metal: implement texture swizzling

include/renderer_mtl/mtl_texture.hpp

@@ -29,6 +29,7 @@ namespace Metal {
 		Interval<u32> range;
 
 		PICA::PixelFormatInfo formatInfo;
+		MTL::Texture* base = nullptr;
 		MTL::Texture* texture = nullptr;
 		MTL::SamplerState* sampler = nullptr;
 

include/renderer_mtl/pica_to_mtl.hpp

@@ -12,7 +12,7 @@ namespace PICA {
 		size_t bytesPerTexel;
 		void (*decoder)(OpenGL::uvec2, u32, u32, std::span<const u8>, std::vector<u8>&);
 		bool needsSwizzle{false};
-		// TODO: swizzle
+		MTL::TextureSwizzleChannels swizzle{.red = MTL::TextureSwizzleRed, .green = MTL::TextureSwizzleGreen, .blue = MTL::TextureSwizzleBlue, .alpha = MTL::TextureSwizzleAlpha};
 	};
 
 	extern PixelFormatInfo pixelFormatInfos[14];