How can I implement gray filter effect on CanvasRenderer?

[Aaron Wang]

I noticed that the built-in GrayFilter only works for WebGLRenderer, but I really need to implement the gray filter effect on all renderers, used to highlight and darken objects, is there any alternatives?

[ivan.popelyshev]

If you want to apply the filter to all the canvas, you can use CSS filter.

[Aaron Wang]

3 hours ago, ivan.popelyshev said:

If you want to apply the filter to all the canvas, you can use CSS filter.

Thanks for you reply, but unfortunately, I need to apply the filter to certain parts of the canvas precisely, I think that'll be verify difficult with CSS.

I just have a thought, can I use half transparent gray picture to cover on target region to simulate the filter effect? Will that be possible?

 

[ivan.popelyshev]

May be something can be done with blendModes: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/globalCompositeOperation

[Aaron Wang]

I end up using transparent dark overlay to highlight/darken objects eventually. 

[Exca]

One option would be to draw the images to separate canvas, then go through all the pixels (in each image you want to grayscale) and calculate gray variation of the image and use that canvas as texture and alphablend between original image and calculated grayscale.

[Edit] To have an area of grayscaled sprites you could then just mask the area which shows grayscaled sprites on an layer above the normal sprites.