Hi Matthias,
I hope you don't mind me sending this reply to the list too.
Matthias Neuenhofer wrote:
Hi Claude,
itŽs not a bug in Gem the depth sorting follows the render order. Normal openGL behaviour.
That's what I suspected, and in that case maybe the wording of [alpha]'s help patch could be better:
"" Inlet 1: message "auto 1" | "auto 0" turn on/off automatic depth detection ""
I thought this would cache all objects following the [alpha] and sort them by depth automatically, or something. Now I'm not sure what the "auto $1" message does at all.
Reading carefully the large paragraph I see it says:
"" Be aware that the rendering order matters, so you probably want to set the gemhead order number high so that the object is rendered after all of the non-alpha blended ones. ""
Maybe this could be made more explicit, saying render order of alpha-blended objects matters as well as alpha vs non-alpha objects.
In the second way you render your patch itŽs well working.
Sure, but naturally the "real patch" has much more complicated geometry, it would be a major pain in Pd as far as I can tell to do some kind of 3 pass rendering, where the first pass gets the depth of each object, the second pass sorts by depth, and the third pass actually draws them.
I guess I'm too ambitious :)
Thanks,
Claude
http://www.opengl.org/resources/faq/technical/transparency.htm When using depth buffering in an application, you need to be careful about the order in which you render primitives. Fully opaque primitives need to be rendered first, followed by partially opaque primitives in back-to-front order. If you don't render primitives in this order, the primitives, which would otherwise be visible through a partially opaque primitive, might lose the depth test entirely.
In a double gemhead patch i see no chance to change. Otherwise with set messages to gemhead.
lg Matthias
Am 02.07.2008 um 19:37 schrieb Claude Heiland-Allen:
Hi,
The attached patch "double-gemhead-auto-alpha.pd" doesn't work as I expect (I don't get any automatic depth sorting). Is there any suggested workaround for repetition with auto alpha depth sorting or is this a bug in Gem?
Thanks,
Claude