我们可以通过创建fabric.Polygon的实例来创建一个Polygon对象。多边形对象的特征可以是由一组连接的直线段组成的任何闭合形状。由于它是 FabricJS 的基本元素之一,因此我们还可以通过应用角度、不透明度等属性轻松自定义它。我们使用 mouseup 和 mousedown 事件来演示如何多边形对象对用户触发的鼠标事件做出反应。
polygon.on(“mouseup”, callbackFunction); polygon.on(“mousedown”, callbackFunction);
让我们看一个代码示例,了解触发 mouseup 事件时多边形对象如何反应。当用户释放鼠标左键时,会发生 mouseup 事件。这里,一旦触发 mouseup 事件,描边宽度就会变为 33。
<!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 the mouseup event</h2> <p> You can select the object and release the left mouse button to see that the stroke width has changed </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, objectCaching: false, } ); // Adding it to the canvas canvas.add(polygon); // Using the mouseup event polygon.on("mouseup", () => { polygon.set("strokeWidth", 33); canvas.renderAll(); }); </script> </body> </html>
让我们看一个代码示例,了解触发 mousedown 事件时多边形对象如何反应。当用户按下按钮时,会发生 mousedown 事件。在这里,我们可以看到该对象通过将其描边宽度从 33 更改为 2 来响应 mousedown 事件。
<!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 the mousedown event</h2> <p> You can press the left mouse button to trigger the mousedown event to see that the stroke width has changed </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: 33, objectCaching: false, } ); // Adding it to the canvas canvas.add(polygon); // Using the mousedown event polygon.on("mousedown", () => { polygon.set("strokeWidth", 2); canvas.renderAll(); }); </script> </body> </html>
在本教程中,我们使用两个简单的示例来演示如何使用 FabricJS 使多边形对象对鼠标事件做出反应。
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