CODEWITHSUNDEEP
opengl-estexturestexture-mappinguv-mapping
Eternal Geek
Eternal Geek

Reputation: 11

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, 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?

Upvotes: 1

Views: 1750

Answers (1)

datenwolf
datenwolf

Reputation: 162164

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

Upvotes: 1

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