From 82582d08bd40270ad89a2d95d26b3d6d2cc305bd Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Tue, 20 Aug 2024 13:32:52 -0500
Subject: [PATCH] Fewer parameters for stroke frag shader

---
 manimlib/shaders/quadratic_bezier/stroke/frag.glsl | 14 ++++++--------
 manimlib/shaders/quadratic_bezier/stroke/geom.glsl | 12 ++++++------
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/manimlib/shaders/quadratic_bezier/stroke/frag.glsl b/manimlib/shaders/quadratic_bezier/stroke/frag.glsl
index 7fb668aa..a26b2334 100644
--- a/manimlib/shaders/quadratic_bezier/stroke/frag.glsl
+++ b/manimlib/shaders/quadratic_bezier/stroke/frag.glsl
@@ -1,18 +1,16 @@
 #version 330
 
-// Value between -1 and 1
-in float dist_to_curve;
-in float half_stroke_width;
-in float half_anti_alias_width;
+// Distance to the curve, and half the curve width, both as
+// a ratio of the antialias width
+in float dist_to_aaw;
+in float half_width_to_aaw;
 in vec4 color;
 
 out vec4 frag_color;
 
 void main() {
-    if(half_stroke_width == 0) discard;
     frag_color = color;
-
     // sdf for the region around the curve we wish to color.
-    float signed_dist_to_region = abs(dist_to_curve) - half_stroke_width;
-    frag_color.a *= smoothstep(half_anti_alias_width, -half_anti_alias_width, signed_dist_to_region);
+    float signed_dist_to_region = abs(dist_to_aaw) - half_width_to_aaw;
+    frag_color.a *= smoothstep(0.5, -0.5, signed_dist_to_region);
 }
\ No newline at end of file
diff --git a/manimlib/shaders/quadratic_bezier/stroke/geom.glsl b/manimlib/shaders/quadratic_bezier/stroke/geom.glsl
index a34db252..d4667bdd 100644
--- a/manimlib/shaders/quadratic_bezier/stroke/geom.glsl
+++ b/manimlib/shaders/quadratic_bezier/stroke/geom.glsl
@@ -17,9 +17,8 @@ in vec4 v_color[3];
 in int v_vert_index[3];
 
 out vec4 color;
-out float dist_to_curve;
-out float half_stroke_width;
-out float half_anti_alias_width;
+out float dist_to_aaw;
+out float half_width_to_aaw;
 
 // Codes for joint types
 const int NO_JOINT = 0;
@@ -169,19 +168,20 @@ void emit_point_with_width(
 
     // Set styling
     color = finalize_color(joint_color, point, unit_normal);
-    half_anti_alias_width = 0.5 * anti_alias_width * pixel_size;
-    half_stroke_width = 0.5 * width;
 
     // Figure out the step from the point to the corners of the
     // triangle strip around the polyline
     vec3 step = step_to_corner(point, tangent, unit_normal, joint_product, inside_curve);
+    float aaw = max(anti_alias_width * pixel_size, 1e-8);
 
     // Emit two corners
     // The frag shader will receive a value from -1 to 1,
     // reflecting where in the stroke that point is
     for (int sign = -1; sign <= 1; sign += 2){
-        dist_to_curve = sign * (half_stroke_width + half_anti_alias_width);
+        float dist_to_curve = sign * 0.5 * (width + aaw);
         emit_gl_Position(point + dist_to_curve * step);
+        half_width_to_aaw = 0.5 * width / aaw;
+        dist_to_aaw = dist_to_curve / aaw;
         EmitVertex();
     }
 }