純js畫點_如何利用 js+html 繪制帶箭頭的弧線

1. 用js能畫一個三維圓嗎

能，而且能根據三維渲染原理得出物體體積、光影、光源方向、材質貼圖、深景等等，只是純js實現的3D如果復雜點的場景速度並不理想。

2. 如何利用 js+html 繪制帶箭頭的弧線

純js不好實現,但是配合html,css就有了近似的辦法.下面提供一個解決方案,已知兩個點的坐標,為它們畫一條帶箭頭的弧線.

<html>

<head>

span { position: absolute; width: 5px; height: 5px; background-color: #0000ff; display: block; border-radius: 50%; }

</style>

function locateO () {

var x0 = parseInt (spnA.style.left, 10), y0 = parseInt (spnA.style.top, 10), x1 = parseInt (spnB.style.left, 10), y1 = parseInt (spnB.style.top, 10), horizontalDistance = Math.abs (x1 - x0), verticalDistance = Math.abs (y1 - y0), x = Math.min (x0, x1) + horizontalDistance / 2, y = Math.min (y0, y1) + verticalDistance / 2, distance = Math.sqrt (Math.pow (horizontalDistance, 2) + Math.pow (verticalDistance, 2)), array = new Array (x0, y0, x1, y1, distance);

spnO.style.left = x;

spnO.style.top = y;

return array;

}

function getRadian (x0, y0, x1, y1) {

var horizontalDistance = Math.abs (x1 - x0), verticalDistance = Math.abs (y1 - y0), rate = horizontalDistance == 0 ? 0 : verticalDistance / horizontalDistance, radian;

if (y1 < y0) {

if (x1 > x0) {

radian = - Math.atan (rate);

} else if (x1 == x0) {

radian = - Math.PI / 2;

} else {

radian = - (Math.PI - Math.atan (rate));

}

} else if (y1 == y0) {

radian = x1 > left ? 0 : - Math.PI;

} else if (x1 < x0) {

radian = - (Math.PI + Math.atan (rate));

} else if (x1 == x0) {

radian = - Math.PI * 3 / 2;

} else {

radian = - 2 * Math.PI + Math.atan (rate);

}

return radian;

}

function getAngle (radian) {

var angle = - radian * 180 / Math.PI;

return angle;

}

function slantArc (x0, y0, x1, y1) {

var radian = getRadian (x0, y0, x1, y1), angle = 360 - getAngle (radian);

cnvArc.style.transform = "rotate(" + angle + "deg)";

}

function drawArc (x0, y0, width) {

var context = cnvArc.getContext ("2d"), radius = width / 2, height = radius / 2;

cnvArc.width = width + 10;

cnvArc.height = height;

cnvArc.style.left = x0;

cnvArc.style.top = y0 - height;

context.ellipse (radius + 5, height, radius, height / 2, 0, 0, Math.PI * 2);

context.strokeStyle = "#00ff00";

context.stroke ();

}

function hex (figure) {

return figure.toString (16);

}

function zeroize (cluster) {

if (cluster.length < 2) {

cluster = 0 + cluster;

}

return cluster;

}

function getColour (red, green, blue) {

return "#" + zeroize (hex (red)) + zeroize (hex (green)) + zeroize (hex (blue));

}

function printArc () {

var width = cnvArc.width, height = cnvArc.height, context = cnvArc.getContext ("2d"), imageData = context.getImageData (0, 0, width, height), data = imageData.data, coordinates = new Array (), cluster = "", i, red, green, blue, colour, index, x, y;

for (i = 0; i < data.length; i += 4) {

red = data [i];

green = data [i + 1];

blue = data [i + 2];

colour = getColour (red, green, blue);

index = i / 4;

y = parseInt (index / width, 10);

x = index % width;

if (x == 0) {

//console.log (y + " " + cluster);

cluster = "";

}

cluster += x + ":" + colour + " ";

if (colour == "#00ff00") {

coordinates.push (new Array (x, y));

}

return coordinates;

}

function sortCoordinates (coordinates, direction) {

var i = 0, flag, j, coordinate;

do {

flag = false;

for (j = 0; j < coordinates.length - 1 - i; j ++) {

if (direction && (coordinates [j] [0] > coordinates [j + 1] [0] || coordinates [j] [0] == coordinates [j + 1] [0] && coordinates [j] [1] > coordinates [j + 1] [1]) || ! direction && (coordinates [j] [0] < coordinates [j + 1] [0] || coordinates [j] [0] == coordinates [j + 1] [0] && coordinates [j] [1] > coordinates [j + 1] [1])) {

coordinate = coordinates [j];

coordinates [j] = coordinates [j + 1];

coordinates [j + 1] = coordinate;

flag = true;

}

i ++;

} while (flag);

}

function drawArrow (x0, y0, x1, y1) {

var context = cnvArc.getContext ("2d"), colour = "#00ff00", angle = (x1 - x0) / (y1 - y0);

context.strokeStyle = colour;

context.fillStyle = colour;

context.setLineDash ([3, 3]);

context.beginPath ();

context.arc (x0, y0, 1, 0, 2 * Math.PI);

context.translate (0, 0, 0);

context.moveTo (x0, y0);

context.lineTo (x1, y1);

context.fill ();

context.stroke ();

context.save ();

context.translate (x1, y1);

angle = Math.atan (angle);

context.rotate ((y1 >= y0 ? 0 : Math.PI) - angle);

context.lineTo (- 3, - 9);

context.lineTo (0, - 3);

context.lineTo (3, - 9);

context.lineTo (0, 0);

context.fill ();

context.restore ();

context.closePath ();

}

function initialize () {

var array = locateO (), x0 = array [0], y0 = array [1], x1 = array [2], y1 = array [3], width = array [4], direction = x1 > x0, coordinates, length, coordinate0, coordinate1, x2, y2, x3, y3;

drawArc (x0, y0, width);

coordinates = printArc ();

length = coordinates.length;

sortCoordinates (coordinates, direction);

coordinate0 = coordinates [length - 2];

x2 = coordinate0 [0];

y2 = coordinate0 [1];

coordinate1 = coordinates [length - 1];

x3 = coordinate1 [0];

y3 = coordinate1 [1];

drawArrow (x2, y2, x3, y3);

slantArc (x0, y0, x1, y1);

}

</script>

</head>

</body>

</html>

復制進來的代碼都不帶縮進的嗎?

該代碼純手寫,不從第三方處盜用.僅供參考.

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