Question

I am trying to get some circles drawn onscreen using OpenGL ES 1.5 for android. They draw, but I want to be able to input x=300, y=500, and it will draw the circle centered at that coordinate (e.g. at the (300,500) pixel on the screen). Currently, I draw and translate the circles, but its not precise, I don’t know how to get it exactly where i want it: here’s some broken code from my last attempt:

//doesn't take w/h ratio into consideration, not sure how to implement that
gl.glViewport(0, 0, windowWidth, windowHeight);
gl.glOrthof(0,windowWidth,   0, windowHeight,    1, 2);
GLU.gluLookAt(gl,   0, 0, 5,    0, 0, 0,    0, 1, 0);

//And for drawing a circle, with the desired x and y coordinates:
for (int j = 0; j &lt number_Triangles; j++) {
  x = Math.cos(theta) + xCoor;
  y = Math.sin(theta) + yCoor;
  z = 1;
 theta += 2 * Math.PI / (number_Triangles);
}

Answer 1

If you are doing 2D graphics, I’d recommend gluOrtho2D(left,right,bottom,top). That way you have exact control over what coordinates will map to each edge of your screen.

So, for example, you could have:

gl.glViewport(0,0,windowWidth,windowHeight);
GLU.gluOrtho2D(-2.0f, 2.0f, -2.0f, 2.0f);

for (int j = …..