Question

I am trying to learn OpenGL ES 2.0 to do some iPhone game development. I have read through multiple tutorials and some of the OpenGL ES 2.0 spec. All of the examples I have seen have created a single mesh, loaded it into a vertex buffer and then rendered it (with the expected translation, rotation, gradient, etc.)

My question is this: how do you render multiple objects in your scene that have different meshes and are moving independently? If I have a car and a motorcycle for example, can I create 2 vertex buffers and keep the mesh data for both around for each render call, and then just send in different matrices for the shader for each object? Or do I need to somehow translate the meshes and then combine them into a single mesh so that they can be rendered in one pass? I’m looking for more of the high-level strategy / program structure rather than code examples. I think I just have the wrong mental modal of how this works.

Thanks!

Answer 1

You maintain separate vertex/index buffers for different objects, yes. For example, you might have a RenderedObject class, and each instance would have it’s own vertex buffer. One RenderedObject might take it’s vertices from a house mesh, one might come from a character mesh, etc.

During rendering you set the appropriate transform/rotation/shading for the vertex buffer you’re working with, perhaps something like:

void RenderedObject::render()
{
    ...
    //set textures/shaders/transformations

    glBindBuffer(GL_ARRAY_BUFFER, bufferID);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, vertexCount);
    ...
}

As mentioned in there other answer, the bufferID is just a GLuint not the entire contents of the buffer. If you need more details on creating vertex buffers and filling them with data, I’m happy to add those as well.