Added a warning to QGLWidget::renderText().

renderText() can't be used while a GL 2 paint engine is active on the
same device, because it will clash with the GL 1 engine and wreck havoc.
We simply don't support that scenario.

Task-number: QTBUG-7592
Reviewed-by: Samuel

1 files changed, 20 insertions, 2 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 48e43b297d..2a607089be 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -4419,8 +4419,17 @@ void QGLWidget::renderText(int x, int y, const QString &str, const QFont &font,
     bool auto_swap = autoBufferSwap();
 
     QPaintEngine::Type oldEngineType = qgl_engine_selector()->preferredPaintEngine();
-    qgl_engine_selector()->setPreferredPaintEngine(QPaintEngine::OpenGL);
+
     QPaintEngine *engine = paintEngine();
+    if (engine && (oldEngineType == QPaintEngine::OpenGL2) && engine->isActive()) {
+        qWarning("QGLWidget::renderText(): Calling renderText() while a GL 2 paint engine is"
+                 " active on the same device is not allowed.");
+        return;
+    }
+
+    // this changes what paintEngine() returns
+    qgl_engine_selector()->setPreferredPaintEngine(QPaintEngine::OpenGL);
+    engine = paintEngine();
     QPainter *p;
     bool reuse_painter = false;
     if (engine->isActive()) {
@@ -4513,8 +4522,17 @@ void QGLWidget::renderText(double x, double y, double z, const QString &str, con
     win_y = height - win_y; // y is inverted
 
     QPaintEngine::Type oldEngineType = qgl_engine_selector()->preferredPaintEngine();
-    qgl_engine_selector()->setPreferredPaintEngine(QPaintEngine::OpenGL);
     QPaintEngine *engine = paintEngine();
+
+    if (engine && (oldEngineType == QPaintEngine::OpenGL2) && engine->isActive()) {
+        qWarning("QGLWidget::renderText(): Calling renderText() while a GL 2 paint engine is"
+                 " active on the same device is not allowed.");
+        return;
+    }
+
+    // this changes what paintEngine() returns
+    qgl_engine_selector()->setPreferredPaintEngine(QPaintEngine::OpenGL);
+    engine = paintEngine();
     QPainter *p;
     bool reuse_painter = false;
     bool use_depth_testing = glIsEnabled(GL_DEPTH_TEST);