Applying multiple shaders to a effect?

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Tjakka5
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Applying multiple shaders to a effect?

Post by Tjakka5 »

Hey all,

Im working on a game in which I will be using a few shaders to make fancy effects and what not; Just some basic ones to change the color of a sprite though.

However, I have noted that you can only load 1 shader at the time, and apply it to a sprite, whereas I would like to be able to apply 2 shaders to a sprite.

For example, normally a sprite would be grayscaled, but when a certain variable is true it should be grayscaled, as well as have a different shader on top of it.


Im thinking I may need to use some kind of loop where I activate shader1, draw it to a canvas, activate shader2, draw it to a canvas, etc, until I get the image I want, then draw it to the screen, but I'm not sure how to do so.

Can anybody help me out here?
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s-ol
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Re: Applying multiple shaders to a effect?

Post by s-ol »

You can draw the original sprite to canvas with one shader set, then draw the canvas onto the screen with the other shader set.

I would not recommend this though. It is probably better to instead write a shader that handles both, based on an externa value that you can set with shader:send().

s-ol.nu /blog  -  p.s-ol.be /st8.lua  -  g.s-ol.be /gtglg /curcur

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print( type(love) )
if false then
  baby:hurt(me)
end
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Fenrir
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Re: Applying multiple shaders to a effect?

Post by Fenrir »

Im thinking I may need to use some kind of loop where I activate shader1, draw it to a canvas, activate shader2, draw it to a canvas, etc, until I get the image I want, then draw it to the screen, but I'm not sure how to do so.
It's exactly the concept of multi-pass rendering, to apply multiple shader to a same object you'll need to render it back to a canvas where you'll apply the new shader. So to achieve what you want you can setup a multi-pass system (but it's really needed in cases where you need the result of the previous shader for your new computation) or just write a "bigger" shader handling all the cases you need (or switch between multiple shaders depending on the situation).

A typical example of multi-pass effects is gaussian blur for instance, you can have an example in this post:
viewtopic.php?f=5&t=80216&start=10#p184638
To apply this effect on my character, I have a total of 5 canvas and 4 shaders.
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s-ol
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Re: Applying multiple shaders to a effect?

Post by s-ol »

Fenrir wrote:
Im thinking I may need to use some kind of loop where I activate shader1, draw it to a canvas, activate shader2, draw it to a canvas, etc, until I get the image I want, then draw it to the screen, but I'm not sure how to do so.
It's exactly the concept of multi-pass rendering, to apply multiple shader to a same object you'll need to render it back to a canvas where you'll apply the new shader. So to achieve what you want you can setup a multi-pass system (but it's really needed in cases where you need the result of the previous shader for your new computation) or just write a "bigger" shader handling all the cases you need (or switch between multiple shaders depending on the situation).

A typical example of multi-pass effects is gaussian blur for instance, you can have an example in this post:
viewtopic.php?f=5&t=80216&start=10#p184638
To apply this effect on my character, I have a total of 5 canvas and 4 shaders.
wouldn't two canvas' be enough? You can just render back-and-forth. Or do you access the other data inbetween?

s-ol.nu /blog  -  p.s-ol.be /st8.lua  -  g.s-ol.be /gtglg /curcur

Code: Select all

print( type(love) )
if false then
  baby:hurt(me)
end
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Tjakka5
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Re: Applying multiple shaders to a effect?

Post by Tjakka5 »

Thing is; I have never actually used canvases (canvas-i, canvasses?) before, so I think I might just go for the "all-in-one" shader, which will have boolean variables that will control which part of the shader to apply.
bobbyjones
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Re: Applying multiple shaders to a effect?

Post by bobbyjones »

Use this as an opportunity to learn all about canvases they will be needed eventually anyway.
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I~=Spam
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Re: Applying multiple shaders to a effect?

Post by I~=Spam »

bobbyjones wrote:Use this as an opportunity to learn all about canvases they will be needed eventually anyway.
* probably it depends on what you are doing ;)
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Tjakka5
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Re: Applying multiple shaders to a effect?

Post by Tjakka5 »

I think I'll probably try to incorporate canvasas as the frame buffer, as I heard its more efficient?
That will also mean I can implement my camera on it a lot more easialy, which would be nice :3
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I~=Spam
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Re: Applying multiple shaders to a effect?

Post by I~=Spam »

Tjakka5 wrote:I think I'll probably try to incorporate canvasas as the frame buffer, as I heard its more efficient?
That will also mean I can implement my camera on it a lot more easialy, which would be nice :3
No it will most likely be slower because you are doing two draw calls to draw one thing (draw calls are a lot more expensive than people think). But most likely you have more than enough processing power so don't worry about it. ;) Just do what makes sense to you as long as you are being reasonable.
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bobbyjones
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Re: Applying multiple shaders to a effect?

Post by bobbyjones »

How will it be slower? Lol he isn't using canvases yet. Once he adds it in his performance should increase lol. That's the point of canvases.
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