我們可以透過建立fabric.Polygon的實例來建立一個Polygon物件。多邊形物件的特徵可以是由一組連接的直線段組成的任何閉合形狀。由於它是 FabricJS 的基本元素之一，我們也可以透過應用角度、不透明度等屬性輕鬆自訂它。我們使用 object:modified 事件使多邊形物件對調整大小做出反應。
object:modified
讓我們看一個程式碼範例，了解當不使用 object:modified 事件時多邊形物件如何顯示。在這種情況下，多邊形物件將被添加到畫布中。
<!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>Default appearance of the polygon object</h2>
<p>You can see that the polygon object has been added to the canvas</p>
<canvas id="canvas"></canvas>
<script>
// Initiate a canvas instance
var canvas = new fabric.Canvas("canvas");
canvas.setWidth(document.body.scrollWidth);
canvas.setHeight(250);
// Initiate a polygon instance
var polygon = new fabric.Polygon(
[
{ x: 0, y: 0 },
{ x: 0, y: 50 },
{ x: 50, y: 50 },
{ x: 50, y: 0 },
],
{
left: 100,
top: 30,
fill: "red",
stroke: "blue",
strokeWidth: 2,
}
);
// Adding it to the canvas
canvas.add(polygon);
</script>
</body>
</html>
讓我們看一個程式碼範例，以查看調整多邊形物件大小時記錄的輸出。我們使用了 object:modified 事件，該事件在任何物件轉換或與物件有關的任何變更結束時觸發。在這種情況下，每次我們更改物件的比例時，縮放後的高度和寬度都會被控制台記錄。
<!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>Displaying how the object reacts to being resized</h2>
<p>
You can scale object using corner and open console from dev tools to see that the scaled width and height value of the polygon object is being logged
</p>
<canvas id="canvas"></canvas>
<script>
// Initiate a canvas instance
var canvas = new fabric.Canvas("canvas");
canvas.setWidth(document.body.scrollWidth);
canvas.setHeight(250);
// Initiate a polygon instance
var polygon = new fabric.Polygon(
[
{ x: 0, y: 0 },
{ x: 0, y: 50 },
{ x: 50, y: 50 },
{ x: 50, y: 0 },
],
{
left: 100,
top: 30,
fill: "red",
stroke: "blue",
strokeWidth: 2,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using object:modified event
canvas.on("object:modified", (e) => {
canvas.getActiveObjects().forEach((o) => {
console.log(
"Scaled Height of the polygon is: ",
o.getScaledHeight(),
"Scaled Width of the polygon is:",
o.getScaledWidth()
);
});
});
</script>
</body>
</html>
在本教學中，我們使用兩個簡單的範例來示範如何使用 FabricJS 讓多邊形物件對調整大小事件做出反應。
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