Quad color shading

OpenGL OpenGL: Advanced Coding
1

hi

i want to render quad with color’s in the vertex, and to use smooth shading when fill the quad.

if for example i have

1.white--------2.black
| |
| |
| |
3.black--------4.white

i will get 2 difrent results if i render
1,2,4,3
or
2,4,3,1

how can i get true smoth shading over the quad?

thanks yuv

2

Well, if neither of the vertex orders provide the shading you want, then you must either change the geometry, or the shading pipeline itself, i.e. don’t use the standard one.

3

You may be able to get the shading you want by adding a vertex in the middle of the quad that has the desired color, and then drawing four triangles.

4

Most graphics hardware renders quads as a pair of triangles. The specific triangulation used by a device would be implementation-dependent.

You may well get completely different images in the opposite black/white case cited above – most scenes will not be that bad, however.

5

Quads must be planar for guaranteed results. ‘Planar’ does not limit itself to geometry, but to all attributes (color, fog coordinate, texture coordinates, whatever).

And you quad is not planar