Workaround EXT_texture_norm16 for OpenGL ES drivers

include/platform/FeaturesGL.h

@@ -386,6 +386,14 @@ struct FeaturesGL : FeatureSetBase
         "All Mac drivers do not handle struct scopes correctly. This workaround overwrites a struct"
         "name with a unique prefix.",
         &members, "http://crbug.com/403957"};
+
+    // Quite some OpenGL ES drivers don't implement readPixels for RGBA/UNSIGNED_SHORT from
+    // EXT_texture_norm16 correctly
+    Feature readPixelsUsingImplementationColorReadFormatForNorm16 = {
+        "read_pixels_using_implementation_color_read_format", FeatureCategory::OpenGLWorkarounds,
+        "Quite some OpenGL ES drivers don't implement readPixels for RGBA/UNSIGNED_SHORT from "
+        "EXT_texture_norm16 correctly",
+        &members, "http://anglebug.com/4214"};
 };
 
 inline FeaturesGL::FeaturesGL()  = default;

src/libANGLE/formatutils.cpp

@@ -992,8 +992,10 @@ static InternalFormatInfoMap BuildInternalFormatInfoMap()
     //                 | Internal format  |sized | R | G | B | A |S | Format           | Type                          | Component type        | SRGB | Texture supported                               | Filterable     | Texture attachment                            | Renderbuffer |
     AddRGBAFormat(&map, GL_RED,            false,  8,  0,  0,  0, 0, GL_RED,            GL_UNSIGNED_BYTE,               GL_UNSIGNED_NORMALIZED, false, RequireExt<&Extensions::textureRG>,               AlwaysSupported, RequireExt<&Extensions::textureRG>,             NeverSupported);
     AddRGBAFormat(&map, GL_RED,            false,  8,  0,  0,  0, 0, GL_RED,            GL_BYTE,                        GL_SIGNED_NORMALIZED,   false, NeverSupported,                                   NeverSupported,  NeverSupported,                                 NeverSupported);
+    AddRGBAFormat(&map, GL_RED,            false, 16,  0,  0,  0, 0, GL_RED,            GL_UNSIGNED_SHORT,              GL_UNSIGNED_NORMALIZED, false, RequireExt<&Extensions::textureNorm16>,           AlwaysSupported, RequireExt<&Extensions::textureNorm16>,         NeverSupported);
     AddRGBAFormat(&map, GL_RG,             false,  8,  8,  0,  0, 0, GL_RG,             GL_UNSIGNED_BYTE,               GL_UNSIGNED_NORMALIZED, false, RequireExt<&Extensions::textureRG>,               AlwaysSupported, RequireExt<&Extensions::textureRG>,             NeverSupported);
     AddRGBAFormat(&map, GL_RG,             false,  8,  8,  0,  0, 0, GL_RG,             GL_BYTE,                        GL_SIGNED_NORMALIZED,   false, NeverSupported,                                   NeverSupported,  NeverSupported,                                 NeverSupported);
+    AddRGBAFormat(&map, GL_RG,             false, 16, 16,  0,  0, 0, GL_RG,             GL_UNSIGNED_SHORT,              GL_UNSIGNED_NORMALIZED, false, RequireExt<&Extensions::textureNorm16>,           AlwaysSupported, RequireExt<&Extensions::textureNorm16>,         NeverSupported);
     AddRGBAFormat(&map, GL_RGB,            false,  8,  8,  8,  0, 0, GL_RGB,            GL_UNSIGNED_BYTE,               GL_UNSIGNED_NORMALIZED, false, AlwaysSupported,                                  AlwaysSupported, RequireES<2, 0>,                                NeverSupported);
     AddRGBAFormat(&map, GL_RGB,            false,  5,  6,  5,  0, 0, GL_RGB,            GL_UNSIGNED_SHORT_5_6_5,        GL_UNSIGNED_NORMALIZED, false, AlwaysSupported,                                  AlwaysSupported, RequireES<2, 0>,                                NeverSupported);
     AddRGBAFormat(&map, GL_RGB,            false,  8,  8,  8,  0, 0, GL_RGB,            GL_BYTE,                        GL_SIGNED_NORMALIZED,   false, NeverSupported,                                   NeverSupported,  NeverSupported,                                 NeverSupported);

