Sector of a Circle

I want to render only a specific part of a sphere which would be given by it's azimuth and elevation angles (spherical coordinate system) and the texture would be mapped on to that part of the sphere. These Coordinates would then be changeable in runtime but I have no idea of how to go by it. I know the mathematics but have zero experience in writing shaders. Any help in this regard would be appreciated.
Thanks.

 

If you can make a texture in the shader in Object coordinates you can set up where the gradient will display from your calculations. In shaders you are effectively making black greyscale gradient textures as masks. You then multiply colors into them.

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