On Mon, 16 Mar 2015 12:11:28 +0100 Thilo Cestonaro <th...@cestona.ro> wrote:
> Hey! > > I try to understand how weston's fbdev compositor trys to transform the > screen. > As it uses pixman to do this, I come here to hopefully get some answers > :). > > Can someone briefly explain the following functions (what they tend to > do and what the parameters mean): > > pixman_transform_init_identity > pixman_transform_rotate > pixman_transform_translate > pixman_image_set_transform > > That would be awesome! Hi, a pixman_transform_t is a 3x3 matrix which represents a projective (much more often an affine) 2d transformation. You can see this in the Pixman header. Rotate and translate modify the transformation. Pixman_image_set_transform sets the destination-to-source transformation in the image, to be used when you use that image as a source in a composite call. The transformation is in the opposite direction than what one might expect, but the rendering code really iterates over the destination coordinates and transforms those into source coordinates to sample from the source image. That's all just an impression I got when working with Weston's pixman-renderer. If you look at weston master branch which contains http://cgit.freedesktop.org/wayland/weston/commit/?id=8870a23fbd6a54d2290d2f5d9c4696e24cec4770 you might have easier time understanding it, I hope. Thanks, pq _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman