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Geometrian

Jumping Shadowmap

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Hi, So, I've got a nice airplane flying over water, complete with reflections and standard shadowmapping. The water is represented as a simple quad, perturbed with a normalmap. Unfortunately, as the plane flies along, particularly as it gets farther from the origin, the shadowmap begins jumping around on the ground. It's not majorly jumping, but it is significant--perhaps 25 pixels on screen every second or so. I don't know what's causing this, though I suspect it might be a precision error (the plane is 1000.0 units square, could that have something to do with it?). Has anyone run into this before, and can anyone tell me how to fix it? Thanks, -G

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I'm not sure what you mean by jumping, could you upload a video to Youtube or something? If the aircraft is getting further away from the shadow reciever then maybe you are seeing the symptoms of one shadow map texel mapping to many terrain pixels.

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I would look into how the lights position is calculated. It's hard to tell from the video what might be wrong. I see your problem (though the water is very dark). Are you sure you are moving the light parallel to the camera? Maybe you could try and render the light's position and see if it jumps too.

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I am certain that the light's position does not jump. Also, the shadowmap appears the same when I examine it in an on-screen window.
Thanks,

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