Spider Web
A simple fragment shader for creating spider webs. Allows adjusting:
- size (relative to r=1),
- color
- thickness
- number of “spikes” (radii)
- number of “strands” (concentric levels),
- “indentation” (sag between radii), and
- limited ability to skew to non-circle.
The example image shows multiple uses in TextureRects in a CanvasLayer.
Shader code
shader_type canvas_item;
uniform vec4 color : source_color = vec4(1);
uniform float thickness : hint_range(0.0, 8., 0.1) = 1.;
uniform int spikes : hint_range(1,20, 1) = 6;
uniform int strands: hint_range(1, 20, 1) = 10;
uniform float indencity : hint_range(0.005, .5, 0.001) = .1;
uniform vec2 center = vec2(.5,.5);
uniform float rel_size : hint_range(0., 1., .1) = 0.01;
uniform vec2 skew = vec2(1., 1.);
void fragment() {
float angle = atan(UV.y-center.y, UV.x-center.x);
COLOR.rgb = color.rgb;
float r = sqrt(pow(UV.x - center.x,2)/skew.x + pow(UV.y - center.y, 2)/skew.y);
float indent_fix = (.3)*r*float(strands);
float b = (r + indencity*abs(sin(angle*float(spikes)/2.0))*indent_fix);
float a = fract(float(strands) * b / rel_size);
COLOR.a = color.a * min(
max(smoothstep(1.-thickness*.1, 1., a),
smoothstep(thickness*.1/(20.*r +.01), 0.0, abs(sin(angle*float(spikes)/2.0)))),
1. - step(0., b - rel_size));
}
