有没有简单的方法可以在画布(JavaScript)中放大和缩小?基本上我有一个 400x400px 的画布,我希望能够使用“mousedown”(2x)放大并使用“mouseup”返回。
过去两天用谷歌搜索,但到目前为止还没有运气。 :(
基于使用drawImage的建议,您还可以将其与缩放功能结合起来。
因此,在绘制图像之前,请将上下文缩放到您想要的缩放级别:
ctx.scale(2, 2) // Doubles size of anything draw to canvas.
我在这里创建了一个小示例http://jsfiddle.net/mBzVR/4/,它使用drawImage和scale在mousedown时放大,在mouseup时缩小。
试试这个:
<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.js"></script>
<style>
body {
margin: 0px;
padding: 0px;
}
#wrapper {
position: relative;
border: 1px solid #9C9898;
width: 578px;
height: 200px;
}
#buttonWrapper {
position: absolute;
width: 30px;
top: 2px;
right: 2px;
}
input[type="button"] {
padding: 5px;
width: 30px;
margin: 0px 0px 2px 0px;
}
</style>
<script>
function draw(scale, translatePos) {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
// clear canvas
context.clearRect(0, 0, canvas.width, canvas.height);
context.save();
context.translate(translatePos.x, translatePos.y);
context.scale(scale, scale);
context.beginPath(); // begin custom shape
context.moveTo(-119, -20);
context.bezierCurveTo(-159, 0, -159, 50, -59, 50);
context.bezierCurveTo(-39, 80, 31, 80, 51, 50);
context.bezierCurveTo(131, 50, 131, 20, 101, 0);
context.bezierCurveTo(141, -60, 81, -70, 51, -50);
context.bezierCurveTo(31, -95, -39, -80, -39, -50);
context.bezierCurveTo(-89, -95, -139, -80, -119, -20);
context.closePath(); // complete custom shape
var grd = context.createLinearGradient(-59, -100, 81, 100);
grd.addColorStop(0, "#8ED6FF"); // light blue
grd.addColorStop(1, "#004CB3"); // dark blue
context.fillStyle = grd;
context.fill();
context.lineWidth = 5;
context.strokeStyle = "#0000ff";
context.stroke();
context.restore();
}
window.onload = function() {
var canvas = document.getElementById("myCanvas");
var translatePos = {
x: canvas.width / 2,
y: canvas.height / 2
};
var scale = 1.0;
var scaleMultiplier = 0.8;
var startDragOffset = {};
var mouseDown = false;
// add button event listeners
document.getElementById("plus").addEventListener("click", function() {
scale /= scaleMultiplier;
draw(scale, translatePos);
}, false);
document.getElementById("minus").addEventListener("click", function() {
scale *= scaleMultiplier;
draw(scale, translatePos);
}, false);
// add event listeners to handle screen drag
canvas.addEventListener("mousedown", function(evt) {
mouseDown = true;
startDragOffset.x = evt.clientX - translatePos.x;
startDragOffset.y = evt.clientY - translatePos.y;
});
canvas.addEventListener("mouseup", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mouseover", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mouseout", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mousemove", function(evt) {
if (mouseDown) {
translatePos.x = evt.clientX - startDragOffset.x;
translatePos.y = evt.clientY - startDragOffset.y;
draw(scale, translatePos);
}
});
draw(scale, translatePos);
};
jQuery(document).ready(function() {
$("#wrapper").mouseover(function(e) {
$('#status').html(e.pageX + ', ' + e.pageY);
