fix metal

Author: halx99

axmol/rhi/metal/RenderContextMTL.mm

@@ -46,6 +46,10 @@ of this software and associated documentation files (the "Software"), to deal
 namespace
 {
 
+// match with axmol 3.1 shader
+static constexpr int VS_UBO_BINDING_INDEX = 0;
+static constexpr int FS_UBO_BINDING_INDEX = 1;
+
 #define byte(n) ((n) * 8)
 #define bit(n)  (n)
 static uint8_t getBitsPerElementMTL(MTLPixelFormat pixleFormat)
@@ -528,19 +532,16 @@ static MTLCullMode toMTLCullMode(CullMode mode)
         for (auto& cb : callbackUniforms)
             cb.second(_programState, cb.first);
 
-        // axslcc spec, bound to 0
-        constexpr int bindingIndex = DriverImpl::VBO_BINDING_INDEX_START;
-
         auto vertexUB = _programState->getVertexUniformBuffer();
         if (!vertexUB.empty())
         {
-            [_mtlRenderEncoder setVertexBytes:vertexUB.data() length:vertexUB.size() atIndex:bindingIndex];
+            [_mtlRenderEncoder setVertexBytes:vertexUB.data() length:vertexUB.size() atIndex:VS_UBO_BINDING_INDEX];
         }
 
         auto fragUB = _programState->getFragmentUniformBuffer();
         if (!fragUB.empty())
         {
-            [_mtlRenderEncoder setFragmentBytes:fragUB.data() length:fragUB.size() atIndex:bindingIndex];
+            [_mtlRenderEncoder setFragmentBytes:fragUB.data() length:fragUB.size() atIndex:FS_UBO_BINDING_INDEX];
         }
     }
 }