Optimize OpenGL binding of ARGB32PM backing store

Detect premultiplied backing store and upload it without conversion
and adjust blend to not multiply alpha again.

Task-number: QTBUG-50381
Change-Id: I51939c4f82fbb0c48eaca6e2475bf4cf3722bc2d
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

4 files changed, 60 insertions, 19 deletions

diff --git a/src/gui/kernel/qplatformgraphicsbufferhelper.cpp b/src/gui/kernel/qplatformgraphicsbufferhelper.cpp
index 1d59c38598..7f2672bc5e 100644
--- a/src/gui/kernel/qplatformgraphicsbufferhelper.cpp
+++ b/src/gui/kernel/qplatformgraphicsbufferhelper.cpp
@@ -64,7 +64,7 @@ QT_BEGIN_NAMESPACE
     bound texture, otherwise returns false.
 */
 bool QPlatformGraphicsBufferHelper::lockAndBindToTexture(QPlatformGraphicsBuffer *graphicsBuffer,
-                                                         bool *swizzle,
+                                                         bool *swizzle, bool *premultiplied,
                                                          const QRect &rect)
 {
     if (graphicsBuffer->lock(QPlatformGraphicsBuffer::TextureAccess)) {
@@ -74,8 +74,10 @@ bool QPlatformGraphicsBufferHelper::lockAndBindToTexture(QPlatformGraphicsBuffer
         }
         if (swizzle)
             *swizzle = false;
+        if (premultiplied)
+            *premultiplied = false;
     } else if (graphicsBuffer->lock(QPlatformGraphicsBuffer::SWReadAccess)) {
-        if (!bindSWToTexture(graphicsBuffer, swizzle, rect)) {
+        if (!bindSWToTexture(graphicsBuffer, swizzle, premultiplied, rect)) {
             qWarning("Failed to bind %sgraphicsbuffer to texture", "SW ");
             return false;
         }
@@ -109,7 +111,7 @@ bool QPlatformGraphicsBufferHelper::lockAndBindToTexture(QPlatformGraphicsBuffer
     Returns true on success, otherwise false.
 */
 bool QPlatformGraphicsBufferHelper::bindSWToTexture(const QPlatformGraphicsBuffer *graphicsBuffer,
-                                                    bool *swizzleRandB,
+                                                    bool *swizzleRandB, bool *premultipliedB,
                                                     const QRect &subRect)
 {
 #ifndef QT_NO_OPENGL
@@ -124,14 +126,30 @@ bool QPlatformGraphicsBufferHelper::bindSWToTexture(const QPlatformGraphicsBuffe
     Q_ASSERT(subRect.isEmpty() || QRect(QPoint(0,0), size).contains(subRect));
 
     bool swizzle = false;
+    bool premultiplied = false;
     QImage::Format imageformat = QImage::toImageFormat(graphicsBuffer->format());
     QImage image(graphicsBuffer->data(), size.width(), size.height(), graphicsBuffer->bytesPerLine(), imageformat);
     if (graphicsBuffer->bytesPerLine() != (size.width() * 4)) {
         image = image.convertToFormat(QImage::Format_RGBA8888);
-    } else if (imageformat == QImage::Format_RGB32) {
-        swizzle = true;
-    } else if (imageformat != QImage::Format_RGBA8888) {
-        image = image.convertToFormat(QImage::Format_RGBA8888);
+    } else {
+        switch (imageformat) {
+        case QImage::Format_ARGB32_Premultiplied:
+            premultiplied = true;
+            // no break
+        case QImage::Format_RGB32:
+        case QImage::Format_ARGB32:
+            swizzle = true;
+            break;
+        case QImage::Format_RGBA8888_Premultiplied:
+            premultiplied = true;
+            // no break
+        case QImage::Format_RGBX8888:
+        case QImage::Format_RGBA8888:
+            break;
+        default:
+            image = image.convertToFormat(QImage::Format_RGBA8888);
+            break;
+        }
     }
 
     QOpenGLFunctions *funcs = QOpenGLContext::currentContext()->functions();
@@ -170,6 +188,8 @@ bool QPlatformGraphicsBufferHelper::bindSWToTexture(const QPlatformGraphicsBuffe
     }
     if (swizzleRandB)
         *swizzleRandB = swizzle;
+    if (premultipliedB)
+        *premultipliedB = premultiplied;
 
     return true;
 
diff --git a/src/gui/kernel/qplatformgraphicsbufferhelper.h b/src/gui/kernel/qplatformgraphicsbufferhelper.h
index ded7810608..cc1a4918cd 100644
--- a/src/gui/kernel/qplatformgraphicsbufferhelper.h
+++ b/src/gui/kernel/qplatformgraphicsbufferhelper.h
@@ -39,8 +39,8 @@
 QT_BEGIN_NAMESPACE
 
 namespace QPlatformGraphicsBufferHelper {
-    bool lockAndBindToTexture(QPlatformGraphicsBuffer *graphicsBuffer, bool *swizzleRandB, const QRect &rect = QRect());
-    bool bindSWToTexture(const QPlatformGraphicsBuffer *graphicsBuffer, bool *swizzleRandB = Q_NULLPTR, const QRect &rect = QRect());
+    bool lockAndBindToTexture(QPlatformGraphicsBuffer *graphicsBuffer, bool *swizzleRandB, bool *premultipliedB, const QRect &rect = QRect());
+    bool bindSWToTexture(const QPlatformGraphicsBuffer *graphicsBuffer, bool *swizzleRandB = Q_NULLPTR, bool *premultipliedB = Q_NULLPTR, const QRect &rect = QRect());
 }
 
