Simple 2D UV mapping problem in openGLES

I'm fairly new to low level openGL coding and I have a problem that perhaps I'm just too tired to find a solution to. I'm sure the answer is simple and I'm doing something utterly stupid but here goes...

I have a texture of 1024 x 512,and I'm rendering a 2D quad which intends to use a portion of that texture. The quad is of the same size as the texture portion I am trying to render开发者_JAVA百科, eg 100 x 100 between vertices to render a 100 x 100 texture portion. The texture pixels are from 0(s) and 104(t) assuming zero based pixel coords, and therefore the UV(st) is being calculated as 0 / 1024 and 104 / 512 to the extents of 100 / 1024 and 204 / 512.

However when I render the quad, I get a line from the pixel coords at 103(t), which is part of a different section of the image so it really stands out. I can get around the problem by setting the UV to 0 / 1024 and 105 / 512, but this seems very wrong to me.

I've been searching for a while and can't find what I'm doing wrong. I've tried GL_LINEAR, GL_NEAREST,clamping etc in glparams to no avail. Can someone please direct me to my error?

That is because texture coordinates don't address pixels, thus your assumption

and therefore the UV(st) is being calculated as 0 / 1024 and 104 / 512 to the extents of 100 / 1024 and 204 / 512

is wrong!

This is kind of a FAQ, I recently answered it in OpenGL Texture Coordinates in Pixel Space