From 4696832ec6e072eb0d1b1e3eb79734e3322afd98 Mon Sep 17 00:00:00 2001
From: Andrzej Kapolka <drzej.k@gmail.com>
Date: Tue, 5 Aug 2014 15:13:50 -0700
Subject: [PATCH] Compute heightfield normals from adjacent values in vertex
 shader.

---
 .../resources/shaders/metavoxel_heightfield.vert     | 12 ++++++++++--
 interface/src/MetavoxelSystem.cpp                    |  5 +++++
 interface/src/MetavoxelSystem.h                      |  2 ++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/interface/resources/shaders/metavoxel_heightfield.vert b/interface/resources/shaders/metavoxel_heightfield.vert
index 3cf43e87cd..cc4f68e9e0 100644
--- a/interface/resources/shaders/metavoxel_heightfield.vert
+++ b/interface/resources/shaders/metavoxel_heightfield.vert
@@ -14,18 +14,26 @@
 // the height texture
 uniform sampler2D heightMap;
 
+// the distance between height points in texture space
+uniform float heightScale;
+
 // the interpolated normal
 varying vec4 normal;
 
 void main(void) {
     // transform and store the normal for interpolation
-    normal = normalize(gl_ModelViewMatrix * vec4(0.0, 1.0, 0.0, 0.0));
+    vec2 heightCoord = gl_MultiTexCoord0.st;
+    float deltaX = texture2D(heightMap, heightCoord - vec2(heightScale, 0.0)).r -
+        texture2D(heightMap, heightCoord + vec2(heightScale, 0.0)).r;
+    float deltaZ = texture2D(heightMap, heightCoord - vec2(0.0, heightScale)).r -
+        texture2D(heightMap, heightCoord + vec2(0.0, heightScale)).r;
+    normal = normalize(gl_ModelViewMatrix * vec4(deltaX, heightScale, deltaZ, 0.0));
     
     // pass along the texture coordinates
     gl_TexCoord[0] = gl_MultiTexCoord0;
     
     // add the height to the position
-    float height = texture2D(heightMap, gl_MultiTexCoord0.st).r;
+    float height = texture2D(heightMap, heightCoord).r;
     gl_Position = gl_ModelViewProjectionMatrix * (gl_Vertex + vec4(0.0, height, 0.0, 0.0));
     
     // the zero height should be invisible
diff --git a/interface/src/MetavoxelSystem.cpp b/interface/src/MetavoxelSystem.cpp
index 7aa6bc4080..f66d71070a 100644
--- a/interface/src/MetavoxelSystem.cpp
+++ b/interface/src/MetavoxelSystem.cpp
@@ -388,6 +388,9 @@ void HeightfieldBuffer::render() {
     glActiveTexture(GL_TEXTURE1);
     glBindTexture(GL_TEXTURE_2D, _colorTextureID);
     
+    DefaultMetavoxelRendererImplementation::getHeightfieldProgram().setUniformValue(
+        DefaultMetavoxelRendererImplementation::getHeightScaleLocation(), 1.0f / _heightSize);
+        
     glDrawRangeElements(GL_QUADS, 0, vertexCount - 1, indexCount, GL_UNSIGNED_INT, 0);
     
     glBindTexture(GL_TEXTURE_2D, 0);
@@ -470,6 +473,7 @@ void DefaultMetavoxelRendererImplementation::init() {
         _heightfieldProgram.bind();
         _heightfieldProgram.setUniformValue("heightMap", 0);
         _heightfieldProgram.setUniformValue("diffuseMap", 1);
+        _heightScaleLocation = _heightfieldProgram.uniformLocation("heightScale");
         _heightfieldProgram.release();
     }
 }
@@ -766,6 +770,7 @@ void DefaultMetavoxelRendererImplementation::render(MetavoxelData& data, Metavox
 ProgramObject DefaultMetavoxelRendererImplementation::_pointProgram;
 int DefaultMetavoxelRendererImplementation::_pointScaleLocation;
 ProgramObject DefaultMetavoxelRendererImplementation::_heightfieldProgram;
+int DefaultMetavoxelRendererImplementation::_heightScaleLocation;
 
 static void enableClipPlane(GLenum plane, float x, float y, float z, float w) {
     GLdouble coefficients[] = { x, y, z, w };
diff --git a/interface/src/MetavoxelSystem.h b/interface/src/MetavoxelSystem.h
index abcc929156..e7ee0d2c18 100644
--- a/interface/src/MetavoxelSystem.h
+++ b/interface/src/MetavoxelSystem.h
@@ -191,6 +191,7 @@ public:
     static void init();
 
     static ProgramObject& getHeightfieldProgram() { return _heightfieldProgram; }
+    static int getHeightScaleLocation() { return _heightScaleLocation; }
 
     Q_INVOKABLE DefaultMetavoxelRendererImplementation();
     
@@ -204,6 +205,7 @@ private:
     static int _pointScaleLocation;
     
     static ProgramObject _heightfieldProgram;
+    static int _heightScaleLocation;
 };
 
 /// Base class for spanner renderers; provides clipping.