Eliminating texture seams at terrain chunk

Bow Vernon · 2015-02-23T17:04:12

Hi, fellow game developer. nice to see you! I've decided that I'd make games for my android phones. It has several limitation such as GLES max texture dimension. So in my terrain editor, I implement a new feature that is basically chunked texture. I store the complete texture data on the memory, but for each terrain chunk (being 32*32 tiles or 33*33 vertices) there is an OpenGL Texture assigned for it (which, dynamically change its data according to the global data). Each chunk texture has x,y coordinate of the global data as well as width and height. Whenever I "paint" the global texture, each affected chunk would apply its changes. It works well, but I notice an artifact when rendering. I understand that it's caused by the GL_LINEAR filter I set for the minification and magnification filter. Each of the chunk texture would samples its own "mipmap" without taking account the neighboring chunk. So it's visually wrong. However, I still don't know how to minimize this effect. How would you solve this kind of problem? I'm trying to think a simple way out but seriously, coding this game editor had me drained inside out. I can't think clearly. PS: these texture aren't diffuse texture. It's alpha map for the terrain texture splatting. For this simple test, I generate the global texture on the fly using simple noise calculation. It's tileable but since there're seams at the edge of each chunk, it breaks realism. Here is how the terrain chunking looks with GL_LINEAR filter And here it is with GL_NEAREST instead. Unsurprisingly, no artifacts is seen here. TL;DR : How would you eliminate the seams at the terrain chunk's edge? Edit : uv wrap mode is GL_CLAMP_TO_EDGE

Graphics and GPU Programming Programming OpenGL

Started by Bow_vernon February 22, 2015 02:33 PM

9 comments, last by Bow_vernon 9 years, 1 month ago

Bow_vernon

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February 23, 2015 05:04 PM

Are you sure your texture is tileable? It certainly doesn't look it. Try downloading a proper tiling texture, and see if the problem still exists..

when I use the complete texture (no chunking), it's continues. as was seen with the GL_NEAREST filter.

Are you sure your texture is tileable? It certainly doesn't look it.

This strikes me as well. Given the random nature of your texture contents, it's not clear you'll be able to tell if it is tiling or not, since with sampling set to GL_NEAREST, it just looks like noise.

Try generating textures with larger-scale features, and see if the feature line up. My guess would be you have an small error in the texture coordinates at the edge of each tile.

You, sir are the real MVP . You are correct. The artifact only shows when the values between the neighboring chunk vary greatly. That should never happen in the real game. And when I fill my global blend map with sane values, the artifact is no more!! see the screenshot below to see the proof.

I think the uv mapping is not continuous, ie if an edge is shared between 2 quads, the uv value of vertex doesn't match.
(assuming that 2 quads uv map doesn't overlap)

The uv mapping is continuous. I've checked it thoroughly at the quadtree creation code.

Update:

Heheh, the artifact is virtually "lost" it only becomes visible when the neighboring chunk has pixel value that is very different. so in my noise texture test it's always visible. But now I've implemented the terrain paint brush. It seems perfect for now. Well the key is simply to not let the difference to be too great for the neighboring chunk's texels. And since it's for alpha map, it would be blurred anyway as to not make it look too sharp which is unnatural for terrain texture splatting. Thanks guys for your input!!

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