In my drawing app, Pixel V, I have a color replace tool that lets you restrict where the brush makes a mark to only a chosen color. When the brush was limited to a single pixel width, I just checked the canvas for the color of the pixel at the coordinates of the brush. Once I increased the brush size, this method was no longer practical, and I had to find a new method. The new method I found was to clip the area that had a certain color, thus only allowing the user to draw over the chosen color…

Tom Cantwell

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