[英]creating gradient/rainbow strokeStyle html5 canvas
我在玩HTML5畫布很開心。 到目前為止,我有這個很酷的繪圖應用程序,我希望筆觸樣式為不同顏色的漸變。 我將如何去做? 這是我到目前為止所擁有的。 http://jsfiddle.net/claireC/4kt38/
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
//puts a circle where the user clicks the mouse
var radius = 10,
dragging = false;
context.lineWidth = radius*2;
var putPoint = function(e){
if(dragging){
context.lineTo(e.clientX, e.clientY);
context.stroke();
context.beginPath();
context.arc(e.clientX, e.clientY, radius, 0, Math.PI*2);
context.fill();
context.beginPath();
context.moveTo(e.clientX, e.clientY);
}
};
var engage = function(e){
dragging = true;
putPoint(e);
};
var disengage = function(){
dragging = false;
context.beginPath();
};
canvas.addEventListener('mousedown', engage);
canvas.addEventListener('mousemove', putPoint);
canvas.addEventListener('mouseup', disengage);
嘗試添加context.fillStyle = grad;
后:
var grad= context.createLinearGradient(50, 50, 150, 150);
grad.addColorStop(0, "red");
grad.addColorStop(1, "green");
context.fillStyle = grad;
我對這樣的快速努力並不滿意,但是這是嘗試彩虹漸變筆畫的開始。
此代碼僅捕獲拖動鼠標的位置和沿拖動的筆觸。
對該代碼的改進將是簡化路徑,而不是抓住每個鼠標移動。
它通過繪制大量垂直於所需路徑的線性漸變線來工作。 愚弄人以為它看到了漸變筆畫。
示例代碼和演示: http : //jsfiddle.net/m1erickson/36F4T/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var $canvas=$("#canvas");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var scrollX=$canvas.scrollLeft();
var scrollY=$canvas.scrollTop();
var PI=Math.PI;
var points=[];
var isDown=false;
var linewidth=15;
var steps=50;
var lastPointX,lastPointY;
ctx.lineWidth=linewidth;
function addPoint(x,y){
var dx=x-lastPointX;
var dy=y-lastPointY;
var angle=Math.atan2(dy,dx)-PI/2;
ctx.strokeStyle=calcGradient(x,y,angle);
ctx.beginPath();
ctx.moveTo(lastPointX,lastPointY);
for(var i=-8;i<steps;i++){
var xx=lastPointX+dx*i/(steps-1);
var yy=lastPointY+dy*i/(steps-1);
ctx.lineTo(xx,yy);
}
ctx.stroke();
lastPointX=x;
lastPointY=y;
}
function calcGradient(x,y,angle){
// calc the topside and bottomside points of the tangent line
var offX1=x+linewidth/2.25*Math.cos(angle);
var offY1=y+linewidth/2.25*Math.sin(angle);
var offX2=x+linewidth/2.25*Math.cos(angle-PI);
var offY2=y+linewidth/2.25*Math.sin(angle-PI);
// create a gradient stretching between
// the calculated top & bottom points
var gradient=ctx.createLinearGradient(offX1,offY1,offX2,offY2);
gradient.addColorStop(0.00, 'red');
gradient.addColorStop(1/6, 'orange');
gradient.addColorStop(2/6, 'yellow');
gradient.addColorStop(3/6, 'green')
gradient.addColorStop(4/6, 'aqua');
gradient.addColorStop(5/6, 'blue');
gradient.addColorStop(1.00, 'purple');
return(gradient);
}
function handleMouseDown(e){
e.preventDefault();
e.stopPropagation();
lastPointX=parseInt(e.clientX-offsetX);
lastPointY=parseInt(e.clientY-offsetY);
isDown=true;
}
function handleMouseUp(e){
e.preventDefault();
e.stopPropagation();
isDown=false;
}
function handleMouseMove(e){
if(!isDown){return;}
e.preventDefault();
e.stopPropagation();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
addPoint(mouseX,mouseY);
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseUp(e);});
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
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