OpenGL SubmissionContext: reset m_renderTargetFormat for default FBO

We rely on m_renderTargetFormat when doing render capture to know
in whick internal format the currently bound FBO is.

m_renderTargetFormat is reset once per surface change based on the
QSurfaceFormat. However, when using custom RenderTargets, it gets
overwritten in the call to SubmissionContext::activateRenderTarget which
happens for each RenderView. If we switch back to the default FBO in a
RenderView that follows one using a custom RenderTarget, both using the same
surface, we failed to reset the m_renderTargetFormat and it would mistakenly
remain to the value set for the custom RenderTarget.
If a RenderCapture were to happen at that stage, this would lead to crashes
as we would compute the capture buffer assuming a format that doesn't
match that of the current FBO.

Pick-to: 6.5 6.4
Change-Id: I5c722f20857b23b5696617065c8f50406e10aea9
Reviewed-by: Mike Krus <mike.krus@kdab.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/plugins/renderers/opengl/graphicshelpers/submissioncontext.cpp b/src/plugins/renderers/opengl/graphicshelpers/submissioncontext.cpp
index ca6e0ce49..814667c10 100644
--- a/src/plugins/renderers/opengl/graphicshelpers/submissioncontext.cpp
+++ b/src/plugins/renderers/opengl/graphicshelpers/submissioncontext.cpp
@@ -466,6 +466,8 @@ void SubmissionContext::endDrawing(bool swapBuffers)
 void SubmissionContext::activateRenderTarget(Qt3DCore::QNodeId renderTargetNodeId, const AttachmentPack &attachments, GLuint defaultFboId)
 {
     GLuint fboId = defaultFboId; // Default FBO
+    resolveRenderTargetFormat(); // Reset m_renderTargetFormat based on the default FBO
+
     if (renderTargetNodeId) {
         // New RenderTarget
         if (!m_renderTargets.contains(renderTargetNodeId)) {
@@ -476,9 +478,10 @@ void SubmissionContext::activateRenderTarget(Qt3DCore::QNodeId renderTargetNodeI
                 fboId = createRenderTarget(renderTargetNodeId, attachments);
             }
         } else {
-            fboId = updateRenderTarget(renderTargetNodeId, attachments, true);
+            fboId = updateRenderTarget(renderTargetNodeId, attachments, true); // Overwrites m_renderTargetFormat based on custom FBO
         }
     }
+
     m_activeFBO = fboId;
     m_activeFBONodeId = renderTargetNodeId;
     m_glHelper->bindFrameBufferObject(m_activeFBO, GraphicsHelperInterface::FBODraw);
@@ -608,6 +611,7 @@ QImage SubmissionContext::readFramebuffer(const QRect &rect)
     QImage::Format imageFormat;
     uint stride;
 
+    // m_renderTargetFormat is set when the current RV FBO is set in activateRenderTarget
     /* format value should match GL internalFormat */
     GLenum internalFormat = m_renderTargetFormat;