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Utility functions for handling geometrically correct panning and zooming of a canvas
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| class Viewport { | |
| constructor(canvas) { | |
| this.canvas = canvas; | |
| this.camera = { | |
| x: 0, | |
| y: 0, | |
| z: 1, | |
| }; | |
| this.pivot = null; | |
| } | |
| startPan(screenPoint) { | |
| this.pivot = { | |
| x: this.camera.x + (screenPoint.x - this.canvas.width / 2) * this.camera.z, | |
| y: this.camera.y + (screenPoint.y - this.canvas.height / 2) * this.camera.z, | |
| }; | |
| } | |
| pan(screenPoint) { | |
| if (this.pivot) { | |
| this.camera.x = this.pivot.x - (screenPoint.x - this.canvas.width / 2) * this.camera.z; | |
| this.camera.y = this.pivot.y - (screenPoint.y - this.canvas.height / 2) * this.camera.z; | |
| } | |
| } | |
| endPan() { | |
| this.pivot = null; | |
| } | |
| zoom(screenPivotPoint, factor) { | |
| const difference = this.camera.z * (1 - factor); | |
| this.camera.x += (screenPivotPoint.x - this.canvas.width / 2) * difference; | |
| this.camera.y += (screenPivotPoint.y - this.canvas.height / 2) * difference; | |
| this.camera.z *= factor; | |
| } | |
| projectToCanvas(screenPoint) { | |
| return { | |
| x: (screenPoint.x - this.canvas.width / 2) * this.camera.z + this.camera.x, | |
| y: (screenPoint.y - this.canvas.height / 2) * this.camera.z + this.camera.y, | |
| }; | |
| } | |
| projectToScreen(canvasPoint) { | |
| return { | |
| x: this.canvas.width / 2 + (canvasPoint.x - this.camera.x) / this.camera.z, | |
| y: this.canvas.height / 2 + (canvasPoint.y - this.camera.y) / this.camera.z, | |
| }; | |
| } | |
| scaleToCanvas(screenScalar) { | |
| return screenScalar * this.camera.z; | |
| } | |
| scaleToScreen(canvasScalar) { | |
| return canvasScalar / this.camera.z; | |
| } | |
| } | |
| const canvas = document.getElementsByTagName('canvas')[0]; | |
| const viewport = new Viewport(canvas); | |
| const ctx = canvas.getContext('2d'); | |
| function resize() { | |
| canvas.width = window.innerWidth; | |
| canvas.height = window.innerHeight; | |
| } | |
| window.addEventListener('resize', resize); | |
| resize(); | |
| window.addEventListener('mousedown', e => { | |
| viewport.startPan({x: e.x, y: e.y}); | |
| }); | |
| window.addEventListener('mousemove', e => { | |
| viewport.pan({x: e.x, y: e.y}); | |
| }); | |
| window.addEventListener('mouseup', e => { | |
| viewport.endPan(); | |
| }); | |
| window.addEventListener("wheel", e => { | |
| const factor = e.deltaY < 0 ? 0.9 : (1 / 0.9); | |
| viewport.zoom({x: e.x, y: e.y}, factor); | |
| }); | |
| function animate() { | |
| ctx.clearRect(0, 0, canvas.width, canvas.height); | |
| // draw a grid of points | |
| for (let y = -2; y <= 2; y++) { | |
| for (let x = -2; x <= 2; x++) { | |
| ctx.beginPath(); | |
| const point = viewport.projectToScreen({x: x * 100, y: y * 100}); | |
| const radius = 10; | |
| ctx.arc(point.x, point.y, viewport.scaleToScreen(radius), 0, Math.PI * 2, false); | |
| ctx.fill(); | |
| } | |
| } | |
| requestAnimationFrame(animate); | |
| } | |
| animate(); |
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