JS實作簡單的Canvas畫圖實例_javascript技巧

定義變數:
[javascript]

複製程式碼 程式碼如下:

var startX;
var startY;
var endX;
var endY;
var radius;
var canvas = document.getElementById("myCanvas"); = canvas.getContext("2d");
var select = document.getElementsByTagName("select");
var startX;
var startY;
var endX;
var; 🎜>var radius;
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var select = document.getElementsByTagName("select");



函數部分:

[javascript]

複製程式碼複製程式碼

複製程式碼



複製程式碼



複製程式碼



複製程式碼



複製程式碼



複製程式碼



複製碼程式碼如下:


window.onload=function() {
    canvas.onmousedown = function(e) {
   ;
    startY = e.clientY;
    if(select[0].value == "arc") {
           canvas.onmousemove = moveShowRect;
    }
    }
    canvas.onmouseup = function() {
    canvas.onmousem = ""); {
    context.clearRect(0, 0, 500, 300);
    endX = e.clientX - startX;
    endY = e.clientY - startYgin;
    endY = e.clientY - startYgin;
    endY = e.clientY - startYgin; rect(startX, startY, endX, endY);
    context.fillStyle = "#8ED6FF";
    context.fill();
 ";
    context.stroke();
}
function moveShowArc(e) {
    context.clearRect(0, 0, 500, 300);     endY = e.clientY - startY;
    radius = Math.sqrt(Math.pow(endX,2) Math.pow(endY,2));
    context.begin(endY,2));
    context.begin(); >    context.arc(startX, startY,radius,0,2 * Math.PI,false);
    context.fillStyle = "#8ED6FF";
    context.fill(); 3;
    context.strokeStyle = "black";
    context.stroke();
}
window.onload=function() {  . 🎜> e = e || event;
 startX = e.clientX;
 startY = e.clientY;
 if(select[0].value == "arcc") { if(select[0].value == "arcc") { if(select. onmousemove = moveShowArc;
 } else {
     canvas.onmousemove = moveShowRect;
 }
 = "";
    }
}
function moveShowRect(e) {
    context.clearRect(0, 0, 500, 300);
  c - startY;
    context.beginPath();
    context.rect(startX, startY, endX, endY);
    context.fillStyle = "#8ED6"; 🎜>    context.lineWidth = 3;
    context.strokeStyle = "black";
    context.stroke();    endX = e.clientX - startX;
    endY = e.clientY - startY;
    endY = e.clientY - startY;
    radius = Math.sqrt(Math.A. endY,2));
    context.beginPath();
    context.arc(startX, startY,radius,0,2 * Math.PI,false);

    context.fillStyle = "#86le ;    context.fill();    context.lineWidth = 3;    context.strokeStyle = "black";    context.strokeStyle = "black"; >