在下面的代码中，我在中心画了一个圆，但是因为它是缩放的，所以这个圆在右下角！var canvas = document.getElementById('mycanvas');context = canvas.getContext("2d");context.canvas.width = 400;context.canvas.height = 200;context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears the canvasvar scale = 2;context.scale(scale, scale);context.beginPath();context.fillStyle = "#ff2626"; // Red colorcontext.arc(context.canvas.width / 2, context.canvas.height / 2, 10, 0, Math.PI * 2); //centercontext.fill();context.closePath();canvas { border: solid 1px #ccc;}<HTML><body><canvas id="mycanvas"></canvas></body></HTML>您可能知道，画布的宽度和高度与在其中绘制的内容无关，尤其是在缩放时。换句话说，当您使用context.scale(scale_x, scale_y);它缩放画布时，它将缩放画布内的所有形状。我想知道，有没有办法获得画布像素范围？我想知道缩放画布时左边缘和右边缘的 X 以及顶部和底部边缘的 Y。
3 回答
RISEBY
TA贡献1856条经验 获得超5个赞
将坐标除以scale应该可以解决问题：
var canvas = document.getElementById('mycanvas');
context = canvas.getContext("2d");
context.canvas.width = 400;
context.canvas.height = 200;
context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears the canvas
var scale = 2;
context.scale(scale, scale);
context.beginPath();
context.fillStyle = "#ff2626"; // Red color
context.arc(context.canvas.width /2/scale, context.canvas.height / 2/scale, 10, 0, Math.PI * 2); //center
context.fill();
context.closePath();
canvas {
border: solid 1px #ccc;
}
<HTML>
<body>
<canvas id="mycanvas"></canvas>
</body>
</HTML>
顺便说一句，context.canvas.width /(2*scale)比 更干净context.canvas.width /2/scale，但我保持这样只是为了显示除以scale.
冉冉说
TA贡献1877条经验 获得超1个赞
你必须考虑你的比例所以 ex (width/2)/scale
var canvas = document.getElementById('mycanvas');
context = canvas.getContext("2d");
context.canvas.width = 400;
context.canvas.height = 200;
context.clearRect(context.canvas.width, context.canvas.height, context.canvas.width, context.canvas.height); // Clears the canvas
var scale = 2;
context.scale(scale, scale);
context.beginPath();
context.fillStyle = "#ff2626"; // Red color
context.arc((context.canvas.width/2)/scale , (context.canvas.height/2)/scale, 10, 0, Math.PI * 2); //center
context.fill();
context.closePath();
canvas {
border: solid 1px #ccc;
}
<HTML>
<body>
<canvas id="mycanvas"></canvas>
</body>
</HTML>
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