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[dspencer]

Hello everyone,

I'm not sure what to call this phenomenon - if I knew, I could probably just have googled for the answer. So, sorry about that!

I'm adding actual graphics to my project, and I'm having some trouble with my textures (in openGL via C++). Right now I've got two tiles - dirt, underground, and the top layer, with some grass on top. I'm finding that sometimes, the tile with grass (which is 32x32 pixels) will have a line of green at the very bottom, just like it does on the top. However, I'm not sure why this is happening... It only happens for some frames, so I think it might be a product of the scrolling (it never happens when the scrolling comes to rest). Does anyone have any ideas? I've tried changing the texture wrapping mode from loop to clamp, but it didnt help.



Thanks!

[Ivan]

See if it's the same issue as this:

http://forums.tigsource.com/index.php?topic=4205.msg131938

[dspencer]

At first glance, it appears so; however, none of the solutions presented on that thread work for mine. Thinking back, though, maybe the problem is in how I load the texture to opengl... Just kidding, tried another method and it has the same problem.

[Aquin]

It sounds like the line of green is coming from the other side of the texture.  "But wait," you say, "I turned off clamping!?"

It doesn't matter.  When you do your mip-mapping, OpenGL will do a wrap-around to calculate how it looks.  Turn on NEAREST filter for the textures and the green line will go away.

[dspencer]

I know - that's what I thought, too. But, I tried that (it was suggested in that other thread) and the green lines are still coming up). I tried changing the colors, so I'm sure the texture is getting wrapped around... but I just don't know why.

[Martin 2BAM]

SFML works around this issue by mapping to a half texel away from the border.
(also changing texture WRAP to CLAMP)

Like:
baseTexCoords = (
  0.5/texturePixelWidth,
  0.5/texturePixelHeight,
  (texturePixelWidth-0.5)/texturePixelWidth,
  (texturePixelHeight-0.5)/texturePixelHeight
)

See if it works for you.

[dspencer]

That works, and looks fine. I guess I misread that solution - I tried something similar which didnt work. I'd still like to find a solution that doesn't rely on me remembering to manually change the texture coords... but still, thank you!

[Martin 2BAM]

Call an intermediate calculateTexCoords(myUsualCoords) to centralize the behaviour, easy cheesy

[Zaphos]

I thought that was what GL_CLAMP_TO_EDGE was supposed to do?

[dspencer]

Found the problem - never set the filter *before* generating mipmaps. Fixed, thread locked, thanks so much for all of your help .