Metal: dedup per-frame uniforms bind and clean up OSD locals

Follow-up cleanup to 5298e70 ("Metal: inline single-call helpers in
render path"), which made two small issues visible:

1. The core-draw, menu-draw, and overlay blocks in -renderFrame: each
   bound _context.uniforms at BufferIndexUniforms on the main render
   command encoder, always with the same buffer. Issue one bind per
   frame instead.

   The bind is placed AFTER [_frameView drawWithContext:_context]
   returns rather than at the top of the frame. FrameView's shader-pass
   loop may, on its back-buffer pass, rebind vertex slots at indices
   determined by .slang shader reflection data, which in principle
   could collide with BufferIndexUniforms. Binding after drawWithContext:
   guarantees the uniforms slot holds what the subsequent menu/overlay
   draws expect.

2. Rename width_n/height_n (awkward names introduced by the inlining
   of -_renderMessage:data:, which previously had its own scope free
   of width/height parameter shadowing) to bg_w/bg_h, matching the
   semantics of the OSD message background quad.

No functional change intended.

Author: LibretroAdmin

gfx/drivers/metal.m

@@ -2487,9 +2487,17 @@ - (bool)renderFrame:(const void *)frame
 
       /* Draw core: back buffer + optional encoder pass. */
       [_frameView drawWithContext:_context];
+
+      /* Bind uniforms once for all subsequent encoder work on the main
+       * command encoder. FrameView's shader passes can rebind vertex
+       * slots at shader-reflection-driven indices on the back-buffer
+       * pass, so bind AFTER drawWithContext: returns, not before.
+       * All subsequent blocks (core encoder pass, menu, overlay) reuse
+       * this binding instead of each rebinding the same uniforms. */
+      [rce setVertexBytes:_context.uniforms length:sizeof(*_context.uniforms) atIndex:BufferIndexUniforms];
+
       if ((_frameView.drawState & ViewDrawStateEncoder) != 0)
       {
-         [rce setVertexBytes:_context.uniforms length:sizeof(*_context.uniforms) atIndex:BufferIndexUniforms];
          [rce setRenderPipelineState:_t_pipelineStateNoAlpha];
          if (_frameView.filter == RTextureFilterNearest)
             [rce setFragmentSamplerState:_samplerStateNearest atIndex:SamplerIndexDraw];
@@ -2505,7 +2513,6 @@ - (bool)renderFrame:(const void *)frame
          if (_menu.hasFrame)
          {
             [_menu.view drawWithContext:_context];
-            [rce setVertexBytes:_context.uniforms length:sizeof(*_context.uniforms) atIndex:BufferIndexUniforms];
             [rce setRenderPipelineState:_t_pipelineState];
             if (_menu.view.filter == RTextureFilterNearest)
                [rce setFragmentSamplerState:_samplerStateNearest atIndex:SamplerIndexDraw];
@@ -2527,7 +2534,6 @@ - (bool)renderFrame:(const void *)frame
       {
          [_context resetRenderViewport:_overlay.fullscreen ? kFullscreenViewport : kVideoViewport];
          [rce setRenderPipelineState:[_context getStockShader:VIDEO_SHADER_STOCK_BLEND blend:YES]];
-         [rce setVertexBytes:_context.uniforms length:sizeof(*_context.uniforms) atIndex:BufferIndexUniforms];
          [rce setFragmentSamplerState:_samplerStateLinear atIndex:SamplerIndexDraw];
          [_overlay drawWithEncoder:rce];
       }
@@ -2563,23 +2569,23 @@ - (bool)renderFrame:(const void *)frame
             float bgcolor_opacity = settings->floats.video_msg_bgcolor_opacity;
             float x               = settings->floats.video_msg_pos_x;
             float y               = 1.0f - settings->floats.video_msg_pos_y;
-            float width_n         = msg_width / (float)_viewport->full_width;
-            float height_n        = font_size / (float)_viewport->full_height;
+            float bg_w            = msg_width / (float)_viewport->full_width;
+            float bg_h            = font_size / (float)_viewport->full_height;
             float x2              = 0.005f; /* extend background around text */
             float y2              = 0.005f;
             float r               = bgcolor_red   / 255.0f;
             float g               = bgcolor_green / 255.0f;
             float b               = bgcolor_blue  / 255.0f;
             float a               = bgcolor_opacity;
 
-            y                    -= height_n;
+            y                    -= bg_h;
             x                    -= x2;
             y                    -= y2;
-            width_n              += x2;
-            height_n             += y2;
+            bg_w                 += x2;
+            bg_h                 += y2;
 
             [_context resetRenderViewport:kFullscreenViewport];
-            [_context drawQuadX:x y:y w:width_n h:height_n r:r g:g b:b a:a];
+            [_context drawQuadX:x y:y w:bg_w h:bg_h r:r g:g b:b a:a];
          }
 
          font_driver_render_msg(data, msg, NULL, NULL);