Texture repeating on quads OpenGL

Question

I am writing a voxel engine and at the moment I am working on the Chunk-Rendering-System but I have a problem. It seems that the textures were repeated on the quads.

  

There is this green line at the bottom of the grass blocks and I don't know why.

This is the OpenGL-Render-Code:

Texture texture = TextureManager.getTexture(block.getTextureNameForSide(Direction.UP));
texture.bind();
GL11.glBegin(GL11.GL_QUADS);
GL11.glTexCoord2d(0, 0); GL11.glVertex3f(0, 1, 0);
GL11.glTexCoord2d(1, 0); GL11.glVertex3f(0, 1, 1);
GL11.glTexCoord2d(1, 1); GL11.glVertex3f(1, 1, 1);
GL11.glTexCoord2d(0, 1); GL11.glVertex3f(1, 1, 0);
GL11.glEnd();

And here is the OpenGL-Setup:

GL11.glEnable(GL11.GL_TEXTURE_2D);
GL11.glShadeModel(GL11.GL_SMOOTH);
GL11.glClearColor(0.1F, 0.4F, 0.6F, 0F);
GL11.glClearDepth(1F);
GL11.glEnable(GL11.GL_DEPTH_TEST);
GL11.glDepthFunc(GL11.GL_LEQUAL);
GL11.glHint(GL11.GL_PERSPECTIVE_CORRECTION_HINT, GL11.GL_NICEST);
GL11.glCullFace(GL11.GL_BACK);
GL11.glEnable(GL11.GL_CULL_FACE);

Answer 1

Make sure GL_TEXTURE_WRAP_S and GL_TEXTURE_WRAP_T are set to GL_CLAMP_TO_EDGE.

Answer 2

^{genpfault's answer should do the trick for you, I just wanted to give you some insight into why you need this particular wrap state.}

To be clear, the green line in your screenshot corresponds to the edges of one of your voxels?

It looks like you are using GL_LINEAR filtering (default) together with an inappropriate texture wrap state (e.g. GL_REPEAT or GL_CLAMP). I will explain why GL_CLAMP is a bad idea later.

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You may think that the texture coordinate 0.0 and 1.0 are perfectly within the normalized texture coordinate range and therefore not subject to wrapping, but you would be wrong.

This particular combination of states will pickup texels from the other side of your texture at either extreme of the [0,1] texture coordinate range. The texture coordinate 1.0 is actually slightly beyond the center of the last texel in your texture, so when GL fetches the 4 nearest texels for linear filtering, it wraps around to the other side of the texture for at least 2 of them.

GL_CLAMP_TO_EDGE modifies this behavior, it clamps the texture coordinates to a range that is actually more restrictive than [0,1] so that no coordinate goes beyond the center of any edge texels in your texture. Linear filtering will not pickup texels from the other side of your texture with this set. You could also (mostly) fix this by using GL_NEAREST filtering, but that will result in a lot of texture aliasing.

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It is also possible that you are using GL_CLAMP, which, by the way was removed in OpenGL 3.1. In older versions of GL it was designed to clamp the coordinates into the range [0,1] and then if linear filtering tried to fetch a texel beyond the edge it would use a special set of border texels rather than wrapping around. Border texels are no longer supported, and thus that wrap mode is gone.

The bottom line is do not use GL_CLAMP, it does not do what most people think. GL_CLAMP_TO_EDGE is almost always what you really want when you think of clamping textures.

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EDIT:

genpfault brings up a good point; this would be a lot easier to understand with a diagram...

The following diagram illustrates the problem in 1 dimension:

   http://i.msdn.microsoft.com/dynimg/IC83860.gif

I have a more thorough explanation of this diagram in an answer I wrote to a similar issue.