How to include model matrix to a VBO?

Question

I want to send a buffer list (to the GPU/vertex shader) which contains information about vertex position, world position, color, scale, and rotation.

If each of my 3

Answer 1

Your method is correct and in someways unavoidable. If you have 1000 different objects that are not static then you will need to (or it is best to) make 1000 draw calls. However, if your objects are static then you can merge them together as long as they use the same material.

Merging static objects is simple. You modify the vertex positions by multiplying by the model matrix in order to transform the vertices into world space. You then render the batch in a single draw call.

If you have many instances of the same object but with different model matrices (i.e. different positions, orientations or scales) then you should use instanced rendering. This will allow you to render all the instances in a single draw call.

Finally, note that draw calls are not necessarily expensive. What happens is that state changes are deferred until you issue your draw call. For example, consider the following:

gl.drawElements(gl.TRIANGLES, vertexIndexCount, gl.UNSIGNED_SHORT, 0);
gl.drawElements(gl.TRIANGLES, vertexIndexCount, gl.UNSIGNED_SHORT, 0);

The second draw call will be much less taxing on the CPU than the second (try it for yourself). This is because there are no state changes between the two draw calls. If you are just updating the model matrix uniform variable between draw calls then that shouldn't add significantly to the cost. It is possible (and recommended) to minimize state changes by sorting your objects by shader program and by material.