Question

在不成功的线程之后，我再次寻求帮助。如何让用户通过将文本拖动到所需位置来在画布上添加一些文本？让我们说，他们以某种方式在某处输入文本，它出现在画布上，然后用户可以将该文本拖动到所需位置。我应该使用哪种技术？有人写任何快速代码吗？

Answer 1

以下是如何在html画布上拖动文字的大纲：

创建一个文本对象，其中包含有关此单词的信息（文本，x，y，宽度，高度）。
创建一个数组以容纳所有文本对象
在mousedown上，点击测试数组中的每个文本对象，看看用户是否已在文本上进行了测试
在鼠标移动时，将所选文本移动到用户拖动鼠标的距离

演示：http://jsfiddle.net/m1erickson/tLvMK/

这是评论代码：

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>

<style>
    body{ background-color: ivory; }
    #canvas{border:1px solid red;}
</style>

<script>
$(function(){

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

    // variables used to get mouse position on the canvas
    var $canvas=$("#canvas");
    var canvasOffset=$canvas.offset();
    var offsetX=canvasOffset.left;
    var offsetY=canvasOffset.top;
    var scrollX=$canvas.scrollLeft();
    var scrollY=$canvas.scrollTop();

    // variables to save last mouse position
    // used to see how far the user dragged the mouse
    // and then move the text by that distance
    var startX;
    var startY;

    // some text objects
    var texts=[];

    // some test texts
    texts.push({text:"Hello",x:20,y:20});
    texts.push({text:"World",x:20,y:70});

    // calculate width of each text for hit-testing purposes
    ctx.font="16px verdana";
    for(var i=0;i<texts.length;i++){
        var text=texts[i];
        text.width=ctx.measureText(text.text).width;
        text.height=16;
    }

    // this var will hold the index of the selected text
    var selectedText=-1;

    // START: draw all texts to the canvas
    draw();

    // clear the canvas draw all texts
    function draw(){
        ctx.clearRect(0,0,canvas.width,canvas.height);
        for(var i=0;i<texts.length;i++){
            var text=texts[i];
            ctx.fillText(text.text,text.x,text.y);
        }
    }

    // test if x,y is inside the bounding box of texts[textIndex]
    function textHittest(x,y,textIndex){
        var text=texts[textIndex];
        return(x>=text.x && 
            x<=text.x+text.width &&
            y>=text.y-text.height && 
            y<=text.y);
    }

    // handle mousedown events
    // iterate through texts[] and see if the user
    // mousedown'ed on one of them
    // If yes, set the selectedText to the index of that text
    function handleMouseDown(e){
      e.preventDefault();
      startX=parseInt(e.clientX-offsetX);
      startY=parseInt(e.clientY-offsetY);

      // Put your mousedown stuff here
      for(var i=0;i<texts.length;i++){
          if(textHittest(startX,startY,i)){
              selectedText=i;
          }
      }
    }

    // done dragging
    function handleMouseUp(e){
      e.preventDefault();
      selectedText=-1;
    }

    // also done dragging
    function handleMouseOut(e){
      e.preventDefault();
      selectedText=-1;
    }

    // handle mousemove events
    // calc how far the mouse has been dragged since
    // the last mousemove event and move the selected text
    // by that distance
    function handleMouseMove(e){
      if(selectedText<0){return;}
      e.preventDefault();
      mouseX=parseInt(e.clientX-offsetX);
      mouseY=parseInt(e.clientY-offsetY);

      // Put your mousemove stuff here
      var dx=mouseX-startX;
      var dy=mouseY-startY;
      startX=mouseX;
      startY=mouseY;

      var text=texts[selectedText];
      text.x+=dx;
      text.y+=dy;
      draw();
    }

    // listen for mouse events
    $("#canvas").mousedown(function(e){handleMouseDown(e);});
    $("#canvas").mousemove(function(e){handleMouseMove(e);});
    $("#canvas").mouseup(function(e){handleMouseUp(e);});
    $("#canvas").mouseout(function(e){handleMouseOut(e);});

}); // end $(function(){});
</script>

</head>

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

“通过将文本拖动到所需位置，可以在画布上移动文本？”

1 个答案: