javaScript canvas实现(画笔大小颜色橡皮的实例)-偶像资源网

实例如下所示：

<!DOCTYPE html>
<html>
 <head>
 <meta charset=\"utf-8\" />
 <title></title>
 </head>
 <body>
 <div>
 <div>
 
 <!--<input type=\"button\" id=\"open\" value=\"open\"></input>
 <input type=\"button\" id= \"save\" value = \"save\"></input> <input type=\"button\" id= \"color\" value=\"color\"></input> -->
 <input type=\"button\" value=\"size\"></input>
 <input type=\"text\" id=\"size\" onchange=\"sizeChange()\"></input>
 <input type=\"button\" id=\"clear\" value=\"clear\"></input>
 <input type=\"button\" id=\"eraser\" value=\"eraser\" onclick=\"doEraser()\"></input>
 <select id = \"shape\" onchange=\"shapeChange()\">
  <option value = \"99\">shape</option>
  <option value = \"1\">rectangle</option>
  <option value = \"0\">circle</option>
  <option value = \"2\">line</option>
 </select>

 
 <input id=\"color\" type=\"color\"/>
 </div>
 <canvas id=\"myCanvas\" style=\" border:1px solid;\" width=\"800\" height=\"500\"></canvas>
 </div>
 </body>
 <script language=\"JavaScript\">
 var shap = 99; //0 is circle; 1 is rectangle
 var orignalX, orignalY;//the coordinate of mouse down
 var lastX, lastY;//the coordinate of last mouse position
 var isMouseDown = false; // flag of mouse pressing down
 var myCanvas = document.getElementById(\"myCanvas\");
 var context = myCanvas.getContext(\'2d\');
 var width = myCanvas.width, height = myCanvas.height;
 var data;//storing last canvas\' content
 context.strokeStyle = \"black\";
 context.strokeWidth=1;
 context.lineWidth = 1;

 
 document.getElementById(\'color\').onchange = function(){
   context.strokeStyle = this.value
 };
 
 function doEraser(){
 context.strokeStyle = \"white\";
 shap = 2;
 }
 function sizeChange(){
 
 context.lineWidth = parseInt(document.getElementById(\'size\').value);
 
 }
 
 function shapeChange(){
 context.strokeStyle = \"black\";
  var myselect = document.getElementById(\"shape\");
 var index=myselect.selectedIndex ; 
 var myvalue = myselect.options[index].value;
 var mytext=myselect.options[index].text; 
 shap = parseInt(myvalue);
 
  }

 

 function myCanvasMouseDown(event) {
 //event.preventDefault();
 
 if(event.button == 0) {
 orignalX = event.offsetX;
 orignalY = event.offsetY;
 context.moveTo(orignalX,orignalY); 
 data = context.getImageData(0, 0, width, height);
 isMouseDown = true;
 
 }
 }

 function myCanvasMouseMove(event) {
 if (isMouseDown){
 //event.preventDefault();
 
 switch(shap){
  case 0:
   context.clearRect(0,0,width,height);
  context.putImageData(data,0,0);
  lastX = event.offsetX;
  lastY = event.offsetY;
  context.beginPath();
  context.arc(orignalX+(lastX-orignalX)/2,orignalY+(lastY-orignalY)/2,Math.abs(lastX-orignalX)/2,0,Math.PI * 2,true);
  context.stroke();
  context.closePath();
  break;
  case 1:
  context.clearRect(0,0,width,height);
  context.putImageData(data,0,0);
  lastX = event.offsetX;
  lastY = event.offsetY;
  context.strokeRect(orignalX, orignalY, lastX-orignalX, lastY-orignalY);
  break;
  case 2:
   lastX = event.offsetX;
   lastY = event.offsetY;
   context.lineTo(lastX, lastY); //根据鼠标路径绘画 
   context.stroke(); //立即渲染 
   break;
  
 }
 }
 }

 function myCanvasMouseUp(event) {
 if (isMouseDown){
 //event.preventDefault();
 
 context.clearRect(0,0,width,height);
 context.putImageData(data,0,0);
 lastX = event.offsetX;
 lastY = event.offsetY;
 switch(shap){
  case 0:
  context.beginPath();
  context.arc(orignalX+(lastX-orignalX)/2,orignalY+(lastY-orignalY)/2,Math.abs(lastX-orignalX)/2,0,Math.PI * 2,true);
  context.stroke();
  context.closePath();
  break;
  case 1:
  context.beginPath();
  context.strokeRect(orignalX, orignalY, lastX-orignalX, lastY-orignalY);
  context.closePath();
  break;
  case 2:
  
  context.lineTo(lastX, lastY); //根据鼠标路径绘画 
   context.stroke(); //立即渲染 
  
  break;
 }
 isMouseDown = false;
 lastX = null;
 lastY = null;
 orignalX = null;
 orignalY = null;
 data = context.getImageData(0, 0, width, height);
 context.beginPath();
 context.clearRect(0,0,width,height);
 context.putImageData(data,0,0);
 context.closePath();
 }
 } 
 myCanvas.addEventListener(\"mousedown\", myCanvasMouseDown, false);
 myCanvas.addEventListener(\"mousemove\", myCanvasMouseMove, false);
 myCanvas.addEventListener(\"mouseup\", myCanvasMouseUp, false);
 </script>
 
</html>

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javaScript canvas实现(画笔大小 颜色 橡皮的实例)

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javaScript canvas实现(画笔大小颜色橡皮的实例)