CODEWITHSUNDEEP
openglgraphicstexture-mapping
chrismanderson
chrismanderson

Reputation: 4813

Texture mapping with cylinder intermediate surface manually

I'm working on a scanline rendering for a class project. The renderer works so far, it reads in a model (using the utah teapot mostly), computes vertex/surface normals, and can do flat and phong shading. I'm now working on adding texture mapping, which is where I'm running into problems (I cannot use any OpenGL methods other than actually drawing the points on the screen).

So, I read in a texture into my app and have a 2D array of RGB values. I know that the concept is to map the texture from 2D texture space to a simple 3D object (in my case, a cylinder). I then now that you then map the intermediate surface onto the object surface.

However, I don't actually know how to do those things :). I've found some formulas as to mapping a texture to a cylinder, but they always seem to leave details out such as which values to use. I also then don't know how to take the vertex coordinate of my object and get the cylinder value for that point. There's some other StackOverflow posts about mapping to a cylinder, but they 1) deal with newer OpenGL with shaders and such and 2) don't deal with intermediate surfaces, so I'm not sure how to translate the knowledge from them.

So, any help on pseudo code for mapping a texture onto a 3D object using a cylinder as an intermediate surface would be greatly appreciated.

Upvotes: 1

Views: 1754

Answers (1)

Rahul Banerjee
Rahul Banerjee

Reputation: 2363

You keep using the phrase "intermediate surface", which does not describe the process correctly, yet hints at what you have in your head.

Basically, you're asking for a way to map every point on the teapot's surface onto a cylinder (assuming that the texture will be "wrapped" on the cylinder).

Just convert your surface point into cylindrical coordinates (r, theta, height), then use theta as u and height as v (texcoords).

This is what you are trying to achieve:

Upvotes: 2

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