WIP Newton's method for stencil AAA
@@ -21,20 +21,26 @@ void main() {
vec2 from = vFrom, ctrl = vCtrl, to = vTo;
// Determine winding, and sort into a consistent order so we only need to find one root below.
- bool winding = from.x < to.x;
- vec2 left = winding ? from : to, right = winding ? to : from;
- vec2 v0 = ctrl - left, v1 = right - ctrl;
+ vec2 v0 = ctrl - from, v1 = to - ctrl;
// Shoot a vertical ray toward the curve.
vec2 window = clamp(vec2(from.x, to.x), -0.5, 0.5);
- float offset = mix(window.x, window.y, 0.5) - left.x;
- float t = offset / (v0.x + sqrt(v1.x * offset - v0.x * (offset - v0.x)));
+ //float offset = mix(window.x, window.y, 0.5) - left.x;
+ //float t = offset / (v0.x + sqrt(v1.x * offset - v0.x * (offset - v0.x)));
+ float t = 0.5;
+ float x = mix(mix(from.x, ctrl.x, t), mix(ctrl.x, to.x, t), t);
+ float dX = 2.0 * mix(v0.x, v1.x, t);
+ t -= x / dX;
+ x = mix(mix(from.x, ctrl.x, t), mix(ctrl.x, to.x, t), t);
+ dX = 2.0 * mix(v0.x, v1.x, t);
+ t -= x / dX;
// Compute position and derivative to form a line approximation.
- float y = mix(mix(left.y, ctrl.y, t), mix(ctrl.y, right.y, t), t);
- float d = mix(v0.y, v1.y, t) / mix(v0.x, v1.x, t);
+ float y = mix(mix(from.y, ctrl.y, t), mix(ctrl.y, to.y, t), t);
+ //float dYDX = mix(v0.y, v1.y, t) / mix(v0.x, v1.x, t);
+ float dYDX = dFdx(y);
// Look up area under that line, and scale horizontally to the window size.
- float dX = window.x - window.y;
- gl_FragColor = vec4(texture2D(uAreaLUT, vec2(y + 8.0, abs(d * dX)) / 16.0).r * dX);
+ dX = (gl_FrontFacing ? 1.0 : -1.0) * (window.x - window.y);
+ gl_FragColor = vec4(texture2D(uAreaLUT, vec2(y + 8.0, abs(dYDX * dX)) / 16.0).r * dX);
}
