Dec
20
2018
shaders // Unity3d

Marching Ants Sprite Outline Shader

Author An article by mgear    Comments 2 Comments

Saw interesting question here https://forum.unity.com/threads/animated-outline-effects-using-shader.600028/

and unity sprite outline https://github.com/wlgys8/Sprites-Outline + stackoverflow https://stackoverflow.com/a/16856878/5452781 to the rescue!
(although this is for 2D sprite..)

Results:

TODO
– Test how this would look with screenspace values (to keep same size even if zoomed)
– Maybe could check neighbor pixel to get “flowing direction” for each pixel ?

Modified shader: *note: hard coded values, could put them into properties, and also download the original github project first to test.


// original source: https://github.com/wlgys8/Sprites-Outline
Shader "Sprites/Outline (Marching Ants)"
{
Properties
{
[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
_Color ("Tint", Color) = (1,1,1,1)
[MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
// Add values to determine if outlining is enabled and outline color.
[PerRendererData] _OutlineSize ("Outline", Float) = 0
[PerRendererData] _OutlineColor("Outline Color", Color) = (1,1,1,1)
}
CGINCLUDE
#include "UnityCG.cginc"
struct appdata_t
{
float4 vertex : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD0;
};
struct v2f
{
float4 vertex : SV_POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
};
fixed4 _Color;
v2f vert_outline(appdata_t IN)
{
v2f OUT;
OUT.vertex = UnityObjectToClipPos(IN.vertex);
OUT.texcoord = IN.texcoord;
OUT.color = IN.color * _Color;
#ifdef PIXELSNAP_ON
OUT.vertex = UnityPixelSnap (OUT.vertex);
#endif
return OUT;
}
sampler2D _MainTex;
sampler2D _AlphaTex;
float4 _MainTex_TexelSize; //magic var
float _OutlineSize; //outline size
fixed4 _OutlineColor; // outlie color
fixed4 SampleSpriteTexture (float2 uv)
{
fixed4 color = tex2D (_MainTex, uv);
return color;
}
ENDCG
SubShader
{
Tags
{
"Queue"="Transparent"
"IgnoreProjector"="True"
"RenderType"="Transparent"
"PreviewType"="Plane"
"CanUseSpriteAtlas"="True"
}
Cull Off
Lighting Off
ZWrite Off
Blend One OneMinusSrcAlpha
//outline down
Pass
{
Offset 1, 1
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#pragma shader_feature ETC1_EXTERNAL_ALPHA
v2f vert(appdata_t IN)
{
return vert_outline(IN);
}
fixed4 frag(v2f IN) : SV_Target
{
fixed4 texColor = SampleSpriteTexture (IN.texcoord + fixed2(0,_MainTex_TexelSize.y*_OutlineSize)) * IN.color;
fixed4 c = _OutlineColor * texColor.a;
int w = ((int)(IN.texcoord.x * 100 + IN.texcoord.y * 100 + _Time.y * 5) & 1);
return c*w;
}
ENDCG
}
//outline up
Pass
{
Offset 1, 1
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#pragma shader_feature ETC1_EXTERNAL_ALPHA
v2f vert(appdata_t IN)
{
return vert_outline(IN);
}
fixed4 frag(v2f IN) : SV_Target
{
fixed4 texColor = SampleSpriteTexture (IN.texcoord + fixed2(0,- _MainTex_TexelSize.y* _OutlineSize)) * IN.color;
fixed4 c = _OutlineColor * texColor.a;
int w = ((int)(IN.texcoord.x * 100 + IN.texcoord.y * 100 + _Time.y * 5) & 1);
return c*w;
}
ENDCG
}
//outline left
Pass
{
Offset 1, 1
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#pragma shader_feature ETC1_EXTERNAL_ALPHA
v2f vert(appdata_t IN)
{
return vert_outline(IN);
}
fixed4 frag(v2f IN) : SV_Target
{
fixed4 texColor = SampleSpriteTexture (IN.texcoord + fixed2(_MainTex_TexelSize.x* _OutlineSize,0)) * IN.color;
fixed4 c = _OutlineColor * texColor.a;
int w = ((int)(IN.texcoord.x * 100 + IN.texcoord.y * 100 + _Time.y * 5) & 1);
return c * w;
}
ENDCG
}
//outline right
Pass
{
Offset 1, 1
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#pragma shader_feature ETC1_EXTERNAL_ALPHA
v2f vert(appdata_t IN)
{
return vert_outline(IN);
}
fixed4 frag(v2f IN) : SV_Target
{
fixed4 texColor = SampleSpriteTexture (IN.texcoord + fixed2(-_MainTex_TexelSize.x* _OutlineSize,0)) * IN.color;
fixed4 c = _OutlineColor * texColor.a;
int w = ((int)(IN.texcoord.x * 100 + IN.texcoord.y * 100 + _Time.y * 5) & 1);
return c * w;
}
ENDCG
}
//
Pass
{
Offset 0, 0
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile _ PIXELSNAP_ON
#pragma shader_feature ETC1_EXTERNAL_ALPHA
v2f vert(appdata_t IN)
{
v2f OUT;
OUT.vertex = UnityObjectToClipPos(IN.vertex);
OUT.texcoord = IN.texcoord;
OUT.color = IN.color * _Color;
#ifdef PIXELSNAP_ON
OUT.vertex = UnityPixelSnap (OUT.vertex);
#endif
return OUT;
}
fixed4 frag(v2f IN) : SV_Target
{
fixed4 c = SampleSpriteTexture (IN.texcoord) * IN.color;
c.rgb *= c.a;
return c;
}
ENDCG
}
}
}

view raw

marching-ants-outline.shader

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Resources:
– wiki https://en.wikipedia.org/wiki/Marching_ants
– rectangle outline marching ants shader https://www.shadertoy.com/view/XltcR2
– 3d marching ants from uvs https://shaderfrog.com/app/view/1847
– marching ant ideas https://losingfight.com/blog/2007/08/30/an-alternate-way-to-implement-marching-ants/
– marching ants done in Flash http://www.quasimondo.com/archives/000573.php

Comparison (photoshop selection line)

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