1 files changed, 21 insertions, 19 deletions

diff --git a/src/opengl/qpaintengine_opengl.cpp b/src/opengl/qpaintengine_opengl.cpp
index 80628a228f..aa6b6c9ac2 100644
--- a/src/opengl/qpaintengine_opengl.cpp
+++ b/src/opengl/qpaintengine_opengl.cpp
@@ -746,7 +746,6 @@ public:
     uint has_brush : 1;
     uint has_fast_pen : 1;
     uint use_stencil_method : 1;
-    uint dirty_stencil : 1;
     uint dirty_drawable_texture : 1;
     uint has_stencil_face_ext : 1;
     uint use_fragment_programs : 1;
@@ -757,6 +756,8 @@ public:
     uint use_system_clip : 1;
     uint use_emulation : 1;
 
+    QRegion dirty_stencil;
+
     void updateUseEmulation();
 
     QTransform matrix;
@@ -1259,7 +1260,9 @@ bool QOpenGLPaintEngine::begin(QPaintDevice *pdev)
     d->matrix = QTransform();
     d->has_antialiasing = false;
     d->high_quality_antialiasing = false;
-    d->dirty_stencil = true;
+
+    QSize sz(d->device->size());
+    d->dirty_stencil = QRect(0, 0, sz.width(), sz.height());
 
     d->use_emulation = false;
 
@@ -1347,7 +1350,6 @@ bool QOpenGLPaintEngine::begin(QPaintDevice *pdev)
 
     d->offscreen.begin();
 
-    QSize sz(d->device->size());
     glViewport(0, 0, sz.width(), sz.height()); // XXX (Embedded): We need a solution for GLWidgets that draw in a part or a bigger surface...
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
@@ -1949,34 +1951,34 @@ void QOpenGLPaintEnginePrivate::fillVertexArray(Qt::FillRule fillRule)
 {
     Q_Q(QOpenGLPaintEngine);
 
-    if (dirty_stencil) {
-        disableClipping();
+    QRect rect = dirty_stencil.boundingRect();
 
-        if (use_system_clip) {
-            glEnable(GL_SCISSOR_TEST);
+    if (use_system_clip)
+        rect = q->systemClip().intersected(dirty_stencil).boundingRect();
 
-            QRect rect = q->systemClip().boundingRect();
+    glStencilMask(~0);
 
-            const int left = rect.left();
-            const int width = rect.width();
-            const int bottom = device->size().height() - (rect.bottom() + 1);
-            const int height = rect.height();
+    if (!rect.isEmpty()) {
+        disableClipping();
 
-            glScissor(left, bottom, width, height);
-        }
+        glEnable(GL_SCISSOR_TEST);
+
+        const int left = rect.left();
+        const int width = rect.width();
+        const int bottom = device->size().height() - (rect.bottom() + 1);
+        const int height = rect.height();
+
+        glScissor(left, bottom, width, height);
 
         glClearStencil(0);
         glClear(GL_STENCIL_BUFFER_BIT);
-        dirty_stencil = false;
+        dirty_stencil -= rect;
 
-        if (use_system_clip)
-            glDisable(GL_SCISSOR_TEST);
+        glDisable(GL_SCISSOR_TEST);
 
         enableClipping();
     }
 
-    glStencilMask(~0);
-
     // Enable stencil.
     glEnable(GL_STENCIL_TEST);