Fix not setting graphics pipeline primitive type for Metal

This information is needed when a vertex shader outputs
[[render_target_array_index]] for a 2D texture array.

The GPU needs to know the primitive topology at pipeline compile time to
determine which vertex's array index value to use when routing fragments
to the indexed texture layer.

Author: tuzz

src/gpu/metal/SDL_gpu_metal.m

@@ -1221,6 +1221,24 @@ static void METAL_ReleaseGraphicsPipeline(
             pipelineDescriptor.vertexDescriptor = vertexDescriptor;
         }
 
+        // Primitive
+
+        switch (createinfo->primitive_type) {
+            case SDL_GPU_PRIMITIVETYPE_TRIANGLELIST:
+            case SDL_GPU_PRIMITIVETYPE_TRIANGLESTRIP:
+                pipelineDescriptor.inputPrimitiveTopology = MTLPrimitiveTopologyClassTriangle;
+                break;
+            case SDL_GPU_PRIMITIVETYPE_LINELIST:
+            case SDL_GPU_PRIMITIVETYPE_LINESTRIP:
+                pipelineDescriptor.inputPrimitiveTopology = MTLPrimitiveTopologyClassLine;
+                break;
+            case SDL_GPU_PRIMITIVETYPE_POINTLIST:
+                pipelineDescriptor.inputPrimitiveTopology = MTLPrimitiveTopologyClassPoint;
+                break;
+        }
+
+        // Props
+
         if (renderer->debugMode && SDL_HasProperty(createinfo->props, SDL_PROP_GPU_GRAPHICSPIPELINE_CREATE_NAME_STRING)) {
             const char *name = SDL_GetStringProperty(createinfo->props, SDL_PROP_GPU_GRAPHICSPIPELINE_CREATE_NAME_STRING, NULL);
             pipelineDescriptor.label = @(name);