

---
 cmake/macros/SetupQt.cmake |  9 ++++++---
 hifi_qt.py                 | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/cmake/macros/SetupQt.cmake b/cmake/macros/SetupQt.cmake
index 4676a00e97..743ac934c4 100644
--- a/cmake/macros/SetupQt.cmake
+++ b/cmake/macros/SetupQt.cmake
@@ -5,6 +5,9 @@
 #  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
 #
 
+# For understanding the execution flow followed by the Qt setup,
+# please look at the comment on top of hifi_qt.py
+
 function(get_sub_directories result curdir)
   file(GLOB children RELATIVE ${curdir} ${curdir}/*)
   set(dirlist "")
@@ -55,7 +58,9 @@ macro(setup_qt)
         # then use it,
         # otherwise, use the vcpkg'ed version
         if(NOT DEFINED QT_CMAKE_PREFIX_PATH)
-            message(FATAL_ERROR "QT_CMAKE_PREFIX_PATH should have been set by hifi_qt.py")
+            # Note: This comes from qt.cmake generated by hifi_qt.py
+            # See the comment on top of hifi_qt.py for details.
+            message(FATAL_ERROR "QT_CMAKE_PREFIX_PATH should have been set by hifi_qt.py through qt.cmake")
         endif()
         if (DEV_BUILD)
           if (DEFINED ENV{QT_CMAKE_PREFIX_PATH})
@@ -63,8 +68,6 @@ macro(setup_qt)
           endif()
         endif()
 
-        message("QT_CMAKE_PREFIX_PATH = " ${QT_CMAKE_PREFIX_PATH})
-
         # figure out where the qt dir is
         get_filename_component(QT_DIR "${QT_CMAKE_PREFIX_PATH}/../../" ABSOLUTE)
         set(QT_VERSION "unknown")
diff --git a/hifi_qt.py b/hifi_qt.py
index 530aaff8ec..56fb3a0ec1 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -10,6 +10,31 @@ import json
 import xml.etree.ElementTree as ET
 import functools
 
+# The way Qt is handled is a bit complicated, so I'm documenting it here.
+#
+# 1. User runs cmake
+# 2. cmake calls prebuild.py, which is referenced in /CMakeLists.txt
+# 3. prebuild.py calls this code.
+# 4. hifi_qt.py determines how to handle cmake: do we need to download a package, and which?
+# 4.a - Using system Qt
+#       No download, most special paths are turned off.
+#       We build in the same way a normal Qt program would.
+# 4.b - Using an user-provided Qt build in a custom directory.
+#       We just need to set the cmakePath to the right dir (qt5-install/lib/cmake)
+# 4.c - Using a premade package.
+#       We check the OS and distro and set qtUrl to the URL to download.
+#       After this, it works on the same pathway as 4.b.
+# 5. We write /qt.cmake, which contains paths that are passed down to SetupQt.cmake
+#    The template for this file is in CMAKE_TEMPLATE just below this comment
+#    and it sets the QT_CMAKE_PREFIX_PATH variable used by SetupQt.cmake.
+# 6. cmake includes /qt.cmake receiving our information
+#    In the case of system Qt, this step is skipped.
+# 7. cmake runs SetupQt.cmake which takes care of the cmake parts of the Qt configuration.
+#    In the case of system Qt, SetupQt.cmake is a no-op. It runs but exits immediately.
+#
+# The format for a prebuilt qt is a package containing a top-level directory named
+# 'qt5-install', which contains the result of a "make install" from a build of the Qt source.
+
 print = functools.partial(print, flush=True)
 
 # Encapsulates the vcpkg system

From f7af9a8b2a742fc3818be73174fcd63a5fb4cdd0 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Thu, 10 Jun 2021 22:48:33 +0200
Subject: [PATCH 14/21] Fix build - missing variable

---
 hifi_qt.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hifi_qt.py b/hifi_qt.py
index 56fb3a0ec1..6174a27505 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -139,6 +139,7 @@ endif()
             self.qtUrl = self.assets_url + '/dependencies/vcpkg/qt5-install-5.15.2-macos.tar.gz'
         elif 'Linux' == system:
             import distro
+            cpu_architecture = platform.machine()
 
             if 'x86_64' == cpu_architecture:
                 if distro.id() == 'ubuntu':

