[Q] Perspective & Orthogonal projection at the same time?


I have a question.
I wonder whether I can use two types of projections at the same time.
The situation is like this.
First, I want to render a 3D mesh in perspective view.
Then I will texture map in 2D over the rendered 3D mesh.
I think I should switch from perspective projection to orthogonal projection.
But it doesn’t work.
Please help me.

I think you misunderstand some points.
For realistic views, one generally uses perspective views. For architectural or conceptional draws like drawing a scheme of a mechanical piece, one uses what you might call orthogonal view: all the dimensions are the same in all the directions: this does not look realistic but that helps a lot those designers.

Now for mapping 2D textures on 3D objects, you simply use a 2D image along with texture coordinates (in 2D) on your 3D models. Modelers generally do the texture coordinates calculations for you. But if you have to do the work yourself, you’ll have to do the mathemtatics yourself. And it depends mainly on 2 factors: planar mapping or spherical mapping. You just project your model into a 2D plane and then do the calculations.

Sorry if it’s hard to understand, I still lack the english vocabulary for that.

Hope that helps.