Canvas 支援2D圖形描繪，因此只要整理好相關的數據，就能透過相關的 API 將其轉換成為視覺化的圖形。
原文：http://www.kangting.tw/2014/03/canvas.html
Canvas 支援2D圖形描繪，因此只要整理好相關的數據，就能透過相關的 API 將其轉換成為視覺化的圖形。考慮以下的資料：
| 月份 | January | February | March | April | May | June | July |
|---|---|---|---|---|---|---|---|
| 銷售額 | 25 | 32 | 40 | 61 | 36 | 25 | 40 |
建立一組對應此資料的資料物件：
var chartdata = {
labels: ["January", "February", "March", "April", "May", "June", "July"],
data: [25, 32, 40, 61, 36, 25, 40],
color: ["red", "orange", "yellow", "green", "blue", "black", "gray"]
}
接下來透過 Canvas API ，於底下配置 Canvas 元素中，逐一描繪對應的圖表。 以下為需要的程式碼：
<script>
//JSON 物件
var start_x = 60;
var start_y = 400;
var chartdata = {
labels: ["January", "February", "March",
"April", "May", "June", "July"],
data: [25, 32, 40, 61, 36, 25, 40],
color: ["red", "orange", "yellow",
"green", "blue", "black", "ghostwhite"]
}
var cvs = document.getElementById('cvs');
var ctx = cvs.getContext('2d');
// Y 軸
ctx.beginPath();
ctx.moveTo(start_x, 100);
ctx.lineTo(start_x, start_y);
ctx.stroke();
// X 軸
ctx.beginPath();
ctx.moveTo(start_x, start_y);
ctx.lineTo(520, start_y);
ctx.stroke();
ctx.lineWidth = 20;
for (i = 0; i < 7; i++) {
ctx.beginPath();
ctx.strokeStyle = chartdata.color[i] ;
ctx.moveTo((i + 1) * start_x + start_x, start_y);
ctx.lineTo((i + 1) * start_x + start_x, start_y –
chartdata.data[i] * 5);
ctx.stroke();
ctx.fillText(chartdata.labels[i], (i + 1) *
start_x + start_x, start_y + 38);
}
</script>
