GameDev Diary – SpaceLife #5

Planet Hacking – scaling objects based on distance

Continuing my experiments into creating large planets, I came across this post where people are simulating large scales by resizing objects based on the distance away from it. I couldn’t get the code in this post to work because I’m still moving the camera and not the world – But I created my own implementation based on the theory, using the downscaled 3d skybox containing the distantCamera and distantSun.

Scale based on distance.png

If you haven’t noticed already, there’s a glaring error with my maths –

  • as you get closer to the object the scale isn’t linear. At a starting distance of 40, if we are 20 units from the planet, it’s scale is multiplied by 40/20 =2, but if we only go 10 closer, we are 40/10 = 4. Are we really twice as close? If we are 2 meters away, the planet is 20 times bigger, and one meter away we are 40 times bigger. That’s not right!
  • Even if the maths were right, we are doubling up distance movements – by scaling AND moving objects. The edge of the object has moved towards or away from us in addition to the movement.

If we want to move around planets, we have to be able to move the camera (or world) around us, so I have to ask the question to myself, why am I concerned with scaling objects by distance? What problem am I solving?

The problem lies that within the mini-skybox, all planets have been downscaled, and when we move around, we need them to be scaled up at runtime. This has two advantages – one we can arrange our solar system with ease (you can’t easily move items that are huge, or even fit them into the scene), and we give the perception that moving 1/100000 unit feels like moving 1 unit. So, back to the drawing board on the maths – trying to take into account a linear progression but also the scale of the camera movement…

I’ve worked out what was wrong with the maths, but there’s another problem – Even if I solve the scale  issue – Unity just can’t handle it. If I want really large planets, drawing really large objects isn’t the way forward. If I have a scale of 1.6m and a distance of 800,400 and a camera far clipping plane of 1000, I can see the planet, but it flickers really badly. Obviously I’m not the first person to try and tackle this problem, and it looks solvable if you know what you’re doing. I currently do not!

The most interesting posts I’ve found so far on this subject are here:

And this awesome video

Either this will inspire or destroy me!




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