});
})
</script>
</head>
<body onmousedown="return false;">
<div id="wrapper">
<canvas id="myCanvas" width="578" height="200">
</canvas>
<div id="buttonWrapper">
<input type="button" id="plus" value="+"><input type="button" id="minus" value="-">
</div>
</div>
<h2 id="status">
0, 0
</h2>
</body>
</html>
这对我来说非常适合缩放和鼠标移动。您可以自定义它以使用鼠标滚轮向上和向下。
如果您有源图像或画布元素以及想要绘制的 400x400 画布,则可以使用 drawImage 方法来实现缩放。
例如,完整视图可能是这样的
ctx.drawImage(img, 0, 0, img.width, img.height, 0, 0, canvas.width, canvas.height);
缩放视图可能是这样的
ctx.drawImage(img, img.width / 4, img.height / 4, img.width / 2, img.height / 2, 0, 0, canvas.width, canvas.height);
drawImage 的第一个参数是要绘制的图像元素或画布元素,接下来的 4 个参数是从源中采样的 x、y、宽度和高度,最后 4 个参数是区域的 x、y、宽度和高度在画布上绘制。然后它会为您处理缩放。
您只需要根据缩放级别选择源样本的宽度和高度,并根据单击鼠标的位置减去计算的宽度和高度的一半来选择x和y(但您需要确保矩形是“ t 出界)。
画布缩放和平移
var ox = 0,
oy = 0,
px = 0,
py = 0,
scx = 1,
scy = 1;
var canvas = document.getElementById("myCanvas");
canvas.onmousedown = (e) => {
px = e.x;
py = e.y;
canvas.onmousemove = (e) => {
ox -= e.x - px;
oy -= e.y - py;
px = e.x;
py = e.y;
};
};
canvas.onmouseup = () => {
canvas.onmousemove = null;
};
canvas.onwheel = (e) => {
let bfzx, bfzy, afzx, afzy;
[bfzx, bfzy] = StoW(e.x, e.y);
scx -= (10 * scx) / e.deltaY;
scy -= (10 * scy) / e.deltaY;
[afzx, afzy] = StoW(e.x, e.y);
ox += bfzx - afzx;
oy += bfzy - afzy;
};
var ctx = canvas.getContext("2d");
function draw() {
window.requestAnimationFrame(draw);
ctx.clearRect(0, 0, canvas.width, canvas.height);
for (let i = 0; i <= 100; i += 10) {
let sx = 0,
sy = i;
let ex = 100,
ey = i;
[sx, sy] = WtoS(sx, sy);
[ex, ey] = WtoS(ex, ey);
ctx.beginPath();
ctx.moveTo(sx, sy);
ctx.lineTo(ex, ey);
ctx.stroke();
}
for (let i = 0; i <= 100; i += 10) {
let sx = i,
sy = 0;
let ex = i,
ey = 100;
[sx, sy] = WtoS(sx, sy);
[ex, ey] = WtoS(ex, ey);
ctx.beginPath();
ctx.moveTo(sx, sy);
ctx.lineTo(ex, ey);
ctx.stroke();
}
}
draw();
function WtoS(wx, wy) {
let sx = (wx - ox) * scx;
let sy = (wy - oy) * scy;
return [sx, sy];
}
function StoW(sx, sy) {
let wx = sx / scx + ox;
let wy = sy / scy + oy;
return [wx, wy];
}
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="" height="" style="border: 1px solid #d3d3d3">
Your browser does not support the canvas element.
</canvas>
</body>
</html>
IIRC Canvas 是一种光栅风格的位图。它无法缩放,因为没有存储的信息可供缩放。
您最好的选择是在内存中保留两个副本(缩放和非缩放)并在鼠标单击时交换它们。
这是我的缩放功能:
Zoom(factor_x, factor_y, graph = this.graph, translate_x=this.ctx.canvas.width/2,translate_y=this.ctx.canvas.height/2){
const new_scale_x = this.scale_x * factor_x
const new_scale_y = this.scale_y * factor_y
// Update values
this.translate_x += translate_x * ((this.scale_x - new_scale_x))
this.translate_y += translate_y * ((this.scale_y - new_scale_y))
this.scale_x = new_scale_x
this.scale_y = new_scale_y
this.ctx.setTransform(this.scale_x, 0, 0, this.scale_y, this.translate_x, this.translate_y) // Transform
DrawGraph(graph)
},
例如,缩放系数可以是 1,3,缩小系数可以是 0,7
一种选择是使用 css 缩放功能:
$("#canvas_id").css("zoom","x%");