Work around Mac glGenerateMipmap with missing levels bug.

include/platform/FeaturesGL.h

@@ -499,6 +499,12 @@ struct FeaturesGL : FeatureSetBase
         "keep_buffer_shadow_copy", FeatureCategory::OpenGLWorkarounds,
         "Maintain a shadow copy of buffer data when the GL API does not permit reading data back.",
         &members};
+
+    // glGenerateMipmap fails if the zero texture level is not set on some Mac drivers
+    Feature setZeroLevelBeforeGenerateMipmap = {
+        "set_zero_level_before_generating_mipmap", FeatureCategory::OpenGLWorkarounds,
+        "glGenerateMipmap fails if the zero texture level is not set on some Mac drivers.",
+        &members};
 };
 
 inline FeaturesGL::FeaturesGL()  = default;

src/libANGLE/renderer/gl/TextureGL.cpp

@@ -265,8 +265,29 @@ angle::Result TextureGL::setImageHelper(const gl::Context *context,
                                            texImageFormat.type, pixels));
     }
 
-    setLevelInfo(context, target, level, 1,
-                 GetLevelInfo(features, internalFormat, texImageFormat.internalFormat));
+    LevelInfoGL levelInfo = GetLevelInfo(features, internalFormat, texImageFormat.internalFormat);
+    setLevelInfo(context, target, level, 1, levelInfo);
+
+    if (features.setZeroLevelBeforeGenerateMipmap.enabled && getType() == gl::TextureType::_2D &&
+        level != 0 && mLevelInfo[0].nativeInternalFormat == GL_NONE)
+    {
+        // Only fill level zero if it's possible that mipmaps can be generated with this format
+        const gl::InternalFormat &internalFormatInfo =
+            gl::GetInternalFormatInfo(internalFormat, type);
+        if (!internalFormatInfo.sized ||
+            (internalFormatInfo.filterSupport(context->getClientVersion(),
+                                              context->getExtensions()) &&
+             internalFormatInfo.textureAttachmentSupport(context->getClientVersion(),
+                                                         context->getExtensions())))
+        {
+            ANGLE_GL_TRY_ALWAYS_CHECK(
+                context,
+                functions->texImage2D(nativegl::GetTextureBindingTarget(target), 0,
+                                      texImageFormat.internalFormat, 1, 1, 0, texImageFormat.format,
+                                      texImageFormat.type, nullptr));
+            setLevelInfo(context, target, 0, 1, levelInfo);
+        }
+    }
 
     return angle::Result::Continue;
 }

src/libANGLE/renderer/gl/renderergl_utils.cpp

@@ -1837,6 +1837,8 @@ void InitializeFeatures(const FunctionsGL *functions, angle::FeaturesGL *feature
     ANGLE_FEATURE_CONDITION(features, disableSyncControlSupport, false);
 
     ANGLE_FEATURE_CONDITION(features, keepBufferShadowCopy, !CanMapBufferForRead(functions));
+
+    ANGLE_FEATURE_CONDITION(features, setZeroLevelBeforeGenerateMipmap, IsApple());
 }
 
 void InitializeFrontendFeatures(const FunctionsGL *functions, angle::FrontendFeatures *features)

src/tests/gl_tests/MipmapTest.cpp

@@ -605,6 +605,38 @@ TEST_P(MipmapTest, DISABLED_ThreeLevelsInitData)
     EXPECT_PIXEL_COLOR_EQ(getWindowWidth() / 8, getWindowHeight() / 8, GLColor::red);
 }
 
+// Test generating mipmaps with base level and max level set. Ported from part of the
+// conformance2/textures/misc/tex-mipmap-levels WebGL2 test.
+TEST_P(MipmapTestES3, GenerateMipmapPartialLevels)
+{
+    const std::vector<GLColor> kRedData(64, GLColor::red);
+    const std::vector<GLColor> kGreenData(16, GLColor::green);
+    const std::vector<GLColor> kBlueData(4, GLColor::blue);
+
+    // Initialize mips 2 to 4
+    GLTexture texture;
+    glBindTexture(GL_TEXTURE_2D, texture);
+    glTexImage2D(GL_TEXTURE_2D, 2, GL_RGBA, 8, 8, 0, GL_RGBA, GL_UNSIGNED_BYTE, kRedData.data());
+    glTexImage2D(GL_TEXTURE_2D, 3, GL_RGBA, 4, 4, 0, GL_RGBA, GL_UNSIGNED_BYTE, kGreenData.data());
+    glTexImage2D(GL_TEXTURE_2D, 4, GL_RGBA, 2, 2, 0, GL_RGBA, GL_UNSIGNED_BYTE, kBlueData.data());
+
+    // Set base and max levels
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 2);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 4);
+
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+
+    // Verify the data
+    clearAndDrawQuad(m2DProgram, 2, 2);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::blue);
+
+    // Test that generateMipmap works with partial levels.
+    glGenerateMipmap(GL_TEXTURE_2D);
+    clearAndDrawQuad(m2DProgram, 2, 2);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+}
+
 // This test generates mipmaps for a 1x1 texture, which should be a no-op.
 TEST_P(MipmapTestES3, GenerateMipmap1x1Texture)
 {