Use env variable to select default backend

This is useful for situations where angle is substituted for the system library underneath an application oblivious to this change. The ANGLE_DEFAULT_PLATFORM variable is used when the display type is default to control the default back-end. Possible values are vulkan, gl and d3d11. If the value of this variable is not valid, or not supported by the current platform, the usual defaults are applied. Bug: angleproject:3125 Change-Id: I304b006e0a4149f78561038d01cede143640dafb Reviewed-on: https://chromium-review.googlesource.com/c/1450211Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>

Use env variable to select default backend
65cd76a7 · Shahbaz Youssefi · Commit Bot · c09ae15c · 65cd76a7
Commit 65cd76a7 authored Feb 01, 2019 by Shahbaz Youssefi Committed by Commit Bot Feb 01, 2019
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Display.cpp src/libANGLE/Display.cpp +41 -0

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--- a/src/libANGLE/Display.cpp
+++ b/src/libANGLE/Display.cpp
@@ -22,6 +22,8 @@
 #include "common/debug.h"
 #include "common/mathutil.h"
 #include "common/platform.h"
+#include "common/string_utils.h"
+#include "common/system_utils.h"
 #include "common/utilities.h"
 #include "libANGLE/Context.h"
 #include "libANGLE/Device.h"
@@ -133,11 +135,50 @@ rx::DisplayImpl *CreateDisplayFromDevice(Device *eglDevice, const DisplayState &
    return impl;
 }

+// On platforms with support for multiple back-ends, allow an environment variable to control
+// the default.  This is useful to run angle with benchmarks without having to modify the
+// benchmark source.  Possible values for this environment variable (ANGLE_DEFAULT_PLATFORM)
+// are: vulkan, gl, d3d11.
+EGLAttrib GetDisplayTypeFromEnvironment()
+{
+    std::string angleDefaultEnv = angle::GetEnvironmentVar("ANGLE_DEFAULT_PLATFORM");
+    angle::ToLower(&angleDefaultEnv);
+
+#if defined(ANGLE_ENABLE_VULKAN)
+    if (angleDefaultEnv == "vulkan")
+    {
+        return EGL_PLATFORM_ANGLE_TYPE_VULKAN_ANGLE;
+    }
+#endif
+
+#if defined(ANGLE_ENABLE_OPENGL)
+    if (angleDefaultEnv == "gl")
+    {
+        return EGL_PLATFORM_ANGLE_TYPE_OPENGLES_ANGLE;
+    }
+#endif
+
+#if defined(ANGLE_ENABLE_D3D11)
+    if (angleDefaultEnv == "d3d11")
+    {
+        return EGL_PLATFORM_ANGLE_TYPE_D3D11_ANGLE;
+    }
+#endif
+
+    return EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE;
+}
+
 rx::DisplayImpl *CreateDisplayFromAttribs(const AttributeMap &attribMap, const DisplayState &state)
 {
    rx::DisplayImpl *impl = nullptr;
    EGLAttrib displayType =
        attribMap.get(EGL_PLATFORM_ANGLE_TYPE_ANGLE, EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE);
+
+    if (displayType == EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE)
+    {
+        displayType = GetDisplayTypeFromEnvironment();
+    }
+
    switch (displayType)
    {
        case EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE: