OpenGL scaling vertex arrays

Question

I have a vertex array that I draw as follows (I am working to convert this to a single glDrawArrays call, so that is not the issue here):

gl.glVertexPointer(3, GL.GL_FLOAT, 0, buff);
for ( int i = 0; i < numPoints; i++  ) {
    gl.glDrawArrays(GL.GL_LINE_LOOP, i*verticesPerPoint, verticesPerPoint);
}

This works, but I would like to scale the line loops being drawn. I tried calling glScaled before calling glDrawArrays, but then the points don't show up. I would've thought the scaling just scales the line loops in place, but that does not seem to be the case.

Note when the vertices in the buffer are unscaled since I was hoping to be able to reuse the same buffer at different scales. The idea is that I can redraw the shapes a constant pixel size without recreating the array on each pass.

Can anyone explain what I am doing wrong or if this is even possible?

Luca, for example, if I had a circle centered at 0,0 with radius 1 and I tried scaling it by 10, then the radius would have circle 10. — Jeff Storey, Oct 26 '11 at 14:21

score 3 · Accepted Answer · answered Oct 26 '11 at 04:54

3

Are you sure glScale is applied with the current matrix mode set to the GL_MODELVIEW matrix mode? If so, is it being called before or after any object space transforms? Using glScale[f/d] is a sound approach - it will be applied to the vertex data - but the mention of 'constant pixel size' suggests this is perhaps a 2D problem. It might be worth looking at the mechanics of glViewport in that case.

answered Oct 26 '11 at 04:54

Brett Hale

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Brett, I think the problem is in the pixel size here. I'll go back and look at that, thanks. – Jeff Storey Oct 26 '11 at 14:22

OpenGL scaling vertex arrays

1 Answers1