Implement MetalRough shader optimization TODO

Calculate specularMipLevels only once, on the CPU.

Change-Id: I694e3d5e45ea369875ac3ecff36f885b3f669bcf
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

5 files changed, 9 insertions, 20 deletions

diff --git a/src/extras/shaders/es3/light.inc.frag b/src/extras/shaders/es3/light.inc.frag
index 18012ccc1..7b6bf3bc5 100644
--- a/src/extras/shaders/es3/light.inc.frag
+++ b/src/extras/shaders/es3/light.inc.frag
@@ -20,6 +20,7 @@ uniform int lightCount;
 struct EnvironmentLight {
     highp samplerCube irradiance; // For diffuse contribution
     highp samplerCube specular; // For specular contribution
+    int specularMipLevels;
 };
 uniform EnvironmentLight envLight;
 uniform int envLightCount;
diff --git a/src/extras/shaders/es3/metalrough.inc.frag b/src/extras/shaders/es3/metalrough.inc.frag
index 188a367f5..fc014b81b 100644
--- a/src/extras/shaders/es3/metalrough.inc.frag
+++ b/src/extras/shaders/es3/metalrough.inc.frag
@@ -59,13 +59,6 @@ const FP float gamma = 2.2;
 
 #pragma include light.inc.frag
 
-int mipLevelCount(const in FP samplerCube cube)
-{
-   int baseSize = textureSize(cube, 0).x;
-   int nMips = int(log2(float(baseSize > 0 ? baseSize : 1))) + 1;
-   return nMips;
-}
-
 FP float remapRoughness(const in FP float roughness)
 {
     // As per page 14 of
@@ -91,10 +84,8 @@ FP float alphaToMipLevel(FP float alpha)
     const FP float k1 = 0.9921;
     FP float glossiness = (pow(2.0, -10.0 / sqrt(specPower)) - k0) / k1;
 
-    // TODO: Optimize by doing this on CPU and set as
-    // uniform int envLight.specularMipLevels say (if present in shader).
     // Lookup the number of mips in the specular envmap
-    int mipLevels = mipLevelCount(envLight.specular);
+    int mipLevels = envLight.specularMipLevels;
 
     // Offset of smallest miplevel we should use (corresponds to specular
     // power of 1). I.e. in the 32x32 sized mip.
diff --git a/src/extras/shaders/gl3/light.inc.frag b/src/extras/shaders/gl3/light.inc.frag
index 0b642638f..a1b07a976 100644
--- a/src/extras/shaders/gl3/light.inc.frag
+++ b/src/extras/shaders/gl3/light.inc.frag
@@ -20,6 +20,7 @@ uniform int lightCount;
 struct EnvironmentLight {
     samplerCube irradiance; // For diffuse contribution
     samplerCube specular; // For specular contribution
+    int specularMipLevels;
 };
 uniform EnvironmentLight envLight;
 uniform int envLightCount = 0;
diff --git a/src/extras/shaders/gl3/metalrough.inc.frag b/src/extras/shaders/gl3/metalrough.inc.frag
index f7e3eecb7..f5fb81f51 100644
--- a/src/extras/shaders/gl3/metalrough.inc.frag
+++ b/src/extras/shaders/gl3/metalrough.inc.frag
@@ -55,13 +55,6 @@ uniform float gamma = 2.2;
 
 #pragma include light.inc.frag
 
-int mipLevelCount(const in samplerCube cube)
-{
-   int baseSize = textureSize(cube, 0).x;
-   int nMips = int(log2(float(baseSize > 0 ? baseSize : 1))) + 1;
-   return nMips;
-}
-
 float remapRoughness(const in float roughness)
 {
     // As per page 14 of
@@ -87,10 +80,8 @@ float alphaToMipLevel(float alpha)
     const float k1 = 0.9921;
     float glossiness = (pow(2.0, -10.0 / sqrt(specPower)) - k0) / k1;
 
-    // TODO: Optimize by doing this on CPU and set as
-    // uniform int envLight.specularMipLevels say (if present in shader).
     // Lookup the number of mips in the specular envmap
-    int mipLevels = mipLevelCount(envLight.specular);
+    int mipLevels = envLight.specularMipLevels;
 
     // Offset of smallest miplevel we should use (corresponds to specular
     // power of 1). I.e. in the 32x32 sized mip.
diff --git a/src/render/lights/qenvironmentlight.cpp b/src/render/lights/qenvironmentlight.cpp
index 977e117db..9510bda8f 100644
--- a/src/render/lights/qenvironmentlight.cpp
+++ b/src/render/lights/qenvironmentlight.cpp
@@ -42,6 +42,8 @@
 #include "qabstracttexture.h"
 #include <QVector3D>
 
+#include <cmath>
+
 QT_BEGIN_NAMESPACE
 
 namespace Qt3DRender
@@ -98,6 +100,9 @@ void QEnvironmentLightPrivate::_q_updateEnvMapsSize()
                                  m_specular->height(),
                                  m_specular->depth());
     m_shaderData->setProperty("specularSize", QVariant::fromValue(specularSize));
+
+    const int levels = int(std::log2(specularSize.x() > 0.0f ? specularSize.x() : 1.0f)) + 1;
+    m_shaderData->setProperty("specularMipLevels", QVariant::fromValue(levels));
 }
 
 Qt3DCore::QNodeCreatedChangeBasePtr QEnvironmentLight::createNodeCreationChange() const