Update FBO docs to describe how QPainter changes the GL state

Using a QPainter on a QGLFramebufferObject will not return the
GL context to its original conditions, especially with the OpenGL2
paint engine.  Update the docs to make this clearer.

Task-number: QTBUG-6712
Reviewed-by: Daniel Pope

1 files changed, 6 insertions, 0 deletions

diff --git a/src/opengl/qglframebufferobject.cpp b/src/opengl/qglframebufferobject.cpp
index d0297c9..4b5c30a 100644
--- a/src/opengl/qglframebufferobject.cpp
+++ b/src/opengl/qglframebufferobject.cpp
@@ -597,6 +597,12 @@ void QGLFramebufferObjectPrivate::init(QGLFramebufferObject *q, const QSize &sz,
     the constructors that take a QGLFramebufferObject parameter, and set the
     QGLFramebufferObject::samples() property to a non-zero value.
 
+    When painting to a QGLFramebufferObject using QPainter, the state of
+    the current GL context will be altered by the paint engine to reflect
+    its needs.  Applications should not rely upon the GL state being reset
+    to its original conditions, particularly the current shader program,
+    GL viewport, texture units, and drawing modes.
+
     For multisample framebuffer objects a color render buffer is created,
     otherwise a texture with the specified texture target is created.
     The color render buffer or texture will have the specified internal