如何解决创建图像以向其绘制东西,然后在画布上绘制图像
大家好!
是否可以使用JavaScript创建图像,然后在其上渲染形状,然后将其绘制到游戏画布上?
在任何一个上都不使用dataurl,url或src!
var ctx = document.getElementById("canvas").getContext("2d");
var img = new Image();
// TODO: Draw stuff to the image img
function game() {
window.requestAnimationFrame(game);
ctx.clearRect(0,ctx.canvas.width,ctx.canvas.height);
ctx.drawImage(img,256,256);
}
window.requestAnimationFrame(game);
解决方法
CanvasRenderingContext2D.drawImage()
函数可以将多种类型的图像用作源,包括另一个Canvas。下面的示例显示在第一个画布中加载了图像。然后,您可以通过按住鼠标并移动它来画图。当您释放第二个画布时,将立即绘制第一个画布的图像。
所有的魔力都在最后一个功能上。
contextTwo.drawImage(canvasOne,256,256);
const canvasOne = document.getElementById('canvas1');
const canvasTwo = document.getElementById('canvas2');
const contextOne = canvasOne.getContext('2d');
const contextTwo = canvasTwo.getContext('2d');
canvasOne.width = 256;
canvasOne.height = 256;
canvasTwo.width = 256;
canvasTwo.height = 256;
const canvasBounds = canvasOne.getBoundingClientRect();
let mouseData = {
isClicked: false,position: [0,0],}
const onMouseDown = event => {
mouseData.isClicked = true;
render();
};
const onMouseMove = ({ clientX,clientY }) => {
const x = clientX - canvasBounds.left;
const y = clientY - canvasBounds.top;
mouseData.position = [x,y];
render();
};
const onMouseUp = event => {
mouseData.isClicked = false;
render();
moveImage();
};
function setup() {
const img = new Image();
img.src = '//picsum.photos/256/256'
img.onload = function() {
contextOne.drawImage(img,256);
}
canvasOne.addEventListener('mousedown',onMouseDown);
canvasOne.addEventListener('mousemove',onMouseMove);
canvasOne.addEventListener('mouseup',onMouseUp);
}
function render() {
requestAnimationFrame(() => {
const { isClicked,position } = mouseData;
const [ x,y ] = position;
if (isClicked) {
contextOne.beginPath();
contextOne.arc(x,y,5,Math.PI * 2)
contextOne.fillStyle = 'red'
contextOne.fill();
contextOne.closePath();
}
});
}
function moveImage() {
contextTwo.drawImage(canvasOne,256);
}
setup();
body {
display: flex;
}
canvas {
width: 256px;
height: 256px;
border: 1px solid #d0d0d0;
}
<canvas id="canvas1"></canvas>
<canvas id="canvas2"></canvas>
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