我的html页面中有9个圆圈。每个圆圈都必须用一定的百分比填充某些颜色。我使用html5画布元素绘制了圆圈。但我只能用颜色填充整个圆圈而不是某些优点area.How我可以实现吗?
Use composite mode:
destination-out
The main code would be:
var o = radius * 2, // diameter => width and height of rect
h = o - (o * percent / 100); // height based on percentage
ctx.beginPath();
ctx.arc(x, y, radius, 0, 6.28);
ctx.fill();
ctx.globalCompositeOperation = "destination-out";
ctx.fillRect(x - radius, y - radius, o, h); // this will remove a part of the top
var ctx = document.querySelector("canvas").getContext("2d"), pst = 0, dlt = 2; ctx.fillStyle = "#28f"; function drawCircle(ctx, x, y, radius, percent) { var o = radius * 2, h = o - (o * percent / 100); ctx.globalCompositeOperation = "source-over"; // make sure we have default mode ctx.beginPath(); // fill an arc ctx.arc(x, y, radius, 0, 6.28); ctx.fill(); ctx.globalCompositeOperation = "destination-out"; // mode to use for next op. ctx.fillRect(x - radius, y - radius, o, h); // "clear" part of arc ctx.globalCompositeOperation = "source-over"; // be polite, set default mode back } (function loop() { ctx.clearRect(0,0,300,150); drawCircle(ctx, 70, 70, 60, pst); pst += dlt; if (pst <= 0 || pst >= 100) dlt = -dlt; requestAnimationFrame(loop); })();
<canvas></canvas>
(tip: closePath()
is really not necessary with fill()
as fill()
will close the path implicit, but it's needed if you want to do a stroke()
instead).
The essential part being:
ctx.beginPath();
ctx.moveTo(x, y);
ctx.arc(x, y, radius, 0, 2 * Math.PI * percent / 100);
//ctx.closePath(); // for stroke, not needed for fill
ctx.fill();
var ctx = document.querySelector("canvas").getContext("2d"), pst = 0, dlt = 2; ctx.fillStyle = "#28f"; function drawPie(ctx, x, y, radius, percent) { ctx.beginPath(); ctx.moveTo(x, y); ctx.arc(x, y, radius, 0, 2 * Math.PI * percent /100); ctx.fill(); } (function loop() { ctx.clearRect(0,0,300,150); drawPie(ctx, 70, 70, 60, pst); pst += dlt; if (pst <= 0 || pst >= 100) dlt = -dlt; requestAnimationFrame(loop); })();
<canvas></canvas>
Almost same as with pie type, but with these changes:
lineWidth
, see demo below) Essential part:
ctx.beginPath();
ctx.moveTo(x + radius, y); // cos(0) for x = 1, so just use radius, sin(0) = 0
ctx.arc(x, y, radius, 0, 2 * Math.PI * percent /100);
ctx.stroke();
You can adjust gap point using rotation transform or calculating the actual point using trigonometry.
var ctx = document.querySelector("canvas").getContext("2d"), pst = 0, dlt = 2; ctx.strokeStyle = "#28f"; ctx.lineWidth = 8; function drawWedge(ctx, x, y, radius, percent) { ctx.beginPath(); ctx.moveTo(x + radius, y); ctx.arc(x, y, radius, 0, 2 * Math.PI * percent /100); ctx.stroke(); } (function loop() { ctx.clearRect(0,0,300,150); drawWedge(ctx, 70, 70, 60, pst); pst += dlt; if (pst <= 0 || pst >= 100) dlt = -dlt; requestAnimationFrame(loop); })();
<canvas></canvas>
You can change the starting point for the arc using rotation transform or calculating the point manually using trigonometry.
To calculate these manually you can do (angles in radians):
x = radius * Math.cos(angleInRad); // end point for x
y = radius * Math.sin(angleInRad); // end point for y
Just add the total angle to the start angle to get end point.
360° in radians = 2 x PI, so if you want to use angles in degrees, convert them using:
angleInRad = angleInDeg * Math.PI / 180;
var ctx = document.querySelector("canvas").getContext("2d"), pst = 0, dlt = 2; ctx.strokeStyle = "#28f"; ctx.lineWidth = 8; function drawWedge(ctx, x, y, radius, percent) { ctx.translate(x, y); // translate to rotating pivot ctx.rotate(Math.PI * 0.5); // rotate, here 90° deg ctx.translate(-x, -y); // translate back ctx.beginPath(); ctx.moveTo(x + radius, y); ctx.arc(x, y, radius, 0, 2 * Math.PI * percent /100); ctx.stroke(); ctx.setTransform(1,0,0,1,0,0); // reset transform } (function loop() { ctx.clearRect(0,0,300,150); drawWedge(ctx, 70, 70, 60, pst); pst += dlt; if (pst <= 0 || pst >= 100) dlt = -dlt; requestAnimationFrame(loop); })();
<canvas></canvas>
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