How can I render a JBox2D ParticleGroup?

Question

I want to render a ParticleGroup from JBox2d using OpenGL. I've managed to define a particle group area, but I'm unsure how to draw the individual particles.

Here's how I create the ParticleGroup:

m_world.setParticleRadius(0.15f);
m_world.setParticleDamping(0.2f);

PolygonShape shape = new PolygonShape();
shape.setAsBox(8, 10, new Vec2(-12, 10.1f), 0);
ParticleGroupDef pd = new ParticleGroupDef();
pd.shape = shape;
m_world.createParticleGroup(pd);

This is how I draw a normal Square (which I don't know how to apply to groups of particles):

public void draw(GLAutoDrawable gLDrawable, Vec3 position, float angle){

    gLDrawable.getGL().getGL2().glEnable(GL.GL_BLEND);
    gLDrawable.getGL().getGL2().glEnable(GL.GL_TEXTURE_2D);

    gLDrawable.getGL().getGL2().glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);

    gLDrawable.getGL().getGL2().glBindTexture(GL2.GL_TEXTURE_2D, TextureFactory.getTextureIndex(TextureCollection.valueOf(getTextureSelection())));
    gLDrawable.getGL().getGL2().glPushMatrix();

    gLDrawable.getGL().getGL2().glTranslatef(position.x * getP2M(), position.y * getP2M(), position.z);
    gLDrawable.getGL().getGL2().glRotated(Math.toDegrees(angle), 0, 0, 1);
    gLDrawable.getGL().getGL2().glBegin(GL2.GL_QUADS);
    gLDrawable.getGL().getGL2().glTexCoord2f(0.0f, 0.0f);
    gLDrawable.getGL().getGL2().glVertex3f(-getWidth() / 2 * getP2M(), -getHeight() / 2 * getP2M(), 0.0f);
    gLDrawable.getGL().getGL2().glTexCoord2f(0.0f, 1.0f);
    gLDrawable.getGL().getGL2().glVertex3f(-getWidth() / 2 * getP2M(), getHeight() / 2 * getP2M(), 0.0f);
    gLDrawable.getGL().getGL2().glTexCoord2f(1.0f, 1.0f);
    gLDrawable.getGL().getGL2().glVertex3f(getWidth() / 2 * getP2M(), getHeight() / 2 * getP2M(), 0.0f);    
    gLDrawable.getGL().getGL2().glTexCoord2f(1.0f, 0.0f);
    gLDrawable.getGL().getGL2().glVertex3f(getWidth() / 2 * getP2M(), -getHeight() / 2 * getP2M(), 0.0f);   
    gLDrawable.getGL().getGL2().glEnd();                
    gLDrawable.getGL().getGL2().glFlush();
    gLDrawable.getGL().getGL2().glPopMatrix();

    gLDrawable.getGL().getGL2().glDisable(GL.GL_TEXTURE_2D);
    gLDrawable.getGL().getGL2().glDisable(GL.GL_BLEND);
}

How should I do this? (Example code would be great.)

Answer 1

Try fetching the position buffer:

Vec2[] positions = m_world.getParticlePositionBuffer();

additionally you might want to grab the colors:

ParticleColor[] colors = m_world.getParticleColorBuffer();

Then I would draw the corresponding color at every position using OpenGL. I believe that you can write a very simple shader that would work very well for this. I would help you on this but I am not very familiar with OpenGL at all, despite my many attempts to learn it.