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Thicker Outline for Toon Shader

Started by richardmonette May 14, 2009 at 1:29 PM 2 replies 2.6k views

Original Post

May 14, 2009 at 1:29 PM

I am currently working on a cartoon style shader in HLSL which uses Sobel edge detection to draw outlines around my models. This is working well, but I would like to make the outlines much, much thicker than they are currently. If I make the kernel larger the lines get a bit thicker but for the extremely thick lines I require the kernel size would ruin performance. Can anyone recommend a good strategy for creating thicker lines?

Krypt0n

May 14, 2009 at 3:35 PM

keep the small kernel and afterwards do some 'postprocess' passes that expand the lines.

of you want thiker lines, you might get away with rendeirng into a smaller buffer and then stretch it over the full resolution rendertarget, that way you'd process less fargment shaders but get thicker lines automatically.

richardmonette

May 15, 2009 at 1:37 PM

Found a decent solution that can produce thicker outlines while still using only a 3x3 kernel.

Basically I create the offsets for the kernel like this:


const float texelSize = 1.0f / 512.0f;
const float2 kernelOffsets[NUM] = {
 float2(-texelSize, texelSize), 
 float2( 0.00 , texelSize),
 float2( texelSize, texelSize),
 float2(-texelSize, 0.00 ),
 float2( 0.0, 0.0),
 float2( texelSize, texelSize ),
 float2(-texelSize,-texelSize),
 float2( 0.00 , -texelSize),
 float2( texelSize,-texelSize),
 }
[\code]

So all I really needed to do was change the texel size so increase the distance of the sampling.

For example, 1.0f/256.0f (even though the texture is still 512x512 produces roughly a doubly thick line.

Jason Z

May 15, 2009 at 4:24 PM

You could potentially do some type of a dilation filter on the outlines as well, but you would have to be careful to only expand the outline in the correct direction... (i.e. only expand outward instead of inward).

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