On Tue, 2009-09-01 at 12:18 +0100, Neil Roberts wrote: > On Tue, 2009-09-01 at 01:01 +0000, jiangwei zhou wrote: > > > we know that at present the clutter's clipping is implemented in > > clip plane/stencil buffer/Scissor. > > > > using stencil buffer, we can implement arbitrarily ploygonous > > clipping. it is one very common way to do the clipping in gles. > > > > but now ,we have a new demand to implement the clipping without > > stencil buffer . because in our target the clipping based on stencil > > buffer is very slow, unacceptable. > > > > we consider two ways. i hope other guys can give me some suggestion > > or new idear. > > > > 1. if only rect clipping is considered,can i clip the actor in > > fragment shader? > > > > the clip arear is in object coordinates, can i in fragment > > shader , convert the fragment coord point from clip coordinates to > > object coordiantes ,then using rect including algorthim to discard > > those not in the area? > > If the clip region is a rectangle, Cogl should already automatically use > glScissor (if possible) or the clip planes if it is not a screen > rectangle. I think the clip planes and scissor rect should be quite fast > so there probably isn't any benefit to using a fragment shader in this > case. To say a bit more here; it's not only cogl_clip_push_window_rect() that will use glScissor. Even if you use cogl_clip_push() cogl will look at the modelview matrix to see if it represents an axis aligned rectangle and use glScissor when possible. Multiple rectangular clip regions may be pushed on to the clip stack, and the glScissor rectangle will correspond to their intersection.
regards, - Robert -- Robert Bragg, Intel Open Source Technology Center -- To unsubscribe send a mail to clutter+unsubscr...@o-hand.com