src/libANGLE/renderer/gl/FramebufferGL.h

@@ -101,6 +101,7 @@ class FramebufferGL : public FramebufferImpl
 
     angle::Result readPixelsRowByRow(const gl::Context *context,
                                      const gl::Rectangle &area,
+                                     GLenum originalReadFormat,
                                      GLenum format,
                                      GLenum type,
                                      const gl::PixelPackState &pack,
@@ -108,6 +109,7 @@ class FramebufferGL : public FramebufferImpl
 
     angle::Result readPixelsAllAtOnce(const gl::Context *context,
                                       const gl::Rectangle &area,
+                                      GLenum originalReadFormat,
                                       GLenum format,
                                       GLenum type,
                                       const gl::PixelPackState &pack,

src/libANGLE/renderer/gl/formatutilsgl.cpp

@@ -655,9 +655,17 @@ static GLenum GetNativeReadType(const FunctionsGL *functions,
 
 static GLenum GetNativeReadFormat(const FunctionsGL *functions,
                                   const angle::FeaturesGL &features,
-                                  GLenum format)
+                                  GLenum attachmentReadFormat,
+                                  GLenum format,
+                                  GLenum type)
 {
     GLenum result = format;
+    if (features.readPixelsUsingImplementationColorReadFormatForNorm16.enabled &&
+        type == GL_UNSIGNED_SHORT && format == GL_RGBA &&
+        (attachmentReadFormat == GL_RED || attachmentReadFormat == GL_RG))
+    {
+        result = attachmentReadFormat;
+    }
     return result;
 }
 
@@ -736,11 +744,12 @@ RenderbufferFormat GetRenderbufferFormat(const FunctionsGL *functions,
 }
 ReadPixelsFormat GetReadPixelsFormat(const FunctionsGL *functions,
                                      const angle::FeaturesGL &features,
+                                     GLenum attachmentReadFormat,
                                      GLenum format,
                                      GLenum type)
 {
     ReadPixelsFormat result;
-    result.format = GetNativeReadFormat(functions, features, format);
+    result.format = GetNativeReadFormat(functions, features, attachmentReadFormat, format, type);
     result.type   = GetNativeReadType(functions, features, type);
     return result;
 }

src/libANGLE/renderer/gl/formatutilsgl.h

@@ -131,6 +131,7 @@ struct ReadPixelsFormat
 };
 ReadPixelsFormat GetReadPixelsFormat(const FunctionsGL *functions,
                                      const angle::FeaturesGL &features,
+                                     GLenum readAttachmentFormat,
                                      GLenum format,
                                      GLenum type);
 }  // namespace nativegl

src/libANGLE/renderer/gl/renderergl_utils.cpp

@@ -1623,6 +1623,12 @@ void InitializeFeatures(const FunctionsGL *functions, angle::FeaturesGL *feature
 
     // Ported from gpu_driver_bug_list.json (#184)
     ANGLE_FEATURE_CONDITION(features, preAddTexelFetchOffsets, IsApple() && isIntel);
+
+    // Workaround for the widespread OpenGL ES driver implementaion bug
+    ANGLE_FEATURE_CONDITION(features, readPixelsUsingImplementationColorReadFormatForNorm16,
+                            functions->standard == STANDARD_GL_ES &&
+                                functions->isAtLeastGLES(gl::Version(3, 1)) &&
+                                functions->hasGLESExtension("GL_EXT_texture_norm16"));
 }
 
 void InitializeFrontendFeatures(const FunctionsGL *functions, angle::FrontendFeatures *features)