Capture/Replay: Init shader outputs during self-tests.

This forces all uninitialized variables to have default values.
For instance if the application doesn't initialize the output
color, or a varying that's use in the output, this will ensure we
don't use any undefined values in the computation.

Found when working on a re-trace of T-Rex, which doesn't write to
the alpha channel in the final rendering pass. Also fixes undefined
values in GLSLTest.InactiveVaryingInVertexActiveInFragment.

Bug: angleproject:5133
Change-Id: Ia291338e5adf23dab5263cb2ebe737dc05852d3e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3110225
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>

include/platform/FrontendFeatures.h

@@ -77,9 +77,16 @@ struct FrontendFeatures : angle::FeatureSetBase
         "enableCompressingPipelineCacheInThreadPool", angle::FeatureCategory::FrontendWorkarounds,
         "Enable compressing pipeline cache in thread pool.", &members, "http://anglebug.com/4722"};
 
+    // Forces on robust resource init. Useful for some tests to avoid undefined values.
     angle::Feature forceRobustResourceInit = {
-        "forceRobustResourceInit", angle::FeatureCategory::FrontendWorkarounds,
+        "forceRobustResourceInit", angle::FeatureCategory::FrontendFeatures,
         "Force-enable robust resource init", &members, "http://anglebug.com/6041"};
+
+    // Forces on shader output initialization to avoid undefined values in tests. Normally this
+    // feature is only enabled for WebGL.
+    angle::Feature forceInitShaderOutputVariables = {
+        "forceInitShaderOutputVariables", angle::FeatureCategory::FrontendFeatures,
+        "Force-enable shader output variable initialization", &members};
 };
 
 inline FrontendFeatures::FrontendFeatures()  = default;

src/libANGLE/Shader.cpp

@@ -356,7 +356,7 @@ void Shader::compile(const Context *context)
         options |= SH_INIT_SHARED_VARIABLES;
     }
 
-    // Some targets (eg D3D11 Feature Level 9_3 and below) do not support non-constant loop
+    // Some targets (e.g. D3D11 Feature Level 9_3 and below) do not support non-constant loop
     // indexes in fragment shaders. Shader compilation will fail. To provide a better error
     // message we can instruct the compiler to pre-validate.
     if (mRendererLimitations.shadersRequireIndexedLoopValidation)
@@ -369,6 +369,11 @@ void Shader::compile(const Context *context)
         options |= SH_SCALARIZE_VEC_AND_MAT_CONSTRUCTOR_ARGS;
     }
 
+    if (context->getFrontendFeatures().forceInitShaderOutputVariables.enabled)
+    {
+        options |= SH_INIT_OUTPUT_VARIABLES;
+    }
+
     mCurrentMaxComputeWorkGroupInvocations =
         static_cast<GLuint>(context->getCaps().maxComputeWorkGroupInvocations);
 

src/tests/capture_replay_tests.py

@@ -566,11 +566,16 @@ class TestBatch():
         test_exe_path = os.path.join(args.out_dir, 'Capture', args.test_suite)
 
         extra_env = {
-            'ANGLE_CAPTURE_FRAME_END': '{}'.format(self.CAPTURE_FRAME_END),
-            'ANGLE_CAPTURE_SERIALIZE_STATE': '1',
-            'ANGLE_FEATURE_OVERRIDES_ENABLED': 'forceRobustResourceInit',
-            'ANGLE_CAPTURE_ENABLED': '1',
-            'ANGLE_CAPTURE_OUT_DIR': self.trace_folder_path,
+            'ANGLE_CAPTURE_FRAME_END':
+                '{}'.format(self.CAPTURE_FRAME_END),
+            'ANGLE_CAPTURE_SERIALIZE_STATE':
+                '1',
+            'ANGLE_FEATURE_OVERRIDES_ENABLED':
+                'forceRobustResourceInit:forceInitShaderOutputVariables',
+            'ANGLE_CAPTURE_ENABLED':
+                '1',
+            'ANGLE_CAPTURE_OUT_DIR':
+                self.trace_folder_path,
         }
 
         env = {**os.environ.copy(), **extra_env}

src/tests/capture_replay_tests/CaptureReplayTests.cpp

@@ -88,8 +88,9 @@ class CaptureReplayTests
         configParams.webGLCompatibility    = testTraceInfo.webGLCompatibility;
         configParams.robustResourceInit    = testTraceInfo.robustResourceInit;
 
-        mPlatformParams.renderer   = testTraceInfo.replayPlatformType;
-        mPlatformParams.deviceType = testTraceInfo.replayDeviceType;
+        mPlatformParams.renderer                       = testTraceInfo.replayPlatformType;
+        mPlatformParams.deviceType                     = testTraceInfo.replayDeviceType;
+        mPlatformParams.forceInitShaderOutputVariables = EGL_TRUE;
 
         if (!mEGLWindow->initializeGL(mOSWindow, mEntryPointsLib.get(),
                                       angle::GLESDriverType::AngleEGL, mPlatformParams,

util/EGLPlatformParameters.h

@@ -66,7 +66,7 @@ struct EGLPlatformParameters
                         hasExplicitMemBarrierFeatureMtl, hasCheapRenderPassFeatureMtl,
                         forceBufferGPUStorageFeatureMtl, supportsVulkanViewportFlip, emulatedVAOs,
                         directSPIRVGeneration, captureLimits, forceRobustResourceInit,
-                        directMetalGeneration);
+                        directMetalGeneration, forceInitShaderOutputVariables);
     }
 
     EGLint renderer                               = EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE;
@@ -93,6 +93,7 @@ struct EGLPlatformParameters
     EGLint captureLimits                          = EGL_DONT_CARE;
     EGLint forceRobustResourceInit                = EGL_DONT_CARE;
     EGLint directMetalGeneration                  = EGL_DONT_CARE;
+    EGLint forceInitShaderOutputVariables         = EGL_DONT_CARE;
 
     angle::PlatformMethods *platformMethods = nullptr;
 };

util/EGLWindow.cpp

@@ -300,6 +300,11 @@ bool EGLWindow::initializeDisplay(OSWindow *osWindow,
         enabledFeatureOverrides.push_back("forceRobustResourceInit");
     }
 
+    if (params.forceInitShaderOutputVariables == EGL_TRUE)
+    {
+        enabledFeatureOverrides.push_back("forceInitShaderOutputVariables");
+    }
+
     const bool hasFeatureControlANGLE =
         strstr(extensionString, "EGL_ANGLE_feature_control") != nullptr;