From 6eb5ff51c5927d80258b56198ebe779ab90004b6 Mon Sep 17 00:00:00 2001
From: Swung0x48 <swung0x48@outlook.com>
Date: Mon, 20 Jul 2026 07:47:08 -0400
Subject: [PATCH] [Fix] (MG_Impl/GLImpl): reject the RGTC internal formats on
 3D texture targets - RGTC compresses 4x4 blocks of a 2D image and has no 3D
 form, and the check must run on the raw enum because RGTC now resolves to
 plain R8/RG8 storage

---
 .../MG_Impl/GLImpl/Texture/GL_Texture.cpp     | 15 +++++++++++++
 MobileGL/MG_Test/Texture/TextureTest.cpp      | 22 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp b/MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp
index 8442938a..753005a3 100644
--- a/MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp
+++ b/MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp
@@ -1724,6 +1724,21 @@ namespace MobileGL::MG_Impl::GLImpl {
             return;
         }
 
+        // RGTC is a 2D-only compression scheme, so a 3D target rejects it. This has to be tested on
+        // the raw enum: the RGTC formats resolve to plain R8/RG8/SNORM storage on the way in (see
+        // GLToMG's TextureEnumConverter), so once the internal format is converted there is nothing
+        // left to distinguish them from an ordinary one- or two-channel upload.
+        if ((textureUploadTarget == TextureUploadTarget::Texture3D ||
+             textureUploadTarget == TextureUploadTarget::ProxyTexture3D) &&
+            (internalformat == GL_COMPRESSED_RED_RGTC1 || internalformat == GL_COMPRESSED_SIGNED_RED_RGTC1 ||
+             internalformat == GL_COMPRESSED_RG_RGTC2 || internalformat == GL_COMPRESSED_SIGNED_RG_RGTC2)) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                             "RGTC compressed formats are invalid for 3D texture targets"));
+            return;
+        }
+
         // TODO: GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the
         // GL_PIXEL_UNPACK_BUFFER target and the buffer object's data store is currently mapped.
         // GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER
diff --git a/MobileGL/MG_Test/Texture/TextureTest.cpp b/MobileGL/MG_Test/Texture/TextureTest.cpp
index 5c9e9baa..a23fd8ea 100644
--- a/MobileGL/MG_Test/Texture/TextureTest.cpp
+++ b/MobileGL/MG_Test/Texture/TextureTest.cpp
@@ -1557,6 +1557,28 @@ TEST_F(TextureTest, CompressedInternalFormatsResolveToTheirUncompressedStorage)
     }
 }
 
+// RGTC compresses 4x4 blocks of a 2D image and has no 3D form, so glTexImage3D must reject it even
+// though the same enum is accepted on a 2D target. The generic compressed formats carry no such
+// restriction and stay legal in 3D.
+TEST_F(TextureTest, RgtcInternalFormatsAreRejectedOnThreeDimensionalTargets) {
+    const GLenum rgtc[] = {GL_COMPRESSED_RED_RGTC1, GL_COMPRESSED_SIGNED_RED_RGTC1, GL_COMPRESSED_RG_RGTC2,
+                           GL_COMPRESSED_SIGNED_RG_RGTC2};
+    for (const GLenum internalFormat : rgtc) {
+        GLuint texture = 0;
+        MG_Impl::GLImpl::GenTextures(1, &texture);
+        MG_Impl::GLImpl::BindTexture(GL_TEXTURE_3D, texture);
+        MG_Impl::GLImpl::TexImage3D(GL_TEXTURE_3D, 0, internalFormat, 4, 4, 4, 0, GL_RED, GL_UNSIGNED_BYTE, nullptr);
+        EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_INVALID_OPERATION)
+            << "internalFormat 0x" << std::hex << internalFormat;
+    }
+
+    GLuint generic = 0;
+    MG_Impl::GLImpl::GenTextures(1, &generic);
+    MG_Impl::GLImpl::BindTexture(GL_TEXTURE_3D, generic);
+    MG_Impl::GLImpl::TexImage3D(GL_TEXTURE_3D, 0, GL_COMPRESSED_RGBA, 4, 4, 4, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+}
+
 TEST_F(TextureTest, TextureStorage3DAndSubImageModifyNamedObjectOnly) {
     GLuint texture = 0;
     MG_Impl::GLImpl::CreateTextures(GL_TEXTURE_3D, 1, &texture);