Rebind window surface fbo after native GL rendering

If the user called QGLFramebufferObject::bind()/release() during a
beginNativePainting() callout, the release() would reset the context's
fbo to zero, not the actual window surface fbo.

Task-number: QTBUG-6204
Reviewed-by: Tom

4 files changed, 14 insertions, 2 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 5ada125..94b8aa5 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -1495,6 +1495,7 @@ void QGLContextPrivate::init(QPaintDevice *dev, const QGLFormat &format)
     version_flags_cached = false;
     version_flags = QGLFormat::OpenGL_Version_None;
     current_fbo = 0;
+    default_fbo = 0;
     active_engine = 0;
 }
 
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index 8e472e5..ab72c9c 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -328,6 +328,7 @@ public:
     GLint max_texture_size;
 
     GLuint current_fbo;
+    GLuint default_fbo;
     QPaintEngine *active_engine;
 
     static inline QGLContextGroup *contextGroup(const QGLContext *ctx) { return ctx->d_ptr->group; }
diff --git a/src/opengl/qglframebufferobject.cpp b/src/opengl/qglframebufferobject.cpp
index d79283e..d0297c9 100644
--- a/src/opengl/qglframebufferobject.cpp
+++ b/src/opengl/qglframebufferobject.cpp
@@ -899,8 +899,8 @@ bool QGLFramebufferObject::release()
 #endif
 
     if (current) {
-        current->d_ptr->current_fbo = 0;
-        glBindFramebuffer(GL_FRAMEBUFFER_EXT, 0);
+        current->d_ptr->current_fbo = current->d_ptr->default_fbo;
+        glBindFramebuffer(GL_FRAMEBUFFER_EXT, current->d_ptr->default_fbo);
     }
 
     return true;
diff --git a/src/opengl/qglpaintdevice.cpp b/src/opengl/qglpaintdevice.cpp
index 2867de5..bcd90a5 100644
--- a/src/opengl/qglpaintdevice.cpp
+++ b/src/opengl/qglpaintdevice.cpp
@@ -89,6 +89,12 @@ void QGLPaintDevice::beginPaint()
         ctx->d_ptr->current_fbo = m_thisFBO;
         glBindFramebuffer(GL_FRAMEBUFFER_EXT, m_thisFBO);
     }
+
+    // Set the default fbo for the context to m_thisFBO so that
+    // if some raw GL code between beginNativePainting() and
+    // endNativePainting() calls QGLFramebufferObject::release(),
+    // painting will revert to the window surface's fbo.
+    ctx->d_ptr->default_fbo = m_thisFBO;
 }
 
 void QGLPaintDevice::ensureActiveTarget()
@@ -101,6 +107,8 @@ void QGLPaintDevice::ensureActiveTarget()
         ctx->d_ptr->current_fbo = m_thisFBO;
         glBindFramebuffer(GL_FRAMEBUFFER_EXT, m_thisFBO);
     }
+
+    ctx->d_ptr->default_fbo = m_thisFBO;
 }
 
 void QGLPaintDevice::endPaint()
@@ -111,6 +119,8 @@ void QGLPaintDevice::endPaint()
         ctx->d_ptr->current_fbo = m_previousFBO;
         glBindFramebuffer(GL_FRAMEBUFFER_EXT, m_previousFBO);
     }
+
+    ctx->d_ptr->default_fbo = 0;
 }
 
 QGLFormat QGLPaintDevice::format() const