Add new flag to allow using SwANGLE as WebGL fallback

Currently, Chrome uses legacy SwiftShader GL as the WebGL fallback when
a hardware GPU isn't usable for the purpuse of rendering WebGL content.

As we're in the process of changing legacy SwiftShader GL to SwANGLE,
this CL adds a new flag which allows using SwANGLE for WebGL only.

To clarify, current switches with legacy SwiftShader GL:
Software GL: --use-gl=swiftshader
Software WebGL only: --use-gl=swiftshader-webgl

With SwANGLE, the new switches will be:
Software GL: --use-gl=angle --use-angle=swiftshader
Software WebGL only: --use-gl=angle --use-angle=swiftshader-webgl

Bug: chromium:1060139
Change-Id: I8d0382ac3a12c1578dfc0e62fc1949a0a9c66bd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2845229
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Cr-Commit-Position: refs/heads/master@{#876794}

docs/gpu/swiftshader.md

@@ -0,0 +1,39 @@
+# Using Chromium with SwiftShader
+
+SwiftShader is an open-source high-performance implementation of the Vulkan and OpenGL ES graphics APIs which runs purely on the CPU. Thus no graphics processor (GPU) is required for advanced (3D) graphics.
+
+Chromium uses SwiftShader in two different ways:
+
+1) **As the OpenGL ES driver**
+
+When Chromium uses SwiftShader as the OpenGL ES driver, Chromium behaves as if it was running a on regular GPU, while actually running on SwiftShader. This allows Chromium to exercise hardware only code paths on GPU-less bots.
+
+2) **As the WebGL fallback**
+
+When Chromium uses SwiftShader as the WebGL fallback, Chromium runs in all software mode and only uses SwiftShader to render WebGL content.
+
+SwiftShader also provides 2 different libraries:
+
+1) **The legacy SwiftShader Open GL ES libraries**
+
+Legacy SwiftShader includes a GLES library and an EGL library, in order to provide a complete solution to run OpenGL ES content.
+
+*Do not use these libraries if possible, they are being phased out in favor of SwANGLE (ANGLE + SwiftShader Vulkan).*
+
+2) **The SwiftShader Vulkan library**
+
+SwiftShader Vulkan can be used both to render Vulkan content directly, or OpenGL ES content when use in conjunction with the ANGLE library.
+
+## Relevant Chromium command line switches
+
+When running the **chrome** executable from the command line, SwiftShader can be enabled using the following Switches:
+1) As the OpenGL ES driver, SwANGLE (ANGLE + SwiftShader Vulkan)
+>**\-\-use-gl=angle \-\-use-angle=swiftshader**
+2) As the WebGL fallback, SwANGLE (ANGLE + SwiftShader Vulkan)
+>**\-\-use-gl=angle \-\-use-angle=swiftshader-webgl**
+3) As the OpenGL ES driver, legacy SwiftShader Open GL ES libraries
+> **\-\-use-gl=swiftshader**
+4) As the WebGL fallback, legacy SwiftShader Open GL ES libraries
+>**\-\-use-gl=swiftshader-webgl**
+5) As the Vulkan driver (requires the [enable_swiftshader_vulkan](https://source.chromium.org/chromium/chromium/src/+/master:gpu/vulkan/features.gni;l=16) feature)
+>**--use-vulkan=swiftshader**

gpu/command_buffer/service/feature_info.cc

@@ -225,7 +225,9 @@ void FeatureInfo::InitializeBasicState(const base::CommandLine* command_line) {
   const auto useANGLE = command_line->GetSwitchValueASCII(switches::kUseANGLE);
 
   feature_flags_.is_swiftshader_for_webgl =
-      (useGL == gl::kGLImplementationSwiftShaderForWebGLName);
+      (useGL == gl::kGLImplementationSwiftShaderForWebGLName) ||
+      ((useGL == gl::kGLImplementationANGLEName) &&
+       (useANGLE == gl::kANGLEImplementationSwiftShaderForWebGLName));
 
   // The shader translator is needed to translate from WebGL-conformant GLES SL
   // to normal GLES SL, enforce WebGL conformance, translate from GLES SL 1.0 to

gpu/config/gpu_util.cc

@@ -498,6 +498,8 @@ GpuFeatureInfo ComputeGpuFeatureInfo(const GPUInfo& gpu_info,
             command_line->GetSwitchValueASCII(switches::kUseANGLE);
         if (use_angle == gl::kANGLEImplementationSwiftShaderName)
           use_swift_shader = true;
+        else if (use_angle == gl::kANGLEImplementationSwiftShaderForWebGLName)
+          return ComputeGpuFeatureInfoForSwiftShader();
       }
     } else if (use_gl == gl::kGLImplementationSwiftShaderForWebGLName)
       return ComputeGpuFeatureInfoForSwiftShader();

gpu/ipc/service/gpu_init.cc

@@ -590,8 +590,13 @@ bool GpuInit::InitializeAndStartSandbox(base::CommandLine* command_line,
   // In SwiftShader case, the implementation is actually EGLGLES2.
   if (!gl_use_swiftshader_ && command_line->HasSwitch(switches::kUseGL)) {
     std::string use_gl = command_line->GetSwitchValueASCII(switches::kUseGL);
+    std::string use_angle =
+        command_line->GetSwitchValueASCII(switches::kUseANGLE);
     if (use_gl == gl::kGLImplementationSwiftShaderName ||
-        use_gl == gl::kGLImplementationSwiftShaderForWebGLName) {
+        use_gl == gl::kGLImplementationSwiftShaderForWebGLName ||
+        (use_gl == gl::kGLImplementationANGLEName &&
+         (use_angle == gl::kANGLEImplementationSwiftShaderName ||
+          use_angle == gl::kANGLEImplementationSwiftShaderForWebGLName))) {
       gl_use_swiftshader_ = true;
     }
   }

ui/gl/gl_surface_egl.cc

@@ -907,7 +907,8 @@ void GetEGLInitDisplays(bool supports_angle_d3d,
   }
 
   if (supports_angle_swiftshader) {
-    if (requested_renderer == kANGLEImplementationSwiftShaderName) {
+    if (requested_renderer == kANGLEImplementationSwiftShaderName ||
+        requested_renderer == kANGLEImplementationSwiftShaderForWebGLName) {
       AddInitDisplay(init_displays, ANGLE_SWIFTSHADER);
     }
   }

ui/gl/gl_switches.cc

@@ -34,6 +34,7 @@ const char kANGLEImplementationOpenGLESEGLName[] = "gles-egl";
 const char kANGLEImplementationNullName[] = "null";
 const char kANGLEImplementationVulkanName[] = "vulkan";
 const char kANGLEImplementationSwiftShaderName[] = "swiftshader";
+const char kANGLEImplementationSwiftShaderForWebGLName[] = "swiftshader-webgl";
 const char kANGLEImplementationMetalName[] = "metal";
 const char kANGLEImplementationNoneName[] = "";
 

ui/gl/gl_switches.h

@@ -34,6 +34,7 @@ GL_EXPORT extern const char kANGLEImplementationOpenGLESEGLName[];
 GL_EXPORT extern const char kANGLEImplementationNullName[];
 GL_EXPORT extern const char kANGLEImplementationVulkanName[];
 GL_EXPORT extern const char kANGLEImplementationSwiftShaderName[];
+GL_EXPORT extern const char kANGLEImplementationSwiftShaderForWebGLName[];
 GL_EXPORT extern const char kANGLEImplementationMetalName[];
 GL_EXPORT extern const char kANGLEImplementationNoneName[];