[Fix, Test] (MG_Impl, MG_State): GL entry points record errors instead of throwing through the C ABI - CopyTexImage superset rule, TEXTURE_BUFFER level queries, indexed cap toggles

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -2809,7 +2809,14 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 break;
             }
             default:
-                THROW_UNIMPL_EXCEPTION;
+                // TextureStorageType is {Mipmap, Buffer}, both handled above, so this is a
+                // backstop for a state object that grew a new storage kind. Skipping the upload
+                // renders wrong; throwing unwinds through the C GL ABI and kills the process.
+                MGLOG_I("DirectGLES texture sync: no upload path for storage type %d on texture %u; "
+                        "skipping this sync",
+                        static_cast<int>(stateTextureObject->GetStorageType()),
+                        stateTextureObject->GetExternalIndex());
+                break;
             }
 
             DebugImpl::ErrorLopper::Loop([file = __FILE__, line = __LINE__, func = __func__](GLenum err) {

MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp

@@ -613,6 +613,23 @@ namespace MobileGL::MG_Impl::GLImpl {
                 MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", caller,
                                              "Compressed texture formats are not supported."));
         }
+
+        // glGetTexLevelParameter{i,f}v answers WIDTH/HEIGHT/DEPTH out of the mipmap chain. The only
+        // other storage type the state layer knows is GL_TEXTURE_BUFFER (TextureStorageType is
+        // {Mipmap, Buffer}), whose level geometry this stack does not track yet. Report that instead
+        // of throwing: THROW_UNIMPL_EXCEPTION unwinds a C++ exception through the C GL ABI and takes
+        // the process down, which is never an acceptable answer to a query - see the same reasoning
+        // above for the compressed-format path.
+        void RecordUnsupportedLevelQueryStorage(const char* caller, GLenum pname) {
+            MGLOG_I("%s: glGetTexLevelParameter(pname=%s) is not implemented for texture-buffer "
+                    "storage; recording GL_INVALID_OPERATION instead of terminating",
+                    caller, MG_Util::ConvertGLEnumToString(pname).c_str());
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>(
+                    "MG_Impl/GLImpl", caller,
+                    "Level queries are not supported for texture-buffer storage."));
+        }
     } // namespace
 
     const SharedPtr<MG_State::GLState::ITextureObject>& GetTextureObjectByName(GLuint texture, const char* caller) {
@@ -2910,7 +2927,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameteriv_State", pname);
+                    break;
                 }
             }
             break;
@@ -2924,7 +2942,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameteriv_State", pname);
+                    break;
                 }
             }
             break;
@@ -2938,7 +2957,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameteriv_State", pname);
+                    break;
                 }
             }
             break;
@@ -3045,7 +3065,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameterfv_State", pname);
+                    break;
                 }
             }
             break;
@@ -3059,7 +3080,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameterfv_State", pname);
+                    break;
                 }
             }
             break;
@@ -3073,7 +3095,8 @@ namespace MobileGL::MG_Impl::GLImpl {
                     break;
                 }
                 default:
-                    THROW_UNIMPL_EXCEPTION;
+                    RecordUnsupportedLevelQueryStorage("GetTexLevelParameterfv_State", pname);
+                    break;
                 }
             }
             break;
@@ -3403,7 +3426,10 @@ namespace MobileGL::MG_Impl::GLImpl {
             GET_SRC_INTERNAL_FORMAT(readBufferType);
         }
 
-        if (!TextureImpl::ValidateBaseInternalFormatMatch(internalFormat, srcInternalFormat)) THROW_UNIMPL_EXCEPTION;
+        // The validator has already recorded GL_INVALID_OPERATION; just decline. Throwing
+        // here unwound a C++ exception through the C GL ABI and killed the process (see the
+        // same reasoning at :604-609).
+        if (!TextureImpl::ValidateCopyTexImageBaseFormatSubset(internalFormat, srcInternalFormat)) return false;
 
