Reset bound fbo at the end of the rendering

The last bound fbo must be reset at the end of the rendering if the bound
fbo was changed due to render-to-texture. Otherwise offscreen rendering(in
scene3d case) might have wrong bound fbo. Also in threaded mode, if the
last renderview was rtt, the current fbo remains bound, and the next frame
doesn't render to the surface as expected.

Change-Id: I842040766aa6010740b008a36f7f9f2c935b0561
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

3 files changed, 12 insertions, 0 deletions

diff --git a/src/render/backend/renderer.cpp b/src/render/backend/renderer.cpp
index c91eff86e..49f2f4434 100644
--- a/src/render/backend/renderer.cpp
+++ b/src/render/backend/renderer.cpp
@@ -908,6 +908,12 @@ Renderer::ViewSubmissionResultData Renderer::submitRenderViews(const QVector<Ren
         frameElapsed = timer.elapsed();
     }
 
+    // Bind lastBoundFBOId back. Needed also in threaded mode.
+    // lastBoundFBOId != m_graphicsContext->activeFBO() when the last FrameGraph leaf node/renderView
+    // contains RenderTargetSelector/RenderTarget
+    if (lastBoundFBOId != m_graphicsContext->activeFBO())
+        m_graphicsContext->bindFramebuffer(lastBoundFBOId);
+
     // Reset state and call doneCurrent if the surface
     // is valid and was actually activated
     if (surface && m_graphicsContext->hasValidGLHelper()) {
diff --git a/src/render/graphicshelpers/graphicscontext.cpp b/src/render/graphicshelpers/graphicscontext.cpp
index 2fc36c306..3a67db729 100644
--- a/src/render/graphicshelpers/graphicscontext.cpp
+++ b/src/render/graphicshelpers/graphicscontext.cpp
@@ -843,6 +843,11 @@ void GraphicsContext::alphaTest(GLenum mode1, GLenum mode2)
     m_glHelper->alphaTest(mode1, mode2);
 }
 
+void GraphicsContext::bindFramebuffer(GLuint fbo)
+{
+    m_glHelper->bindFrameBufferObject(fbo);
+}
+
 void GraphicsContext::depthTest(GLenum mode)
 {
     m_glHelper->depthTest(mode);
diff --git a/src/render/graphicshelpers/graphicscontext_p.h b/src/render/graphicshelpers/graphicscontext_p.h
index 1aa4c3e5a..cc63a03b6 100644
--- a/src/render/graphicshelpers/graphicscontext_p.h
+++ b/src/render/graphicshelpers/graphicscontext_p.h
@@ -180,6 +180,7 @@ public:
 
     // Wrapper methods
     void    alphaTest(GLenum mode1, GLenum mode2);
+    void    bindFramebuffer(GLuint fbo);
     void    bindBufferBase(GLenum target, GLuint bindingIndex, GLuint buffer);
     void    bindFragOutputs(GLuint shader, const QHash<QString, int> &outputs);
     void    bindUniformBlock(GLuint programId, GLuint uniformBlockIndex, GLuint uniformBlockBinding);