Quad rendering bug

[Ian]

I've never seen the winding bit set
Gonna have a go at this one this evening

[Ian]

Well this is my first attempt at this problem ..

[HarryTuttle]

Great! If you need some screenshot or savestate to help analyze the problem just tell me.

[Ian]

Sure, would definitely be useful
Anything you have !

[HarryTuttle]

First bunch of screens (left Abe's footage, right Supermodel).

Good quad:

hl_01.jpeg (229.3 KiB) Viewed 6876 times

Good quad (however in Abe's video the transition seems smoother, save for a seemingly interlacing artifact, like a perfect planar quad):

hl_02.jpeg (226.11 KiB) Viewed 6876 times

Bad quad (hard to spot):

hl_03.jpeg (230.71 KiB) Viewed 6876 times

[HarryTuttle]

Second bunch...

BAD quad on left car, good on the right:

hl_04.jpeg (242.33 KiB) Viewed 6862 times

Good quad:

hl_05.jpeg (232.43 KiB) Viewed 6862 times

Good quad:

hl_06.jpeg (232.42 KiB) Viewed 6862 times

Basically I always check how the highlight is distributed inside the quad, since it evidenciates better any anomaly.

[HarryTuttle]

Dirt Devils.

Good quad (the highlight differs a bit 'cause the cars' movements and position also differ from the original):

dd_01.jpeg (247.6 KiB) Viewed 6848 times

Dirt Devils' save state here: https://expirebox.com/download/bdf4d943eaafe952eb4219efd691e728.html; it's the start of the buggy demo sequence in attract mode

Harley's save state here: https://expirebox.com/download/cdc68d2e6edceeec4e8fa3b7f0ffc146.html; starts at the point of the first Harley's screen i posted, and during about the following 25 seconds I took all the other screenshots.

I usually check this few sequences beside the Scud's one on which you worked.

IMPORTANT: Forgot to say that i took those images with the quad's edge flipped for every counter-clockwise winding poly, just for testing. In the official build there could be more errors...

[Ian]

Well my changes worked for that car in scud.. but unfortunately introduced bugs on other cars
Maybe i'll disable textures and draw the vert positions as individual colours.
Like
vert1 = red
vert2 = green
very4 = blue
very4 = black

Might be able to get a better grip on how the h/w decides to swap the split..

[Ian]

I drew the vertices as colours
Also marked on the winding values

vert1 = red
vert2 = green
very4 = blue
very4 = black

This one I marked which vertices are shared from the previous poly



When vertices 1 and 4 are used from the previous poly the winding seems to switch ..
Also looks like the split direction should change too

[Ian]

Harry,
can you find any bad quads that are the first ones in the list? (Ie no shared verts). If they are, then the gpu is deciding to split them somehow. If not perhaps they are just related to how they are coming out of memory ..
Lost world doesn't use any shared vertices, so every quad would be a first quad :p