From 1d77f1ca38f88b79a39b418fe3dc7899887d186a Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sat, 31 Jan 2026 12:02:06 +0000
Subject: Tidy networkCurve shaders

Arrays for start/end position/angle, smaller centre position, dynamic
segment count based on max error, calculate distance in tessellation
evaluation, use start/end position directly to avoid rounding errors at
joins.

See https://schneide.blog/2025/05/21/calculating-the-number-of-segments-for-accurate-circle-rendering/
---
 gfx/gl/shaders/networkCurve.tese | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

(limited to 'gfx/gl/shaders/networkCurve.tese')

diff --git a/gfx/gl/shaders/networkCurve.tese b/gfx/gl/shaders/networkCurve.tese
index a02503c..82e6a13 100644
--- a/gfx/gl/shaders/networkCurve.tese
+++ b/gfx/gl/shaders/networkCurve.tese
@@ -1,17 +1,22 @@
 #version 460 core
+
 layout(isolines, equal_spacing, cw) in;
 
-flat in ivec3 c_apos[];
-flat in ivec3 c_bpos[];
-flat in ivec3 c_cpos[];
+uniform ivec3 viewPoint;
+
+flat in ivec3 c_pos[][2];
+flat in ivec2 c_cpos[];
 flat in float c_reps[];
-flat in float c_aangle[];
-flat in float c_bangle[];
+flat in float c_angles[][2];
 flat in float c_radius[];
 
 flat out ivec3 pos;
 flat out mat2 rot;
 flat out float tpos;
+flat out float dist;
+
+const float startTolerance = 1. / 200.;
+const float endTolerance = 1. - startTolerance;
 
 mat2
 getRot(float angle)
@@ -22,9 +27,19 @@ getRot(float angle)
 void
 main()
 {
-	float angle = mix(c_bangle[0], c_aangle[0], gl_TessCoord.x);
-	int height = int(mix(c_bpos[0].z, c_apos[0].z, gl_TessCoord.x)) - c_cpos[0].z;
+	const float angle = mix(c_angles[0][1], c_angles[0][0], gl_TessCoord.x);
 	rot = getRot(angle);
+	if (gl_TessCoord.x < startTolerance) {
+		pos = c_pos[0][1];
+	}
+	else if (gl_TessCoord.x > endTolerance) {
+		pos = c_pos[0][0];
+	}
+	else {
+		const int height = int(mix(c_pos[0][1].z, c_pos[0][0].z, gl_TessCoord.x));
+		pos = ivec3(c_cpos[0] + ivec2(rot * vec2(c_radius[0], 0)), height);
+	}
+
 	tpos = c_reps[0] * gl_TessCoord.x;
-	pos = c_cpos[0] + ivec3(rot * vec2(c_radius[0], 0), height);
+	dist = length(vec3(viewPoint - pos));
 }
-- 
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