         GLenum outInternalFormat = MG_Util::ConvertTextureInternalFormatToGLEnum(srcInternalFormat);
         GLenum realInternalFormat = GL_RGBA8;
@@ -3426,8 +3452,13 @@ namespace MobileGL::MG_Impl::GLImpl {
 
     void CopyTexImage1D_State(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width,
                               GLint border) {
-        // TODO: implement
-        THROW_UNIMPL_EXCEPTION;
+        // 1D textures are not implemented by this backend set. Record the error the way every
+        // other unsupported entry point does - throwing unwinds through the C GL ABI and kills
+        // the process, which is never an acceptable answer to an unsupported call.
+        MG_State::pGLContext->RecordError(
+            ErrorCode::InvalidOperation,
+            MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", "CopyTexImage1D",
+                                         "1D textures are not supported by this implementation"));
     }
 
     void CompressedTexSubImage3D_State(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint zoffset,

MobileGL/MG_Impl/GLImpl/Texture/Validators.cpp

@@ -424,19 +424,81 @@ namespace MobileGL::MG_Impl::GLImpl::TextureImpl {
         return true;
     }
 
+    namespace {
+        // Component set of an UNSIZED base internal format, as the bitmask GL 4.6 SS 8.6
+        // reasons about. Colour components are independent bits so "subset" is a plain
+        // mask test; depth and stencil are their own components and never satisfy a
+        // colour request (or each other).
+        enum : Uint32 {
+            kComponentR = 1u << 0,
+            kComponentG = 1u << 1,
+            kComponentB = 1u << 2,
+            kComponentA = 1u << 3,
+            kComponentDepth = 1u << 4,
+            kComponentStencil = 1u << 5,
+        };
+
+        Uint32 BaseFormatComponents(TextureInternalFormat unsizedFormat) {
+            switch (unsizedFormat) {
+            case TextureInternalFormat::Red:
+                return kComponentR;
+            case TextureInternalFormat::RG:
+                return kComponentR | kComponentG;
+            case TextureInternalFormat::RGB:
+                return kComponentR | kComponentG | kComponentB;
+            case TextureInternalFormat::RGBA:
+                return kComponentR | kComponentG | kComponentB | kComponentA;
+            case TextureInternalFormat::DepthComponent:
+                return kComponentDepth;
+            case TextureInternalFormat::DepthStencil:
+                return kComponentDepth | kComponentStencil;
+            default:
+                return 0;
+            }
+        }
+    } // namespace
+
     Bool ValidateBaseInternalFormatMatch(TextureInternalFormat format1, TextureInternalFormat format2) {
-        auto unsizedFormat1 = MG_Util::ConvertInternalFormatToUnsized(format1);
-        auto unsizedFormat2 = MG_Util::ConvertInternalFormatToUnsized(format2);
+        const auto unsizedFormat1 = MG_Util::ConvertInternalFormatToUnsized(format1);
+        const auto unsizedFormat2 = MG_Util::ConvertInternalFormatToUnsized(format2);
         if (unsizedFormat1 != unsizedFormat2) {
+            // The 3-argument GenericErrorInfo constructor used to be spelled as a single
+            // std::format() call whose format string was the component name, so every
+            // diagnostic collapsed to the literal "MG_Impl/GLImpl". Format the message, then
+            // hand over component/function/message separately.
             MG_State::pGLContext->RecordError(
                 ErrorCode::InvalidOperation,
                 MakeUnique<GenericErrorInfo>(
-                    std::format("MG_Impl/GLImpl", "ValidateBaseInternalFormatMatch",
-                                "The base internal format of the two formats do not match ({} vs. {})",
-                                MG_Util::ConvertTextureInternalFormatToString(unsizedFormat1).c_str(),
-                                MG_Util::ConvertTextureInternalFormatToString(unsizedFormat2).c_str())));
+                    "MG_Impl/GLImpl", "ValidateBaseInternalFormatMatch",
+                    std::format("The base internal format of the two formats do not match ({} vs. {})",
+                                MG_Util::ConvertTextureInternalFormatToString(unsizedFormat1),
+                                MG_Util::ConvertTextureInternalFormatToString(unsizedFormat2))));
             return false;
         }
         return true;
-    } // namespace TextureImpl
+    }
+
+    Bool ValidateCopyTexImageBaseFormatSubset(TextureInternalFormat destFormat, TextureInternalFormat srcFormat) {
+        const auto unsizedDest = MG_Util::ConvertInternalFormatToUnsized(destFormat);
+        const auto unsizedSrc = MG_Util::ConvertInternalFormatToUnsized(srcFormat);
+        // GL 4.6 SS 8.6: glCopyTexImage* may request a SUBSET of the read buffer's components,
+        // not an exact match - GL_RGB from an RGBA8 framebuffer is textbook legal and is what
+        // Minecraft and its mods do. glCopyTexImage2D used to run the exact-match predicate
+        // above and turn its rejection into an uncaught exception through the C GL ABI, so the
+        // app died rather than seeing a GL error.
+        const Uint32 destComponents = BaseFormatComponents(unsizedDest);
+        const Uint32 srcComponents = BaseFormatComponents(unsizedSrc);
+        if (destComponents == 0 || srcComponents == 0 || (destComponents & ~srcComponents) != 0) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>(
+                    "MG_Impl/GLImpl", "ValidateCopyTexImageBaseFormatSubset",
+                    std::format("the read buffer's base internal format {} does not provide every component of "
+                                "the requested internal format {}",
+                                MG_Util::ConvertTextureInternalFormatToString(unsizedSrc),
+                                MG_Util::ConvertTextureInternalFormatToString(unsizedDest))));
+            return false;
+        }
+        return true;
+    }
 } // namespace MobileGL::MG_Impl::GLImpl::TextureImpl

