Small clean up

manimlib/shaders/quadratic_bezier_stroke/frag.glsl

@@ -12,18 +12,21 @@ out vec4 frag_color;
 
 const float QUICK_DIST_WIDTH = 0.2;
 
-// Distance from (x0, y0) to the curve y = x^2
-float dist_to_curve(float x0, float y0){
+float dist_to_curve(){
+    // Returns distance from uv_coords to the curve v = u^2
+    float x0 = uv_coords.x;
+    float y0 = uv_coords.y;
+
     // In the linear case, the curve will have
     // been set to equal the x axis
-    if(bool(is_linear)) return y0;
+    if(bool(is_linear)) return abs(y0);
 
     if(uv_stroke_width < QUICK_DIST_WIDTH){
         // This is a quick approximation for computing
         // the distance to the curve.
         // Evaluate F(x, y) = y - x^2
         // divide by its gradient's magnitude
-        return (y0 - x0 * x0) / sqrt(1 + 4 * x0 * x0);
+        return abs((y0 - x0 * x0) / sqrt(1 + 4 * x0 * x0));
     }
     // Otherwise, solve for the minimal distance.
     // The distance squared between (x0, y0) and a point (x, x^2) looks like
@@ -50,9 +53,8 @@ float dist_to_curve(float x0, float y0){
 void main() {
     if (uv_stroke_width == 0) discard;
 
-    // Compute sdf for the region around the curve we wish to color.
-    float dist = dist_to_curve(uv_coords.x, uv_coords.y);
-    float signed_dist = abs(dist) - 0.5 * uv_stroke_width;
+    // sdf for the region around the curve we wish to color.
+    float signed_dist = dist_to_curve() - 0.5 * uv_stroke_width;
 
     frag_color = color;
     frag_color.a *= smoothstep(0.5, -0.5, signed_dist / uv_anti_alias_width);