[Feat] (Diligent, EGL): forward eglSwapInterval to swap chain Present

- Renderer stores the requested swap interval and passes it to ISwapChain::Present
- SetSwapInterval now updates the active renderer instead of being a no-op

HANDOFF_DILIGENT.md

@@ -220,7 +220,7 @@ Notes:
 - User framebuffers now support texture color attachments, renderbuffer color readback, multiple simultaneous color targets, and depth/stencil texture or renderbuffer attachments.
 - Textures auto-sync `ITextureObject` → Diligent resources, including mip levels and sampler state; compressed textures and integer/3-channel formats that Diligent lacks are still skipped.
 - 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.
-- Swapchain creation and resize are wired for native EGL window surfaces via `Diligent::ISwapChain`; `Present()` presents the active swap chain when present and otherwise flushes the offscreen target. Actual on-screen EGL presentation is still untested in this headless environment, and the X11 display/connection fields are not yet plumbed through `WindowHandle`. `SetSwapInterval` remains a no-op.
+- Swapchain creation and resize are wired for native EGL window surfaces via `Diligent::ISwapChain`; `Present()` presents the active swap chain when present and otherwise flushes the offscreen target. Actual on-screen EGL presentation is still untested in this headless environment, and the X11 display/connection fields are not yet plumbed through `WindowHandle`. `SetSwapInterval` now forwards the requested sync interval to `ISwapChain::Present()`.
 - No transform feedback / GPU-accelerated queries / non-color readback; fence sync and timer queries use CPU fallbacks.
 - Draw range, multi-draw, instanced-draw wrappers, clear-buffer, blit, read-pixels, CopyTexImage*, CopyImageSubData, GenerateMipmap, GetTexImage/GetTextureImage and indirect draws are now wired; 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.

MobileGL/MG_Backend/Diligent/BackendObject_Diligent.cpp

@@ -659,8 +659,10 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         }
 
         void SetSwapInterval(Int interval) {
-            // No native swapchain yet; the offscreen renderer ignores the interval.
-            (void)interval;
+            auto* renderer = GetActiveRenderer();
+            if (renderer != nullptr) {
+                renderer->SetSwapInterval(interval > 0 ? static_cast<Uint32>(interval) : 0);
+            }
         }
 
         void Present() {

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.cpp

@@ -2040,13 +2040,17 @@ void main()
         return true;
     }
 
+    void DiligentRenderer::SetSwapInterval(Uint32 interval) {
+        m_swapInterval = interval;
+    }
+
     void DiligentRenderer::ReleaseSwapChain() {
         m_pSwapChain.Release();
     }
 
     void DiligentRenderer::Present() {
         if (m_pSwapChain) {
-            m_pSwapChain->Present(0);
+            m_pSwapChain->Present(m_swapInterval);
         } else if (m_pContext) {
             // Offscreen renderer: nothing to present yet.
             m_pContext->Flush();

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.h

@@ -65,6 +65,7 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         Bool CreateSwapChain(::Diligent::IEngineFactoryVk* factory, const WindowHandle& handle,
                              Uint32 width, Uint32 height);
         Bool ResizeSwapChain(Uint32 width, Uint32 height);
+        void SetSwapInterval(Uint32 interval);
         // Creates a simple 2D RGBA8 texture from CPU data and makes it available
         // to state PSOs under the shader variable name "g_Texture".
         Bool CreateTestTexture(const void* data, Uint32 width, Uint32 height);
@@ -143,6 +144,7 @@ namespace MobileGL::MG_Backend::DiligentBackend {
         UnorderedMap<Uint64, ::Diligent::RefCntAutoPtr<::Diligent::IBuffer>> m_namedUboCache;
         Uint32 m_width = 256;
         Uint32 m_height = 256;
+        Uint32 m_swapInterval = 0;
         Uint32 m_lastDrawVertexCount = 0;
         Uint64 m_lastPSOKey = 0;
         Bool m_hasCachedPSO = false;