OpenGL drawing thousands of 2D circles
In my application, I am rendering thousands (~10k) 2D circles on top of a 3D scene. I have it working, but the performance is very slow when there are this many circles (the circles are small, ~16 pixels diameter). My code for drawing the circles looks like:
for开发者_开发问答 ( int i = 0; i < numCircles; i++) {
int attributeMask = GL.GL_DEPTH_BUFFER_BIT | GL.GL_TRANSFORM_BIT
| GL.GL_VIEWPORT_BIT | GL.GL_CURRENT_BIT
| GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT
| GL.GL_ENABLE_BIT | GL.GL_LIGHTING_BIT;
gl.glPushAttrib(attributeMask);
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glDisable(GL.GL_LIGHTING);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glOrtho(0d, dc.getView().getViewport().width, 0d, dc.getView()
.getViewport().height, -1, 1);
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glDisable(GL.GL_DEPTH_TEST);
Vec4 screenPt // this is calculated for each circle
double size = 16;
gl.glTranslated(screen.x, screen.y, 0d);
gl.glScaled(size, size, size);
gl.glCallList(fillListId);
gl.glCallList(outlineListId);
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glPopMatrix();
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glPopMatrix();
gl.glPopAttrib();
}
The lists are generated as follows:
NUM_SEGMENTS = 18;
double[][] vertices = new double[2][NUM_SEGMENTS];
for (int i = 0; i < NUM_SEGMENTS; i++)
{
double rad = -2 * Math.PI * ((double) i) / ((double) NUM_SEGMENTS);
double x = Math.cos(rad);
double y = Math.sin(rad);
vertices[0][i] = x;
vertices[1][i] = y;
}
gl.glNewList(id, GL.GL_COMPILE);
gl.glBegin(GL.GL_LINE_LOOP); // 2 lists are actually created, the first time GL.GL_LINE_LOOP IS is used for the outline, and the second time GL.GL_POLYGON is used for the fill
for (int j = 0; j < vertices[0].length; j++)
{
gl.glVertex2d(vertices[0][j], vertices[1][j]);
}
gl.glEnd();
gl.glEndList();
Is there something I'm doing obviously wrong here to slow down the rendering? Should I consider using vertex buffers here? Or are there other techniques to speed this up?
Thanks, Jeff
You can generate a single circle, blit it to a texture, then just create surfaces (of two triangles) that are textured with that circle.
I would think all of this code
int attributeMask = GL.GL_DEPTH_BUFFER_BIT | GL.GL_TRANSFORM_BIT
| GL.GL_VIEWPORT_BIT | GL.GL_CURRENT_BIT
| GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT
| GL.GL_ENABLE_BIT | GL.GL_LIGHTING_BIT;
gl.glPushAttrib(attributeMask);
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glDisable(GL.GL_LIGHTING);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glOrtho(0d, dc.getView().getViewport().width, 0d, dc.getView()
.getViewport().height, -1, 1);
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glPushMatrix();
gl.glLoadIdentity();
gl.glDisable(GL.GL_DEPTH_TEST);
and all of this code
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glPopMatrix();
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glPopMatrix();
gl.glPopAttrib();
could be done outside of the loop, and just done once.
You would just need to push and pop a matrix for the object translate/scale.
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