我们可以通过创建一个 fabric.Polygon 的实例来创建一个多边形对象。多边形对象可以由一组相连的直线段组成的任何封闭形状来描述。由于它是FabricJS的基本元素之一，我们还可以通过应用属性如角度、不透明度等来轻松地自定义它。为了给多边形添加图案和颜色，我们可以使用FabricJS中的Pattern类。
语法
new fabric.Pattern( options: Object, callback: function )
参数
options (optional) − This parameter is an Object which provides additional customizations to our object. Using this parameter offsetX, cross-origin and a lot of other properties can be changed related to the Pattern.
callback − 此参数是一个在回调初始化后调用的函数。此参数是可选的。
示例1：创建fabric.Pattern()的实例并将其添加到我们的多边形对象中
让我们看一个代码示例，看看如何创建一个 fabric.Pattern 的实例并将其添加到画布中。在这里，我们创建了一个多边形对象，它的形状是一个矩形（一个不规则的多边形）。我们初始化了 createPattern 函数，该函数将把图案添加到我们的矩形中。最后，我们调用了 createPattern 函数，并将所需的 URL 传递给它。
<!DOCTYPE html>
<html>
<head>
<!-- Adding the Fabric JS Library-->
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
<h2>
Creating an instance of fabric.Pattern() and adding it to our Polygon object
</h2>
<p>You can see that a pattern has been created</p>
<canvas id="canvas"></canvas>
<script>
// Initiate a canvas instance
var canvas = new fabric.Canvas("canvas");
canvas.setWidth(document.body.scrollWidth);
canvas.setHeight(250);
// Initiating the createPattern function which loads image
// and adds the image as pattern to the rect object
function createPattern(url) {
fabric.util.loadImage(url, function (img) {
rect.set(
"fill",
new fabric.Pattern({
source: img,
})
);
canvas.renderAll();
});
}
// Initiating a Polygon object
var rect = new fabric.Polygon(
[
{ x: 0, y: 0 },
{ x: 500, y: 0 },
{ x: 500, y: 200 },
{ x: 0, y: 200 },
],
{
left: 50,
top: 20,
stroke: "black",
}
);
// Adding it to the canvas
canvas.add(rect);
// Calling the createPattern function
createPattern("https://www.tutorialspoint.com/images/logo.png");
</script>
</body>
</html>
示例2：在我们的多边形中添加图像和颜色的模式
让我们看一个代码示例，看看如何为我们的多边形对象创建一个带有图像和颜色的动态模式。在这种情况下，我们使用了fromURL方法来加载图像，并初始化了一个fabric.StaticCanvas()对象，这是FabricJS的主要渲染表面之一，对于创建动态模式至关重要。
我们使用了 setBackgroundColor 方法来为多边形设置背景颜色。最后，我们将多边形对象添加到画布中。
<!DOCTYPE html>
<html>
<head>
<!-- Adding the Fabric JS Library-->
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
<h2>Adding a pattern with Image and Colour to our Polygon</h2>
<p>You can see that a pattern with image and colour has been created and further use the number field to change the pattern density</p>
<label>Add a width value(50-500): </label>
<input type="number" id="changeWidth" value="50"/>
<canvas id="canvas"></canvas>
<script>
// Initiate a canvas instance
var canvas = new fabric.Canvas("canvas");
canvas.setWidth(document.body.scrollWidth);
canvas.setHeight(250);
// Initiating the colour that we want to fill the pattern with
var imgColor = "rgba(216,228,188,0.5)";
// Using fromURL method to load image and add to canvas
// further setting the dimensions and background colour
fabric.Image.fromURL(
"https://www.tutorialspoint.com/images/logo.png",
function (img) {
img.scaleToWidth(100);
img.scaleToHeight(90);
var patternSourceCanvas = new fabric.StaticCanvas();
patternSourceCanvas.add(img);
patternSourceCanvas.renderAll();
patternSourceCanvas.setBackgroundColor(
imgColor,
patternSourceCanvas.renderAll.bind(patternSourceCanvas)
);
// Initiating a Pattern object
var pattern = new fabric.Pattern({
source: patternSourceCanvas.getElement(),
repeat: "repeat",
});
// Adding a polygon object to the canvas
canvas.add(
// Initiate a polygon object
new fabric.Polygon(
[
{ x: -100, y: -175 },
{ x: 100, y: -175 },
{ x: 200, y: 0 },
{ x: 100, y: 175 },
{ x: -100, y: 175 },
{ x: -200, y: 0 },
],
{
top: 30,
left: 10,
strokeWidth: 3,
stroke: "#96c8a2",
fill: pattern,
objectCaching: false,
scaleX: 0.5,
scaleY: 0.5,
}
)
);
// Using getElementById and targeting the input tag with the id as "changeWidth"
document.getElementById("changeWidth").oninput = function () {
img.scaleToWidth(parseInt(this.value, 10));
patternSourceCanvas.setDimensions({
width: img.getScaledWidth(),
height: img.getScaledHeight(),
});
canvas.requestRenderAll();
};
}
);
</script>
</body>
</html>
结论
在本教程中，我们使用了两个简单的示例来演示如何使用FabricJS向多边形添加图像和颜色的模式。