From 3ebcced301377eeec0cabdb29967e418df009b07 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Thu, 10 Jun 2021 22:48:43 +0200
Subject: [PATCH 15/21] Fix build -- screenshare is not found

---
 interface/CMakeLists.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index f6d84e4e4b..72ab17a6f2 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -197,8 +197,8 @@ if (BUILD_TOOLS AND NPM_EXECUTABLE)
   add_dependencies(resources jsdoc)
 endif()
 
-if ((WIN32 OR APPLE OR UNIX) AND NOT ANDROID)
-    add_dependencies(${TARGET_NAME} resources screenshare)
+if (WIN32 OR APPLE)
+    add_dependencies(${TARGET_NAME} resources)
 endif()
 
 if (SCREENSHARE)

From 3f8159b3c478ab926bc4815e6b7843ab51994c82 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Thu, 10 Jun 2021 22:51:11 +0200
Subject: [PATCH 16/21] Formatting fix

---
 BUILD_LINUX.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/BUILD_LINUX.md b/BUILD_LINUX.md
index 3bae13df9e..e5b6165da1 100644
--- a/BUILD_LINUX.md
+++ b/BUILD_LINUX.md
@@ -97,12 +97,12 @@ Qt binaries are only provided for Ubuntu. In order to build on other distributio
  needs to be provided by setting the `VIRCADIA_QT_PATH` environment variable to a directory containing
  a Qt install.
 
- ### Using the system's Qt
+### Using the system's Qt
 
  The system's Qt can be used, if the development packages are installed, by setting the
  `VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.0.
 
