在OpenGL中将纹理映射到顶点

Question

I'm trying to render textured meshes with OpenGL. Currently, my main class holds a state consisting of :

• std::vector<vec3d> vertices
• std::vector<face> mesh
• std::vector<vec3d> colors

vec3d is an implementation of 3D vectors - nothing particular - and face a class holding 3 integers pointing to the index of a vertice in vertices .

So far, I rendered my meshes without a texture with the following code (working fine) :

glShadeModel(params.smooth ? GL_SMOOTH : GL_FLAT);

glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);

/*This is my attempt to add the texture
 *
 *if (_colors.size() != 0) {
 *  cout << "Hello" << endl;
 *  glClientActiveTexture(GL_TEXTURE0);
 *  glEnableClientState(GL_TEXTURE_COORD_ARRAY);
 *  glTexCoordPointer(3,GL_FLOAT,0,&_colors[0].x);
}*/
glNormalPointer(GL_FLOAT,0,&normals[0].x);
glVertexPointer(3,GL_FLOAT,0,&vertices[0].x);

glDrawElements(GL_TRIANGLES,mesh.size()*3,GL_UNSIGNED_INT,&mesh[0].v1);

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);

My texture is stored in colors as a list of triples of floats between 0 and 1. However, colors are not applied. I read many examples of texture mapping and tried to do the same, with no luck. Any idea of what I'm doing wrong ?

Answer 1

As seen from your comments, you are using the wrong OpenGL feature to achieve what you want. Texturing means to stick a 2d image onto a mesh by using eg uv-coordinates.

What you are doing is to specify a color on each vertex, so you will need to enable GL_COLOR_ARRAY instead of GL_TEXTURE_COORD_ARRAY and use the respective functions for that.

One additional hint: If you are learning OpenGL from scratch you should consider using only modern OpenGL (3.2+)

To answer the last comment:

Well, I read those colors from a texture file, that's what I meant. Is there a way to use such an array to display my mesh in color ?

Yes and no: You will most probably not get the result you expect when doing this. In general there will be multiple pixels in a texture that should be mapped to a face. With vertex-colors you can only apply one color-value per vertex which gets interpolated over the triangle. Have a look on how to apply textures to a mesh, you should be able to find a lot of resources on the internet.