Question

我有一个画布，我已经创建了两个圆圈。我面临的问题是两个箭头都依赖于另一个如果我将对内圈箭头的程度进行更改，那么外部箭头也会从他们的位置旋转。我只想要两个圆圈和它们相互独立的相应箭头。

<!DOCTYPE html>
<html>
<head>
<style>
    body{
        background: #666;
    }
    #canvas1{
        background: blue;
    }
</style>
<script>
function start(){
    start1();
    start2();
}



function start1() {   // inner circle
    var ctx = document.getElementById("canvas1").getContext("2d");

    var cx = 200;
    var cy = 200;
    var radius = 100;

    ctx.beginPath();  // inner circle creation
    ctx.arc(cx, cy, radius, 0, Math.PI * 2);
    ctx.stroke();

        var e = xy1(cx, cy, radius, 0 *(Math.PI/180));  //
        ctx.fillStyle = "#000000"
        ctx.translate(cx,cy);
        ctx.rotate(0 * (Math.PI/180));  // for arrow rotation
        ctx.translate(-cx,-cy);
        ctx.save();
        ctx.beginPath();  // generate inner arrow
        ctx.moveTo(e.x,e.y);
        ctx.lineTo(e.x + 0 ,e.y + 10);
        ctx.lineTo(e.x + 60 ,e.y + 10);
        ctx.lineTo(e.x + 60 ,e.y + 20);
        ctx.lineTo(e.x + 75 ,e.y + 0);
        ctx.lineTo(e.x + 60 ,e.y - 20);
        ctx.lineTo(e.x + 60 ,e.y - 10);
        ctx.lineTo(e.x + 0 ,e.y - 10);
        ctx.closePath();
        ctx.fill();
        ctx.restore();



}


function start2(){   // outer circle
    var ctx1 = document.getElementById("canvas1").getContext("2d");

    var cx2 = 200;
    var cy2 = 200;
    var radius2 = 120;

    ctx1.beginPath(); // outer circle creation
    ctx1.arc(cx2, cy2, radius2, 0, Math.PI * 2);
    ctx1.stroke();


        var f = xy2(cx2, cy2, radius2, 0 *(Math.PI/180));
        ctx1.fillStyle = "#000000"
        ctx1.translate(cx2,cy2);
        ctx1.rotate(90 * (Math.PI/180)); // for arrow rotation
        ctx1.translate(-cx2,-cy2);
        ctx1.save();
        ctx1.beginPath(); // generate arrow
        ctx1.moveTo(f.x2,f.y);
        ctx1.lineTo(f.x2 + 0 ,f.y2 + 10);
        ctx1.lineTo(f.x2 + 60 ,f.y2 + 10);
        ctx1.lineTo(f.x2 + 60 ,f.y2 + 20);
        ctx1.lineTo(f.x2 + 75 ,f.y2 + 0);
        ctx1.lineTo(f.x2 + 60 ,f.y2 - 20);
        ctx1.lineTo(f.x2 + 60 ,f.y2 - 10);
        ctx1.lineTo(f.x2 + 0 ,f.y2 - 10);
        ctx1.closePath();
        ctx1.stroke();
        ctx1.restore();
}
function xy1(cx, cy, radius, radianAngle) {  // for inner circle
        var x = cx + radius * Math.cos(radianAngle);
        var y = cy + radius * Math.sin(radianAngle);
        return ({
            x: x,
            y: y
        });
    }
function xy2(cx2, cy2, radius2, radianAngle2) { // for outer circle
        var x2 = cx2 + radius2 * Math.cos(radianAngle2);
        var y2 = cy2 + radius2 * Math.sin(radianAngle2);
        return ({
            x2: x2,
            y2: y2
        });
    }

window.onload=start;
</script>


</head>

<body>
  <canvas id="canvas1" width=400 height=400></canvas>

</body>

</html>

Answer 1

您只是在旋转之前不保存上下文。在应用任何转换之前已经保存。

    ctx1.save();    //save first
    ctx1.translate(cx2,cy2);
    ctx1.rotate(90 * (Math.PI/180)); // for arrow rotation
    ctx1.translate(-cx2,-cy2);

    ctx1.beginPath(); // generate arrow
    ctx1.moveTo(f.x2,f.y);
    ctx1.lineTo(f.x2 + 0 ,f.y2 + 10);
    ctx1.lineTo(f.x2 + 60 ,f.y2 + 10);
    ctx1.lineTo(f.x2 + 60 ,f.y2 + 20);
    ctx1.lineTo(f.x2 + 75 ,f.y2 + 0);
    ctx1.lineTo(f.x2 + 60 ,f.y2 - 20);
    ctx1.lineTo(f.x2 + 60 ,f.y2 - 10);
    ctx1.lineTo(f.x2 + 0 ,f.y2 - 10);
    ctx1.closePath();
    ctx1.stroke();
    ctx1.restore();     //and restore in the end (as you already did)

无法使用画布在特定角度围绕圆圈旋转箭头

1 个答案: