仅在onmouseover上显示Canvas上的文本

时间:2013-08-30 18:39:00

标签: javascript css html5 canvas

我用Canvas元素创建了一个三角形图像蒙版。我有一个文本字段,我想在鼠标悬停时显示在此三角形的底线。我不知道如何只在悬停时显示文本。

我是这方面的初学者...任何有用的帮助!

这是我到目前为止的代码:

HTML code:

<body>
    <a href="#"><canvas id="canvas" width=300 height=300></canvas></a>
  </body>

使用Javascript:

function masks() {

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");

    var img=new Image();
    img.onload=function(){
        draw(ctx,img,"Hello!");
    }
    img.src="canvas01.png";
    function draw(ctx,img,text){
        ctx.beginPath();
        ctx.moveTo(canvas.width / 2, 0);
        ctx.lineTo(canvas.width, canvas.height);            
        ctx.lineTo(0, canvas.height);
        ctx.closePath();                                          
        ctx.clip();                        
        ctx.drawImage(img,0,0);
        if(text){
            ctx.fillStyle = "#f30";
            ctx.fillRect(0,canvas.height-20,canvas.width,20);
            ctx.fillStyle = "black";
            ctx.font="14pt Verdana";
            var textWidth=ctx.measureText(text).width;
            ctx.fillText(text,(canvas.width-textWidth)/2,canvas.height-3); 
        }

    }

};

1 个答案:

答案 0 :(得分:3)

以下是......

当用户的鼠标位于canvas元素上时,您可以使用:

绘制文本
        canvas.addEventListener("mouseover",function(){
            draw(ctx,img,"Hello!");
        });

当用户的鼠标移动到canvas元素之外时,您可以使用以下方法清除文本:

        canvas.addEventListener("mouseout",function(){
            draw(ctx,img);
        });

请注意,您的绘图功能现在会清除画布以准备重绘:

    function draw(ctx,img,text){
        ctx.clearRect(0,0,canvas.width,canvas.height);
        ctx.save();
        ctx.beginPath();
        ctx.moveTo(canvas.width / 2, 0);
        ctx.lineTo(canvas.width, canvas.height);            
        ctx.lineTo(0, canvas.height);
        ctx.closePath();                                          
        ctx.clip();                        
        ctx.drawImage(img,0,0);
        if(text){
            ctx.fillStyle = "#f30";
            ctx.fillRect(0,canvas.height-20,canvas.width,20);
            ctx.fillStyle = "black";
            ctx.font="14pt Verdana";
            var textWidth=ctx.measureText(text).width;
            ctx.fillText(text,(canvas.width-textWidth)/2,canvas.height-3);
        }
        ctx.restore();
    }

这是代码和小提琴:http://jsfiddle.net/m1erickson/Q4TKC/

<!doctype html>
<html>
<head>
<style>
    body{ background-color: ivory; padding:10px; }
    #canvas{border:1px solid lightgray;}
</style>

<script>
window.onload=function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");

    var img=new Image();
    img.onload=function(){

        canvas.addEventListener("mouseover",function(){
            draw(ctx,img,"Hello!");
        });
        canvas.addEventListener("mouseout",function(){
            draw(ctx,img);
        });

        draw(ctx,img);
    }
    img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/sky-bg2.jpg";


    function draw(ctx,img,text){
        ctx.clearRect(0,0,canvas.width,canvas.height);
        ctx.save();
        ctx.beginPath();
        ctx.moveTo(canvas.width / 2, 0);
        ctx.lineTo(canvas.width, canvas.height);            
        ctx.lineTo(0, canvas.height);
        ctx.closePath();                                          
        ctx.clip();                        
        ctx.drawImage(img,0,0);
        if(text){
            ctx.fillStyle = "#f30";
            ctx.fillRect(0,canvas.height-20,canvas.width,20);
            ctx.fillStyle = "black";
            ctx.font="14pt Verdana";
            var textWidth=ctx.measureText(text).width;
            ctx.fillText(text,(canvas.width-textWidth)/2,canvas.height-3);
        }
        ctx.restore();
    }

};  // end window.onload

</script>

</head>

<body>
    <canvas id="canvas" width=300 height=300></canvas>
</body>
</html>