MobileGL/MG_Impl/GLImpl/Texture/Validators.h

@@ -40,5 +40,9 @@ namespace MobileGL::MG_Impl::GLImpl::TextureImpl {
                                          TextureTarget target);
     Bool ValidateTextureSubImageOffsets(const SharedPtr<MG_State::GLState::ITextureObject>& textureObject, Int xoffset,
                                         Int width, Int yoffset = 0, Int height = 0, Int zoffset = 0, Int depth = 0);
+    // Exact base-format equality - what glCopyImageSubData's format compatibility needs.
     Bool ValidateBaseInternalFormatMatch(TextureInternalFormat format1, TextureInternalFormat format2);
+    // GL 4.6 SS 8.6 subset rule for glCopyTexImage*: the read buffer must supply every component
+    // the requested internalformat asks for, but may supply more.
+    Bool ValidateCopyTexImageBaseFormatSubset(TextureInternalFormat destFormat, TextureInternalFormat srcFormat);
 } // namespace MobileGL::MG_Impl::GLImpl::TextureImpl

MobileGL/MG_State/GLState/RenderState/RenderState.cpp

@@ -7,6 +7,7 @@
 // End of Source File Header
 
 #include "RenderState.h"
+#include "MG_Util/Debug/Log.h"
 #include "MG_Util/Types.h"
 
 namespace MobileGL {
@@ -268,9 +269,14 @@ namespace MobileGL {
             }
 
             void RenderState::SetCapabilityIndexed(CapabilityInput cap, Uint index, Bool enabled) {
-                // Only for BlendState currently
+                // Only for BlendState currently. The GL entry points (glEnablei/glDisablei) already
+                // reject every non-GL_BLEND target with GL_INVALID_ENUM before reaching here, so this
+                // is a backstop - but it must stay a backstop: THROW_UNIMPL_EXCEPTION unwinds a C++
+                // exception through the C GL ABI and terminates the process.
                 if (cap != CapabilityInput::Blend) {
-                    THROW_UNIMPL_EXCEPTION;
+                    MGLOG_I("RenderState::SetCapabilityIndexed: indexed capability state exists only for "
+                            "GL_BLEND (cap=%d, index=%u); ignoring",
+                            static_cast<int>(cap), index);
                     return;
                 }
                 if (index >= MG_State::GLState::FramebufferObject::MAX_DRAW_BUFFERS) {
@@ -284,9 +290,13 @@ namespace MobileGL {
             }
 
             Bool RenderState::IsCapabilityEnabledIndexed(CapabilityInput cap, Uint index) const {
-                // Only for BlendState currently
+                // Only for BlendState currently - same backstop reasoning as SetCapabilityIndexed:
+                // glIsEnabledi has already answered GL_INVALID_ENUM/GL_FALSE for anything else, and a
+                // query must never be able to terminate the process.
                 if (cap != CapabilityInput::Blend) {
-                    THROW_UNIMPL_EXCEPTION;
+                    MGLOG_I("RenderState::IsCapabilityEnabledIndexed: indexed capability state exists only "
+                            "for GL_BLEND (cap=%d, index=%u); reporting disabled",
+                            static_cast<int>(cap), index);
                     return false;
                 }
                 if (index >= MG_State::GLState::FramebufferObject::MAX_DRAW_BUFFERS) {

