On 24 May '08, at 10:55 PM, Graham Cox wrote:
The purpose is to test whether a given rect intersects a rendered object (path), not just test a point against it.
There are geometric techniques for doing this, that wouldn't require working with pixels. Computing the bounding box of a Bézier curve is very easy, so you can usually trivially reject most of them by checking the rects for intersection. For the rest, you have to flatten them into polygons and test each segment. (Doesn't Quartz 2D have functions to do this?)
Is there any faster way of doing this than just iterating over the pixels like this? I can't think of anything but someone might have a bright idea.
If you do test against pixels, work with the raw pixmap instead of making an Obj-C call to get every pixel. Get the pointer to its pixel data, and use the rowbytes and the pixel size to iterate over pixels. If the pixmap is always in a known format, it's pretty easy. (Sounds like it's 8-bit grayscale, which is as easy as it gets, with one byte per pixel.)
—Jens
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