Problem, Opengl renders the texture inverted..

OpenGL OpenGL: Basic Coding
1

Hello all,

I have a tricky problem that i don’t know how to solve. I’m making an application that loads a figure from a .txt and then renders it. All is ok, then the application can apply a texture for the 3D figure. Well firstly i did it well, i loaded a sphere and applied it a world.bmp texture on it, and it worked very well, (i have calculated the texture coords). BUT
BUUUUT…

i Reworked the main code for the application, so i changed things and now the texture is rendered inverted. I don’t know what is causing that and i hope that somebody can point me to a possible conflict.

Here you can see better what i am talking about.

If you need portions of code to help me, i will be there.
Thanks! And sorry ofr my poor english I hope you understood me.

2

This can come from a lot of things.
Can you diff your before/after source codes ? If not, well, that is bad practice. You should at least try to keep some older version manually, or even better, use a version control system (SVN, …). It helps.

Usual suspects:

  • bmp loader, check in-memory representation
  • texture coordinates, as well as texture matrix.
  • backface culling (maybe everything is correct, but you see only backfaces)
  • model and viewport transformations : glScale, gl*Matrix, gluPerspective… (strong suspect)
  • screen shot program (probably not)
3

Thank you ZbuffeR.

I know that i should use a version control system but well you know im in the university and i dont know how SVN works yet. But when i finish those examns i will go to try SVN.

Well

Usual suspects:

  • bmp loader, check in-memory representation (I think that no, i didn’t touched the loader)

  • texture coordinates, as well as texture matrix.
    (i have figures with the texture coordinates precalculated, and i didnt changed anything) Texture matrix? can you explain me more?

  • backface culling (maybe everything is correct, but you see only backfaces)

well yes, but i dont suspect that is this.

  • model and viewport transformations : glScale, gl*Matrix, gluPerspective… (strong suspect)

Yes, i touched a lot of these ^^U…

  • screen shot program (probably not)

Ok i go to eat something, then i will upload some code i hope this will clear something.

Thanks for your time ZbuffeR!

4

Even without SVN, keeping older copies on your work on dated directories is good practice. Memory is cheap.

work/assignment31 // <- current working directory
work/assignment31_2008-12-02 // yesterday
work/assignment31_2008-11-25 // older …
work/assignment31_2008-11-15

…

Texture matrix? can you explain me more?

Yeah sure, there are 3 transformation matrices in opengl : projection, modelview, and texture matrix. But your problem is more likely to be in the other transformations.

5

ZbuffeR I observed with more attention the images, and… there is a small diference that i think it’s the problem.

The sphere is centered on 0 0 0 , and the axis lines too. In the NEW image i can see the axis arriving at (0,0,0) in the OLD image, no…

Then this is indicating that it’s the - backface culling (maybe everything is correct, but you see only backfaces) problem?

If it’s that the error :S how i can solve it? i accept that i don’t know what is causing this and i don’t know what to touch to change this.

Thanks

6

Ok, i solved it:

// glEnable(GL_CULL_FACE);
// glCullFace(GL_BACK);

[censored]… easy :).

Thank you ZbuffeR.