问题
I'm trying to create, modify and update (directional only for now) lights and shadowmaps dynamically. The light, shadow and shadow camera helper gets updated correctly as I move the light around or change shadow properties, except from the light's point of view, everything behind the origin (0,0,0) is shadowed for no apparent reason.
Screenshots:
http://i.imgur.com/n4AHvle.png
http://i.imgur.com/l0uaZHD.jpg
http://i.imgur.com/brKwCof.jpg
http://i.imgur.com/a6dqMGo.jpg (new, with spotlight)
You can see a scene with car and a piece of ground, they belong to a geometry imported with ColladaLoader. The problem is with shadowmapping, the car throws shadow correctly, but there are stripy shadows on the ground even though there is nothing else than the car obscuring light.
If I add more similar lights, they also have the same 4 stripes. They also appear with spotlight. If I change shadow map resolution, the stripes' size changes relative to each other, but there seems to be always four of them, spaced from center to both directions.
EDIT: JSFiddle here: http://jsfiddle.net/cL3hX/1/ There shouldn't be any shadows in the scene, unless some new geometry is introduced inside the shadow camera frustum.
Couple of notes on the fiddle:
I have r55, but the demo is r54 because jsfiddle apparently does not yet have r55.
I could only reproduce this with a Collada file. So it probably has something to do with the model. I created a simple cube in Sketchup 8, and tried to export it with various collada options.
In the JSFiddle I could only reproduce the bug with a file exported with "doublesided faces" -setting enabled. In my own application code, I do have the same bug on models created with or without that setting enabled, but in the fiddle, the bug seems to be triggered only when "doublesided faces" are exported. Anyway I do need to somehow show backsides of faces, because the tool I'm developing must work with Sketchup exports, and it's very hard to make models in Sketchup without having a mess of frontsides/backsides visible.
The very simple Collada file is included in the JSFiddle as javascript variable. Here's a download link for the same file: https://dl.dropbox.com/u/14489569/shadowmapdemo.dae
回答1:
The problem is your Collada model.
Your "plane" is actually multiple coplanar faces back-to-back in a single geometry.
It's no wonder there are artifacts.
Replace it with a THREE.CubeGeometry.
来源：https://stackoverflow.com/questions/14539747/three-js-shadow-map-stripes-in-each-light-now-simplified-and-with-jsfiddle