#175687 - Rajveer - Sun Jan 16, 2011 11:06 pm
Is there a gfx command for beginning a new triangle strip in a display list, without using a BEGIN_VTXS/ END_VTXS combination? I'm saving a few strips of triangles to a display list, and since I'm not beginning drawing of a new type of polygon, I'm curious if there is a way to avoid using those vertex commands between strips.
#175688 - elhobbs - Mon Jan 17, 2011 12:49 am
BEGIN_VTXS is required. END_VTXS is not required on hardware. triangle strips use connected trianges - so, no you can not skip BEGIN_VTXS to start a new strip.
#175689 - Rajveer - Mon Jan 17, 2011 1:27 pm
Cool, at least I can skip the END_VTXS command, thanks for that tip. I read that the BEGIN_VTXS and END_VTXS commands should be used sparingly as they're relatively slow, so was just curious.
#175698 - ritz - Tue Jan 18, 2011 3:01 pm
Those commands are only a single cycle, shouldn't be a big deal.
| Code: |
Address Cmd Pa.Cy.
4000500h 40h 1 1 BEGIN_VTXS - Start of Vertex List (W)
4000504h 41h - 1 END_VTXS - End of Vertex List (W)
|
http://nocash.emubase.de/gbatek.htm#ds3diomap
#175708 - Rajveer - Tue Jan 18, 2011 11:27 pm
Oh yeah, so they are, thanks. Forgot that gbatek has the number of cycles for hardware commands :)
#175709 - TwentySeven - Wed Jan 19, 2011 2:46 am
You can in fact do what you originally asked, by using duplicate vertexes to create a degenerate triangle to branch to the start of a new spatially discreet strip.
The simplest way to think of it is if you have two disconnected strips consisting of say:
a-b-c-d-e-f-g and h-i-j-k-l-m-n-o-p
you would pack it as a single strip like so
a-b-c-d-e-f-g-h-h-h-i-j-k-l-m-n-o-p
the triangle formed by h-h-h would be degenerate and invisible, allowing you to span space without drawing anything.
This pointless tip brought to you by: "Starting a new strip is cheaper because of vertex counts", and "This doesn't save you anything on the PC either because of vertex transform caching and indexed triangles are cheaper anyhow"