Platform: new "android-generic-hostname-might-be-swiftshader" workaround.

As documented. Yes, Android, I hate you, in case that wasn't clear. And
all other Google code as well.

doc/changelog.dox

@@ -136,6 +136,9 @@ See also:
 -   A new @cpp "angle-chatty-shader-compiler" @ce workaround for silencing
     useless linker output on ANGLE. See @ref opengl-workarounds for more
     information.
+-   A new @cpp "android-generic-hostname-might-be-swiftshader" @ce workaround
+    needed for testing against Android Emulator SwiftShader GPU. See
+    @ref opengl-workarounds for more information.
 
 @subsubsection changelog-latest-new-math Math library
 

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -44,6 +44,18 @@ using namespace Containers::Literals;
 /* Search the code for the following strings to see where they are implemented */
 constexpr Containers::StringView KnownWorkarounds[]{
 /* [workarounds] */
+#if defined(CORRADE_TARGET_ANDROID) && defined(MAGNUM_TARGET_GLES)
+/* Android Emulator can run with a SwiftShader GPU and thus needs some of the
+   SwiftShader context creation workarounds. However, it's impossible to
+   detect, as EGL_VERSION is always "1.4 Android META-EGL" and EGL_VENDOR
+   always "Android". As there's nothing that would hint at SwiftShader being
+   used, we conservatively assume every emulator can be a SwiftShader. But
+   that's not easy either, the only vague hint that we're dealing with an
+   emulator is the HOSTNAME env var, which is set to e.g. generic_x86, but to
+   e.g. HWVTR on a device, so try that. */
+"android-generic-hostname-might-be-swiftshader"_s,
+#endif
+
 #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
 /* ANGLE's shader linker insists on returning a message consisting of a
    single newline on success, causing annoying noise in the console. Similar to
@@ -212,13 +224,18 @@ constexpr Containers::StringView KnownWorkarounds[]{
 #endif
 
 #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
-/* Empty EGL_CONTEXT_FLAGS_KHR cause SwiftShader 3.3.0.1 to fail context
+/* Empty EGL_CONTEXT_FLAGS_KHR cause SwiftShader 3.3 to fail context creation
-   creation with EGL_BAD_ATTRIBUTE. Not sending the flags then. Relevant code:
+   with EGL_BAD_ATTRIBUTE. Not sending the flags then. Relevant code:
-   https://github.com/google/swiftshader/blob/5fb5e817a20d3e60f29f7338493f922b5ac9d7c4/src/OpenGL/libEGL/libEGL.cpp#L794-L810 */
+    https://github.com/google/swiftshader/blob/5fb5e817a20d3e60f29f7338493f922b5ac9d7c4/src/OpenGL/libEGL/libEGL.cpp#L794-L810
+   Version 4.1 suffers from the same thing, but 4.0 on Android not, for some
+   reason. */
 "swiftshader-no-empty-egl-context-flags"_s,
 
 /* SwiftShader 3.3.0.1 crashes deep inside eglMakeCurrent() when using
-   EGL_NO_SURFACE. Supplying a 32x32 PBuffer to work around that. */
+   EGL_NO_SURFACE. Supplying a 32x32 PBuffer to work around that. (Android's)
+   SwiftShader 4.0 needs it too, but doesn't crash, only fails to make the
+   context current with EGL_BAD_MATCH. Version 4.1 doesn't seem to need this
+   workaround anymore. */
 "swiftshader-egl-context-needs-pbuffer"_s,
 #endif
 

src/Magnum/Platform/WindowlessEglApplication.cpp

@@ -364,7 +364,11 @@ WindowlessEglContext::WindowlessEglContext(const Configuration& configuration, G
     /* SwiftShader 3.3.0.1 blows up on encountering EGL_CONTEXT_FLAGS_KHR with
        a zero value, so erase these. It also doesn't handle them as correct
        flags, but instead checks for the whole value, so a combination won't
-       work either: https://github.com/google/swiftshader/blob/5fb5e817a20d3e60f29f7338493f922b5ac9d7c4/src/OpenGL/libEGL/libEGL.cpp#L794-L8104 */
+       work either: https://github.com/google/swiftshader/blob/5fb5e817a20d3e60f29f7338493f922b5ac9d7c4/src/OpenGL/libEGL/libEGL.cpp#L794-L8104
+
+       Interestingly, on Android Emulator SwiftShader 4.0 this workaround isn't
+       needed, so we don't need to use the isSwiftShader variable (from below)
+       in this case. */
     if(!(UnsignedLong(flags) & 0xffffffffu) && version.contains("SwiftShader"_s) && (!magnumContext || !magnumContext->isDriverWorkaroundDisabled("swiftshader-no-empty-egl-context-flags"_s))) {
         auto& contextFlags = attributes[nextAttribute - 2];
         CORRADE_INTERNAL_ASSERT(contextFlags == EGL_CONTEXT_FLAGS_KHR);
@@ -486,9 +490,27 @@ WindowlessEglContext::WindowlessEglContext(const Configuration& configuration, G
     }
 
     #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
-    /* SwiftShader 3.3.0.1 needs some pbuffer, otherwise it crashes somewhere
+    /* Android Emulator can run with a SwiftShader GPU and thus needs some of
-       deep inside when making the context current */
+       the SwiftShader context creation workarounds. However, it's impossible
-    if(version.contains("SwiftShader"_s) && (!magnumContext || !magnumContext->isDriverWorkaroundDisabled("swiftshader-egl-context-needs-pbuffer"_s))) {
+       to detect, as EGL_VERSION is always "1.4 Android META-EGL" and
+       EGL_VENDOR always "Android". As there's nothing that would hint at
+       SwiftShader being used, we conservatively assume every emulator can be a
+       SwiftShader. But that's not easy either, the only vague hint that we're
+       dealing with an emulator is the HOSTNAME env var, which is set to e.g.
+       generic_x86, but to e.g. HWVTR on a device, so try that. */
+    const bool isSwiftShader =
+        #ifndef CORRADE_TARGET_ANDROID
+        version.contains("SwiftShader"_s)
+        #else
+        Containers::StringView{std::getenv("HOSTNAME")}.contains("generic"_s) && (!magnumContext || !magnumContext->isDriverWorkaroundDisabled("android-generic-hostname-might-be-swiftshader"_s))
+        #endif
+        ;
+
+    /* SwiftShader 3.3 needs some pbuffer, otherwise it crashes somewhere deep
+       inside when making the context current. (Android's) SwiftShader 4.0
+       needs it too, but doesn't crash, only fails to make the context current
+       with EGL_BAD_MATCH. Version 4.1 doesn't need this workaround anymore. */
+    if(isSwiftShader && (!magnumContext || !magnumContext->isDriverWorkaroundDisabled("swiftshader-egl-context-needs-pbuffer"_s))) {
         EGLint surfaceAttributes[] = {
             EGL_WIDTH, 32,
             EGL_HEIGHT, 32,