js canvas畫帶箭頭的虛線
<html lang="en"><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>HTML Canvas Dotted Lines</title>
<style type="text/css" media="screen">
body { background:#ddd; text-align:center; }
canvas { margin:2em auto; display:block; border:1px solid #666; }
label { padding-right:2em }
</style>
<script type="text/javascript" src="excanvas.js" ></script>
<script type="text/javascript" src="jCanvaScript.1.5.15.min.js" ></script>
</head>
<body>
<!--這個地方需要注意，在IE下面經過轉換如果不在這裏設置canvas的高和寬就會造成畫布很小-->
<canvas width="800" height="600"></canvas>
<p>
<label>Line Width: <input id="width" value="2" size="1"></label>
<label>Dashes/Gaps: <input id="dashes" value="10 20" size="15"></label>
<label>Line Cap: <select id="linecap"><option>butt</option><option selected>round</option><option>square</option></select></label>
</p>
<!--這個是老外寫的用canvas畫虛線的方法，直接使用-->
<script type="text/javascript" charset="utf-8">
if (window.CanvasRenderingContext2D && CanvasRenderingContext2D.prototype.lineTo){
CanvasRenderingContext2D.prototype.dashedLine = function(x,y,x2,y2,dashArray){
if (!dashArray) dashArray=[10,5];
var dashCount = dashArray.length;
this.moveTo(x, y);
var dx = (x2-x), dy = (y2-y);
var slope = dy/dx;
var distRemaining = Math.sqrt( dx*dx + dy*dy );
var dashIndex=0, draw=true;
while (distRemaining>=0.1 && dashIndex<10000){
var dashLength = dashArray[dashIndex++%dashCount];
if (dashLength==0) dashLength = 0.001; // Hack for Safari
if (dashLength > distRemaining) dashLength = distRemaining;
var xStep = Math.sqrt( dashLength*dashLength / (1 + slope*slope) );
x += xStep
y += slope*xStep;
this[draw ? 'lineTo' : 'moveTo'](x,y);
distRemaining -= dashLength;
draw = !draw;
}
// Ensure that the last segment is closed for proper stroking
//this.moveTo(0,0);
}
}
</script>
<script type="text/javascript" charset="utf-8">
var c = document.getElementsByTagName('canvas')[0];
c.width = 800; c.height = 600;
var defaultX = 350, defaultY = 350;
function drawArr(x, y){
//值初始化，default用於頁面沒有點擊的時候初始化。
var x, y, arr;
if(0 == arguments.length) {
x = 667;
y= 470;
}
else {
x = x;
y= y;
}
var ctx = c.getContext('2d');
ctx.strokeStyle = 'black';
//這3個是用來獲取頁面的自動設置配置。
var width = document.getElementById('width');
var linecap = document.getElementById('linecap');
var dashes = document.getElementById('dashes');
//這個是核心用來畫每個線段。
var drawDashes = function(){
ctx.clearRect( 0, 0, c.width, c.height );
var dashGapArray = dashes.value.replace(/^\s+|\s+$/g,'').split(/\s+/);
if (!dashGapArray[0] || (dashGapArray.length==1 && dashGapArray[0]==0)) return;
ctx.lineWidth = width.value;
ctx.lineCap = linecap.value;
ctx.beginPath();
ctx.fillStyle = "#8BC54B";
ctx.strokeStyle = 'rgb(0, 0, 100)'
//開始畫虛線。
//當 x > 起始點的x座標（即點擊點 在起始點的右邊）的時候 不需要 改變這4個座標，但是當x < 起始點的X座標（點擊點在起始點左邊的時候）需要改變這4個座標的位置
if(x > defaultX) {
ctx.dashedLine(defaultX, defaultY, x, y, dashGapArray );
}
else {
ctx.dashedLine(x, y, defaultX, defaultY, dashGapArray );
}
//虛線畫完了開始畫箭頭的4個線段
//計算4個點的座標
arr = jisuan(x, y);
//設定開始點。
ctx.moveTo(arr[0],arr[1]);
ctx.lineTo(x,y)
ctx.lineTo(arr[2],arr[3]);
//下面這個計算是用來在箭頭與虛線的交叉點。直角三角形計算原理。。
ctx.lineTo(x-parseInt(25*Math.cos(arr[4]*Math.PI/180)), y-parseInt(25*Math.sin(arr[4]*Math.PI/180)));
ctx.lineTo(arr[0],arr[1]);
ctx.closePath();
ctx.stroke();
};
drawDashes();
width.onkeyup = drawDashes;
linecap.onchange = drawDashes;
dashes.onkeyup = drawDashes;
}
//該函數用來根據鼠標點擊點 計算箭頭4個點的座標，在JS中cos和SIN都是計算的弧度，所以需要轉換。至於計算方法屬於屬性範疇這裏不累述。
//對於該函數，如果需要修改箭頭的大小 只需修改 45: 箭頭兩邊的長度； 35:箭頭與中間虛線的角度即可。
function jisuan(x, y) {
var angle = parseInt(Math.atan2(y-defaultX,x-defaultY)/Math.PI*180);
var arr = [];
arr[0] = x - parseInt(45 * Math.cos(Math.PI/180*(angle - 35)));
arr[1] = y - parseInt(45 * Math.sin(Math.PI/180*(angle - 35)));
arr[2] = x - parseInt(45 * Math.cos(Math.PI/180*(angle + 35)));
arr[3] = y - parseInt(45 * Math.sin(Math.PI/180*(angle + 35)));
arr[4] = angle
return arr;
}
drawArr();
document.body.onmousedown = function(event) {
var event = event || window.event;
var mousePos = getMousePos(event);
drawArr(mousePos.x, mousePos.y);
}
getMousePos = function(event) {
if (event.pageX || event.pageY) {
mousePos = {
x: event.pageX,
y: event.pageY
};
}
/*ie 與 ff的邊界 處理不同*/
if (!+"\v1") {
mousePos = {
x: event.clientX,
y: event.clientY
}
}
else {
mousePos = {
x:event.clientX+document.body.scrollLeft+document.documentElement.scrollLeft,
y:event.clientY+document.body.scrollTop+document.documentElement.scrollTop
}
}
//return mousePos
//程序到這裏就是一個標準獲取頁面上鼠標的座標函數，下面的代碼是因爲 畫布的點不是以瀏覽器的左上角爲起始點所以需要減去多餘的距離方法如下：
var pos = c.getBoundingClientRect();
mousePos.x = mousePos.x - pos.left;
mousePos.y = mousePos.y - pos.top;
return mousePos;
}
</script>
</body>
</html>
發表評論
所有評論
還沒有人評論，想成為第一個評論的人麼? 請在上方評論欄輸入並且點擊發布.
相關文章