第 3 课：Grass - 3D Blade

实现

uniform float iTime;

attribute int index;

vec3 bezier3D(vec3 p0, vec3 p1, vec3 p2, float t) {
    float u = 1.0 - t;
    float tt = t * t;
    float uu = u * u;

    vec3 p = uu * p0;
    p += 2.0 * u * t * p1;
    p += tt * p2;

    return p;
}

void main() {
  int localIndex = index % 20;
  float h = float(localIndex / 2) / 9.0;
  float sideX = mod(float(localIndex), 2.0) * 2.0 - 1.0;
  float bend = sin(iTime) * 1.5;

  vec3 curve = bezier3D(
    vec3(0.0, 0.0, 0.0),
    vec3(0.0, 0.5, 0.0),
    vec3(0.0, cos(bend), sin(bend)),
    h
  );

  float dw = mix(0.1, 0.0, h * h);
  vec3 pos = vec3(curve.x + sideX * dw, curve.y, curve.z);

  gl_Position = projectionMatrix * viewMatrix * vec4(pos, 1.0);
}