nxtSwapChainNextTexture: make texture a union of ptr, u32, u64

Making all textures represented by pointers is a problem for Vulkan
where VkImage is a 64bit type and wouldn't fit in a pointer on 32bit
builds. Make texture contain on of each useful type so that each backend
can choose which one it wants to receive.

src/backend/d3d12/SwapChainD3D12.cpp

@@ -40,7 +40,7 @@ namespace backend { namespace d3d12 {
             return nullptr;
         }
 
-        ID3D12Resource* nativeTexture = reinterpret_cast<ID3D12Resource*>(next.texture);
+        ID3D12Resource* nativeTexture = reinterpret_cast<ID3D12Resource*>(next.texture.ptr);
         return new Texture(builder, nativeTexture);
     }
 

src/backend/metal/SwapChainMTL.mm

@@ -40,7 +40,7 @@ namespace backend { namespace metal {
             return nullptr;
         }
 
-        id<MTLTexture> nativeTexture = reinterpret_cast<id<MTLTexture>>(next.texture);
+        id<MTLTexture> nativeTexture = reinterpret_cast<id<MTLTexture>>(next.texture.ptr);
         return new Texture(builder, nativeTexture);
     }
 

src/backend/opengl/SwapChainGL.cpp

@@ -37,7 +37,7 @@ namespace backend { namespace opengl {
             GetDevice()->HandleError(error);
             return nullptr;
         }
-        GLuint nativeTexture = static_cast<GLuint>(reinterpret_cast<uintptr_t>(next.texture));
+        GLuint nativeTexture = next.texture.u32;
         return new Texture(builder, nativeTexture);
     }
 

src/include/nxt/nxt_wsi.h

@@ -23,7 +23,11 @@ constexpr nxtSwapChainError NXT_SWAP_CHAIN_NO_ERROR = nullptr;
 
 typedef struct {
     /// Backend-specific texture id/name/pointer
-    void* texture = nullptr;
+    union {
+        void* ptr;
+        uint64_t u64;
+        uint32_t u32;
+    } texture;
 } nxtSwapChainNextTexture;
 
 typedef struct {

src/utils/D3D12Binding.cpp

@@ -177,7 +177,7 @@ namespace utils {
         }
 
         nxtSwapChainError GetNextTexture(nxtSwapChainNextTexture* nextTexture) {
-            nextTexture->texture = mRenderTargetResources[mRenderTargetIndex].Get();
+            nextTexture->texture.ptr = mRenderTargetResources[mRenderTargetIndex].Get();
             return NXT_SWAP_CHAIN_NO_ERROR;
         }
 

src/utils/MetalBinding.mm

@@ -86,7 +86,7 @@ namespace utils {
             mCurrentTexture = mCurrentDrawable.texture;
             [mCurrentTexture retain];
 
-            nextTexture->texture = reinterpret_cast<void*>(mCurrentTexture);
+            nextTexture->texture.ptr = reinterpret_cast<void*>(mCurrentTexture);
 
             return NXT_SWAP_CHAIN_NO_ERROR;
         }

src/utils/OpenGLBinding.cpp

@@ -74,7 +74,7 @@ namespace utils {
         }
 
         nxtSwapChainError GetNextTexture(nxtSwapChainNextTexture* nextTexture) {
-            nextTexture->texture = reinterpret_cast<void*>(static_cast<size_t>(mBackTexture));
+            nextTexture->texture.u32 = mBackTexture;
             return NXT_SWAP_CHAIN_NO_ERROR;
         }