在CoreGraphics绘图中，如何避免重叠点比线的其余部分更暗? [英] In CoreGraphics drawing how can I keep the point of overlap from being darker than the rest of the line?

问题描述

我的应用程序使用核心图形进行自定义手指画图.我允许用户更改线条的Alpha，并且在移动的触摸上会不断绘制新的线条.当我使Alpha低于1.0时，重叠点比该行的其余部分更暗.我知道为什么会发生这种情况，但是如何才能阻止这种情况发生?

My app uses core graphics for custom finger paint drawing. I allow the user to change the alpha of the line and a new line is continuously drawn on touches moved. When I make the alpha lower than 1.0 the point of overlap is darker than the rest of the line. I know why this occurs but how can I stop this?

推荐答案

我想您希望单个笔触不要使其自身变暗，而仍要使以前的笔触变暗(这就是大多数绘画应用程序的工作方式).

I suppose you want a single stroke not to darken itself, but still to darken previous strokes (that's how most painting apps work).

要执行此操作，您需要两个视图/缓冲区，一个用于当前背景"，一个用于当前笔划.松开手指时将后者与背景合并.

For this to work, you need two views/buffers, one for the 'current background' and one for the current stroke. Merge the latter with the background when the finger is released.

在当前的笔划缓冲区中始终使用alpha 1进行绘制，但是将其显示并与较低的alpha合并.

You always draw with alpha 1 in the current stroke buffer, but you display and merge it with a lower alpha.

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