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Texture mapping

Started by WildFire716 Oct 13, 2004 at 9:17 AM 2 replies 500+ views

Original Post

Oct 13, 2004 at 9:17 AM

hey seeing im quite new to opengl ive been studying nehes tutorials. well for texture mapping to load the bitmap into memory he uses the glaux library. well after a long time of searching for all the needed components his code works. my question is how does just 2 coordinates plot a texture? for each glVertex3f before it he uses at texture command not quite sure of name atm but it uses 2 coords not 3. is this because he is just plotting x and y for that face and if so can someone explain how to understand the x and y coords? thanks in advance =D

stroma

Oct 13, 2004 at 9:25 AM

no need to define z value on 2d textures.

CodeMunkie

Oct 13, 2004 at 11:33 AM

A texture coordinate in OpenGL has a range of 0.0-1.0. Usually, you will see texture coordinates defined as a pair called u,v:

v1.0 ^ |xxxxxxxxxxxx |xxxxxxxxxxxx |xxxxxxxxxxxx |xxxxxxxxxxxx |xxxxxxxxxxxx |xxxxxxxxxxxx0.0----------->1.0 u

A triangle exists in 3D space, the texture exists in 2D space. What you are doing is simply telling OpenGL where a vertex should lay on the texture and then where it should exist in the world. Think of a triangle as silly putty, the vertices as points of the putty you can pull, and the texture as a newspaper comic (did you ever do this as a kid?). You tell OpenGL where to place the vertices of the silly putty on the comic (you give a u,v pair), and then you peel the putty off and you have an image on your putty. Then you can take the putty and stretch it, move it, rotate it, whatever you want to with it. If you put a bunch of those pieces of putty together, you have a monster or a jet or asteroid or whatever image you are trying to produce. I know this is not 100% how OpenGL operates, but it might give you a better conceptual model to work with.

WildFire716

Oct 13, 2004 at 2:18 PM

Hey the makes a bit of sence and no i didnt do that as a kid seeing im only 14

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