From cbd28775246409df2e70b7f8ab2151d34ad061ba Mon Sep 17 00:00:00 2001
From: Olivier Prat <olivier@zvork.fr>
Date: Fri, 10 Nov 2017 11:26:20 +0100
Subject: [PATCH] Optimized shadow shader evaluation by computing concatenated
 shadow reprojection matrix on CPU

---
 libraries/render-utils/src/LightStage.cpp | 11 +++++++----
 libraries/render-utils/src/LightStage.h   |  6 ++++--
 libraries/render-utils/src/Shadow.slh     | 18 ++++--------------
 3 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/libraries/render-utils/src/LightStage.cpp b/libraries/render-utils/src/LightStage.cpp
index 411f179d49..eb712b075c 100644
--- a/libraries/render-utils/src/LightStage.cpp
+++ b/libraries/render-utils/src/LightStage.cpp
@@ -14,6 +14,11 @@
 #include "LightStage.h"
 
 std::string LightStage::_stageName { "LIGHT_STAGE"};
+const glm::mat4 LightStage::Shadow::_biasMatrix{
+    0.5, 0.0, 0.0, 0.0,
+    0.0, 0.5, 0.0, 0.0,
+    0.0, 0.0, 0.5, 0.0,
+    0.5, 0.5, 0.5, 1.0 };
 
 LightStage::LightStage() {
 }
@@ -92,8 +97,7 @@ void LightStage::Shadow::setKeylightFrustum(const ViewFrustum& viewFrustum,
     _frustum->calculate();
 
     // Update the buffer
-    _schemaBuffer.edit<Schema>().projection = ortho;
-    _schemaBuffer.edit<Schema>().viewInverse = viewInverse.getMatrix();
+    _schemaBuffer.edit<Schema>().reprojection = _biasMatrix * ortho * viewInverse.getMatrix();
 }
 
 void LightStage::Shadow::setFrustum(const ViewFrustum& shadowFrustum) {
@@ -102,8 +106,7 @@ void LightStage::Shadow::setFrustum(const ViewFrustum& shadowFrustum) {
 
     *_frustum = shadowFrustum;
     // Update the buffer
-    _schemaBuffer.edit<Schema>().projection = shadowFrustum.getProjection();
-    _schemaBuffer.edit<Schema>().viewInverse = viewInverse.getMatrix();
+    _schemaBuffer.edit<Schema>().reprojection = _biasMatrix * shadowFrustum.getProjection() * viewInverse.getMatrix();
 }
 
 const glm::mat4& LightStage::Shadow::getView() const {
diff --git a/libraries/render-utils/src/LightStage.h b/libraries/render-utils/src/LightStage.h
index 3a2a77055f..c45627c89b 100644
--- a/libraries/render-utils/src/LightStage.h
+++ b/libraries/render-utils/src/LightStage.h
@@ -62,6 +62,9 @@ public:
         gpu::TexturePointer map;
 
     protected:
+
+        static const glm::mat4 _biasMatrix;
+
         model::LightPointer _light;
         std::shared_ptr<ViewFrustum> _frustum;
 
@@ -70,8 +73,7 @@ public:
 
             Schema();
 
-            glm::mat4 projection;
-            glm::mat4 viewInverse;
+            glm::mat4 reprojection;
 
             glm::float32 bias;
             glm::float32 scale;
diff --git a/libraries/render-utils/src/Shadow.slh b/libraries/render-utils/src/Shadow.slh
index 300fa5e7b9..8abbc1de3e 100644
--- a/libraries/render-utils/src/Shadow.slh
+++ b/libraries/render-utils/src/Shadow.slh
@@ -15,8 +15,7 @@
 uniform sampler2DShadow shadowMap;
 
 struct ShadowTransform {
-	mat4 projection;
-	mat4 viewInverse;
+	mat4 reprojection;
 
 	float bias;
 	float scale;
@@ -26,12 +25,8 @@ uniform shadowTransformBuffer {
 	ShadowTransform _shadowTransform;
 };
 
-mat4 getShadowViewInverse() {
-	return _shadowTransform.viewInverse;
-}
-
-mat4 getShadowProjection() {
-	return _shadowTransform.projection;
+mat4 getShadowReprojection() {
+	return _shadowTransform.reprojection;
 }
 
 float getShadowScale() {
@@ -44,14 +39,9 @@ float getShadowBias() {
 
 // Compute the texture coordinates from world coordinates
 vec4 evalShadowTexcoord(vec4 position) {
-	mat4 biasMatrix = mat4(
-		0.5, 0.0, 0.0, 0.0,
-		0.0, 0.5, 0.0, 0.0,
-		0.0, 0.0, 0.5, 0.0,	
-		0.5, 0.5, 0.5, 1.0);
 	float bias = -getShadowBias();
 
-	vec4 shadowCoord = biasMatrix * getShadowProjection() * getShadowViewInverse() * position;
+	vec4 shadowCoord = getShadowReprojection() * position;
 	return vec4(shadowCoord.xy, shadowCoord.z + bias, 1.0);
 }