From: <jos...@ju...> - 2007-05-15 10:32:14
|
Gustavo wrote: > I want to know how difficult would be to implement support for clip > using gradient objects. > ... > ... > = > We are willing to implement it if you give us some hints :-) = Just thought I'd go back to this a bit here, and see if I can give you an idea of what's 'really' needed for this. The way Carsten setup clip-object semantics in evas is that any object can clip any other, and this can be arbitrarily iterated (since a clip object can have a clip object as well). Also, an object can clip any number of objects. It's a very nice idea, though with that kind of generality it's going to be tough to do anything involved very efficiently. However, the real problem in evas right now is just trying to get this implemented *at all*. The way the internals are set up, it's just not feasible.. and neither is doing *anything* much beyond what raster initially set things up for (eg. rotations or any kind of transforms on image objs.. just can't really be 'done' right now, no matter how 'easy' it might be to accomplish that with any of the gfx backends). I've pointed this out several times in the past, but let me explain in a bit more detail exactly why this situation exists and what's needed to correct it. The canvas level has a structure that holds the state for an evas object (eg. size, clip-obj, etc). This structure also has a pointer to any type specific state (ie. things for rects, images, etc). It also has a pointer to a 'render' function that is called whenever a given object needs to be drawn - this function is given for each specific type of object, and has a generic form, eg. draw something to some dst at some point... and such things. The way these object render functions are obtained is in turn via certain other 'engine functions' which are implemented by the various engines, ie. by the various rendering backends. The problem is that this set of 'engine functions' then defines an immediate mode rendering api which is ALL that the canvas can work with. It ties the canvas lib's capabilities to the specific rendering model/api that this set of interfaces defines. Unfortunately, the current such interfaces, ie. the rendering model.. is extremely limited. That's the source of all the problems that evas faces right now as far as extending its capabilities to allow for such things as obj transforms, clipping, texturing, and any number of other gfx aspects. Now, one can say "Well, let's use eg. a vgfx rendering model, that's a powerful one...", or maybe say "No, let's use a compositing rendering model, it's more flexible yet smaller...", or any number of other things.. and how is one to choose? (and the choice must make it easy for it to be realized with various other gfx libs. eg. xrender, gl, cairo, ...) Very easily: Let the canvas api be the rendering model, rather than impose some other. After all, what one wants is to modify 'obj' state, setup things, and draw the 'obj' as need be. What that means is that one needs to push all relevant canvas level 'object' state down to the engines level, and let things be implemented there as each 'engine' sees fit. Do this, and all the things everyone wants for evas to be able to do, and things that no one has maybe even thought of... will at least be feasible to *attempt* to implement. It simply isn't feasible or reasonable right now to even try otherwise. jose. |