canvas 環形圖繪製

查看環形圖效果

主要用到幾個知識點

一、lineCap：如何繪製每一條線段末端的屬性。有3個可能的值，分別是：butt(線段末端以方形結束), round （線段末端圓形結束）and square（線段末端以方形結束，可是增長了一個寬度和線段相同，高度是線段厚度一半的矩形區域）。默認值是 butt。 

二、圓弧起始點與結束點的設置

在本里中設置方式   ctx.arc(110, 110, 100, 0.75 * Math.PI, 0.75 * Math.PI + step * 1.5 * Math.PI, false); // false 是順時針

三、LinearGradient的使用方法

完整的代碼以下 

<div class="container">
        <div class="progress_box">
            <!-- 必定要設置width 和 height 不然圖形會變形 -->
            <canvas id="progress_bg" width="220" height="220"></canvas>
            <canvas id="progress_canvas" width="220" height="220"></canvas>
            <div class="progress_text" id="progress_text">正在加載中...</div>
        </div>
    </div>

<style>
    .progress_box {
        position: relative;
        width: 220px;
        height: 220px;
        display: flex;
        align-items: center;
        justify-content: center;
        background: #140c33;
    }

    #progress_bg {
        position: absolute;
        width: 220px;
        height: 220px;
    }

    #progress_canvas {
        width: 220px;
        height: 220px;
        z-index: 1;
    }

    .progress_text {
        position: absolute;
        display: flex;
        align-items: center;
        justify-content: center;
        color: #ddd;
    }

    .progress_info {
        font-size: 20px;
        padding-left: 16px;
        letter-spacing: 2px;
    }

    .progress_dot {
        width: 16px;
        height: 16px;
        border-radius: 50%;
        background: #fb9126
    }
    </style>

<script>
    function drawProgressBg() {
        var canvas = document.getElementById("progress_bg");
        var ctx = canvas.getContext("2d");
        ctx.lineWidth = 4;
        ctx.strokeStyle = "#20183b";
        ctx.lineCap = "round";
        ctx.beginPath();
        ctx.arc(110, 110, 100, 0, 2 * Math.PI, false);
        ctx.stroke();
    }
    drawProgressBg()

    function drawCircle(step) {
        var canvas = document.getElementById("progress_canvas");
        var ctx = canvas.getContext("2d");
        var gradient = ctx.createLinearGradient(200, 100, 100, 200);
        gradient.addColorStop(0, "#2661DD");
        gradient.addColorStop(0.5, "#40ED94");
        gradient.addColorStop(1.0, "#5956CC");
        ctx.lineWidth = 10;
        ctx.strokeStyle = gradient;
        ctx.lineCap = "round";
        ctx.beginPath();
        ctx.arc(110, 110, 100, 0.75 * Math.PI, 0.75 * Math.PI + step * 1.5 * Math.PI, false); // false 是順時針
        ctx.stroke();
    }
    //drawCircle()

    function countInterval() {
        var count = 0
        var counterTimer = setInterval(function() {
            if (count <= 60) {
                this.drawCircle(count / 60)
                count += 2;
            } else {
                var text = document.getElementById("progress_text")
                text.innerHTML = "加載完成"
                clearInterval(counterTimer)
            }
        }, 100)
    }
    countInterval()
    </script>

注意：必定要設置 Canvas 的 width 和 height 不然圖形會變形。