Screen Coverage

Hi, does anyone know how I would go about calculating a 3d model’s screen coverage/percentage of screen coverage based on its bounding box or the amount of pixels it is using on screen?

I had Chat GPT have a go, but although it speaks with confidence it failed miserably even after about 20 tweaks to my responses. :slight_smile:


Hi @Grimmy,

  1. You could use the camera worldToScreen method on the corners of the total bounding box of your model.

That would be 8 points in 2D coordinates, from these points you could calculate either another bounding box or to be more precise a polygon. And get its pixel volume (=screen coverage). ChatGPT may be of help here to give you an algorithm for this last bit.

  1. Another way would be to use a camera to get a screenshot (on a render target) just of this model (add it to a layer to control rendering). From there read the pixels of the texture buffer and count how many pixels are colored from model.

From there you can get the screen coverage if you divide that number from the total pixels of your screen. This method would be quite precise but slightly slower given reading the pixels from the texture can introduce a performance hit.

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There’s a private function which does something similar

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Any pointer on how I would go about this? Is it possible to do the calculation (render to texture) every frame without the game dying?
I figured I would have a different solid colour for each model and then count the number of those coloured pixels for each model. Then from there I can get a screen coverage for each model by dividing by the full screen area.

Hi @Grimmy,

If you’re looking to do this per frame I’d not recommend that way.

What @mvaligursky shared above would be the most performant option in this case.