- ### Compiling
+### Compiling
 
 Create the build directory:
 ```bash

From 586de4d712d8a4962488dedad61f269e1cf2936d Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Thu, 10 Jun 2021 22:51:50 +0200
Subject: [PATCH 17/21] More formatting fixes

---
 BUILD_LINUX.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/BUILD_LINUX.md b/BUILD_LINUX.md
index e5b6165da1..0c2fd23ba3 100644
--- a/BUILD_LINUX.md
+++ b/BUILD_LINUX.md
@@ -94,13 +94,13 @@ git checkout master
 ### Using a custom Qt build
 
 Qt binaries are only provided for Ubuntu. In order to build on other distributions, a Qt5 install
- needs to be provided by setting the `VIRCADIA_QT_PATH` environment variable to a directory containing
- a Qt install.
+needs to be provided by setting the `VIRCADIA_QT_PATH` environment variable to a directory containing
+a Qt install.
 
 ### Using the system's Qt
 
- The system's Qt can be used, if the development packages are installed, by setting the
- `VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.0.
+The system's Qt can be used, if the development packages are installed, by setting the
+`VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.0.
 
 ### Compiling
 

From f90d872752dc0f2e552cc34efb0b9272a00e6594 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sat, 19 Jun 2021 19:38:07 +0200
Subject: [PATCH 18/21] Formatting cleanup

---
 hifi_qt.py                                                | 2 +-
 interface/CMakeLists.txt                                  | 2 +-
 libraries/controllers/src/controllers/UserInputMapper.cpp | 4 ----
 prebuild.py                                               | 2 +-
 tools/skeleton-dump/src/SkeletonDumpApp.cpp               | 5 -----
 5 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/hifi_qt.py b/hifi_qt.py
index 6174a27505..34b9536b0c 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -119,7 +119,7 @@ endif()
                     raise Exception("Failed to find Qt5 directory under " + self.cmakePath + ". There should be a " + qt5_dir)
                 else:
                     print("Qt5 check passed, found " + qt5_dir)
-                    
+
             # I'm not sure why this is needed. It's used by hifi_singleton.
             # Perhaps it stops multiple build processes from interferring?
             lockDir, lockName = os.path.split(self.path)
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index 72ab17a6f2..a2a29ed4ba 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -198,7 +198,7 @@ if (BUILD_TOOLS AND NPM_EXECUTABLE)
 endif()
 
 if (WIN32 OR APPLE)
-    add_dependencies(${TARGET_NAME} resources)
+  add_dependencies(${TARGET_NAME} resources)
 endif()
 
 if (SCREENSHARE)
diff --git a/libraries/controllers/src/controllers/UserInputMapper.cpp b/libraries/controllers/src/controllers/UserInputMapper.cpp
index b5e07d5691..6333792b3f 100755
--- a/libraries/controllers/src/controllers/UserInputMapper.cpp
+++ b/libraries/controllers/src/controllers/UserInputMapper.cpp
@@ -44,10 +44,6 @@
 #include "impl/Route.h"
 #include "impl/Mapping.h"
 
-#if QT_VERSION > QT_VERSION_CHECK(5, 13, 0)
-// FIXME: Remove this after Qt 5.15 upgrade
-#define endl Qt::endl
-#endif
 
 namespace controller {
     const uint16_t UserInputMapper::STANDARD_DEVICE = 0;
diff --git a/prebuild.py b/prebuild.py
index 34549b038c..b5390362e8 100644
--- a/prebuild.py
+++ b/prebuild.py
@@ -139,7 +139,7 @@ def main():
         if qtInstallPath is not None:
             # qtInstallPath is None when we're doing a system Qt build
             print("cmake path: " + qtInstallPath)
-            
+
             with hifi_singleton.Singleton(qt.lockFile) as lock:
                 with timer('Qt'):
                     qt.installQt()
diff --git a/tools/skeleton-dump/src/SkeletonDumpApp.cpp b/tools/skeleton-dump/src/SkeletonDumpApp.cpp
index e3169098d6..42a1c78090 100644
--- a/tools/skeleton-dump/src/SkeletonDumpApp.cpp
+++ b/tools/skeleton-dump/src/SkeletonDumpApp.cpp
@@ -15,11 +15,6 @@
 #include <FBXSerializer.h>
 #include <AnimSkeleton.h>
 
-#if QT_VERSION > QT_VERSION_CHECK(5, 13, 0)
-// FIXME: Remove this after Qt 5.15 upgrade
-#define endl Qt::endl
-#endif
-
 SkeletonDumpApp::SkeletonDumpApp(int argc, char* argv[]) : QCoreApplication(argc, argv) {
 
     // parse command-line

From 2a07f5fd5a9739b5678da155eb8bd6064edbac51 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sun, 20 Jun 2021 12:59:47 +0200
Subject: [PATCH 19/21] Nice colored unsupported distro messages

---
 BUILD_LINUX.md |  4 +++-
 CMakeLists.txt |  7 +++++--
 hifi_qt.py     | 32 ++++++++++++++++++++++++++++----
 hifi_utils.py  | 26 ++++++++++++++++++++++++++
 prebuild.py    |  5 ++++-
