From 56c1e10e066b4e0621fca8a629277019515ebd5e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mikael=20L=C3=B6vqvist?= <mikael.lovqvist.mail@gmail.com>
Date: Mon, 21 Jul 2025 18:42:27 +0200
Subject: [PATCH] Added corrected offset triangular lattice

---
 canvas/triangular-lattice-offset-corrected.js | 82 +++++++++++++++++++
 index.html                                    |  1 +
 2 files changed, 83 insertions(+)
 create mode 100644 canvas/triangular-lattice-offset-corrected.js

diff --git a/canvas/triangular-lattice-offset-corrected.js b/canvas/triangular-lattice-offset-corrected.js
new file mode 100644
index 0000000..e8a062c
--- /dev/null
+++ b/canvas/triangular-lattice-offset-corrected.js
@@ -0,0 +1,82 @@
+//Create useful variables
+const aspect = W / H;
+const scale = aspect >= 1 ? H / 2 : W / 2;
+
+function setup() {
+	// Reset transform
+	C.setTransform(1, 0, 0, 1, 0, 0);
+
+	// Clear canvas
+	C.clearRect(0, 0, W, H);
+
+	// Reset common properties
+	C.globalCompositeOperation = 'source-over';
+	C.fillStyle = 'rgba(255,200,100,1)';
+	C.strokeStyle = 'rgba(0,0,0,1)';
+
+
+	// Set up transform to map -1,-1..1,1 to canvas with aspect fit
+	const offsetX = W / 2;
+	const offsetY = H / 2;
+
+	//Apply transform
+	C.translate(offsetX, offsetY);
+	C.scale(scale, -scale);
+
+	// Set 1 pixel wide lines
+	C.lineWidth = 1 / scale;
+}
+
+
+setup();
+
+function hash(x, y, low, high) {
+	const seed = x * 374761393 ^ y * 668265263; // Large primes
+	let h = seed ^ (seed >> 3) ^ (seed >> 13) ^ (seed << 2);
+	h = (h * 1274126177) & 0xffffffff;
+	return (h >>> 0) % (high - low) + low;
+}
+
+
+const s = 0.2;
+for (let y = -3; y < 3; y++) {
+    const xo = y & 1 ? s * .5 : 0;
+	for (let x = -3; x < 3; x++) {
+		const p0 = [xo + (x + .5) * s, y * s];
+		const p1 = [xo + (x + 1.5) * s, y * s];
+		const p2 = [xo + (x + 1) * s, (y + 1) * s];
+		const p3 = [xo + (x + 0) * s, (y + 1) * s];
+
+		// Filled parallelogram
+		C.beginPath();
+		C.moveTo(...p0);
+		C.lineTo(...p1);
+		C.lineTo(...p2);
+		C.lineTo(...p3);
+		C.closePath();
+        const hue = hash(x, y, 0, 360);
+        const sat = hash(x, y, 20, 80);
+        const light = hash(x, y, 60, 90);
+		C.fillStyle = `hsl(${hue}, ${sat}%, ${light}%)`;
+		C.fill();
+
+		// Triangle lines
+		C.strokeStyle = 'black';
+		C.lineWidth = 1 / scale;
+
+		// Outline parallelogram
+		C.beginPath();
+		C.moveTo(...p0);
+		C.lineTo(...p1);
+		C.lineTo(...p2);
+		C.lineTo(...p3);
+		C.closePath();
+		C.stroke();
+
+		// Diagonal from p0 to p2
+		C.beginPath();
+		C.moveTo(...p0);
+		C.lineTo(...p2);
+		C.stroke();
+	}
+}
diff --git a/index.html b/index.html
index ac379f1..58fdd29 100644
--- a/index.html
+++ b/index.html
@@ -10,6 +10,7 @@
 			<ul>
 				<li><a href="canvas/test1.html">Default configuration</a></li>
 				<li><a href="canvas/test1.html?src=triangular-lattice.js">Triangular lattice</a></li>
+				<li><a href="canvas/test1.html?src=triangular-lattice-offset-corrected.js">Triangular lattice - corrected offset</a></li>
 			</ul>
 		</li>
 	</ul>