Hi,
I’m currently trying to do texture mapping without the functions from openGL.
Let’s say, i build a quad with opengl like this:
glBegin(GL_QUADS);
glVertex3f(0.0f,0.0f,0.0f);
glVertex3f(1.0f,0.0f,0.0f);
glVertex3f(1.0f,1.0f,0.0f);
glVertex3f(0.0f,1.0f,0.0f);
glEnd();
Is it possible that i do texture mapping on that quad without the use of glTexCoord(), glBindTexture(), and other functions?
Any advice is welcome.
Yes, draw on your screen with the crayons the warden gave you.
so i that take as a no for an answer!
Any other suggestions? Anyone?
You could draw a ton of quads, each a pixel in size and set the quad’s color to the corresponding pixel in your texture.
Can you tell us why you are asking this?
You can get rid of glTexCoord2f() calls by using glTexGen().
Originally posted by jra101:
You could draw a ton of quads, each a pixel in size and set the quad’s color to the corresponding pixel in your texture.
this is also very very fast
Hi raverbach,
I think you solution could be the answer to my question. But i have a small request, how exactly should i get the color value from the texture and how to convert it to RGB and put the corresponding values into glColor3f()?
Thank you very much!
??
Jacky,
Why can’t you just use the texture mapping API?
You could do your own software rasterization and shading and draw everything with glDrawPixels(), but at some point we cross over into absurdity.
You need to explain why you can’t use the texture mapping API first.
Thanks -
Cass
To tell you the truth, it’s part of a project that i’m doing. The objective is to achieve texture mapping without using openGL’s texture mapping functions.
I hope this clears your doubt on me. So, is this acceptable?
Not really. Is it your school assignment question which came up by your professor?
Or it is a course project which you came up this goal?
To further clarify your doubt on me, yes this is a course project that i came up with to achieve this goal…
Can you pls. tell me whether this is possible?
Thats a strange goal. But I think it could be accomplished with fragment shaders. Just send in the texture without uv data, then create some uv data within the shader.
Complicated solution to a simple problem. I still like the crayon idea 
First of all, i would like to thank all the contributors for spending their precious time looking into this problem for me…Actually i already tried to build tons of polygon. This idea came from some of the contributors and i would like to take this opportunity to thank them again.
Although i’ve manage to build 1000 x 1000 for a quad, but i still can’t manage to figure out how to get the texels colour and apply it into glColor3f(). Can anyone show me how?
I can send those who are interested and willing to help me, the application + source codes.
Regards,
Jacky
Might as well forget about opengl and write your own rasterizer. That way it’d make some sense, but trying to do texturing in opengl without the opengl texturing functions… Why don’t you draw triangle meshes without using triangles while you’re at it 
-Ilkka
I say sorry if programmers out there think that my objective in this project is foolish, but i have no turning back except find a solution to my problem!
I hope some of the programmers can give me an answer.
Thank you in advance!
Whip out your copy of Foley, and VanDam and start writing your own software renderer.
That’s what you seem to be wanting to do.
Jacky,
I apologize if I sounded unduly harsh. It’s more interesting to work on a problem if it’s not just “make work”, so if you had a real need for this kind of functionality and you couldn’t use the texture mapping API, then it might have been semi-interesting.
Ultimately, though, texture mapping - while straightforward - is fairly expensive. You can display images that use texture mapping in OpenGL without using OpenGL texture mapping, but to do so you have to implement texture mapping in software, and that makes OpenGL (and any hardware support it provides) pretty much irrelevant.
So your options are:
I’ll leave it to you to figure out how to implement these options.
Thanks -
Cass
I’m sorry too, if I sounded harsh. But you are trying to find a solution to a solved problem and your solution is obviously going to be slower and more difficult than the existing one.
Maybe you could implement displacement mapping instead? You could subdivide the polys and do the lookups just like you would with texturing, but then you’d displace the surfaces instead of just painting them. That way you’ll get an effect that’s remotely worth the effort.
With that I’ll be glad to help you.
-Ilkka
Are you only trying to draw a single quad?
Or are you trying to draw more complex geometry with texture mapping and not using the gl Functions?
If it’s the latter I’d say “Good luck” or “Use D3D (booo!)”.
If it’s the former then just create a number of quads (x by y quads) where x by y is the dimension of your image and build the color values for your vertices according to the corresponding pixel color in your image. Each quad will be x -> x+ 1 and y -> y+ 1 with z = 0.
It’s quite easy in reality but it’s going to be flipping slow (256 x 256 will equal 65536 quads and 262144 vertices!)
Of course you could just do something sensible and use the gl functions. Or, if you don’t want to use glTexCoord() you could use TexPointer() and DrawElements…