I'm using X Render, and want to draw a playing card image onto my window, rotated (e.g. as part of a fan of cards in hand).
For simplicity, suppose that playing cards are square and the rotation is by 45 degrees. The result is a diamond shape, so that in its bounding box, the pixels in (1) and out of (0) that diamond looks like: 00100 01110 11111 01110 00100 Labeling the interesting points on the edges of that bounding box as: ABC HXD GFE with the center point as X, that means that the bounding box is ACEG and the playing card is BDFH. For a fully opaque source image, the result is the same inside the diamond BDFH, for the Src and Over Render PICTOPs. I am also guessing that, in general, the Src operator is faster than Over, since it does not have to read and blend the destination pixels at all. Thus, I'd like to use the Src operator if possible. The thing is, outside the diamond, in the '0' pixels above, the resultant pixels are black with Src, and unchanged, obviously, with Over. In contrast, in OpenGL say, if my (transformed) vertices are BDFH, then the pixel shader only touches the '1' pixels and leaves the '0' pixels alone, regardless of whether I use the equivalent of Src or Over in my pixel shader. Is there a way I can use the Src operator, in Render, and touch only the '1' pixels? I've tried a mixture of the Composite and TriStrip requests, with SetPictureTransform, and setting a clip (but SetPictureClipRectangles takes a union of axis-aligned rects, AFAICT), but I haven't been able to make it do what I want. Am I missing something obvious? Sure, technically, I could calculate the diamond client-side, and send a series of one-pixel-high strips to the server, but that feels inelegant at best. For this particular card-playing app, an easy, practical solution is to just use the Over operator instead of Src. I'm not really writing a card-playing app, though. I'm writing a graphics library, for which there'll be both OpenGL-based and X11/Render-based backends, and I'd like 'draw this texture with this affine transform and this Porter-Duff operator' to work the same on both backends. I had a quick skim through the cairo xlib render source code, but nothing leapt out as specifically looking at this case. _______________________________________________ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: %(user_address)s
