[Feat] (Diligent, MG_Impl): wire CopyTexImage2D/CopyTexSubImage2D readback copy

- Copy current read-FBO color attachment into the bound GL_TEXTURE_2D
- Uses whole-color CopyTexture fallback for now; 13 Diligent tests pass

HANDOFF_DILIGENT.md

@@ -151,6 +151,7 @@ Verified locally on Turnip Adreno 750:
   - `DrawArraysInstanced` / `DrawElementsInstanced` family
   - `ClearBufferfv` / `ClearBufferiv` / `ClearBufferuiv`
   - `BlitFramebuffer` (same-size color copy between current read/draw FBOs)
+  - `CopyTexImage2D` / `CopyTexSubImage2D` (whole-color copy fallback)
   - `ReadPixels` from default and user color attachments
 - Primitive expansion:
   - `GL_TRIANGLE_FAN` expanded to triangle list
@@ -210,7 +211,7 @@ Notes:
 - Global UBO (default-block `glUniform*`) and named application UBO blocks (through `glBindBufferBase`/`glUniformBlockBinding`) now upload and bind; SSBOs are still not fed from frontend buffer bindings.
 - No swapchain / EGL window surface presentation yet; `Present()` only flushes.
 - No transform feedback / queries / sync / readback of non-color resources.
-- Draw range, multi-draw, instanced-draw wrappers, clear-buffer, blit and read-pixels are now wired; indirect draws, CopyTexImage/GetTexImage and buffer subdata paths still remain.
+- Draw range, multi-draw, instanced-draw wrappers, clear-buffer, blit, read-pixels and CopyTexImage* are now wired; indirect draws, GetTexImage and buffer subdata paths still remain.
 - A last-PSO cache now avoids recreating the pipeline when program/render-state/topology/VAO layout is unchanged; texture/UBO resources are still rebound dynamically per draw.
 - The `GLFunctionsTable` is only partially populated.
 
@@ -242,7 +243,7 @@ Notes:
    - [x] `MultiDraw*`
    - [x] `BlitFramebuffer` (same-size color copy)
    - [x] `ReadPixels` from non-default framebuffer
-   - [ ] `GetTexImage` / `CopyTexImage*` / indirect draws
+   - [~] `CopyTexImage*` wired as whole-color copy; `GetTexImage` / indirect draws remain
 
 6. **Expand local test suite**
    - [x] Scissor test

MobileGL/MG_Backend/Diligent/BackendObject_Diligent.cpp

@@ -238,6 +238,46 @@ namespace MobileGL::MG_Backend::DiligentBackend {
             }
         }
 
+        void CopyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y,
+                            GLsizei width, GLsizei height, GLint border) {
+            (void)level;
+            (void)internalformat;
+            (void)x;
+            (void)y;
+            (void)width;
+            (void)height;
+            (void)border;
+            auto* renderer = GetActiveRenderer();
+            if (renderer == nullptr || MG_State::pGLContext == nullptr || target != GL_TEXTURE_2D) {
+                return;
+            }
+            auto& unit = MG_State::pGLContext->GetTextureUnitObject(MG_State::pGLContext->GetActiveTextureUnit());
+            auto texture = unit.GetBindingSlot(TextureTarget::Texture2D).GetBoundObject();
+            if (texture) {
+                renderer->CopyReadFramebufferToTexture(*texture);
+            }
+        }
+
+        void CopyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y,
+                               GLsizei width, GLsizei height) {
+            (void)level;
+            (void)xoffset;
+            (void)yoffset;
+            (void)x;
+            (void)y;
+            (void)width;
+            (void)height;
+            auto* renderer = GetActiveRenderer();
+            if (renderer == nullptr || MG_State::pGLContext == nullptr || target != GL_TEXTURE_2D) {
+                return;
+            }
+            auto& unit = MG_State::pGLContext->GetTextureUnitObject(MG_State::pGLContext->GetActiveTextureUnit());
+            auto texture = unit.GetBindingSlot(TextureTarget::Texture2D).GetBoundObject();
+            if (texture) {
+                renderer->CopyReadFramebufferToTexture(*texture);
+            }
+        }
+
         void Present() {
             auto* renderer = GetActiveRenderer();
             if (renderer != nullptr) {
@@ -342,6 +382,8 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         m_functions.GL.ClearBufferiv = ClearBufferiv;
         m_functions.GL.ClearBufferuiv = ClearBufferuiv;
         m_functions.GL.BlitFramebuffer = BlitFramebuffer;
+        m_functions.GL.CopyTexImage2D = CopyTexImage2D;
+        m_functions.GL.CopyTexSubImage2D = CopyTexSubImage2D;
         m_functions.GL.ReadPixels = ReadPixels;
         m_functions.Present = Present;
 

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.cpp

@@ -1701,6 +1701,46 @@ void main()
         m_pContext->CopyTexture(copyAttribs);
     }
 
+    void DiligentRenderer::CopyReadFramebufferToTexture(MG_State::GLState::ITextureObject& dst) {
+        if (!m_initialized || !m_pContext || !m_pColorTarget) {
+            return;
+        }
+
+        ::Diligent::RefCntAutoPtr<::Diligent::ITexture> pSrcTexture = m_pColorTarget;
+        if (MG_State::pGLContext != nullptr) {
+            auto readFbo = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Read).GetBoundObject();
+            if (readFbo && !readFbo->IsDefaultFramebuffer()) {
+                auto readBuffer = readFbo->GetReadBuffer();
+                if (readBuffer == FramebufferAttachmentType::None) {
+                    readBuffer = FramebufferAttachmentType::Color0;
+                }
+                const auto& att = readFbo->GetAttachment(readBuffer);
+                if (att.IsTexture() && SyncTexture(*att.GetTexture()) != nullptr) {
+                    auto it = m_textureCache.find(att.GetTexture()->GetLifetimeId());
+                    if (it != m_textureCache.end() && it->second.Texture) {
+                        pSrcTexture = it->second.Texture;
+                    }
+                }
+            }
+        }
+
+        if (SyncTexture(dst) == nullptr) {
+            return;
+        }
+        auto it = m_textureCache.find(dst.GetLifetimeId());
+        if (it == m_textureCache.end() || !it->second.Texture) {
+            return;
+        }
+        auto pDstTexture = it->second.Texture;
+        if (pSrcTexture == pDstTexture) {
+            return;
+        }
+        ::Diligent::CopyTextureAttribs copyAttribs(
+            pSrcTexture, ::Diligent::RESOURCE_STATE_TRANSITION_MODE_TRANSITION,
+            pDstTexture, ::Diligent::RESOURCE_STATE_TRANSITION_MODE_TRANSITION);
+        m_pContext->CopyTexture(copyAttribs);
+    }
+
     void DiligentRenderer::Present() {
         // Offscreen renderer: nothing to present yet.
         if (m_pContext) {

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.h

@@ -64,6 +64,7 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         void BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
                              GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
                              GLbitfield mask, GLenum filter);
+        void CopyReadFramebufferToTexture(MG_State::GLState::ITextureObject& dst);
         void Present();
 
         ::Diligent::IRenderDevice* GetDevice() const { return m_pDevice; }