 5 files changed, 66 insertions(+), 8 deletions(-)

diff --git a/BUILD_LINUX.md b/BUILD_LINUX.md
index 0c2fd23ba3..1996360fed 100644
--- a/BUILD_LINUX.md
+++ b/BUILD_LINUX.md
@@ -100,7 +100,9 @@ a Qt install.
 ### Using the system's Qt
 
 The system's Qt can be used, if the development packages are installed, by setting the
-`VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.0.
+`VIRCADIA_USE_SYSTEM_QT` environment variable. The minimum recommended version is Qt 5.15.2, which is
+also the last version available in the Qt 5 branch. It is expected that Linux distributions will have
+Qt 5.15.2 available for a long time.
 
 ### Compiling
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index bbeb92ca4c..853d00c7f3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -77,7 +77,7 @@ endif()
 if (HIFI_ANDROID)
     execute_process(
         COMMAND ${HIFI_PYTHON_EXEC} ${CMAKE_CURRENT_SOURCE_DIR}/prebuild.py --release-type ${RELEASE_TYPE} --android ${HIFI_ANDROID_APP} --build-root ${CMAKE_BINARY_DIR}
-        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} RESULTS_VARIABLE PREBUILD_RET
     )
 else()
     set(VCPKG_BUILD_TYPE_PARAM "")
@@ -86,7 +86,7 @@ else()
     endif()
     execute_process(
         COMMAND ${HIFI_PYTHON_EXEC} ${CMAKE_CURRENT_SOURCE_DIR}/prebuild.py --release-type ${RELEASE_TYPE} --build-root ${CMAKE_BINARY_DIR} ${VCPKG_BUILD_TYPE_PARAM}
-        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} RESULTS_VARIABLE PREBUILD_RET
     )
     # squelch the Policy CMP0074 warning without requiring an update to cmake 3.12.
     if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.12)
@@ -94,6 +94,9 @@ else()
     endif()
 endif()
 
+if ("${PREBUILD_RET}" GREATER 0)
+  message(FATAL_ERROR "prebuild.py failed with error ${PREBUILD_RET}")
+endif()
 if(NOT EXISTS "${CMAKE_BINARY_DIR}/vcpkg.cmake")
     message(FATAL_ERROR "vcpkg configuration missing.")
 endif()
diff --git a/hifi_qt.py b/hifi_qt.py
index 34b9536b0c..72dcb97211 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -37,6 +37,29 @@ import functools
 
 print = functools.partial(print, flush=True)
 
+def unsupported_error():
+    import distro
+    cpu_architecture = platform.machine()
+
+    print('')
+    hifi_utils.color('red')
+    print("Sorry, we don't have a prebuilt Qt package for " + distro.name(pretty=True) + " on " + cpu_architecture + ".")
+    hifi_utils.color('white')
+    print('')
+    print("If this is a recent distribution, dating from 2021 or so, you can try building")
+    print("against the system Qt by running this command, and trying again:")
+    print("    export VIRCADIA_USE_SYSTEM_QT=1")
+    print("")
+    hifi_utils.color('clear')
+    print("If you'd like to try to build Qt from source either for building Vircadia, or")
+    print("to contribute a prebuilt package for your distribution, please see the")
+    print("documentation at: ", end='')
+    hifi_utils.color('blue')
+    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
+    hifi_utils.color('clear')
+    print('')
+
+    raise hifi_utils.SilentFatalError(2)
 # Encapsulates the vcpkg system
 class QtDownloader:
     CMAKE_TEMPLATE = """
@@ -155,10 +178,11 @@ endif()
                         print("Sorry, " + distro.name(pretty=True) + " is old and won't be officially supported. Please consider upgrading.");
                         raise Exception('UNKNOWN LINUX DISTRO VERSION!!!')
                 else:
-                    print("Sorry, " + distro.name(pretty=True) + " is not supported on x86_64. Please consider helping us out.")
-                    print("It's also possible to build Qt for your distribution, please see the documentation at:")
-                    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
-                    raise Exception('UNKNOWN LINUX VERSION!!!')
+                    unsupported_error()
+#                    print("Sorry, " + distro.name(pretty=True) + " is not supported on x86_64. Please consider helping us out.")
+#                    print("It's also possible to build Qt for your distribution, please see the documentation at:")
+#                    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
+#                    raise Exception('UNKNOWN LINUX VERSION!!!')
             elif 'aarch64' == cpu_architecture:
                 if distro.id() == 'ubuntu':
                     u_major = int( distro.major_version() )
diff --git a/hifi_utils.py b/hifi_utils.py
index 157e5858a8..19290dbc42 100644
--- a/hifi_utils.py
+++ b/hifi_utils.py
@@ -16,6 +16,18 @@ import functools
 
 print = functools.partial(print, flush=True)
 
+ansi_colors = {
+    'black' : 30,
