[Feat] (Diligent): wire viewport/scissor state into state draws

DrawFromState now uses MG_State viewport (with full-target fallback when the
viewport is uninitialized) and applies the scissor test rect when enabled.
The state-driven test sets an explicit glViewport and passes again.

MobileGL/MG_Backend/Diligent/Renderer/DiligentRenderer.cpp

@@ -396,9 +396,32 @@ void main()
         ::Diligent::ITextureView* rtvs[] = {m_pColorRTV};
         m_pContext->SetRenderTargets(1, rtvs, nullptr, ::Diligent::RESOURCE_STATE_TRANSITION_MODE_TRANSITION);
 
-        ::Diligent::Viewport viewport{0, 0, static_cast<Float>(m_width), static_cast<Float>(m_height), 0.0f, 1.0f};
+        auto glViewport = MG_State::pGLContext->GetViewport();
+        if (glViewport.z() <= 0 || glViewport.w() <= 0) {
+            glViewport = IntVec4(0, 0, static_cast<Int32>(m_width), static_cast<Int32>(m_height));
+        }
+        ::Diligent::Viewport viewport{
+            static_cast<Float>(glViewport.x()),
+            static_cast<Float>(glViewport.y()),
+            static_cast<Float>(glViewport.z()),
+            static_cast<Float>(glViewport.w()),
+            0.0f, 1.0f};
         m_pContext->SetViewports(1, &viewport, m_width, m_height);
 
+        if (MG_State::pGLContext->IsCapabilityEnabled(CapabilityInput::ScissorTest)) {
+            const auto scissor = MG_State::pGLContext->GetScissorBox();
+            ::Diligent::Rect rect{
+                scissor.x(),
+                scissor.y(),
+                scissor.x() + scissor.z(),
+                scissor.y() + scissor.w()};
+            m_pContext->SetScissorRects(1, &rect, m_width, m_height);
+        } else {
+            ::Diligent::Rect rect{0, 0, static_cast<::Diligent::Int32>(m_width),
+                                  static_cast<::Diligent::Int32>(m_height)};
+            m_pContext->SetScissorRects(1, &rect, m_width, m_height);
+        }
+
         ::Diligent::IBuffer* pVBs[] = {m_pVertexBuffer};
         m_pContext->SetVertexBuffers(0, 1, pVBs, nullptr,
                                      ::Diligent::RESOURCE_STATE_TRANSITION_MODE_TRANSITION,

MobileGL/MG_Test/Backend/Diligent/SanityTest.cpp

@@ -12,6 +12,7 @@
 #include <MG_Backend/BackendObjects.h>
 #include <MG_Impl/GLImpl/Buffer/GL_Buffer.h>
 #include <MG_Impl/GLImpl/Program/GL_Program.h>
+#include <MG_Impl/GLImpl/RenderState/GL_RenderState.h>
 #include <MG_Impl/GLImpl/VertexArray/GL_VertexArray.h>
 #include <MG_State/GLState/Core.h>
 #include <Init.h>
@@ -94,6 +95,7 @@ void main() { Color = vec4(1.0, 0.0, 0.0, 1.0); }
     AttachShader(program, fs);
     LinkProgram(program);
     UseProgram(program);
+    Viewport(0, 0, 256, 256);
 
     // Upload a triangle into a real GL buffer and describe it through a VAO.
     const float vertices[] = {