 QT_END_NAMESPACE
diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index 4b725fc79f..ef1652b48b 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -92,6 +92,7 @@ public:
     mutable GLuint textureId;
     mutable QSize textureSize;
     mutable bool needsSwizzle;
+    mutable bool premultiplied;
     QOpenGLTextureBlitter *blitter;
 #endif
 };
@@ -323,9 +324,6 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
             blitTextureForWidget(textures, i, window, deviceWindowRect, d_ptr->blitter, offset);
     }
 
-    funcs->glEnable(GL_BLEND);
-    funcs->glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
-
     // Backingstore texture with the normal widgets.
     GLuint textureId = 0;
     QOpenGLTextureBlitter::Origin origin = QOpenGLTextureBlitter::OriginTopLeft;
@@ -345,7 +343,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
             funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
             funcs->glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
-            if (QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle)) {
+            if (QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle, &d_ptr->premultiplied)) {
                 d_ptr->textureSize = graphicsBuffer->size();
             } else {
                 d_ptr->textureSize = QSize(0,0);
@@ -354,7 +352,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
             graphicsBuffer->unlock();
         } else if (!region.isEmpty()){
             funcs->glBindTexture(GL_TEXTURE_2D, d_ptr->textureId);
-            QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle);
+            QPlatformGraphicsBufferHelper::lockAndBindToTexture(graphicsBuffer, &d_ptr->needsSwizzle, &d_ptr->premultiplied);
         }
 
         if (graphicsBuffer->origin() == QPlatformGraphicsBuffer::OriginBottomLeft)
@@ -364,10 +362,17 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
         TextureFlags flags = 0;
         textureId = toTexture(deviceRegion(region, window, offset), &d_ptr->textureSize, &flags);
         d_ptr->needsSwizzle = (flags & TextureSwizzle) != 0;
+        d_ptr->premultiplied = (flags & TexturePremultiplied) != 0;
         if (flags & TextureFlip)
             origin = QOpenGLTextureBlitter::OriginBottomLeft;
     }
 
+    funcs->glEnable(GL_BLEND);
+    if (d_ptr->premultiplied)
+        funcs->glBlendFuncSeparate(GL_ONE, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
+    else
+        funcs->glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE);
+
     if (textureId) {
         if (d_ptr->needsSwizzle)
             d_ptr->blitter->setSwizzleRB(true);
@@ -443,10 +448,26 @@ GLuint QPlatformBackingStore::toTexture(const QRegion &dirtyRegion, QSize *textu
     QImage image = toImage();
     QSize imageSize = image.size();
 
+    bool needConvert = false;
     *flags = 0;
-    if (image.format() == QImage::Format_RGB32)
+    switch (image.format()) {
+    case QImage::Format_ARGB32_Premultiplied:
+        *flags |= TexturePremultiplied;
+        // no break
+    case QImage::Format_RGB32:
+    case QImage::Format_ARGB32:
         *flags |= TextureSwizzle;
-
+        break;
+    case QImage::Format_RGBA8888_Premultiplied:
+        *flags |= TexturePremultiplied;
+        // no break
+    case QImage::Format_RGBX8888:
+    case QImage::Format_RGBA8888:
+        break;
+    default:
+        needConvert = true;
+        break;
+    }
     if (imageSize.isEmpty()) {
         *textureSize = imageSize;
         return 0;
@@ -460,8 +481,7 @@ GLuint QPlatformBackingStore::toTexture(const QRegion &dirtyRegion, QSize *textu
 
     *textureSize = imageSize;
 
-    // Fast path for RGB32 and RGBA8888, convert everything else to RGBA8888.
-    if (image.format() != QImage::Format_RGB32 && image.format() != QImage::Format_RGBA8888)
+    if (needConvert)
         image = image.convertToFormat(QImage::Format_RGBA8888);
 
     QOpenGLFunctions *funcs = QOpenGLContext::currentContext()->functions();
diff --git a/src/gui/painting/qplatformbackingstore.h b/src/gui/painting/qplatformbackingstore.h
index eac97e9cf6..9c8da0d1db 100644
--- a/src/gui/painting/qplatformbackingstore.h
+++ b/src/gui/painting/qplatformbackingstore.h
@@ -118,7 +118,8 @@ public:
     virtual QImage toImage() const;
     enum TextureFlag {
         TextureSwizzle = 0x01,
-        TextureFlip = 0x02
+        TextureFlip = 0x02,
+        TexturePremultiplied = 0x04,
     };
     Q_DECLARE_FLAGS(TextureFlags, TextureFlag)
     virtual GLuint toTexture(const QRegion &dirtyRegion, QSize *textureSize, TextureFlags *flags) const;