Replicate in space an object with position and orientation from GPU kernel

Context

I am doing swarm simulation using GPU programming (both OpenCL and CUDA, but not at the same time of course) for scientific purpose. I use OpenGL for display.

Goal

I would like to draw the same object —namely the swarming particle, can be a simple triangle in 2D— N times at different positions and with different orientations in the most efficient way knowing that:

• the object is always exactly the same

• the positions and orientations are calculated on the GPU and thus stored in the GPU memory

• the number of particles N can be large

Current solution

So far, to avoid sending back the data to the CPU, I store the position and orientation arrays in a VBO and use:

glBindBuffer(GL_ARRAY_BUFFER, position_vbo);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, 0);

glBindBuffer(GL_ARRAY_BUFFER, velocity_vbo);
glEnableClientState(GL_COLOR_ARRAY);
glColorPointer(4, GL_FLOAT, 0, 0);

glDrawArrays(GL_POINTS, 0, N);

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);
glBindBuffer(GL_ARRAY_BUFFER, 0);

to draw a set of points with color-coded velocity without copying back the arrays to the CPU.

What I would like to do is something like drawing a full object instead of a simple point using a similar way ie without copying back the VBO's to the CPU.

Basically I would like to store on the GPU the model of an object (a Display List? a Vertex Array?) and to use the positions and orientations on the GPU to draw the object N times without sending data back to the CPU.

Is it possible and how? Else, how should I do it?

PS: I like keeping the code clean 开发者_高级运维so I would rather separate the display issues from the swarming kernel.

I believe you can do this with a geometry shader (available in OpenGL 3.2). See this tutorial for specific information.

In your case, you need to make the input type and output type of the geometry shader to GL_POINTS and GL_TRIANGLES respectively, and in your geometry shader, emit the 3 vertices of your triangle for each incoming point vertex.