HTML5畫布canvas隨機生成圓形和正方形

weixin_34357887發表於2016-12-07
HTMLCanvas隨機

<!DOCTYPE html>
<html lang="en">
<head>
<title>TweetShirt</title>
<meta charset="utf-8">
<style type="text/css">
canvas {
border: 1px solid black;
}
</style>
<script>
window.onload = function() {
var button = document.getElementById("previewButton");
button.onclick = previewHandler;
function previewHandler() {
var canvas = document.getElementById("tshirtCanvas");
var context = canvas.getContext("2d");
fillBackgroundColor(canvas,context);

    var selectObj = document.getElementById("shape");
    var index = selectObj.selectedIndex;
    var shape = selectObj[index].value;

//判斷是方形還是圓形
if (shape == "squares") {
for (var squares = 0; squares < 20; squares++){
drawSquare(canvas,context);
}
}else if(shape == "circles"){
for (var circles = 0; circles < 20; circles++){
drawCircle(canvas,context);
}
}
}

  function fillBackgroundColor(canvas,context){
    var selectObj = document.getElementById("backgroundColor");
    var index = selectObj.selectedIndex;
    var bgColor = selectObj.options[index].value;
    context.fillStyle = bgColor;
    context.fillRect(0,0,canvas.width,canvas.height);
  }

//封裝方形
function drawSquare(canvas,context){
var w = Math.floor(Math.random() * 40);
var x = Math.floor(Math.random() * canvas.width);
var y = Math.floor(Math.random() * canvas.height);

    context.fillStyle = "lightblue";
    context.fillRect(x,y,w,w);
  }

//封裝圓形
function drawCircle(canvas,context){
var radius = Math.floor(Math.random() * 40);
var x = Math.floor(Math.random() * canvas.width);
var y = Math.floor(Math.random() * canvas.height);

    context.beginPath();
    context.arc(x,y,radius,0,degreesToRadians(360),true);
    context.fillStyle = "lightblue";
    context.fill();
  }
  function degreesToRadians(degrees){
    return (degrees * Math.PI)/180;
  }
}

</script>
</head>
<body>
<canvas id="tshirtCanvas" width="600" height="200">
<p>Please update your brower to use TweetShirt</p>
</canvas>
<form>
<p>
<label for="backgroundColor">Select background color:</label>
<select id="backgroundColor">
<option value="white" selected="selected">White</option>
<option value="black">Black</option>
</select>
</p>
<p>
<label for="shape">Circles or squares?</label>
<select id="shape">
<option value="none" selected="selected">Neither</option>
<option value="circles">Circles</option>
<option value="squares">squares</option>
</select>
</p>
<p>
<input type="button" name="previewButton" id="previewButton" value="Preview">
</p>
</form>
</body>
</html>

3877064-712d4ad0f07506a4.png
h5.png

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