如何在中间创建一个带有孔的画布html5剪裁区域？

Question

我正在尝试使用HTML5 Canvas / Javascript：

动态编码此图像

中间的孔必须是透明的，因为我将此图像叠加到背景上。我的代码绘制了两个椭圆形路径，一个在另一个内部。 我假设最好的方法是创建一个剪切区域，允许在较大的椭圆形内部填充但在较小的椭圆形外部填充。我该怎么做呢？请帮忙！

我的代码（不能解决问题，因为它对较小的椭圆使用了白色填充）：

var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
//parameters of the ovals;

var height = 20;
var curve1 = 0.56;
var curve2 = 0.44;
var width_ratio = 0.38;
var x_pos = 0;
var y_pos = 0;var x1 = x_pos;
var y1 = y_pos - height/2;
var x2 = x_pos + height * width_ratio;
var y2 = y_pos;
var x3 = x_pos;
var y3 = y_pos + height/2;
var x4 = x_pos - height * width_ratio;
var y4 = y_pos;

var xv1 = x1 + ((x2 - x1) * curve1);
var yv1 = y1;
var xv2 = x2;
var yv2 = y1 + ((y2 - y1) * curve2);
var xv3 = x2;
var yv3 = y2 + (height/2 - (height/2 * curve2));
var xv4 = xv1;
var yv4 = y3;
var xv5 = x3 - ((x2 - x1) * curve1);
var yv5 = y3;
var xv6 = x4;
var yv6 = yv3;
var xv7 = x4;
var yv7 = y4 - (height/2 - (height/2 * curve2));
var xv8 = x1 - ((x2 - x1) * curve1);
var yv8 = y1;

var x5 = x1;
var y5 = y1 + height / 10;
var x6 = x2 - height / 5;//x2
var y6 = y2;//y2
var x7 = x5;//x3
var y7 = y3 - height / 10;//y3
var x8 = x4 + height / 5;
var y8 = y4;//y4


var xv9 = x5 + ((x6 - x5) * curve1);//xv1
var yv9 = y5;//yv1
var xv10 = x6;//xv2
var yv10 = y5 + ((y6 - y5) * curve2);//yv2 
var xv11 =  x6;//xv3
var yv11 = y7 - ((y7 - y6) * curve2);//yv3
var xv12 = xv9;//xv4
var yv12 = y7;//yv4
var xv13 = x5 - ((x6 - x5) * curve1);//xv5
var yv13 = y7;//yv5
var xv14 = x7 - height / 5;//xv6
var yv14 = yv11;//yv6
var xv15 = x8;//xv7
var yv15 = yv10;
var xv16 = x5 - ((x6 - x5) * curve1);
var yv16 = yv9;

context.save();
context.scale(5,5);
context.translate(50, 50);
context.rotate(60*Math.PI/180); 

context.beginPath();
context.fillStyle = "black";
context.moveTo(x1,y1); //0,0
context.bezierCurveTo(xv1,yv1,xv2,yv2,x2,y2);
context.bezierCurveTo(xv3,yv3,xv4,yv4,x3,y3);
context.bezierCurveTo(xv5,yv5,xv6,yv6,x4,y4);
context.bezierCurveTo(xv7,yv7,xv8,yv8,x1,y1);
context.closePath();
context.fill();
//context.clip()??? ---- HELP HERE!

context.beginPath();
context.fillStyle = "white";
context.moveTo(x5,y5); //0,0
context.bezierCurveTo(xv9,yv9,xv10,yv10,x6,y6);
context.bezierCurveTo(xv11,yv11,xv12,yv12,x7,y7);
context.bezierCurveTo(xv13,yv13,xv14,yv14,x8,y8);
context.bezierCurveTo(xv15,yv15,xv16,yv16,x5,y5);
context.closePath();
context.fill();//doesn't really work for my purposes

Answer 1

您只需要反转第二条路径。另外，不要在两个路径之间创建beginPath的新路径。

示例使用您的代码进行修改以创建剪辑区域。然后我在它的顶部画一个大矩形来显示剪辑的形状。

当你有大量的数字时，你也应该使用数组。会为你节省很多打字。

var context = canvas.getContext("2d");
//parameters of the ovals;

var height = 20;
var curve1 = 0.56;
var curve2 = 0.44;
var width_ratio = 0.38;
var x_pos = 0;
var y_pos = 0;var x1 = x_pos;
var y1 = y_pos - height/2;
var x2 = x_pos + height * width_ratio;
var y2 = y_pos;
var x3 = x_pos;
var y3 = y_pos + height/2;
var x4 = x_pos - height * width_ratio;
var y4 = y_pos;

var xv1 = x1 + ((x2 - x1) * curve1);
var yv1 = y1;
var xv2 = x2;
var yv2 = y1 + ((y2 - y1) * curve2);
var xv3 = x2;
var yv3 = y2 + (height/2 - (height/2 * curve2));
var xv4 = xv1;
var yv4 = y3;
var xv5 = x3 - ((x2 - x1) * curve1);
var yv5 = y3;
var xv6 = x4;
var yv6 = yv3;
var xv7 = x4;
var yv7 = y4 - (height/2 - (height/2 * curve2));
var xv8 = x1 - ((x2 - x1) * curve1);
var yv8 = y1;

var x5 = x1;
var y5 = y1 + height / 10;
var x6 = x2 - height / 5;//x2
var y6 = y2;//y2
var x7 = x5;//x3
var y7 = y3 - height / 10;//y3
var x8 = x4 + height / 5;
var y8 = y4;//y4


var xv9 = x5 + ((x6 - x5) * curve1);//xv1
var yv9 = y5;//yv1
var xv10 = x6;//xv2
var yv10 = y5 + ((y6 - y5) * curve2);//yv2 
var xv11 =  x6;//xv3
var yv11 = y7 - ((y7 - y6) * curve2);//yv3
var xv12 = xv9;//xv4
var yv12 = y7;//yv4
var xv13 = x5 - ((x6 - x5) * curve1);//xv5
var yv13 = y7;//yv5
var xv14 = x7 - height / 5;//xv6
var yv14 = yv11;//yv6
var xv15 = x8;//xv7
var yv15 = yv10;
var xv16 = x5 - ((x6 - x5) * curve1);
var yv16 = yv9;

context.save();
context.scale(5,5);
context.translate(50, 50);
context.rotate(60*Math.PI/180); 

context.beginPath();
context.fillStyle = "black";
context.moveTo(x1,y1); //0,0
context.bezierCurveTo(xv1,yv1,xv2,yv2,x2,y2);
context.bezierCurveTo(xv3,yv3,xv4,yv4,x3,y3);
context.bezierCurveTo(xv5,yv5,xv6,yv6,x4,y4);
context.bezierCurveTo(xv7,yv7,xv8,yv8,x1,y1);


context.moveTo(x5,y5); //0,0

context.bezierCurveTo(xv16,yv16,xv15,yv15,x8,y8);
context.bezierCurveTo(xv14,yv14,xv13,yv13,x7,y7);
context.bezierCurveTo(xv12,yv12,xv11,yv11,x6,y6);
context.bezierCurveTo(xv10,yv10,xv9,yv9,x5,y5);

context.clip();
//context.setTransform(1,0,0,1,0,0)
context.fillRect(-500,-500,1024,1024);

<canvas id = "canvas" width = 1024 height = 1024></canvas>