+    'red': 31,
+    'green': 32,
+    'yellow': 33,
+    'blue': 34,
+    'magenta': 35,
+    'cyan': 36,
+    'white': 37,
+    'clear': 0
+}
+
 def scriptRelative(*paths):
     scriptdir = os.path.dirname(os.path.realpath(sys.argv[0]))
     result = os.path.join(scriptdir, *paths)
@@ -125,3 +137,17 @@ def downloadAndExtract(url, destPath, hash=None, hasher=hashlib.sha512(), isZip=
 def readEnviromentVariableFromFile(buildRootDir, var):
     with open(os.path.join(buildRootDir, '_env', var + ".txt")) as fp:
         return fp.read()
+
+class SilentFatalError(Exception):
+    """Thrown when some sort of fatal condition happened, and we already reported it to the user.
+    This excecption exists to give a chance to run any cleanup needed before exiting.
+
+    It should be handled at the bottom of the call stack, where the only action is to call
+    sys.exit(ex.exit_code)
+    """
+    def __init__(self, exit_code):
+        self.exit_code = exit_code
+
+def color(color_name):
+    # Ideally we'd use the termcolor module, but this avoids adding it as a dependency.
+    print("\033[1;{}m".format(ansi_colors[color_name]), end='')
\ No newline at end of file
diff --git a/prebuild.py b/prebuild.py
index b5390362e8..f272b04b23 100644
--- a/prebuild.py
+++ b/prebuild.py
@@ -207,4 +207,7 @@ def main():
     logger.info('end')
 
 print(sys.argv)
-main()
+try:
+    main()
+except hifi_utils.SilentFatalError as fatal_ex:
+    sys.exit(fatal_ex.exit_code)

From 588528306e29c731d304de4069d4b880c8796b30 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sun, 20 Jun 2021 13:01:04 +0200
Subject: [PATCH 20/21] Cmake cleanup

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 853d00c7f3..facc1c999f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -94,7 +94,7 @@ else()
     endif()
 endif()
 
-if ("${PREBUILD_RET}" GREATER 0)
+if (PREBUILD_RET GREATER 0)
   message(FATAL_ERROR "prebuild.py failed with error ${PREBUILD_RET}")
 endif()
 if(NOT EXISTS "${CMAKE_BINARY_DIR}/vcpkg.cmake")

From 6342a8aee3b88bde05d30691eaab5855081a5cd0 Mon Sep 17 00:00:00 2001
From: Dale Glass <dale@daleglass.net>
Date: Sun, 20 Jun 2021 16:22:39 +0200
Subject: [PATCH 21/21] Better Qt error messages

---
 hifi_qt.py | 93 +++++++++++++++++++++++++++---------------------------
 1 file changed, 47 insertions(+), 46 deletions(-)

diff --git a/hifi_qt.py b/hifi_qt.py
index 72dcb97211..078f80c38d 100644
--- a/hifi_qt.py
+++ b/hifi_qt.py
@@ -37,29 +37,6 @@ import functools
 
 print = functools.partial(print, flush=True)
 
-def unsupported_error():
-    import distro
-    cpu_architecture = platform.machine()
-
-    print('')
-    hifi_utils.color('red')
-    print("Sorry, we don't have a prebuilt Qt package for " + distro.name(pretty=True) + " on " + cpu_architecture + ".")
-    hifi_utils.color('white')
-    print('')
-    print("If this is a recent distribution, dating from 2021 or so, you can try building")
-    print("against the system Qt by running this command, and trying again:")
-    print("    export VIRCADIA_USE_SYSTEM_QT=1")
-    print("")
-    hifi_utils.color('clear')
-    print("If you'd like to try to build Qt from source either for building Vircadia, or")
-    print("to contribute a prebuilt package for your distribution, please see the")
-    print("documentation at: ", end='')
-    hifi_utils.color('blue')
-    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
-    hifi_utils.color('clear')
-    print('')
-
-    raise hifi_utils.SilentFatalError(2)
 # Encapsulates the vcpkg system
 class QtDownloader:
     CMAKE_TEMPLATE = """
@@ -172,17 +149,12 @@ endif()
                     if u_major == 18:
                         self.qtUrl = self.assets_url + '/dependencies/vcpkg/qt5-install-5.15.2-ubuntu-18.04-amd64.tar.xz'
                     elif u_major > 19:
-                        print("We don't support " + distro.name(pretty=True) + " yet. Perhaps consider helping us out?")
-                        raise Exception('LINUX DISTRO IS NOT SUPPORTED YET!!!')
+                        self.__no_qt_package_error()
                     else:
-                        print("Sorry, " + distro.name(pretty=True) + " is old and won't be officially supported. Please consider upgrading.");
-                        raise Exception('UNKNOWN LINUX DISTRO VERSION!!!')
+                        self.__unsupported_error()
                 else:
-                    unsupported_error()
-#                    print("Sorry, " + distro.name(pretty=True) + " is not supported on x86_64. Please consider helping us out.")
-#                    print("It's also possible to build Qt for your distribution, please see the documentation at:")
