How to draw texts on a 3D objects (such as sphere)

Question

I learn OpenGL under Linux platform. Recently, I try to use texts created by glutBitmapCharacter() as the texture of some quadrics objects provided by glu or glut. However, glutBitmapCharacter() does not return a pointer so that I can't feed it to the glTexImage2D() . I had google it for quite a while, but all I found is some topic related to Android SDK which I have no experience to it.

All I can think of is to render texts and read it form buffer using glReadPixels() , then save it to a file. Next, read the pixels back from the file and refer it to a pointer. Finally, draw 3D objects with these texts as the texture (ie feed the pointer to the glTexImage2D() ).

However, it's kind of silly. What I want to ask is: Are there some other alternative way to this?

Answer 1

Applying text on top of a 3D surface is not trivial with pure OpenGL. GLUT does not provide any tools for that. One possible option would be for you to implement your own text rendering methods, possibly loading glyphs using Freetype then create a texture with the glyphs and apply that texture to the polygons. Freetype-GL is a tiny helper library that would facilitate a lot if you were to do that.

Another option would be to again load the text glyphs into a texture and then apply them as decals over the geometry. That way you could still simulate a 2D text drawing in a flat surface (the decal) and then apply that on top of a 3D object.