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Rain; Best way to go about it
Topic Started: Mar 14 2009, 06:05 AM (380 Views)
Gandalf20000
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Particles are great for a lot of things. Until, of course, you start reaching stuff like rain. It's the whole billboard thing. Yeah, it's fine when you're looking straight at it, but what about if you look up? You shouldn't see the entire raindrop undistorted, yet, because of the way billboards work, it always appears as if you are staring at it head on, when you're not. Therefore, particles aren't really an option here.

So, ending my rant, how would one properly go about making rain?

(By the way, I couldn't really tell very well if this should go in Game Graphics or this forum. So don't hesitate to move it if it doesn't belong here.)
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skarik
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kitten eating scum
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Same way as I proposed the grass.

Edit:
Nah, not really, but you get an idea. You can have one model with one shader. Since you can't see raindrops far away, it doesn't need to be that much geometry. The problem would be you need at least four to make it seem like the rain isn't traveling with you. Although, I think you could get away with two: one on you, and the other in front of you, snapped to a grid, where you're looking.
Edited by skarik, Mar 14 2009, 06:15 AM.
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Dr. Best
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I am quite sure that modern games usually use post screen shaders for this. Basically you would just bring some odd stripes onto the screen, which move quite random and change dependent on the camera movement and the camera orientation. It would be hard with PS 1.4, but it would be possible.
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Gandalf20000
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Maybe... But the thing is, you would need a depth test (so the rain doesn't always appear in front), and several other complicated things so that it didn't get the same effect as the particles.
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Dr. Best
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I didn't say that it's easy, did I ^_^ ? It can be done, but it is complicated.

Another option would be scrolling layers in front of the camera, but I don't really like that. In every case the rain should be quite blurry. This way it will not be too obvious that it is all just a fake.
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Gandalf20000
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Maybe one could do something like the multiple models technique... Create a bunch of primitives in a list (or, if absolutely required, models), and then run through the list every step to move down some of the drops, and when they move too far down, they appear back above the character... I dunno, though...

I tried doing rain a while back with particles, using a round texture, hoping that the illusion of the drop moving would make it look elongated, but that would require a motion blur, so it didn't work so well... It ended up looking like snow in the end.

The scrolling layers thing might be a good idea. Each layer is an uncapped cylinder that has flipped normals so you see the inside, and they are scaled according to the layer, and then have a slightly blurred rain texture running down to appear like the rain is moving... But then again, you'd probably also want a soft edges shader incorporated with the scrolling shader to prevent clipping that might give away the illusion.
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Reikyrr
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why not make tilted 2 axis billboards that move to a predetermend position when they get to close/far away from the camera.
~Inspirational quote~
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Gandalf20000
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If you stare straight up in the sky, you need to see rain falling like it would in reality.
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skarik
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kitten eating scum
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Hey, I'll try with my technique, and I'm not going to do PSS's. It seems like a bit of hell to me, and I don't know if you've got a depth texture yet.
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Gandalf20000
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Thanks to you people's help, I've made an example on making rain in U3D, found here.
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Reikyrr
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Gandalf20000
Mar 14 2009, 06:55 PM
If you stare straight up in the sky, you need to see rain falling like it would in reality.
I mean it only rotates on the Z axis and is slightly tilted on the X and Y.
Edited by Reikyrr, Mar 15 2009, 11:59 AM.
~Inspirational quote~
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