微信小程序 转盘抽奖, 逻辑讲解原理, 包括源码

微信小程序转盘抽奖的逻辑原理是：用户点击转盘，程序随机生成一个中奖结果，然后将结果返回给用户。具体实现方式是：使用canvas绘制转盘，将转盘分成多个扇形区域，每个扇形区域对应一个奖品。当用户点击转盘时，程序随机生成一个中奖结果，然后计算出中奖扇形区域的角度范围，最后使用canvas动画将转盘旋转到中奖扇形区域的位置。

以下是微信小程序转盘抽奖的源码示例：

wxml代码：

<canvas canvas-id="myCanvas" style="width: 100%; height: 100%;"></canvas>

js代码：

Page({
  data: {
    canvasWidth: 0,
    canvasHeight: 0,
    ctx: null,
    prizeList: ['一等奖', '二等奖', '三等奖', '谢谢参与'],
    prizeColors: ['#FFD700', '#FFA500', '#FFC0CB', '#FFFFFF'],
    prizeAngles: [],
    startAngle: 0,
    endAngle: 0,
    isRunning: false,
    prizeIndex: -1,
  },

  onLoad: function () {
    var that = this;
    wx.getSystemInfo({
      success: function (res) {
        that.setData({
          canvasWidth: res.windowWidth,
          canvasHeight: res.windowHeight,
        });
      },
    });
  },

  onReady: function () {
    var that = this;
    var ctx = wx.createCanvasContext('myCanvas');
    that.setData({
      ctx: ctx,
    });
    that.drawPrize();
  },

  drawPrize: function () {
    var that = this;
    var ctx = that.data.ctx;
    var canvasWidth = that.data.canvasWidth;
    var canvasHeight = that.data.canvasHeight;
    var prizeList = that.data.prizeList;
    var prizeColors = that.data.prizeColors;
    var prizeAngles = that.data.prizeAngles;
    var startAngle = that.data.startAngle;
    var endAngle = that.data.endAngle;
    var angle = 2 * Math.PI / prizeList.length;

    ctx.clearRect(0, 0, canvasWidth, canvasHeight);
    ctx.translate(canvasWidth / 2, canvasHeight / 2);
    ctx.rotate(-Math.PI / 2);

    for (var i = 0; i < prizeList.length; i++) {
      ctx.beginPath();
      ctx.moveTo(0, 0);
      ctx.arc(0, 0, canvasWidth / 2 - 50, startAngle, endAngle, false);
      ctx.closePath();
      ctx.fillStyle = prizeColors[i];
      ctx.fill();

      ctx.save();
      ctx.rotate(endAngle - angle / 2);
      ctx.fillStyle = '#000000';
      ctx.font = 'bold 20px Arial';
      ctx.fillText(prizeList[i], canvasWidth / 3 - 30, 0);
      ctx.restore();

      prizeAngles.push({
        startAngle: startAngle,
        endAngle: endAngle,
      });

      startAngle = endAngle;
      endAngle += angle;
    }

    that.setData({
      prizeAngles: prizeAngles,
    });
  },

  start: function () {
    var that = this;
    var ctx = that.data.ctx;
    var prizeAngles = that.data.prizeAngles;
    var isRunning = that.data.isRunning;
    var prizeIndex = that.data.prizeIndex;

    if (isRunning) {
      return;
    }

    isRunning = true;
    prizeIndex = -1;
    that.setData({
      isRunning: isRunning,
      prizeIndex: prizeIndex,
    });

    var animation = wx.createAnimation({
      duration: 4000,
      timingFunction: 'ease',
    });

    animation.rotate(3600).step();

    ctx.draw(true);

    setTimeout(function () {
      that.setData({
        isRunning: false,
      });

      var animationData = animation.export();
      var currentAngle = 0;

      animationData.actions.forEach(function (action) {
        if (action.method == 'rotate') {
          currentAngle = action.args[0] % 360;
        }
      });

      for (var i = 0; i < prizeAngles.length; i++) {
        if (currentAngle >= prizeAngles[i].startAngle && currentAngle < prizeAngles[i].endAngle) {
          prizeIndex = i;
          break;
        }
      }

      that.setData({
        prizeIndex: prizeIndex,
      });

      wx.showModal({
        title: '恭喜您',
        content: that.data.prizeList[prizeIndex],
        showCancel: false,
      });
    }, 4000);
  },
});

以上是微信小程序转盘抽奖的逻辑讲解原理及源码。