MobileGL/MG_Test/State/CMakeLists.txt

@@ -25,3 +25,28 @@ endif()
 
 include(GoogleTest)
 gtest_discover_tests(ObjectLifetimeIdTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
+
+add_executable(
+        RenderStateTest
+        RenderStateTest.cpp
+)
+
+target_include_directories(RenderStateTest PRIVATE
+        ${MGL_ROOT}/include
+        ${MGL_ROOT}/MobileGL
+        ${MGL_ROOT}/3rdparty/xxHash
+        ${MGL_ROOT}/3rdparty/Vulkan-Headers/include
+        ${MGL_ROOT}/3rdparty/SPIRV-Reflect
+)
+
+target_link_libraries(
+        RenderStateTest PRIVATE
+        GTest::gtest_main
+        ${LINK_LIBRARIES}
+)
+
+if (MSVC)
+        target_compile_options(RenderStateTest PRIVATE /Zc:preprocessor)
+endif()
+
+gtest_discover_tests(RenderStateTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)

MobileGL/MG_Test/State/RenderStateTest.cpp

@@ -0,0 +1,91 @@
+// MobileGL - MobileGL/MG_Test/State/RenderStateTest.cpp
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+//
+// Indexed capability state (glEnablei/glDisablei/glIsEnabledi) exists only for GL_BLEND in this
+// stack. Every other capability must come back as GL_INVALID_ENUM per GL 4.6 sec. 17.3.3 - and,
+// far more importantly, must come back at all: RenderState::SetCapabilityIndexed and
+// IsCapabilityEnabledIndexed used to answer a non-blend capability with THROW_UNIMPL_EXCEPTION,
+// which unwinds a C++ exception through the C GL ABI and terminates the process.
+
+#include <gtest/gtest.h>
+
+#include "Includes.h"
+#include "Init.h"
+
+#include <MG_Impl/GLImpl/Getter/GL_Getter.h>
+#include <MG_Impl/GLImpl/RenderState/GL_RenderState.h>
+#include <MG_State/GLState/Core.h>
+#include <MG_State/GLState/FramebufferState/FramebufferObject.h>
+
+using namespace MobileGL;
+
+namespace {
+    class RenderStateTest: public ::testing::Test {
+    protected:
+        // GL error flags are sticky per code and the context outlives an individual test in this
+        // binary, so a pending error from an earlier case would be handed to the next GetError().
+        static void DrainPendingGlErrors() {
+            for (Int drained = 0; drained < 16 && MG_Impl::GLImpl::GetError() != GL_NO_ERROR; ++drained) {
+            }
+        }
+
+        static void ExpectSingleGlError(GLenum expected) {
+            EXPECT_EQ(MG_Impl::GLImpl::GetError(), expected);
+            EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "the call recorded more than one error";
+        }
+
+        void SetUp() override {
+            MobileGL::Initialize();
+            DrainPendingGlErrors();
+        }
+
+        void TearDown() override {
+            EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "test left an unconsumed GL error behind";
+        }
+    };
+} // namespace
+
+TEST_F(RenderStateTest, IndexedCapabilityTogglesRejectNonBlendCapabilities) {
+    // GL_CLIP_DISTANCE0 is a real capability, just not an indexed one - the shape an application or
+    // a CTS negative test would hit.
+    for (const GLenum cap : {GL_CLIP_DISTANCE0, GL_DEPTH_TEST, GL_SCISSOR_TEST}) {
+        MG_Impl::GLImpl::Enablei(cap, 0);
+        ExpectSingleGlError(GL_INVALID_ENUM);
+
+        MG_Impl::GLImpl::Disablei(cap, 0);
+        ExpectSingleGlError(GL_INVALID_ENUM);
+
+        EXPECT_EQ(MG_Impl::GLImpl::IsEnabledi(cap, 0), GL_FALSE);
+        ExpectSingleGlError(GL_INVALID_ENUM);
+    }
+}
+
+TEST_F(RenderStateTest, IndexedCapabilityTogglesRejectAnOutOfRangeBufferIndex) {
+    const GLuint outOfRange = MG_State::GLState::FramebufferObject::MAX_DRAW_BUFFERS;
+
+    MG_Impl::GLImpl::Enablei(GL_BLEND, outOfRange);
+    ExpectSingleGlError(GL_INVALID_VALUE);
+
+    MG_Impl::GLImpl::Disablei(GL_BLEND, outOfRange);
+    ExpectSingleGlError(GL_INVALID_VALUE);
+
+    EXPECT_EQ(MG_Impl::GLImpl::IsEnabledi(GL_BLEND, outOfRange), GL_FALSE);
+    ExpectSingleGlError(GL_INVALID_VALUE);
+}
+
+TEST_F(RenderStateTest, IndexedBlendTogglesStillWork) {
+    // The rejection path must not have cost the one capability that is genuinely indexed.
+    MG_Impl::GLImpl::Enablei(GL_BLEND, 1);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+    EXPECT_EQ(MG_Impl::GLImpl::IsEnabledi(GL_BLEND, 1), GL_TRUE);
+
+    MG_Impl::GLImpl::Disablei(GL_BLEND, 1);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+    EXPECT_EQ(MG_Impl::GLImpl::IsEnabledi(GL_BLEND, 1), GL_FALSE);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+}

