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Index › Programming Questions & Help › OpenGL and 3D Libraries › problem with texture mapping in opengl

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problem with texture mapping in opengl (Read 615 times)

pelintra

problem with texture mapping in opengl
Aug 30^th, 2008, 6:14pm

hi. i was making some experiments with texture mapping, trying to apply a texture to a sphere.

i'm creating my own sphere, but as soon as i bind the texture about half of my sphere disappears.

the texture coordinates are being determined by the variables 'v' and 'u' and these are ranging from 0 to 1 as expected

i've made a simple applet to show what is happening: http://www.rui-m.com/p5/texmapping_test/

pressing 't' will bind/unbind the texture, and pressing 'p' will render the sphere using points or triangle strips (just because its easier to see whats happening to the sphere using points).

does anyone know whats happening?
i've never done any texture mapping or used textures that much, its probably some noob mistake

thanks

pelintra

Re: problem with texture mapping in opengl
Reply #1 - Sep 1^st, 2008, 12:44am

well.. i just found out something strange...
i'm using the variables 'u' and 'v' to define the texture coordinates in the gl.glTexCoord2f function. if i divide these values by 1.6 it kinda works. i'm not sure if it is precise, but the texture now fully wraps the sphere.

printing the 'u' and 'v' variables to the console they range from 0 to 0.625. so i have no idea why this seems to work. aren't the texture coordinates supposed to range between 0 and 1?
if i dont divide the values they do range between 0 and 1 but the texture only wraps around about half of the sphere as you can see in the example. does any one know whats happening??
thanks

koogy

Re: problem with texture mapping in opengl
Reply #2 - Sep 1^st, 2008, 11:24am

textures in openGl are only generally available in sizes that are powers of two, ie 512x512, 1024x1024, 2048x2048 etc.

your image is 1350x675. i would guess that 1350 is .625 of 2048 - the next power of two up.

(.66, close enough)

try resizing the image to 1024x1024 (the stretching doesn't matter) and see if it changes.

pelintra Ex Member	Re: problem with texture mapping in opengl Reply #3 - Sep 1^st, 2008, 1:52pm so as expected... it was a noob mistake!! but now it works. thanks a lot!!! it was driving me nuts

fry YaBB Moderator Offline Posts: 2623 mass, usa	Re: problem with texture mapping in opengl Reply #4 - Sep 1^st, 2008, 1:52pm right, this is happening because you're using glTexCoord2f instead of the texture() and vertex() commands built into processing, which hide those details.

koogy God Member Offline Posts: 788	Re: problem with texture mapping in opengl Reply #5 - Sep 1^st, 2008, 6:47pm pelintra wrote on Sep 1^st, 2008, 1:52pm: but now it works. thanks a lot!! cool. was a lucky guess 8)

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