Premultiply clear color before clear

The framebuffer holds premultiplied colors so the clear color must be
premultiplied before clearing.

Task-number: QT3DS-3689
Change-Id: I5064321d2cacd21bcf9939b7ae195804938859aa
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Jari Karppinen <jari.karppinen@qt.io>
Reviewed-by: Pasi Keränen <pasi.keranen@qt.io>
 

3 files changed, 36 insertions, 5 deletions

diff --git a/src/runtimerender/Qt3DSRenderContextCore.cpp b/src/runtimerender/Qt3DSRenderContextCore.cpp
index 7c84a5a..b5f9bc9 100644
--- a/src/runtimerender/Qt3DSRenderContextCore.cpp
+++ b/src/runtimerender/Qt3DSRenderContextCore.cpp
@@ -708,6 +708,12 @@ struct SRenderContext : public IQt3DSRenderContext
                 theClearColor = m_MatteColor;
             else if (m_SceneColor.hasValue())
                 theClearColor = m_SceneColor;
+            //premultiply the clear color
+            if (theClearColor.w < 1.0f) {
+                theClearColor.x *= theClearColor.w;
+                theClearColor.y *= theClearColor.w;
+                theClearColor.z *= theClearColor.w;
+            }
             m_RenderContext->SetClearColor(theClearColor);
             m_RenderContext->Clear(qt3ds::render::NVRenderClearValues::Color);
         }
@@ -727,7 +733,13 @@ struct SRenderContext : public IQt3DSRenderContext
                     m_RotationDepthBuffer = NULL;
                 }
                 if (m_SceneColor.hasValue() && m_SceneColor.getValue().w != 0.0f) {
-                    m_RenderContext->SetClearColor(m_SceneColor);
+                    QT3DSVec4 theClearColor = m_SceneColor;
+                    if (theClearColor.w < 1.0f) {
+                        theClearColor.x *= theClearColor.w;
+                        theClearColor.y *= theClearColor.w;
+                        theClearColor.z *= theClearColor.w;
+                    }
+                    m_RenderContext->SetClearColor(theClearColor);
                     m_RenderContext->Clear(qt3ds::render::NVRenderClearValues::Color);
                 }
             } else {
@@ -758,7 +770,13 @@ struct SRenderContext : public IQt3DSRenderContext
                 }
                 m_RenderContext->SetRenderTarget(m_RotationFBO);
                 if (m_SceneColor.hasValue()) {
-                    m_RenderContext->SetClearColor(m_SceneColor);
+                    QT3DSVec4 theClearColor = m_SceneColor;
+                    if (theClearColor.w < 1.0f) {
+                        theClearColor.x *= theClearColor.w;
+                        theClearColor.y *= theClearColor.w;
+                        theClearColor.z *= theClearColor.w;
+                    }
+                    m_RenderContext->SetClearColor(theClearColor);
                     m_RenderContext->Clear(qt3ds::render::NVRenderClearValues::Color);
                 }
             }
diff --git a/src/runtimerender/rendererimpl/Qt3DSRendererImplLayerRenderData.cpp b/src/runtimerender/rendererimpl/Qt3DSRendererImplLayerRenderData.cpp
index 362a602..43934b1 100644
--- a/src/runtimerender/rendererimpl/Qt3DSRendererImplLayerRenderData.cpp
+++ b/src/runtimerender/rendererimpl/Qt3DSRendererImplLayerRenderData.cpp
@@ -1490,8 +1490,15 @@ namespace render {
                 theRenderContext, &NVRenderContext::GetViewport, &NVRenderContext::SetViewport,
                 theNewViewport);
             QT3DSVec4 clearColor(0.0f);
-            if (m_Layer.m_Background == LayerBackground::Color)
+            if (m_Layer.m_Background == LayerBackground::Color) {
                 clearColor = m_Layer.m_ClearColor;
+                // Framebuffer holds premultiplied colors so the clearcolor must be premultiplied
+                if (clearColor.w < 1.0f) {
+                    clearColor.x *= clearColor.w;
+                    clearColor.y *= clearColor.w;
+                    clearColor.z *= clearColor.w;
+                }
+            }
 
             NVRenderContextScopedProperty<QT3DSVec4> __clearColor(
                 theRenderContext, &NVRenderContext::GetClearColor, &NVRenderContext::SetClearColor,
@@ -1776,9 +1783,16 @@ namespace render {
             theContext.SetScissorRect(
                 m_LayerPrepResult->GetLayerToPresentationScissorRect().ToIntegerRect());
             if (m_Layer.m_Background == LayerBackground::Color) {
+                QT3DSVec4 clearColor = m_Layer.m_ClearColor;
+                // Framebuffer holds premultiplied colors so the clearcolor must be premultiplied
+                if (clearColor.w < 1.0f) {
+                    clearColor.x *= clearColor.w;
+                    clearColor.y *= clearColor.w;
+                    clearColor.z *= clearColor.w;
+                }
                 NVRenderContextScopedProperty<QT3DSVec4> __clearColor(
                     theContext, &NVRenderContext::GetClearColor, &NVRenderContext::SetClearColor,
-                    m_Layer.m_ClearColor);
+                    clearColor);
                 theContext.Clear(NVRenderClearValues::Color);
             }
             RenderToViewport();
diff --git a/src/runtimerender/rendererimpl/Qt3DSRendererImplShaders.cpp b/src/runtimerender/rendererimpl/Qt3DSRendererImplShaders.cpp
index a3d3fab..eb560aa 100644
--- a/src/runtimerender/rendererimpl/Qt3DSRendererImplShaders.cpp
+++ b/src/runtimerender/rendererimpl/Qt3DSRendererImplShaders.cpp
@@ -2399,7 +2399,6 @@ namespace render {
         fragmentGenerator.Append("void main() {");
         fragmentGenerator.Append("\tvec2 theCoords = uv_coords;\n");
         fragmentGenerator.Append("\tvec4 theLayerTexture = texture2D( layer_image, theCoords );\n");
-        fragmentGenerator.Append("\tif( theLayerTexture.a == 0.0 ) discard;\n");
         fragmentGenerator.Append("\tfragOutput = theLayerTexture;\n");
         fragmentGenerator.Append("}");
         NVRenderShaderProgram *theShader = GetProgramGenerator().CompileGeneratedShader(