From bc6f5873f17ae10f42f87825ac64b136cfee3d72 Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Sun, 29 May 2022 17:11:48 -0500
Subject: add zooming and panning

---
 src/Canvas.js       | 95 +++++++++++++++++++++++++++++++++++++++++++++--------
 src/main.js         | 17 +++++++---
 src/modules/Util.js |  6 +++-
 3 files changed, 98 insertions(+), 20 deletions(-)

diff --git a/src/Canvas.js b/src/Canvas.js
index 590034a..bd39f47 100644
--- a/src/Canvas.js
+++ b/src/Canvas.js
@@ -1,46 +1,113 @@
+import { clamp } from './modules/Util.js';
+
 class Canvas {
 	constructor(rootId) {
 		const root = document.getElementById(rootId);
 
 		this.element = document.createElement('canvas');
 		this.context = this.element.getContext('2d');
-		this.fillWindow();
-		window.addEventListener('resize', () => this.fillWindow());
 
-		root.appendChild(this.element);
+		/* state variables */
+		this.scale = 1;
+		this.zoom = 1;
+		const ZOOM_SPEED = 1.2;
+		
+		this.mousePos = { x: 0, y: 0 };
+		this.pan = { x: 0, y: 0 };
+		this.panning = false;
 
-		this.ondraw = null;
+		/* callbacks */
+		this.onDraw = null;
+		this.onMouseMove = null;
 
-		/* automatically compute drawing-space mouse coordinates */
-		this.mousePos = { x: 0, y: 0 };
-		this.onmousemove = null;
+		/* register event listeners */
+
+		/* mouse movement */
 		this.element.addEventListener('mousemove', e => {
 			const matrix = this.context.getTransform();
 			matrix.invertSelf();
-
 			const screenX = e.offsetX; const screenY = e.offsetY;
-			this.mousePos.x = matrix.a*screenX + matrix.b*screenY;
-			this.mousePos.y = matrix.c*screenX + matrix.d*screenY;
 
-			if (this.onmousemove) this.onmousemove(this.mousePos);
+			/* compute drawing-space position */
+			const x = matrix.a*screenX + matrix.b*screenY + matrix.e;
+			const y = matrix.c*screenX + matrix.d*screenY + matrix.f;
+
+			/* compute movement */
+			const dx = e.movementX / (this.zoom * this.scale);
+			const dy = e.movementY / (this.zoom * this.scale);
+
+			/* pan? */
+			if (this.panning) {
+				this.pan.x += dx;
+				this.pan.y += dy;
+				this.setTransform();
+			}
+
+			this.mousePos.x = x;
+			this.mousePos.y = y;
+
+			if (this.onMouseMove) this.onMouseMove(this.mousePos);
 		});
 
+		/* clicking */
+		this.element.addEventListener('mousedown', e => {
+			if (e.button === 1) this.panning = true;
+		});
+		this.element.addEventListener('mouseup', e => {
+			if (e.button === 1) this.panning = false;
+		}); 
+
+		/* mouse leave */
+		this.element.addEventListener('mouseleave', e => {
+			this.panning = false;
+		});
+
+		/* mouse wheel */
+		this.element.addEventListener('wheel', e => {
+			if (this.panning) return; // don't zoom and pan simultaneously
+			const delta = e.deltaY < 0 ? ZOOM_SPEED : 1/ZOOM_SPEED;
+			this.zoom *= delta;
+			this.zoom = clamp(this.zoom, 1, Infinity);
+			this.setTransform();
+			this.draw();
+		});
+		
+		/* finalize setup */
+		this.fillWindow();
+		window.addEventListener('resize', () => this.fillWindow());
+		root.appendChild(this.element);
+	}
+
+	setTransform() {
+		/* clamp pan */
+		console.log('---');
+		console.log(this.pan);
+		const xMax = this.element.width / (this.zoom * this.scale) - 1;
+		const yMax = this.element.height / (this.zoom * this.scale) - 1;
+		this.pan.x = clamp(this.pan.x, xMax, 0);
+		this.pan.y = clamp(this.pan.y, yMax, 0);
+		console.log(xMax, yMax);
+		console.log(this.pan);
+
+		this.context.setTransform(1, 0, 0, 1, 0, 0);
+		this.context.scale(this.zoom * this.scale, this.zoom * this.scale);
+		this.context.translate(this.pan.x, this.pan.y);
 	}
 
 	fillWindow() {
 		const width = window.innerWidth;
 		const height = window.innerHeight;
-		const scale = Math.max(width, height);
+		this.scale = Math.max(width, height);
 
 		this.element.width = width; this.element.height = height;
-		this.context.scale(scale, scale);
+		this.setTransform();
 
 		this.draw();
 	}
 
 	draw() {
 		this.context.clearRect(0, 0, 1, 1);
-		if (this.ondraw) this.ondraw(this.context);
+		if (this.onDraw) this.onDraw(this.context);
 	}
 }
 
diff --git a/src/main.js b/src/main.js
index 40c3f83..5c9b085 100644
--- a/src/main.js
+++ b/src/main.js
@@ -6,15 +6,22 @@ window.onload = () => {
 	const canvas = new Canvas('root');
 
 	const pos = canvas.mousePos;
-	canvas.onmousemove = () => canvas.draw();
+	canvas.onMouseMove = () => canvas.draw();
 	
-	canvas.ondraw = ct => {
-		ct.fillRect(0, 0, 0.5, 0.5);
+	canvas.onDraw = ct => {
+		ct.fillStyle = '#f00';
+		ct.fillRect(0, 0, 1/3, 1/3);
+		ct.fillStyle = '#0f0';
+		ct.fillRect(2/3, 0, 1/3, 1/3);
+		ct.fillStyle = '#ff0';
+		ct.fillRect(0, 2/3, 1/3, 1/3);
+		ct.fillStyle = '#00f';
+		ct.fillRect(2/3, 2/3, 1/3, 1/3);
 
 		ct.strokeStyle = '#fff';
-		ct.lineWidth = 0.001;
+		ct.lineWidth = 1/(canvas.zoom * canvas.scale);
 		ct.beginPath();
-		ct.arc(pos.x, pos.y, 0.1, 0, 2*Math.PI);
+		ct.arc(pos.x, pos.y, 30 /(canvas.zoom * canvas.scale), 0, 2*Math.PI);
 		ct.closePath();
 		ct.stroke();
 	};
diff --git a/src/modules/Util.js b/src/modules/Util.js
index cbe466d..2375f10 100644
--- a/src/modules/Util.js
+++ b/src/modules/Util.js
@@ -10,4 +10,8 @@ function useAverage() {
 	return [() => avg, append];
 }
 
-export { useAverage };
+function clamp(value, min, max) {
+	return Math.min(Math.max(value, min), max);
+}
+
+export { useAverage, clamp };
-- 
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