How to render shadow map one time

Questions
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1

I found a tip of threejs about shadow rendering here:

Shadows

  1. If your scene is static, only update the shadow map when something changes, rather than every frame

Is there anyone can tell me how to achieve this? when I set the castShadow to false. the shadow map just disappear.

2

You can do this by setting renderer.shadowMap.autoUpdate to false. If an update is required, set renderer.shadowMap.needsUpdate to true.

Demo: https://jsfiddle.net/2xbje0sn/

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3

Oh yes! that’s really cool!

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4

I found this trick can’t significantly improve performance of shadow rendering on smart phone. see pictures below:
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test code (most of them copied from mugen87’s jsfiddle demo): https://codepen.io/iamnotstone/pen/yWJKzx
@Mugen87 @looeee

5

Probably because computing the shadow map is no real performance bottleneck in this simple app.

6

But, if I disable the shadowmap, and fps value will up to 60.

7

I think we need to differentiate between rendering a shadow map and just updating it.

9

what do you mean by just updating it? You mean eliminate the animations and timeout ? If so, I have already do that , and it is unhelpful.

10

There are two steps when using shadow mapping. The shadow map is generated and then used as a texture. renderer.shadowMap.autoUpdate controls the first part of this process.

11

Does this controls the projection of a shadowMap to every surface?

12

As I said before, it just controls the update process of the shadow map. I suggest you study in more detail how shadow mapping works, then this topic will be more clear to you.

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