GL paint engine: Fix drawPixmapFragments when using buffer objects

Until recently the buffer object-based code path (so not client-side
pointers) was only hit with a core profile context. This changed at
some point in 6.4 and later to support WebGL (that has no client-side
pointers, unlike OpenGL ES 2.0 it is based on). Now buffer objects
are preferred over client-side pointers, always. Problem is,
drawPixmapFragment() was never functional on this code path, it seems.

Expecting that transferMode() does all the uploadData() needed is wrong.
transferMode() bails out if the mode is the same as before, and that's
exactly what happens when an application calls drawPixmapFragments()
on the painter twice, after each other.

How exactly this works with client-side pointers is not fully clear, but
presumably the data buffer address stays the same so all pointers passed
in to the glVertexAttribPointer calls are valid, and it sources the data
for each draw call (probably), thus the rendering is all correct even
though only the first, not the second, drawPixmapFragment() led to
calling uploadData() internally.

Amends e487b07e18f1cb7ff126744be57b2ae1b9839c6c although this patch on
its own is just as applicable pre-6.4 as well (to fix drawPixmapFragments
when using a core profile context).

Pick-to: 6.5.0 6.5 6.4 6.2
Fixes: QTBUG-111416
Change-Id: I2ad358424e613192a51b99b937aef7660f5dbe08
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/opengl/qopenglpaintengine.cpp b/src/opengl/qopenglpaintengine.cpp
index 062eaa6a53..f78ad26551 100644
--- a/src/opengl/qopenglpaintengine.cpp
+++ b/src/opengl/qopenglpaintengine.cpp
@@ -2133,6 +2133,10 @@ void QOpenGL2PaintEngineExPrivate::drawPixmapFragments(const QPainter::PixmapFra
 
     transferMode(ImageOpacityArrayDrawingMode);
 
+    uploadData(QT_VERTEX_COORDS_ATTR, (GLfloat*)vertexCoordinateArray.data(), vertexCoordinateArray.vertexCount() * 2);
+    uploadData(QT_TEXTURE_COORDS_ATTR, (GLfloat*)textureCoordinateArray.data(), textureCoordinateArray.vertexCount() * 2);
+    uploadData(QT_OPACITY_ATTR, (GLfloat*)opacityArray.data(), opacityArray.size());
+
     GLenum filterMode = q->state()->renderHints & QPainter::SmoothPixmapTransform ? GL_LINEAR : GL_NEAREST;
     updateTexture(QT_IMAGE_TEXTURE_UNIT, pixmap, GL_CLAMP_TO_EDGE, filterMode);