Unbind fbo before context switching for PowerVR GPUs

Imagination GL drivers are buggy with context switching.
We need to ubind fbo to workaround a crash in the driver.

Bug: chromium:1187513
Change-Id: Ie5142b5f43a3f23a9743ba7af0d90567fedd00d3
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2841083
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>

include/platform/FeaturesGL.h

@@ -542,6 +542,13 @@ struct FeaturesGL : FeatureSetBase
         "sanitize_amdgpu_renderer_string", FeatureCategory::OpenGLWorkarounds,
         "Strip precise kernel and DRM version information from amdgpu renderer strings.", &members,
         "http://crbug.com/1181193"};
+
+    // Imagination GL drivers are buggy with context switching. We need to ubind fbo to workaround a
+    // crash in the driver.
+    Feature unbindFBOOnContextSwitch = {"unbind_fbo_before_switching_context",
+                                        FeatureCategory::OpenGLWorkarounds,
+                                        "Imagination GL drivers are buggy with context switching.",
+                                        &members, "http://crbug.com/1181193"};
 };
 
 inline FeaturesGL::FeaturesGL()  = default;

src/libANGLE/renderer/gl/ContextGL.cpp

@@ -845,6 +845,15 @@ angle::Result ContextGL::onMakeCurrent(const gl::Context *context)
     return mRenderer->getStateManager()->onMakeCurrent(context);
 }
 
+angle::Result ContextGL::onUnMakeCurrent(const gl::Context *context)
+{
+    if (getFeaturesGL().unbindFBOOnContextSwitch.enabled)
+    {
+        mRenderer->getStateManager()->bindFramebuffer(GL_FRAMEBUFFER, 0);
+    }
+    return ContextImpl::onUnMakeCurrent(context);
+}
+
 gl::Caps ContextGL::getNativeCaps() const
 {
     return mRenderer->getNativeCaps();

src/libANGLE/renderer/gl/ContextGL.h

@@ -235,6 +235,7 @@ class ContextGL : public ContextImpl
 
     // Context switching
     angle::Result onMakeCurrent(const gl::Context *context) override;
+    angle::Result onUnMakeCurrent(const gl::Context *context) override;
 
     // Caps queries
     gl::Caps getNativeCaps() const override;

src/libANGLE/renderer/gl/renderergl_utils.cpp

@@ -2094,6 +2094,11 @@ void InitializeFeatures(const FunctionsGL *functions, angle::FeaturesGL *feature
     // On desktop Linux/AMD when using the amdgpu drivers, the precise kernel and DRM version are
     // leaked via GL_RENDERER. We workaround this too improve user security.
     ANGLE_FEATURE_CONDITION(features, sanitizeAmdGpuRendererString, IsLinux() && hasAMD);
+
+    // http://crbug.com/1187513
+    // Imagination drivers are buggy with context switching. It needs to unbind fbo before context
+    // switching to workadround the driver issues.
+    ANGLE_FEATURE_CONDITION(features, unbindFBOOnContextSwitch, IsPowerVR(vendor));
 }
 
 void InitializeFrontendFeatures(const FunctionsGL *functions, angle::FrontendFeatures *features)