Clear VxWorks MESA display artifacts on startup

This cherry-pick is a preparatory change as eglfs is not yet enabled on
Intel VxWorks.

Cherry-picked commit e39f3ebba61acddea2e6dfe6e9506ce0441bfd8b
Author: Cliff Bilbrey <[email protected]>
Date:   Fri Jun 9 13:56:14 2023 -0500

Display artifacts are sometimes seen at startup in VxWorks applications
that make use of the MESA OpenGL libraries. This issue has been
demonstrated in the Wind River MESA OpenGL demos, which use the same
technique incorporated here to mask the problem. Cyling through the
complete set of framebuffers and clearing each during the initialization
process creates a clean slate that prevents the artifacts from being
noticeable to the end user.

Task-number: QTBUG-115777
Change-Id: Ifce9074eac687c002c215c531ddff1443a4df6a0
Reviewed-by: Laszlo Agocs <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/gui/opengl/platform/egl/qeglplatformcontext.cpp b/src/gui/opengl/platform/egl/qeglplatformcontext.cpp
index 0a6e83e875e..e1bf056d655 100644
--- a/src/gui/opengl/platform/egl/qeglplatformcontext.cpp
+++ b/src/gui/opengl/platform/egl/qeglplatformcontext.cpp
@@ -378,6 +378,21 @@ bool QEGLPlatformContext::makeCurrent(QPlatformSurface *surface)
             if (eglSurface != EGL_NO_SURFACE) // skip if using surfaceless context
                 eglSwapInterval(eglDisplay(), m_swapInterval);
         }
+#if defined(Q_OS_VXWORKS) && defined(Q_PROCESSOR_X86_64)
+        // Clear set of framebuffers as workaround for display artifacts found
+        // in Wind River's Mesa OpenGL implementation
+        static bool firstWindow = true;
+        if (firstWindow && (QSurface::Window == surface->surface()->surfaceClass())) {
+            glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+            swapBuffers(surface);
+            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+            swapBuffers(surface);
+            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+            swapBuffers(surface);
+            firstWindow = false;
+        }
+#endif
     } else {
         qWarning("QEGLPlatformContext: eglMakeCurrent failed: %x", eglGetError());
     }