Add support for advanced blend equations to our OpenGL QPainter

Mesa and NVidia have been supporting these extensions several years now.
It also means we can get rid of the dead unused code we had for advanced
compositions.

Change-Id: I6a2fcda13490abd977eb4cc3d8b34f186d05ca25
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 68 insertions, 1 deletions

diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index 17dc9df619..fb7e6fce97 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -87,8 +87,27 @@
 
 #include <QDebug>
 
-QT_BEGIN_NAMESPACE
+#ifndef GL_KHR_blend_equation_advanced
+#define GL_KHR_blend_equation_advanced 1
+#define GL_MULTIPLY_KHR                   0x9294
+#define GL_SCREEN_KHR                     0x9295
+#define GL_OVERLAY_KHR                    0x9296
+#define GL_DARKEN_KHR                     0x9297
+#define GL_LIGHTEN_KHR                    0x9298
+#define GL_COLORDODGE_KHR                 0x9299
+#define GL_COLORBURN_KHR                  0x929A
+#define GL_HARDLIGHT_KHR                  0x929B
+#define GL_SOFTLIGHT_KHR                  0x929C
+#define GL_DIFFERENCE_KHR                 0x929E
+#define GL_EXCLUSION_KHR                  0x92A0
+#endif /* GL_KHR_blend_equation_advanced */
+
+#ifndef GL_KHR_blend_equation_advanced_coherent
+#define GL_KHR_blend_equation_advanced_coherent 1
+#define GL_BLEND_ADVANCED_COHERENT_KHR    0x9285
+#endif /* GL_KHR_blend_equation_advanced_coherent */
 
+QT_BEGIN_NAMESPACE
 
 
 Q_GUI_EXPORT QImage qt_imageForBrush(int brushStyle, bool invert);
@@ -498,6 +517,21 @@ void QOpenGL2PaintEngineExPrivate::updateCompositionMode()
     // NOTE: The entire paint engine works on pre-multiplied data - which is why some of these
     //       composition modes look odd.
 //     qDebug() << "QOpenGL2PaintEngineExPrivate::updateCompositionMode() - Setting GL composition mode for " << q->state()->composition_mode;
+    if (ctx->functions()->hasOpenGLFeature(QOpenGLFunctions::BlendEquationAdvanced)) {
+       if (q->state()->composition_mode <= QPainter::CompositionMode_Plus) {
+           funcs.glDisable(GL_BLEND_ADVANCED_COHERENT_KHR);
+           funcs.glBlendEquation(GL_FUNC_ADD);
+       } else {
+           funcs.glEnable(GL_BLEND_ADVANCED_COHERENT_KHR);
+       }
+       shaderManager->setCompositionMode(q->state()->composition_mode);
+    } else {
+        if (q->state()->composition_mode > QPainter::CompositionMode_Plus) {
+            qWarning("Unsupported composition mode");
+            compositionModeDirty = false;
+            return;
+        }
+    }
     switch(q->state()->composition_mode) {
     case QPainter::CompositionMode_SourceOver:
         funcs.glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
@@ -538,6 +572,39 @@ void QOpenGL2PaintEngineExPrivate::updateCompositionMode()
     case QPainter::CompositionMode_Plus:
         funcs.glBlendFunc(GL_ONE, GL_ONE);
         break;
+    case QPainter::CompositionMode_Multiply:
+        funcs.glBlendEquation(GL_MULTIPLY_KHR);
+        break;
+    case QPainter::CompositionMode_Screen:
+        funcs.glBlendEquation(GL_SCREEN_KHR);
+        break;
+    case QPainter::CompositionMode_Overlay:
+        funcs.glBlendEquation(GL_OVERLAY_KHR);
+        break;
+    case QPainter::CompositionMode_Darken:
+        funcs.glBlendEquation(GL_DARKEN_KHR);
+        break;
+    case QPainter::CompositionMode_Lighten:
+        funcs.glBlendEquation(GL_LIGHTEN_KHR);
+        break;
+    case QPainter::CompositionMode_ColorDodge:
+        funcs.glBlendEquation(GL_COLORDODGE_KHR);
+        break;
+    case QPainter::CompositionMode_ColorBurn:
+        funcs.glBlendEquation(GL_COLORBURN_KHR);
+        break;
+    case QPainter::CompositionMode_HardLight:
+        funcs.glBlendEquation(GL_HARDLIGHT_KHR);
+        break;
+    case QPainter::CompositionMode_SoftLight:
+        funcs.glBlendEquation(GL_SOFTLIGHT_KHR);
+        break;
+    case QPainter::CompositionMode_Difference:
+        funcs.glBlendEquation(GL_DIFFERENCE_KHR);
+        break;
+    case QPainter::CompositionMode_Exclusion:
+        funcs.glBlendEquation(GL_EXCLUSION_KHR);
+        break;
     default:
         qWarning("Unsupported composition mode");
         break;