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February 20, 2022 22:23
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Boilerplate for canvas with zoom and panning with minimal code
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| <html> | |
| <head> | |
| <title>Visualizer boilerplate</title> | |
| </head> | |
| <body> | |
| <style> | |
| body { | |
| background-color: #303030; | |
| margin: 0; | |
| padding: 0; | |
| overflow: hidden; | |
| } | |
| </style> | |
| <canvas></canvas> | |
| <script> | |
| const canvas = document.querySelector('canvas'); | |
| const ctx = canvas.getContext('2d'); | |
| function draw(){ | |
| ctx.fillStyle = "#ff00ff"; | |
| ctx.fillRect(50,50,100,100); | |
| } | |
| function onClick(x, y, button) { | |
| console.log("onClick", x, y, button); | |
| } | |
| </script> | |
| <script> | |
| let dirty = true; | |
| let scale = 1; | |
| let pos = { x: 0, y: 0 }; | |
| let panning = false; | |
| function pan(amount) { | |
| if(amount.x !== 0 || amount.y !== 0) { | |
| panning = true; | |
| dirty = true; | |
| pos.x += amount.x; | |
| pos.y += amount.y; | |
| } | |
| } | |
| function scaleAt(at, amount) { | |
| scale *= amount; | |
| pos.x = at.x - (at.x - pos.x) * amount; | |
| pos.y = at.y - (at.y - pos.y) * amount; | |
| dirty = true; | |
| } | |
| function drawCanvas() { | |
| requestAnimationFrame(drawCanvas); | |
| if (dirty) { | |
| dirty = false; | |
| canvas.width = window.innerWidth; | |
| canvas.height = window.innerHeight; | |
| ctx.setTransform(1, 0, 0, 1, 0, 0); | |
| ctx.clearRect(0, 0, canvas.width, canvas.height); | |
| ctx.setTransform( | |
| scale, 0, | |
| 0, scale, | |
| pos.x, pos.y | |
| ); | |
| draw(); | |
| } | |
| } | |
| window.onresize = () => dirty = true; | |
| canvas.oncontextmenu = e => e.preventDefault(); | |
| canvas.addEventListener("mousemove", mouseEvent); | |
| canvas.addEventListener("mousedown", mouseEvent); | |
| canvas.addEventListener("mouseup", mouseEvent); | |
| canvas.addEventListener("mouseout", mouseEvent); | |
| canvas.addEventListener("wheel", mouseWheelEvent, { passive: false }); | |
| const mouse = { x: 0, y: 0, oldX: 0, oldY: 0, button: false }; | |
| function mouseEvent(event) { | |
| if (event.type === "mousedown") { | |
| mouse.button = true; | |
| panning = false; | |
| } | |
| if (event.type === "mouseup" || event.type === "mouseout") { | |
| if(mouse.button && panning == false) { | |
| const invScale = (1/scale); | |
| onClick( | |
| Math.ceil((mouse.x - pos.x) * invScale), | |
| Math.ceil((mouse.y - pos.y) * invScale), | |
| event.button | |
| ); | |
| } | |
| mouse.button = false; | |
| } | |
| mouse.oldX = mouse.x; | |
| mouse.oldY = mouse.y; | |
| mouse.x = event.offsetX; | |
| mouse.y = event.offsetY; | |
| if(mouse.button) pan({ x: mouse.x - mouse.oldX, y: mouse.y - mouse.oldY }); | |
| } | |
| function mouseWheelEvent(event) { | |
| var x = event.offsetX; | |
| var y = event.offsetY; | |
| if (event.deltaY < 0) { scaleAt({x, y}, 1.1) } | |
| else { scaleAt({x, y}, 1 / 1.1) } | |
| event.preventDefault(); | |
| } | |
| requestAnimationFrame(drawCanvas); | |
| </script> | |
| </body> | |
| </html> |
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