Merge pull request #16 from TimOliver/efficient-gradient

Increase the efficiency of the gradient renderer

Author: TimOliver

BlurUIKit/Internal/GradientImageRenderer.swift

@@ -81,31 +81,33 @@ import UIKit
         // Clamp startLocation to valid range
         let clampedStartLocation = min(max(startLocation, 0.0), 1.0)
 
-        // Calculate gradient values for each pixel
-        for i in 0..<length {
-            // Determine normalized position along the gradient (0.0 to 1.0)
-            let normalizedPosition = length > 1 ? CGFloat(i) / CGFloat(length - 1) : 0.0
-
-            // Calculate alpha with starting inset
-            let alpha: CGFloat = {
-                // Adjust for starting inset - pixels before startLocation are fully opaque/transparent
-                let adjustedPosition: CGFloat
-                if clampedStartLocation >= 1.0 {
-                    adjustedPosition = 0.0
-                } else if normalizedPosition <= clampedStartLocation {
-                    adjustedPosition = 0.0
-                } else {
-                    adjustedPosition = (normalizedPosition - clampedStartLocation) / (1.0 - clampedStartLocation)
-                }
-
-                // Apply easing for smooth transition, or use linear interpolation
-                let finalPosition = smooth ? easeInOutSine(adjustedPosition) : adjustedPosition
-
-                // Apply direction
-                return reversed ? finalPosition : 1.0 - finalPosition
-            }()
-
-            // Write gray (0) and alpha values
+        // Precompute reciprocals used in the gradient calculation
+        let lengthReciprocal: CGFloat = length > 1 ? 1.0 / CGFloat(length - 1) : 0.0
+        let gradientRangeReciprocal: CGFloat = clampedStartLocation < 1.0 ? 1.0 / (1.0 - clampedStartLocation) : 0.0
+
+        // Calculate the pixel boundary where the gradient transition starts.
+        // Pixels before this boundary all share the same constant alpha value.
+        let gradientStartPixel: Int = {
+            guard length > 1, clampedStartLocation > 0.0 else { return 0 }
+            return min(Int(clampedStartLocation * CGFloat(length - 1)) + 1, length)
+        }()
+
+        // Bulk-fill the constant region before the gradient (no per-pixel math needed)
+        if gradientStartPixel > 0 {
+            let constantAlpha: UInt8 = reversed ? 0 : 255
+            for i in stride(from: 0, to: gradientStartPixel * bytesPerPixel, by: bytesPerPixel) {
+                pixels[i] = 0
+                pixels[i + 1] = constantAlpha
+            }
+        }
+
+        // Generate the gradient transition for the remaining pixels
+        for i in gradientStartPixel..<length {
+            let normalizedPosition = CGFloat(i) * lengthReciprocal
+            let adjustedPosition = (normalizedPosition - clampedStartLocation) * gradientRangeReciprocal
+            let eased = smooth ? easeInOutSine(adjustedPosition) : adjustedPosition
+            let alpha = reversed ? eased : 1.0 - eased
+
             let pixelIndex = i * bytesPerPixel
             pixels[pixelIndex] = 0
             pixels[pixelIndex + 1] = UInt8(min(max(alpha * 255.0, 0.0), 255.0))

BlurUIKit/SwiftUI/VariableBlur.swift

@@ -55,7 +55,7 @@ public struct VariableBlur: UIViewRepresentable {
     private var blurStartingInset: GradientSizing?
     private var dimmingTintColor: UIColor? = .systemBackground
     private var dimmingAlpha: DimmingAlpha? = .interfaceStyle(lightModeAlpha: 0.5, darkModeAlpha: 0.25)
-    private var dimmingOvershoot: GradientSizing? = .relative(fraction: 0.25)
+    private var dimmingOvershoot: GradientSizing? = .relative(fraction: 1.25)
     private var dimmingStartingInset: GradientSizing?
 
     // MARK: - Initializer
@@ -138,7 +138,7 @@ public struct VariableBlur: UIViewRepresentable {
     ///
     /// - Parameter overshoot: The overshoot distance, expressed as either an absolute point
     ///   value or a fraction of the view's size. Pass `nil` to confine the dimming gradient
-    ///   to the view's bounds. Defaults to `.relative(fraction: 0.25)`.
+    ///   to the view's bounds. Defaults to `.relative(fraction: 1.25)`.
     /// - Returns: A modified `VariableBlur` with the updated dimming overshoot.
     public func dimmingOvershoot(_ overshoot: GradientSizing?) -> VariableBlur {
         var copy = self

BlurUIKit/UIKit/VariableBlurView.swift

@@ -41,7 +41,7 @@ public class VariableBlurView: UIView {
     public enum GradientSizing {
         // The amount of on-screen UI points starting from the origin, as a static value.
         case absolute(position: CGFloat)
-        // A value between 0.0 and 1.0 relative to the size of the view. A value of 0.5 would be half the size of this view.
+        // A relative fraction of this view's size along the gradient direction. (0.0 = 0%, 1.5 = 150%)
         case relative(fraction: CGFloat)
     }
 
@@ -83,7 +83,7 @@ public class VariableBlurView: UIView {
     }
 
     /// An optional overshoot value to allow the colored gradient to extend outside the blur view's bounds
-    public var dimmingOvershoot: GradientSizing? = .relative(fraction: 0.25) {
+    public var dimmingOvershoot: GradientSizing? = .relative(fraction: 1.25) {
         didSet { resetDimmingImage() }
     }
 
@@ -372,7 +372,7 @@ extension VariableBlurView {
         case .absolute(position: let position):
             return (value + position).rounded(.up)
         case .relative(fraction: let fraction):
-            return (value + (value * fraction)).rounded(.up)
+            return (value * fraction).rounded(.up)
         }
     }
 }

README.md

@@ -35,7 +35,7 @@ let blurView = VariableBlurView()
 blurView.dimmingTintColor = .red
 
 // The tint color can 'overshoot' the blur view to add more gradual transition
-blurView.dimmingOvershoot = .relative(fraction: 0.25)
+blurView.dimmingOvershoot = .relative(fraction: 1.25)
 
 ```
 
@@ -46,7 +46,7 @@ blurView.dimmingOvershoot = .relative(fraction: 0.25)
 // Use the VariableBlur view with chainable modifiers
 VariableBlur(direction: .down)
     .dimmingTintColor(.red)
-    .dimmingOvershoot(.relative(fraction: 0.25))
+    .dimmingOvershoot(.relative(fraction: 1.25))
 
 ```