我有一个包含图像的大画布,如下例所示:
我有红色矩形的位置和旋转角度:
red : {
top : top,
left : left,
width : width,
height : height,
angle : angle
}
我还有一整套平移坐标,表示红色旋转矩形的实际角点。
最后,我将蓝色矩形相对的位置设置为红色矩形:
blue : {
left : left,
top: top,
width : width,
height : height
}
我需要做的是创建一个新的画布,蓝色矩形的大小,包含蓝色矩形中包含的图像的正确旋转部分在这样的图像中:
我在使用HTML5画布的javascript中这样做。我遇到的问题是在旋转矩形时获得正确的图像部分。
任何肝脏都会受到高度赞赏
编辑:这是我到目前为止所做的: var c = getCenterPoint(); // returns center x/y positions of the RED rectangle
canvas.width = blue.width;
canvas.height = blue.height;
var blueX = red.left + blue.left;
var blueY = red.top + blue.top;
var tx = blueX - c.x;
var ty = blueY - c.y;
this.cursorContext.translate(tx, ty);
this.cursorContext.rotate(angle * (Math.PI / 180));
this.cursorContext.translate(-tx, -ty);
this.cursorContext.drawImage(image, -blueX, -blueY, blue.width, blue.height);
答案 0 :(得分:6)
您可以使用临时画布剪辑和取消旋转蓝框
从图像中剪切蓝色矩形的边界框
取消旋转边界框,使蓝色矩形不旋转(角度== 0)
剪掉额外的边界框区域,仅显示蓝色矩形
将蓝色矩形绘制到显示画布
这是代码和演示:http://jsfiddle.net/m1erickson/28EkG/
<!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");
// blue rect's info
var blueX=421;
var blueY=343;
var blueWidth=81;
var blueHeight=44;
var blueAngle=-25.00*Math.PI/180;
// load the image
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/temp6.jpg";
function start(){
// create 2 temporary canvases
var canvas1=document.createElement("canvas");
var ctx1=canvas1.getContext("2d");
var canvas2=document.createElement("canvas");
var ctx2=canvas2.getContext("2d");
// get the boundingbox of the rotated blue box
var rectBB=getRotatedRectBB(blueX,blueY,blueWidth,blueHeight,blueAngle);
// clip the boundingbox of the rotated blue rect
// to a temporary canvas
canvas1.width=canvas2.width=rectBB.width;
canvas1.height=canvas2.height=rectBB.height;
ctx1.drawImage(img,
rectBB.cx-rectBB.width/2,
rectBB.cy-rectBB.height/2,
rectBB.width,
rectBB.height,
0,0,rectBB.width,rectBB.height
);
// unrotate the blue rect on the temporary canvas
ctx2.translate(canvas1.width/2,canvas1.height/2);
ctx2.rotate(-blueAngle);
ctx2.drawImage(canvas1,-canvas1.width/2,-canvas1.height/2);
// draw the blue rect to the display canvas
var offX=rectBB.width/2-blueWidth/2;
var offY=rectBB.height/2-blueHeight/2;
canvas.width=blueWidth;
canvas.height=blueHeight;
ctx.drawImage(canvas2,-offX,-offY);
} // end start
// Utility: get bounding box of rotated rectangle
function getRotatedRectBB(x,y,width,height,rAngle){
var absCos=Math.abs(Math.cos(rAngle));
var absSin=Math.abs(Math.sin(rAngle));
var cx=x+width/2*Math.cos(rAngle)-height/2*Math.sin(rAngle);
var cy=y+width/2*Math.sin(rAngle)+height/2*Math.cos(rAngle);
var w=width*absCos+height*absSin;
var h=width*absSin+height*absCos;
return({cx:cx,cy:cy,width:w,height:h});
}
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>