SDF-fake-triangle.py

# -----------------------------------------------------------------------------
# Python & OpenGL for Scientific Visualization
# www.labri.fr/perso/nrougier/python+opengl
# Copyright (c) 2017, Nicolas P. Rougier
# Distributed under the 2-Clause BSD License.
# -----------------------------------------------------------------------------
import numpy as np
from glumpy import app, gloo, gl

vertex = """
    attribute vec2 position;
    varying vec2 v_position;
    void main(){
        v_position = position;
        gl_Position = vec4(position, 0.0, 1.0);
    } """

fragment = """
  float SDF_fake_triangle(vec2 p0, vec2 p1, vec2 p2, vec2 p)
  {
      vec2 e0 = p1 - p0;
      vec2 e1 = p2 - p1;
      vec2 e2 = p0 - p2;

      vec2 v0 = p - p0;
      vec2 v1 = p - p1;
      vec2 v2 = p - p2;

      vec2 o0 = normalize(vec2(e0.y, -e0.x));
      vec2 o1 = normalize(vec2(e1.y, -e1.x));
      vec2 o2 = normalize(vec2(e2.y, -e2.x));

      return max(max(dot(o0,v0),  dot(o1,v1)), dot(o2,v2));
  }

  vec4 color(float d)
  {
      vec3 white = vec3(1.0, 1.0, 1.0);
      vec3 blue  = vec3(0.1, 0.4, 0.7);
      vec3 color = white - sign(d)*blue;
      color *= (1.0 - exp(-4.0*abs(d))) * (0.8 + 0.2*cos(140.0*d));
      color = mix(color, white, 1.0-smoothstep(0.0,0.02,abs(d)) );
      return vec4(color, 1.0);
  }

  varying vec2 v_position;
  uniform vec2 p0, p1, p2;
  void main()
  {
      float d = SDF_fake_triangle(p0, p1, p2, v_position);
      gl_FragColor = color(d);
  } """

window = app.Window(512, 512)
quad = gloo.Program(vertex, fragment, count=4)
quad['position'] = (-1,+1), (+1,+1), (-1,-1), (+1,-1)

phi = 0
@window.event
def on_draw(dt):
    global phi

    phi0 = np.pi*phi/180.0
    phi1 = np.pi*(phi+120)/180.0
    phi2 = np.pi*(phi+240)/180.0
    rho0 = rho1 = rho2 = 0.75
    quad["p0"] = rho0*np.cos(phi0), rho0*np.sin(phi0)
    quad["p1"] = rho1*np.cos(phi1), rho1*np.sin(phi1)
    quad["p2"] = rho2*np.cos(phi2), rho2*np.sin(phi2)
    
    window.clear()
    quad.draw(gl.GL_TRIANGLE_STRIP)
    phi += 1.0

app.run(framerate=60, framecount=360)