Hello Sandro,
[Note I missed the original posting] Sunday, November 4, 2007, 12:56:07 PM, you wrote: >> I've been thinking about the point_test issue some more. In my opinion, >> point testing should be done by the renderer, because... Hmm, it's not a very elegant way IMHO because it forces the renderer to deal with hit testing, while that has nothing to do with rendering at all. So we have a different implementation (= potentially different behaviour!) depending on what renderer you use. A hit_test() algorithm should not be hard to implement at all. The most difficult part is probably handling of the quadratic bezier curves, but with some math one should find the right formula for these. I haven't the current implementation in mind, but essentially it would work this way (simplified for lines only): STEP 1: apply the world matrix to the paths So we have the vertices like they would appear on screen STEP 2: find "edges" (=lines) crossing the requested Y coordinate Just browse through all lines, see if they cross the Y coordinate (ignore lines that do not). If it does, then calculate the X coordinate of the crossing. If it is smaller than the previously checked crossing, jump over to the next edge. If the X coordinate is larger than the hit test X coordinate, ignore the edge too. Otherwise check it's fill styles. If the direction of the line is downwards (growing Y), then check fill style 0, otherwise check fill style 1. Ignore the line if it is perfectly horizontal. If the choosen fill style is not -1 (ie. it refers to a fill style) then set the temporary result of the hit test to TRUE, otherwise set it to FALSE. With other words: Find the nearest edge at the left side of the requested X coordinate crossing the Y coordinate and check if the fill style, which directs to the hit test coordinate, is set. Curves make it a *bit* more complicated because you have to (a) calculate the crossing with the Y coordinate, and (b) deal with two crossings Question: Does Flash' hit test method work with thick outlines too (or just fills)? >> a) The renderer must know about fully qualified shapes and fill styles >> anyway, in order to render anything. Yes, but implementations may vary (and what is when rendering is disabled?). >> b) Each renderer library we currently use has a method just for this >> purpose (Agg: hit_test(), Cairo: cairo_in_fill(), OpenGL: selection >> mode). Cool. Didn't know aboud AGG's hit_test() method! :) >> c) If we let the renderer deal with point_test, we avoid duplicating the >> effort in the Gnash core. Effort should be minimal. BTW, what is the problem with the current implementation? >> Of course we would need to design a nice interface. We might also >> implement a caching mechanism. All this will make Gnash faster than it >> currently is. Is hit testing currently really a bottleneck? BTW, how would the caching mechanism work? >> What do you think? SS> Seems an easy path, we may try that as a start. SS> Doing so shouldn't preclude future changes. SS> We do already have a caching architecture (where caches are bitmaps) SS> so adding normalized topology to the caches shouldn't be too hard. SS> The interface should be simple: Agree with the interface, but matrix information should be passed just like with draw_shape() because the AGG backend uses the internal matrix transformation methods of the AGG lib. SS> The renderer will need a way to tell wheter the cache was invalidated. uuuhuuh, hold on...! The *renderer* tells when the cache was invalidated? That's completely the wrong direction to go! The renderer is a (mostly) stateless thing - it can draw any frame at any time if requested. It can *use* some kind of cache but invalidation should *always* happen in the core since that's the only place where we know what's going on. Again, I think it's a bad idea to let the renderer do other things than rendering. If, at all, then caching should be implemented outside the renderer. Still interested in the way such a cache would be implemented. I also think that a caching mechanism for hit_test is overkill. Compared to the real rendering it is done really quickly. SS> Note that taking care of normalization in the core lib would SS> reduce memory usage (ie: the core SS> lib won't need to keep both the normalized and source SS> representations) and leverage eventual SS> differences/bugs in the renderers. But could be eventually a SS> separate step. What do you mean by "normalized and source representations" ? What are you normalizing? Udo _______________________________________________ Gnash-dev mailing list [email protected] http://lists.gnu.org/mailman/listinfo/gnash-dev
