Eraser enabled

Example/MaLiang.xcodeproj/project.pbxproj

@@ -33,6 +33,7 @@
 		C388DE5A22550F1200CE19C6 /* pen.png in Resources */ = {isa = PBXBuildFile; fileRef = C388DE5822550F1200CE19C6 /* pen.png */; };
 		C388DE5B22550F1200CE19C6 /* pencil.png in Resources */ = {isa = PBXBuildFile; fileRef = C388DE5922550F1200CE19C6 /* pencil.png */; };
 		C3E122562255CC6800114EBD /* MLTexture.swift in Sources */ = {isa = PBXBuildFile; fileRef = B69E669C208C6117005ED0E1 /* MLTexture.swift */; };
+		C3E7B55122599CB8001D45EC /* Eraser.swift in Sources */ = {isa = PBXBuildFile; fileRef = C3E7B55022599CB8001D45EC /* Eraser.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -67,6 +68,7 @@
 		C388DE562254FB6900CE19C6 /* Maths.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Maths.swift; sourceTree = "<group>"; };
 		C388DE5822550F1200CE19C6 /* pen.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = pen.png; sourceTree = "<group>"; };
 		C388DE5922550F1200CE19C6 /* pencil.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = pencil.png; sourceTree = "<group>"; };
+		C3E7B55022599CB8001D45EC /* Eraser.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Eraser.swift; sourceTree = "<group>"; };
 		E4F56C2627A50ADFF8265C8F /* Pods-MaLiang_Example.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-MaLiang_Example.debug.xcconfig"; path = "Pods/Target Support Files/Pods-MaLiang_Example/Pods-MaLiang_Example.debug.xcconfig"; sourceTree = "<group>"; };
 		F3CBFDC0B0167759FA9BD760 /* MaLiang.podspec */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text; name = MaLiang.podspec; path = ../MaLiang.podspec; sourceTree = "<group>"; };
 		F4B98B2F9C80C87DAC438AFA /* LICENSE */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text; name = LICENSE; path = ../LICENSE; sourceTree = "<group>"; };
@@ -177,6 +179,7 @@
 			children = (
 				B69E669D208C6117005ED0E1 /* Canvas.swift */,
 				B69E66A2208C6117005ED0E1 /* Brush.swift */,
+				C3E7B55022599CB8001D45EC /* Eraser.swift */,
 				B6F023B1208F2A4700D5CFA7 /* Document.swift */,
 				B6F023B0208F1E9200D5CFA7 /* Utils */,
 				C388DE512254F57800CE19C6 /* MetalBase */,
@@ -341,6 +344,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				C3E7B55122599CB8001D45EC /* Eraser.swift in Sources */,
 				C3E122562255CC6800114EBD /* MLTexture.swift in Sources */,
 				C388DE552254F7CC00CE19C6 /* Shaders.metal in Sources */,
 				B604919D209A71C000372B21 /* PaintingGestureRecognizer.swift in Sources */,

Example/MaLiang/Images.xcassets/image.imageset/Contents.json

@@ -0,0 +1,21 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "image@2x.jpg",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

Example/MaLiang/ViewController.swift

@@ -38,6 +38,7 @@ class ViewController: UIViewController {
         canvas.backgroundColor = .clear
 
         let pen = canvas.defaultBrush!
+        pen.opacity = 1
         pen.pointSize = 5
         pen.pointStep = 1
         pen.color = color
@@ -54,9 +55,15 @@ class ViewController: UIViewController {
         brush.forceSensitive = 0.6
         brush.color = color
 
-//        let eraser = Eraser.global
+        // make eraser with a texture for pencil
+//        let path = Bundle.main.path(forResource: "pencil", ofType: "png")!
+//        let texture = try? canvas.makeTexture(with: URL(fileURLWithPath: path))
+//        let eraser = Eraser(texture: texture, target: canvas)
 
-        brushes = [pen, pencil, brush]
+        /// make eraser with default round point
+        let eraser = Eraser(target: canvas)
+
+        brushes = [pen, pencil, brush, eraser]
 
         brushSegement.removeAllSegments()
         for i in 0 ..< brushes.count {

MaLiang/Classes/Brush.swift

@@ -42,7 +42,7 @@ open class Brush {
     /// target to draw
     weak var target: Canvas?
 
-    init(texture: MTLTexture?, target: Canvas) {
+    init(texture: MTLTexture? = nil, target: Canvas) {
         self.texture = texture
         self.target = target
         self.updatePointPipeline()
@@ -149,26 +149,3 @@ open class Brush {
     }
 
 }
-
-public final class Eraser: Brush {
-
-    /// only a global eraser needed
-//    public static let global = Eraser()
-
-//    private init() {
-//        super.init(texture: nil, target: nil)
-//        pointSize = 10
-//        opacity = 1
-//        forceSensitive = 0
-//    }
-
-    // color of eraser can't be changed
-    override public var color: UIColor {
-        get {
-            return .clear
-        }
-        set {
-            // set color of eraser will do nothing
-        }
-    }
-}

MaLiang/Classes/Eraser.swift

@@ -0,0 +1,24 @@
+//
+//  Eraser.swift
+//  MaLiang_Example
+//
+//  Created by Harley-xk on 2019/4/7.
+//  Copyright © 2019 Harley-xk. All rights reserved.
+//
+
+import Foundation
+import UIKit
+import Metal
+
+open class Eraser: Brush {
+
+    open override func setupBlendOptions(for attachment: MTLRenderPipelineColorAttachmentDescriptor) {
+        attachment.isBlendingEnabled = true
+        attachment.alphaBlendOperation = .reverseSubtract
+        attachment.rgbBlendOperation = .reverseSubtract
+        attachment.sourceRGBBlendFactor = .zero
+        attachment.sourceAlphaBlendFactor = .one
+        attachment.destinationRGBBlendFactor = .one
+        attachment.destinationAlphaBlendFactor = .one
+    }
+}

MaLiang/Classes/MetalBase/MetalView.swift

@@ -21,6 +21,11 @@ open class MetalView: MTKView {
         return try textureLoader.newTexture(data: data, options: [.SRGB : false])
     }
 
+    func makeTexture(with file: URL) throws -> MTLTexture {
+        let data = try Data(contentsOf: file)
+        return try makeTexture(with: data)
+    }
+
     // MARK: - Render Target
 
     /// final render target, contents of this texture will be rendered into drawables

MaLiang/Classes/MetalBase/Shaders.metal

@@ -67,6 +67,9 @@ fragment float4 fragment_point_func_without_texture(Point point_data [[stage_in]
 {
     float dist = length(pointCoord - float2(0.5));
     float4 out_color = point_data.color;
-    out_color.a = 1.0 - smoothstep(0.3, 0.5, dist);
+    if (dist >= 0.5) {
+        out_color.a = 0;
+    }
+//    out_color.a = out_color.a * (1.0 - smoothstep(0.4, 0.5, dist));
     return float4(out_color);
 }