使用顶点缓冲对象渲染不同的三角形类型和三角形扇形？ （OpenGL的）

Question

About half of my meshes are using triangles, another half using triangle fans. I'd like to offload these into a vertex buffer object but I'm not quite sure how to do this. The triangle fans all have a different number of vertices... for example, one might have 5 and another 7.

VBO's are fairly straight forward using plain triangles, however I'm not sure how to use them with triangle fans or with different triangle types. I'm fairly sure I need an index buffer, but I'm not quite sure what I need to do this.

I know how many vertices make up each fan during run time... I'm thinking I can use that to call something like glArrayElement

Any help here would be much appreciated!

Answer 1

VBOs and index buffers are an orthogonal things. If you're not using index buffers yet, maybe it is wiser to move one step at a time.

So... regarding your question. If you put all your triangle fans in a vbo, the only thing you need to draw them is to setup your vbo and pass the index in it for your fan start

   glBindBuffer(GL_VERTEX_BUFFER, buffer);
   glVertexPointer(3, GL_FLOAT, 0, NULL); // 3 floats per vertex
   for each i in fans
       glDrawArrays(GL_TRIANGLE_FAN, indef_of_first_vertex_for_fan[i], fan_vertex_count[i])

Edit : I'd have to say that you're probably better off transforming your fans to a regular triangle set, and use glDrawArrays(GL_TRIANGLES) for all your triangles. A call per primitive is rarely efficient.