From a6b3f313e32996fdb36aec9dbf349a338707d9a1 Mon Sep 17 00:00:00 2001
From: Brandon Dyck <brandon@dyck.us>
Date: Sun, 23 Oct 2022 12:36:16 -0600
Subject: [PATCH] Generate vertices for a cylinder

---
 panorama-viewer.js | 85 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/panorama-viewer.js b/panorama-viewer.js
index e48043e..2c676a9 100644
--- a/panorama-viewer.js
+++ b/panorama-viewer.js
@@ -1,5 +1,90 @@
 "use strict";
 (() => {
+	const makeCylinder = (meridians = 3, parallels = 3) => {
+		// The number of meridians dividing the sphere's surface.
+		// Two meridians would make an XZ plane.
+		if (meridians < 3) {
+			throw "meridians must be ≥ 3";
+		}
+
+		// The number of parallels, including the poles, dividing the sphere's surface.
+		// Two parallels would make a vertical line segment.
+		if (parallels < 3) {
+			throw "parallels must be ≥ 3";
+		}
+
+		const radius = 1;
+
+		const positions = new Float32Array(meridians * parallels * 3);
+		let positionsIdx = 0;
+		for (let p = 0; p < parallels; p++) {
+			const y = -radius + p * 2 * radius / parallels;
+			for (let m = 0; m < meridians; m++) {
+				const θ = 2 * Math.PI / meridians;
+				const x = Math.sin(θ) * radius;
+				const z = Math.cos(θ) * radius;
+
+				const currPosition = [
+					Math.sin(θ) * radius,
+					y,
+					Math.cos(θ) * radius,
+				];
+				for (const coord of currPosition) {
+					positions[positionsIdx++] = coord;
+				}
+			}
+		}
+
+		const indices = new Uint16Array(meridians * (parallels - 1) * 6);
+		const textureCoords = new Float32Array(meridians * (parallels - 1) * 12);
+		let indicesIdx = 0;
+		let textureCoordsIdx = 0;
+		for (let p = 0; p < parallels - 1; p++) {
+			for (let m = 0; m < meridians; m++) {
+				const lowerLeft = p * meridians + m;
+				const lowerRight = p * meridians + (m + 1) % meridians;
+				const upperLeft = (p + 1) * meridians + m;
+				const upperRight = (p + 1) * meridians + (m + 1) % meridians;
+				const currIndices = [
+					// Lower triangle
+					lowerLeft, lowerRight, upperRight,
+
+					// Upper triangle
+					lowerLeft, upperRight, upperLeft,
+				];
+				for (const index of currIndices) {
+					indices[indicesIdx++] = index;
+				}
+
+				const currTextureCoords = [
+					// Lower triangle
+					m / meridians, p / parallels,
+					(m + 1) / meridians, p / parallels,
+					(m + 1) / meridians, (p + 1) / parallels,
+
+					// Upper triangle
+					m / meridians, p / parallels,
+					(m + 1) / meridians, (p + 1) / parallels,
+					m / meridians, (p + 1) / parallels,
+				];
+				for (const coord of currTextureCoords) {
+					textureCoords[textureCoordsIdx++] = coord;
+				}
+			}
+		}
+
+		for (let p = 0; p < parallels; p++) {
+			for (let m = 0; m < meridians; m++) {
+				/*
+				
+				*/
+			}
+		}
+
+		return { positions, textureCoords, indices };
+	}
+	console.log(makeCylinder());
+
 	const initShaderProgram = (gl) => {
 		const vShaderSrc = `
 			attribute vec3 position;