MobileGL/MG_Test/Texture/TextureTest.cpp

@@ -3176,3 +3176,115 @@ TEST_F(TextureTest, WidenedRenderTargetUploadExpandsThreeChannelDataWithOpaqueAl
         EXPECT_EQ(PrepareChannelWidenedUpload(3, texelSize, nullptr, 0, GL_FLOAT, widened), nullptr);
     }
 }
+
+// ---------------------------------------------------------------------------------------------
+// A GL entry point may return an error, but it may never throw through the C GL ABI: unwinding a
+// C++ exception across it terminates the process. These cover the sites that used to do exactly
+// that (KHR-GL30.api.coverage died on the first of them on both backends).
+// ---------------------------------------------------------------------------------------------
+
+namespace {
+    struct CopyTexImage2DCall {
+        Bool Called = false;
+        GLenum Target = 0;
+        GLint Level = 0;
+        GLenum InternalFormat = 0;
+        GLsizei Width = 0;
+        GLsizei Height = 0;
+    };
+
+    CopyTexImage2DCall g_copyTexImage2DCall;
+
+    void RecordCopyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint, GLint, GLsizei width,
+                              GLsizei height, GLint) {
+        g_copyTexImage2DCall = {true, target, level, internalformat, width, height};
+    }
+
+    // A colour read framebuffer of the requested sized format, bound to GL_READ_FRAMEBUFFER, which
+    // is what glCopyTexImage2D takes its source base format from.
+    void BindReadFramebufferWithColorFormat(GLenum sizedInternalFormat) {
+        GLuint framebuffer = 0;
+        GLuint texture = 0;
+        MG_Impl::GLImpl::CreateFramebuffers(1, &framebuffer);
+        MG_Impl::GLImpl::CreateTextures(GL_TEXTURE_2D, 1, &texture);
+        MG_Impl::GLImpl::TextureStorage2D(texture, 1, sizedInternalFormat, 16, 16);
+        MG_Impl::GLImpl::NamedFramebufferTexture(framebuffer, GL_COLOR_ATTACHMENT0, texture, 0);
+        MG_Impl::GLImpl::BindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
+    }
+
+    GLuint BindFreshMutableTexture2D() {
+        GLuint texture = 0;
+        MG_Impl::GLImpl::CreateTextures(GL_TEXTURE_2D, 1, &texture);
+        MG_Impl::GLImpl::BindTexture(GL_TEXTURE_2D, texture);
+        return texture;
+    }
+} // namespace
+
+TEST_F(TextureTest, CopyTexImage2DAcceptsEveryComponentSubsetOfTheReadBuffer) {
+    const ScopedTextureBackendFunctionsOverride backendGuard;
+    MG_Backend::gBackendFunctionsTable.GL.CopyTexImage2D = RecordCopyTexImage2D;
+
+    BindReadFramebufferWithColorFormat(GL_RGBA8);
+    ASSERT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "read framebuffer setup itself failed";
+
+    // GL 4.6 sec. 8.6: internalformat may name a SUBSET of the read buffer's components. This is
+    // exactly the list KHR-GL30.api.coverage walks against an rgba8888 colour buffer, and it is
+    // also what an ordinary GL app does with glCopyTexImage2D(GL_RGB) from an RGBA8 framebuffer.
