[Fix] (MG_Util/Converters): resolve the GL_COMPRESSED_* internal formats to the uncompressed storage that backs them instead of rejecting them as unknown - GL prescribes this base-format fallback for the six generic formats, and RGTC stores uncompressed because ES exposes no compressor

MobileGL/MG_Test/Texture/TextureTest.cpp

@@ -1516,6 +1516,47 @@ TEST_F(TextureTest, TexStorage2DTrimsALongerPreExistingMipChain) {
     EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
 }
 
+// glTexImage2D used to reject every GL_COMPRESSED_* internal format with GL_INVALID_ENUM, because
+// none of them mapped to a TextureInternalFormat and the "unknown format" gate fired. They now
+// resolve to the uncompressed storage that backs them - what GL prescribes for the generic formats,
+// and a deliberate deviation for RGTC, which ES cannot compress. The (format, type) pairs below are
+// the ones KHR-GL33.packed_pixels uploads with, so this table doubles as a pin for those 480 cases.
+TEST_F(TextureTest, CompressedInternalFormatsResolveToTheirUncompressedStorage) {
+    struct Case {
+        GLenum internalFormat;
+        GLenum format;
+        GLenum type;
+        TextureInternalFormat expected;
+    };
+    const Case cases[] = {
+        {GL_COMPRESSED_RED, GL_RED, GL_UNSIGNED_BYTE, TextureInternalFormat::R8},
+        {GL_COMPRESSED_RG, GL_RG, GL_UNSIGNED_BYTE, TextureInternalFormat::RG8},
+        {GL_COMPRESSED_RGB, GL_RGB, GL_UNSIGNED_BYTE, TextureInternalFormat::RGB8},
+        {GL_COMPRESSED_RGBA, GL_RGBA, GL_UNSIGNED_BYTE, TextureInternalFormat::RGBA8},
+        {GL_COMPRESSED_SRGB, GL_RGB, GL_UNSIGNED_BYTE, TextureInternalFormat::SRGB8},
+        {GL_COMPRESSED_SRGB_ALPHA, GL_RGBA, GL_UNSIGNED_BYTE, TextureInternalFormat::SRGB8Alpha8},
+        {GL_COMPRESSED_RED_RGTC1, GL_RED, GL_UNSIGNED_BYTE, TextureInternalFormat::R8},
+        {GL_COMPRESSED_RG_RGTC2, GL_RG, GL_UNSIGNED_BYTE, TextureInternalFormat::RG8},
+        // The signed RGTC pair is uploaded as GL_BYTE and must land on SNORM storage - resolving
+        // them to plain R8/RG8 would silently reinterpret negative texels.
+        {GL_COMPRESSED_SIGNED_RED_RGTC1, GL_RED, GL_BYTE, TextureInternalFormat::R8Snorm},
+        {GL_COMPRESSED_SIGNED_RG_RGTC2, GL_RG, GL_BYTE, TextureInternalFormat::RG8Snorm},
+    };
+
+    MG_Impl::GLImpl::PixelStorei(GL_UNPACK_ALIGNMENT, 1);
+    for (const auto& c : cases) {
+        GLuint texture = 0;
+        MG_Impl::GLImpl::GenTextures(1, &texture);
+        MG_Impl::GLImpl::BindTexture(GL_TEXTURE_2D, texture);
+        MG_Impl::GLImpl::TexImage2D(GL_TEXTURE_2D, 0, c.internalFormat, 4, 4, 0, c.format, c.type, nullptr);
+
+        const auto textureObject = MG_State::pGLContext->GetTextureObject(texture);
+        ASSERT_NE(textureObject, nullptr) << "internalFormat 0x" << std::hex << c.internalFormat;
+        EXPECT_EQ(textureObject->GetFormat(), c.expected) << "internalFormat 0x" << std::hex << c.internalFormat;
+        EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "internalFormat 0x" << std::hex << c.internalFormat;
+    }
+}
+
 TEST_F(TextureTest, TextureStorage3DAndSubImageModifyNamedObjectOnly) {
     GLuint texture = 0;
     MG_Impl::GLImpl::CreateTextures(GL_TEXTURE_3D, 1, &texture);

MobileGL/MG_Util/Converters/GLToMG/TextureEnumConverter.cpp

@@ -255,6 +255,37 @@ namespace MobileGL {
                 return TextureInternalFormat::DepthComponent;
             case GL_DEPTH_STENCIL:
                 return TextureInternalFormat::DepthStencil;
+            // Compressed internal formats resolve to the uncompressed storage that backs them.
+            //
+            // For the six generic formats this is exactly what GL prescribes: the implementation
+            // picks a specific compressed format, and when none is available it falls back to the
+            // corresponding base format. Nothing downstream ever sees a compressed enum, so the
+            // metrics, pixel-store and backend tables keep their "one format, N bytes per texel"
+            // invariant instead of each needing a compressed-aware arm.
+            //
+            // The four RGTC formats are a deliberate deviation: they are specific formats that GL
+            // 3.3 requires, but ES exposes no RGTC compressor to hand the data to. Storing the
+            // texels uncompressed keeps them renderable at the cost of the memory saving, which is
+            // strictly better than the INVALID_ENUM the application used to get. Note the signed
+            // variants must land on SNORM storage - CTS uploads them as GL_BYTE.
+            case GL_COMPRESSED_RED:
+            case GL_COMPRESSED_RED_RGTC1:
+                return TextureInternalFormat::R8;
+            case GL_COMPRESSED_SIGNED_RED_RGTC1:
+                return TextureInternalFormat::R8Snorm;
+            case GL_COMPRESSED_RG:
+            case GL_COMPRESSED_RG_RGTC2:
+                return TextureInternalFormat::RG8;
+            case GL_COMPRESSED_SIGNED_RG_RGTC2:
+                return TextureInternalFormat::RG8Snorm;
+            case GL_COMPRESSED_RGB:
+                return TextureInternalFormat::RGB8;
+            case GL_COMPRESSED_RGBA:
+                return TextureInternalFormat::RGBA8;
+            case GL_COMPRESSED_SRGB:
+                return TextureInternalFormat::SRGB8;
+            case GL_COMPRESSED_SRGB_ALPHA:
+                return TextureInternalFormat::SRGB8Alpha8;
             case GL_ALPHA:
             case GL_RED:
                 return TextureInternalFormat::Red;