-#                    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
-#                    raise Exception('UNKNOWN LINUX VERSION!!!')
+                    self.__no_qt_package_error()
+
             elif 'aarch64' == cpu_architecture:
                 if distro.id() == 'ubuntu':
                     u_major = int( distro.major_version() )
@@ -191,11 +163,9 @@ endif()
                     if u_major == 18:
                         self.qtUrl = 'http://motofckr9k.ddns.net/vircadia_packages/qt5-install-5.15.2-ubuntu-18.04-aarch64_test.tar.xz'
                     elif u_major > 19:
-                        print("We don't support " + distro.name(pretty=True) + " on aarch64 yet. Perhaps consider helping us out?")
-                        raise Exception('LINUX DISTRO IS NOT SUPPORTED YET!!!')
+                        self.__no_qt_package_error()
                     else:
-                        print("Sorry, " + distro.name(pretty=True) + " is old and won't be officially supported. Please consider upgrading.");
-                        raise Exception('UNKNOWN LINUX DISTRO VERSION!!!')
+                        self.__unsupported_error()
 
                 elif distro.id() == 'debian':
                     u_major = int( distro.major_version() )
@@ -203,20 +173,14 @@ endif()
 
                     if u_major == 10:
                         #self.qtUrl = self.assets_url + '/dependencies/vcpkg/qt5-install-5.12.3-ubuntu-16.04-with-symbols.tar.gz'
-                        print("We don't support " + distro.name(pretty=True) + " on aarch64 yet. Perhaps consider helping us out?")
-                        raise Exception('LINUX DISTRO IS NOT SUPPORTED YET!!!')
+                        self.__no_qt_package_error()
                     elif u_major > 10:
-                        print("We don't support " + distro.name(pretty=True) + " on aarch64 yet. Perhaps consider helping us out?")
-                        raise Exception('LINUX DISTRO IS NOT SUPPORTED YET!!!')
+                        self.__no_qt_package_error()
                     else:
-                        print("Sorry, " + distro.name(pretty=True) + " is old and won't be officially supported. Please consider upgrading.");
-                        raise Exception('UNKNOWN LINUX DISTRO VERSION!!!')
+                        self.__unsupported_error()
 
                 else:
-                    print("Sorry, " + distro.name(pretty=True) + " is not supported on aarch64. Please consider helping us out.")
-                    print("It's also possible to build Qt for your distribution, please see the documentation at:")
-                    print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
-                    raise Exception('UNKNOWN LINUX VERSION!!!')
+                    self.__no_qt_package_error()
             else:
                 raise Exception('UNKNOWN CPU ARCHITECTURE!!!')
 
@@ -248,3 +212,40 @@ endif()
             hifi_utils.downloadAndExtract(self.qtUrl, self.path)
         else:
             print ('Qt has already been downloaded')
+
+
+    def __unsupported_error(self):
+        import distro
+        cpu_architecture = platform.machine()
+
+        print('')
+        hifi_utils.color('red')
+        print("Sorry, " + distro.name(pretty=True) + " on " + cpu_architecture + " is too old and won't be officially supported.")
+        hifi_utils.color('white')
+        print("Please upgrade to a more recent Linux distribution.")
+        hifi_utils.color('clear')
+        print('')
+        raise hifi_utils.SilentFatalError(3)
+
+    def __no_qt_package_error(self):
+        import distro
+        cpu_architecture = platform.machine()
+
+        print('')
+        hifi_utils.color('red')
+        print("Sorry, we don't have a prebuilt Qt package for " + distro.name(pretty=True) + " on " + cpu_architecture + ".")
+        hifi_utils.color('white')
+        print('')
+        print("If this is a recent distribution, dating from 2021 or so, you can try building")
+        print("against the system Qt by running this command, and trying again:")
+        print("    export VIRCADIA_USE_SYSTEM_QT=1")
+        print("")
+        hifi_utils.color('clear')
+        print("If you'd like to try to build Qt from source either for building Vircadia, or")
+        print("to contribute a prebuilt package for your distribution, please see the")
+        print("documentation at: ", end='')
+        hifi_utils.color('blue')
+        print("https://github.com/vircadia/vircadia/tree/master/tools/qt-builder")
+        hifi_utils.color('clear')
+        print('')
+        raise hifi_utils.SilentFatalError(2)