+    for (const GLenum internalFormat : {GL_RED, GL_RG, GL_RGB, GL_RGBA}) {
+        BindFreshMutableTexture2D();
+        g_copyTexImage2DCall = {};
+
+        MG_Impl::GLImpl::CopyTexImage2D(GL_TEXTURE_2D, 0, internalFormat, 0, 0, 1, 1, 0);
+
+        EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "internalformat " << internalFormat;
+        EXPECT_TRUE(g_copyTexImage2DCall.Called) << "internalformat " << internalFormat;
+        EXPECT_EQ(g_copyTexImage2DCall.InternalFormat, internalFormat);
+        EXPECT_EQ(g_copyTexImage2DCall.Width, 1);
+        EXPECT_EQ(g_copyTexImage2DCall.Height, 1);
+    }
+}
+
+TEST_F(TextureTest, CopyTexImage2DRejectsAFormatTheReadBufferCannotSupply) {
+    const ScopedTextureBackendFunctionsOverride backendGuard;
+    MG_Backend::gBackendFunctionsTable.GL.CopyTexImage2D = RecordCopyTexImage2D;
+
+    BindReadFramebufferWithColorFormat(GL_R8);
+    ASSERT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR) << "read framebuffer setup itself failed";
+
+    BindFreshMutableTexture2D();
+    g_copyTexImage2DCall = {};
+
+    // The subset rule still has a wrong side: GL_RGBA asks for components a GL_R8 read buffer does
+    // not have. That must be GL_INVALID_OPERATION and nothing else - not a throw, not silence.
+    MG_Impl::GLImpl::CopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, 1, 1, 0);
+
+    ExpectSingleGlError(GL_INVALID_OPERATION);
+    EXPECT_FALSE(g_copyTexImage2DCall.Called) << "a rejected copy must not reach the backend";
+}
+
+TEST_F(TextureTest, CopyTexImage1DReportsUnsupportedInsteadOfTerminating) {
+    // 1D textures have no upload path in this stack; the entry point used to throw unconditionally.
+    MG_Impl::GLImpl::CopyTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, 0, 0, 1, 0);
+    ExpectSingleGlError(GL_INVALID_OPERATION);
+}
+
+TEST_F(TextureTest, GetTexLevelParameterOnBufferStorageReportsErrorInsteadOfTerminating) {
+    // TextureStorageType is {Mipmap, Buffer} and the level queries only answer out of a mipmap
+    // chain, so every glGetTexLevelParameter* on a GL_TEXTURE_BUFFER texture reached a
+    // THROW_UNIMPL_EXCEPTION default: label and killed the process.
+    GLuint texture = 0;
+    MG_Impl::GLImpl::CreateTextures(GL_TEXTURE_BUFFER, 1, &texture);
+    MG_Impl::GLImpl::BindTexture(GL_TEXTURE_BUFFER, texture);
+    MG_Impl::GLImpl::TexBuffer(GL_TEXTURE_BUFFER, GL_R8, 0);
+    DrainPendingGlErrors();
+
+    for (const GLenum pname : {GL_TEXTURE_WIDTH, GL_TEXTURE_HEIGHT, GL_TEXTURE_DEPTH}) {
+        GLint intParam = 0x20202020;
+        MG_Impl::GLImpl::GetTexLevelParameteriv(GL_TEXTURE_BUFFER, 0, pname, &intParam);
+        ExpectSingleGlError(GL_INVALID_OPERATION);
+
+        GLfloat floatParam = 12345.0f;
+        MG_Impl::GLImpl::GetTexLevelParameterfv(GL_TEXTURE_BUFFER, 0, pname, &floatParam);
+        ExpectSingleGlError(GL_INVALID_OPERATION);
+    }
+}