Closes #2

Author: frzi

Sources/DoomWipe/DoomWipeShader.swift

@@ -38,16 +38,16 @@ public struct DoomWipeShader {
 	/// - Parameter animationPosition: The current time position of the animation. 0 = start, 1 = end.`
 	/// - Parameter seed: The random seed that affects the pattern of the wipe effect.
 	/// - Parameter direction: Whether the wipe goes downwards (original), or upwards.
-	public init(dimensions: CGSize, animationPosition: CGFloat, seed: Int = 0, direction: WipeDirection) {
+	public init(progress: CGFloat, seed: Int = 0, direction: WipeDirection) {
 		let offsets = Self.getOffset(seed: seed)
+		let scale = CGSize(width: 2, height: 2)
 
 		shader = Shader(
 			function: ShaderFunction(library: .bundle(.module), name: "doomWipe"),
 			arguments: [
-				.data(offsets),
-				.float2(dimensions), // View dimensions.
-				.float2(CGSize(width: 2, height: 2)), // Transition scale.
-				.float(min(max(animationPosition, 0), 1)), // Animation position.
+				.data(offsets), // Offset pattern.
+				.float2(scale), // Transition scale.
+				.float(min(max(progress, 0), 1)), // Animation position.
 				.float(direction.rawValue), // Direction (1 = down (original), -1 = up).
 			]
 		)

Sources/DoomWipe/Resources/DoomWipe.metal

@@ -12,7 +12,6 @@ using namespace metal;
 	SwiftUI::Layer layer,
 	device const float *offsets,
 	int offsetsSize,
-	float2 layerSize,
 	float2 scale,
 	float value,
 	float direction
@@ -23,11 +22,20 @@ using namespace metal;
 
 	int column = int(position.x / (scale.x * 2)) & 0xFF;
 	float offset = offsets[column] * offsetScale;
-	offset = min((offset * layerSize.y) - (layerSize.y * value), 0.0);
-	float y = position.y + offset * direction;
+	offset = min(offset - value, 0.0);
+	offset *= direction;
 
-	float2 uv = float2(position.x, y);
-	half4 color = layer.sample(uv);
+	// Attempt to get normalized 0..1 UV coordinates.
+	// We're actually copying `SwiftUI::Layer`'s `sample` method implementation.
+	float2 p = metal::fma(position.x, layer.info[0], metal::fma(position.y, layer.info[1], layer.info[2]));
+	p = metal::clamp(p, layer.info[3], layer.info[4]);
+	p.y += offset;
+	half4 color = layer.tex.sample(metal::sampler(metal::filter::linear), p);
+
+	// Alpha = 0 when going out of bounds.
+	if (p.y > layer.info[4].y) {
+		color.a = 0.0;
+	}
 
 	return color;
 }

Sources/DoomWipe/Transition.swift

@@ -3,6 +3,7 @@
  *  Created by Freek (github.com/frzi).
  */
 
+import AVKit
 import SwiftUI
 
 /// The Doom Wipe transition modifier
@@ -16,36 +17,28 @@ struct DoomWipeTransitionModifier: ViewModifier {
 		return globalRandomSeed
 	}
 
-	@State private var viewDimensions: CGSize = .zero
 	@State private var randomSeed = Self.globalAdvancedRandomSeed()
 
-	let animationPosition: CGFloat
+	let progress: CGFloat
 	let direction: DoomWipeShader.WipeDirection
 
 	private var shader: Shader {
 		DoomWipeShader(
-			dimensions: viewDimensions,
-			animationPosition: animationPosition,
+			progress: progress,
 			seed: randomSeed,
 			direction: direction
 		).shader
 	}
 
-	init(animationPosition: CGFloat, direction: DoomWipeShader.WipeDirection = .down) {
-		self.animationPosition = animationPosition
+	init(progress: CGFloat, direction: DoomWipeShader.WipeDirection = .down) {
+		self.progress = progress
 		self.direction = direction
 	}
 
 	func body(content: Content) -> some View {
 		content
 			.compositingGroup()
 			.layerEffect(shader, maxSampleOffset: .zero, isEnabled: true)
-			.background(GeometryReader { reader in
-				HStack {}
-					.onAppear {
-						viewDimensions = reader.size
-					}
-			})
 	}
 }
 
@@ -55,8 +48,8 @@ extension AnyTransition {
 		.asymmetric(
 			insertion: .identity,
 			removal: .modifier(
-				active: DoomWipeTransitionModifier(animationPosition: 1),
-				identity: DoomWipeTransitionModifier(animationPosition: 0)
+				active: DoomWipeTransitionModifier(progress: 1),
+				identity: DoomWipeTransitionModifier(progress: 0)
 			)
 		)
 	}
@@ -66,8 +59,8 @@ extension AnyTransition {
 		.asymmetric(
 			insertion: .identity,
 			removal: .modifier(
-				active: DoomWipeTransitionModifier(animationPosition: 1, direction: direction),
-				identity: DoomWipeTransitionModifier(animationPosition: 0, direction: direction)
+				active: DoomWipeTransitionModifier(progress: 1, direction: direction),
+				identity: DoomWipeTransitionModifier(progress: 0, direction: direction)
 			)
 		)
 	}