SwiftUI 路径作为 contentShape，与图像不一致

Question

TL;DR：我正在使用 Path 来指定 Image 的命中区域。但我不知道如何调整 Path 坐标以匹配 SwiftUI 决定的布局......或者我是否需要这样做。

运行时间

我的（测试）应用程序看起来像这样，Image 边框（不是框架）为清晰起见着色：

我想要的是 Image 处理不透明橙色中的点击。在不透明的橙色之外点击——即使在橙色图像的边界内——应该 "fall through" 到绿色图像或灰色背景。但不是。（紫色轮廓根据自身显示路径的位置；请参阅下面的代码）。

详情

这是图像的固有（以像素为单位）布局：

不透明部分周围的路径通常被视为

[(200, 200), (600, 200), (600, 600), (200, 600)]

这些坐标和 Image 坐标有什么关系？

代码

extension CGPoint {
    typealias Tuple = (x:CGFloat, y:CGFloat)
    init(tuple t: Tuple) {
        self.init(x: t.x, y: t.y)
    }
}

struct ContentView: View {

    var points = [(200, 200), (600, 200), (600, 600), (200, 600)]
        .map(CGPoint.init(tuple:))
        // .map { p in p.shifted(dx:-64, dy:-10)}  // Didn't seem to help.

    var path : Path {
        var result = Path()
        result.move(to: points.first!)
        result.addLines(points)
        result.closeSubpath()
        return result
    }

    var body: some View {
        ZStack{
            Image("gray")       // Just so we record all touches.
            .resizable()
            .frame(maxWidth : .infinity,maxHeight: .infinity)
            .onTapGesture {
                print("background")
            }

            Image("square_green")
            .resizable()
            .scaledToFit()
            .border(Color.green, width: 4)
            .offset(x: 64, y:10)    // So the two Images don't overlap completely.
            .onTapGesture {
                print("green")
            }

            Image("square_orange")
            .resizable()
            .scaledToFit()
            .contentShape(path)        // Magic should happen here.
            .border(Color.orange, width: 4)
            .offset(x: -64, y:-10)
            // .contentShape(path)     // Didn't work here either.
            .onTapGesture {
                 print("orange")
            }

            path.stroke(Color.purple)  // Origin at absolute (200,200) as expected.

        }
    }
}

Answer 1

1) .offset只是移动了内容，但是视图在视图层级布局中的位置没有改变，所以改用.position；

2) contentShape 的形状应该在视图坐标 space

中构建

Answer 2

Asperi 是正确的，当我阅读 Paul Hudson 并掌握了 Shape 的（单一）要求时，我恍然大悟——一条路径（in rect: CGRect) -> 路径方法。 rect 参数告诉你所有你需要知道的关于局部坐标系的信息：即它的大小。

我的工作代码现在看起来像这样。

帮手

extension CGPoint {
    func scaled(xFactor:CGFloat, yFactor:CGFloat) -> CGPoint {
        return CGPoint(x: x * xFactor, y: y * yFactor)
    }

    typealias SelfMap = (CGPoint) -> CGPoint
    static func scale(_ designSize: CGSize, into displaySize: CGSize) -> SelfMap {{
        [=10=].scaled(
            xFactor: displaySize.width  / designSize.width,
            yFactor: displaySize.height / designSize.height
        )
    }}

    typealias Tuple = (x:CGFloat, y:CGFloat)
    init(tuple t: Tuple) {
        self.init(x: t.x, y: t.y)
    }
}

在适当的上下文中绘制路径

// This is just the ad-hoc solution. 
// You will want to parameterize the designSize and points.

let designSize = CGSize(width:800, height:800)
let opaqueBorder = [(200, 200), (600, 200), (600, 600), (200, 600)]

// To find boundary of real-life images, see Python code below.

struct Mask : Shape {
    func path(in rect: CGRect) -> Path {
        let points = opaqueBorder
            .map(CGPoint.init(tuple:))

            // *** Here we use the context *** (rect.size)
            .map(CGPoint.scale(designSize, into:rect.size))

        var result = Path()
        result.move(to: points.first!)
        result.addLines(points)
        result.closeSubpath()
        return result
    }
}

使用面具

struct ContentView: View {
    var body: some View {
        ZStack{
            Image("gray")           // Just so we record all touches.
            .resizable()
            .frame(
                maxWidth : .infinity,
                maxHeight: .infinity
            )
            .onTapGesture {
                    print("background")
            }

            // Adding mask here left as exercise.
            Image("square_green")
            .resizable()
            .scaledToFit()
            .border(Color.green, width: 4)
            .offset(x: 64, y:10)    // So the two Images don't overlap completely.
            .onTapGesture {
                print("green")
            }

            Image("square_orange")
            .resizable()
            .scaledToFit()
            .border(Color.orange, width: 4)

           // Sanity check shows the Mask outline.
            .overlay(Mask().stroke(Color.purple))

            // *** Actual working Mask ***
            .contentShape(Mask())

            .offset(x: -64, y:-10)
            .onTapGesture {
                print("orange")
            } 
        }
    }
}

获取大纲

#!/usr/bin/python3

# From https://www.reddit.com/r/Python/comments/f2kv1/question_on_tracing_an_image_in_python_with_pil

import sys
import os
os.environ['PYGAME_HIDE_SUPPORT_PROMPT'] = "hide"
import pygame

# Find simple border.

fname   = sys.argv[1]
image   = pygame.image.load(fname)
bitmask = pygame.mask.from_surface(image) 
comp    = bitmask.connected_component() 
outline = comp.outline(48)

print("name:  ", fname)
print("size:  ", image.get_rect().size)
print("points:", outline)

# Sanity check.
# From https://www.geeksforgeeks.org/python-pil-imagedraw-draw-polygon-method

from PIL import Image, ImageDraw, ImagePath
import math

box = ImagePath.Path(outline).getbbox()
bsize = list(map(int, map(math.ceil, box[2:])))

im = Image.new("RGB", bsize, "white")
draw = ImageDraw.Draw(im)
draw.polygon(outline, fill="#e0c0ff", outline="purple")

im.show()      # That this works is amazing.

SwiftUI 路径作为 contentShape，与图像不一致

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