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Editorial Team
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Asked: 2026-05-31T16:23:00+00:00

I’ve created an OpenGL ES game which is being rendered using a GLKView on

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I’ve created an OpenGL ES game which is being rendered using a GLKView on iOS. I’ve also added some custom UIButtons which are positioned on top of the GLKView. In the rendering I’m drawing some stars using the GL_POINTS rendering mode. Everything renders fine in the simulator but looks terrible on the device.

I was wondering if anyone had any advice as to things I should be configuring/looking out for on the device that may need to be set up in order to get the correct rendered image.

Here are a couple of images of the results:

Simulator

Screenshot of game running on iPhone simulator.

Device

enter image description here

(Please ignore the difference in scaling of the custom buttons – the device screenshot was taken on an iPad).

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1 Answer

  1. Editorial Team

    It turns out the issue was to do with not setting gl_PointSize in the shader for OpenGL ES. The screenshots actually led me to this solution because the stars (drawn using the GL_POINTS rendering mode) are so radically wrong on the device than on the simulator.

    Presumably for the desktop version of OpenGL, the point size is set using the glPointSize function by default (unless GL_VERTEX_PROGRAM_POINT_SIZE is enabled). On OpenGL ES there is no glPointSize function, so the point size value must always be specified using the built-in gl_PointSize variable in the vertex shader.

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