I have the following object in the gameIt is a dial with the little triangle showing what part of the disk is being valued.The dial serves as a controller that sets a variable from 0-1. If the disk has 0 degrees facing left then it is 0, if the disk has 180 degrees facing left then it is 0.5. Somehow I will eventually find a way to express that so the disk will not be uniform.Anyway so the inner disk you see will spin meanwhile the outer disk with the triangle thing will stay in place.Something that would be nice is if the area of the spinning disk that is inside of the triangle would disappear.The problem is I have no clue how to do this.Currently the rotation of the disk is done by a matrix that rotates the quad that is rendering this.I have two ideas1. Edit the quad into a mesh cutting out the triangle, however this would not work as the mesh is translated in my current model.2. Run costly trigonometric calculations to figure out where each fragment is in real space then figure out its angle and distance from the center of the circle.I know doing a little trig on each fragment might not sound like much, however just rendering the disk adds 1ms of rendering time when rendering on the lowest possible hardware this could run on.How do people achieve real-time masking in opengl?
Mask out parts of an image in OpenGL ES
masking