I'm rendering as a bunch of triangles, and when it comes to applying materials to the tris I'm in doubt on how to do it most efficiently..
I want to be able to support multiple materials per vbo.
What I'd love to do is something like creating an array of material properties, and then somehow tell that triangle n..N should use mat 0 from the array, and so on, in order to avoid several glmaterialfv calls (for ambient, diffuce, spec, and friends).
I have no idea if anything like that is even remotely possible, but in short, I'd like to simply pump my materials properties into opengl once and for all, like I'm doing with the vertex data.
The only thing I can think of is something like a material group, and material properties structs
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typedef struct {
int matIndex; //Index into material array.
int start; //Apply this material from this offset into VBO.
int stop; //and this many triangles
} matGroup;
typedef struct {
GLuint textureID; //there may be a diffrent texture for this part of the model
.. a bunch of material properties, like GLfloat spec[3]; for specular light color
} matProps;
struct model {
GLuint vboName; //Name given to VBO
matProp* materials; //Array of materials.
matGroup* groups; //Array of material groups
int groupCount; //Number of groups
}
Then, when rendering the model, the code would loop the groups, something like
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for(i=0; i < model->groupCount; i++)
{
//Set texture (maybe do a check to see that it's not allready bound
glBindTexture(GL_TEXTURE_2D, model->materials[ model->groups[i].matIndex ].textureID);
// Set material properties for this group of triangles.
glMaterialfv( someGlEnum, model->materials[ model->groups[i].matIndex ].someMaterialProperty );
... multiple glMaterialfv calls here, one for each property.
//Finally, render this part of the geometry
glDrawArrays(GL_TRIANGLES, model->groups[i].start, model->groups[i].stop);
}
This is just pseudo C, nothing I've done, the general idea would be to keep a list of indicies into the geometry in the buffer object, and then set material properties and render, for each chunk of geometry.
It's not too pretty, any way to get opengl to remember material properties, and save a lot of calls? The idea of VBOs was to save lots of calls, so it's counterproductive to have to split the objects into parts based on material properties/textures and such.
I'm stuck, and any hint as to what I need to read would be much appreciated
Keywords of sorts ? I have the red book for opengl 2.1 and if there's a chapter there I could read that'd be great, I've gone through the pages about VBOs but no mention of material properties there.
