From 4998f5936dc7da36aba0cd018de2a1a6127dda08 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Tom=C3=A1s?= <jtomas1815@gmail.com>
Date: Tue, 19 Jan 2021 09:06:32 -0300
Subject: Make shader sample intervals uniform

---
 src/main.rs | 61 ++++++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 44 insertions(+), 17 deletions(-)

(limited to 'src/main.rs')

diff --git a/src/main.rs b/src/main.rs
index f01526b..a61478f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -37,25 +37,47 @@ fn compile_bezier_shader(c: &Bezier) -> GLuint {
     #version 410 core
     out vec4 FragColor;
 
-    float inf = 1000000;
     float vx[{s}] = float[{s}]({vx});
     float vy[{s}] = float[{s}]({vy});
+
     float px[{sx}] = float[{sx}]({px});
     float py[{sy}] = float[{sy}]({py});
+
+    float dpx[{dsx}] = float[{dsx}]({dpx});
+    float dpy[{dsy}] = float[{dsy}]({dpy});
+
     float thr = 32;
+    float step_size = 10;
+    float inf = 1000000;
 
-    float eval_a(float[{sx}] v, float t) {{
+    float eval_px(float t) {{
         float result = 0.0;
         for (int i = 0; i < {sx}; i++) {{
-          result += v[i] * pow(t, i);
+          result += px[i] * pow(t, i);
         }}
         return result;
     }}
 
-    float eval_b(float[{sy}] v, float t) {{
+    float eval_py(float t) {{
         float result = 0.0;
         for (int i = 0; i < {sy}; i++) {{
-          result += v[i] * pow(t, i);
+          result += py[i] * pow(t, i);
+        }}
+        return result;
+    }}
+
+    float eval_dpx(float t) {{
+        float result = 0.0;
+        for (int i = 0; i < {dsx}; i++) {{
+          result += dpx[i] * pow(t, i);
+        }}
+        return result;
+    }}
+
+    float eval_dpy(float t) {{
+        float result = 0.0;
+        for (int i = 0; i < {dsy}; i++) {{
+          result += dpy[i] * pow(t, i);
         }}
         return result;
     }}
@@ -72,13 +94,14 @@ fn compile_bezier_shader(c: &Bezier) -> GLuint {
     }}
 
     float inside(vec2 pos) {{
-      float res = 100;
       float closest = inf;
       float t = 0.0;
-      while (t < 1.0 - 1.0 / res) {{
-        float step = t + 1.0 / res;
-        vec2 a = vec2(eval_a(px, t), eval_b(py, t));
-        vec2 b = vec2(eval_a(px, step), eval_b(py, step));
+      float dstep = 0.0;
+      while (t < 1.0 - dstep) {{
+        dstep = step_size / length(vec2(eval_dpx(t), eval_dpy(t)));
+        float step = t + dstep;
+        vec2 a = vec2(eval_px(t), eval_py(t));
+        vec2 b = vec2(eval_px(step), eval_py(step));
         float c = pow(length(a - b), 2);
         float d = distance(pos, a + clamp(dot(pos - a, b - a) / c, 0, 1) * (b - a));
         if (d < closest) {{
@@ -95,13 +118,17 @@ fn compile_bezier_shader(c: &Bezier) -> GLuint {
       FragColor = vec4(r, c, 0.0, 1.0);
     }}
     ",
-        sx = c.px.degree() + 1,
-        sy = c.py.degree() + 1,
-        px = &c.px,
-        py = &c.py,
-        s  = c.degree,
-        vx = c.show_x(),
-        vy = c.show_y(),
+        s   = c.degree,
+        vx  = c.show_x(),
+        vy  = c.show_y(),
+        px  = &c.px,
+        py  = &c.py,
+        sx  = c.px.degree() + 1,
+        sy  = c.py.degree() + 1,
+        dpx = &c.dpx,
+        dpy = &c.dpy,
+        dsx = c.dpx.degree() + 1,
+        dsy = c.dpy.degree() + 1,
     )
     .into_bytes();
 
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