Norris's picture

Strange gap between triangles after changing my computer

Hi !
I have recently changed my computer and I'm now under Windows 7. Before, I run under XP and all my OpenTK projects looks good.
Today, I just restart one project and I have a strange artefact. Now we can see a small gap between polygons in the linked image.
I have the same problems with all my old projects !
Does someone have an idea ?
I have all my drivers installed for my graphic card (nvidia). Could it be a settings in the cg manager software ?

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james_lohr's picture

This usually happens when you don't use identical coordinates for your polygons.

I've had the exact same problem before where it looked fine on one PC, but "seams" were visible on another PC. It turned out the issue was with my code (how I had tessellated my polygons). My guess is that it's the same issue you are encountering.

Norris's picture

Thanks for your suggestion, but the coordinates are hard coded in my app for testing.
After searching, I think I have an answer.
With my old computer, I have set my CG contol panel to force the antialiasing. Now, with my my Nvidia control panel, I can see by default for antialiasing : "let application set antialiasing". I use a the GLcontrol with a default constructor with a default GraphicsMode. I tried with a "custom" GraphicsMode with 2 "samples", and that seems to do the work !

The only thing that look strange to me now is that with my old XP, even with default samples, Ok I haven't antialiasing without setting it explicitily, but I haven't gaps between polys.

Another problem, I can't change the value of "samples" property in my GraphicsMode instance and I must set it in his constructor. The constructor of the GraphicsMode needs values for parameters. And I imagine we can't use arbitrary values without surprises on some configurations.

Is there a way to get the supported settings for any config for this constructor ?

Very sorry for my bad english :s

Norris's picture

Hi guys !
I come back here because I encounter the same problem another one time !
I reinstalled my computer (always windows 7 and NVIDIA (Asus) GTX 550TI card), and the same "bug" came back again.
Since my last message, simply settings 2 samples in "GraphicsMode" always worked, but now, I can't get rid of this.

And no, vertices of polygons share the exactly same position (I have read the same comment on another forum).

Ohhhh ! I try many things during writing this message, I tried disabling "EnableCap" and that worked !!!

Why using multisample give me those artefacts ? Why during one year and half, multisample enabled doesn't gave me those artefacts ?
It seems that multisample count was not the solution ... but I can't understand why I did not have the problem during this time. Could it be a settings in my graphic card configuration software ?

While searching on internet for this, I found topics where guys say that it's a Nvidia bug ... since 1999 wow !!!