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#version 330 core
// --------------------------------------------------------------------------------
// Regular polygon shader
//
// ref: https://thndl.com/square-shaped-shaders.html
// ref: https://thebookofshaders.com/07/
//
// @model quad
// @uniform int u_n 3 3 12
// @uniform color u_bg 0 0 0 1
// @uniform color u_fg 1 1 1 1
//
// SPDX-License-Identifier: 0BSD
// --------------------------------------------------------------------------------
// --------------------------------------------------------------------------------
// Uniforms
// --------------------------------------------------------------------------------
uniform float u_time;
uniform vec2 u_res;
uniform int u_n;
uniform vec4 u_bg;
uniform vec4 u_fg;
// --------------------------------------------------------------------------------
// Vertex outputs
// --------------------------------------------------------------------------------
in vec2 v_p;
in vec2 v_t;
// --------------------------------------------------------------------------------
// Fragment outputs
// --------------------------------------------------------------------------------
out vec4 f_c;
// --------------------------------------------------------------------------------
// Entry point
// --------------------------------------------------------------------------------
#define PI 3.14159265359
void main()
{
// Centered with square aspect ratio
vec2 st = gl_FragCoord.xy / u_res.xy;
float aspect = u_res.x / u_res.y;
if (aspect > 1.0f) { st.x = (st.x - 0.5f) * aspect + 0.5f; }
else { st.y = (st.y - 0.5f) / aspect + 0.5f; }
// Remap [0, 1] to [-1, 1]
st = st * 2.0f - 1.0f;
// Angle of pixel from center + rotation
float a = atan(st.y, st.x) + u_time * 0.2f;
// Angle of each sector from center
float r = (PI * 2.0f) / float(u_n);
// Polar polygon edge test. cos(theta) = dot product.
float d = cos(floor(0.5f + a / r) * r - a) * length(st);
f_c = vec4(vec3(mix(u_bg, u_fg, 1.0f - step(0.5f, d))), 1.0f);
}
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