切割多点ploygon出位图，并把它放在透明 [英] Cutting a multipoint ploygon out of Bitmap and placing it on transparency

问题描述

我有一个位图外面，我切了multipi点多边形。我很好奇的正确处理是用于取任意形状内的像素，并将它们拷贝到一个新的位图，其中的像素的其余部分是透明的。其目的是使用户能够跟踪形状，然后除去该多边形外一切

I have a bitmap out of which I'm cutting out a multipi point polygon. I'm curious what the correct process is for taking the pixels within the arbitrary shape and copying them onto a new bitmap where the rest of the pixels are transparent. The objective is to allow the user to trace the shape and then remove everything outside the polygon.

我有多边形组成部分制定（如点的数组），但现在很为难，如何只选择像素转移到一个新的位图。

I have the polygon part worked out (as a an array of points), but now am stumped as to how to transfer just the selected pixels to a new Bitmap.

TIA

推荐答案

不知道如何你的code ++工程，但这里是如何做到这一点的想法：

Not sure how your code works, but here's an idea on how to do it:

1. 计算所选区域（找分钟X，最小Y，最大x和最大Y点从点）的边框。
2. 裁剪图像使用任何的边框的位图或画布 - 方法。
3. 创建一个 路径 从你的观点，全部搬迁到新的位图（X- =其minX，Y = MINY）;
4. 设置你的路径<一个href="http://developer.android.com/reference/android/graphics/Path.FillType.html"><$c$c>FillType一个是反向（补外）。
5. 在新的裁剪画布，画用油漆与Xfermode为<一个路径href="http://developer.android.com/reference/android/graphics/PorterDuff.Mode.html"><$c$c>PorterDuff.CLEAR,这将删除所有的颜色。

1. Calculate the bounding rectangle of the selected area (find min x, min y, max x and max y from your points).
2. Crop your image to the bounding rectangle using any of the Bitmap or Canvas-methods.
3. Create a Path from your points, all moved into your new bitmap (x-=minX, y-=minY);
4. Set your Paths FillType to one that is inverse (fill the outside).
5. On your new cropped canvas, draw the Path using a paint with the Xfermode as PorterDuff.CLEAR, which removes all color.

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