read-write texture feature (#115)

* add readWriteTexture feature

* naming fix

* update ignore list

.gitignore

@@ -6,3 +6,4 @@ Demo/Demo.xcodeproj/xcuserdata/
 Demo/Demo.xcworkspace/xcuserdata/
 *gen
 .swiftpm
+.build

Sources/Alloy/Core/Extensions/Metal/MTLDevice+Features.swift

@@ -2,6 +2,7 @@ import Metal
 
 public enum Feature {
     case nonUniformThreadgroups
+    case readWriteTextures(MTLPixelFormat)
 }
 
 public extension MTLDevice {
@@ -15,6 +16,24 @@ public extension MTLDevice {
             #elseif os(macOS)
             return self.supportsFeatureSet(.macOS_GPUFamily1_v3)
             #endif
+
+        case let .readWriteTextures(pixelFormat):
+            let tierOneSupportedPixelFormats: Set<MTLPixelFormat> = [
+                .r32Float, .r32Uint, .r32Sint
+            ]
+            let tierTwoSupportedPixelFormats: Set<MTLPixelFormat> = tierOneSupportedPixelFormats.union([
+                .rgba32Float, .rgba32Uint, .rgba32Sint, .rgba16Float,
+                .rgba16Uint, .rgba16Sint, .rgba8Unorm, .rgba8Uint,
+                .rgba8Sint, .r16Float, .r16Uint, .r16Sint,
+                .r8Unorm, .r8Uint, .r8Sint
+            ])
+
+            switch self.readWriteTextureSupport {
+            case .tier1: return tierOneSupportedPixelFormats.contains(pixelFormat)
+            case .tier2: return tierTwoSupportedPixelFormats.contains(pixelFormat)
+            case .tierNone: return false
+            @unknown default: return false
+            }
         }
     }
 }