我在尝试使用画布实现“奖品轮”时遇到了麻烦。我正在使用类似于 在 StackOverflow 周围浮动的画布“轮盘赌” http://jsfiddle.net/wYhvB/4/的东西。我的困境是，当您单击旋转时，我在后台进行了一个 API 调用，该调用返回一个实际应该选择哪个奖品的 id，界面不过是养眼。我将所有奖品描述推送到第一个数组中，如何在每个弧中添加一个 id 并在特定的弧上停止而不是在特定的随机时间停止？IE 如果 API 返回“汽车”，我希望这个轮子旋转几次并停在汽车上。
var colors = ["##eaeaea", "##cccccc", "##eaeaea", "##cccccc",
"##eaeaea", "##cccccc", "##eaeaea", "##cccccc"];
// NEED to pre load this data prior
var prize_descriptions = ["car","house","etc..."]; // These are injected on an init call from an api
var current_user_status = {};
var startAngle = 0;
var arc = Math.PI / 4;
var spinTimeout = null;
var spinArcStart = 10;
var spinTime = 0;
var spinTimeTotal = 0;
var current_user_status = null;
var spin_results = null;
var ctx;
function drawSpinnerWheel() {
var canvas = document.getElementById("canvas");
if (canvas.getContext) {
var outsideRadius = 200;
var textRadius = 160;
var insideRadius = 125;
ctx = canvas.getContext("2d");
ctx.clearRect(0,0,500,500);
ctx.strokeStyle = "black";
ctx.lineWidth = 2;
ctx.font = 'bold 12px Helvetica, Arial';
for(var i = 0; i < 8; i++) {
var angle = startAngle + i * arc;
ctx.fillStyle = colors[i];
ctx.beginPath();
ctx.arc(250, 250, outsideRadius, angle, angle + arc, false);
ctx.arc(250, 250, insideRadius, angle + arc, angle, true);
ctx.stroke();
ctx.fill();
ctx.save();
ctx.shadowOffsetX = -1;
ctx.shadowOffsetY = -1;
ctx.shadowBlur = 0;
ctx.shadowColor = "rgb(220,220,220)";
ctx.fillStyle = "black";
ctx.translate(250 + Math.cos(angle + arc / 2) * textRadius,
250 + Math.sin(angle + arc / 2) * textRadius);
ctx.rotate(angle + arc / 2 + Math.PI / 2);
var text = prize_descriptions[i];
if (text == undefined)
text = "Not this time! "+i;
ctx.fillText(text, -ctx.measureText(text).width / 2, 0);
ctx.restore();
}
//Arrow
ctx.fillStyle = "black";
ctx.beginPath();
ctx.moveTo(250 - 4, 250 - (outsideRadius + 5));
ctx.lineTo(250 + 4, 250 - (outsideRadius + 5));
ctx.lineTo(250 + 4, 250 - (outsideRadius - 5));
ctx.lineTo(250 + 9, 250 - (outsideRadius - 5));
ctx.lineTo(250 + 0, 250 - (outsideRadius - 13));
ctx.lineTo(250 - 9, 250 - (outsideRadius - 5));
ctx.lineTo(250 - 4, 250 - (outsideRadius - 5));
ctx.lineTo(250 - 4, 250 - (outsideRadius + 5));
ctx.fill();
}
}
function spin() {
spinAngleStart = Math.random() * 10 + 10;
spinTime = 0;
spinTimeTotal = Math.random() * 3 + 4 * 1000;
rotateWheel();
}
function rotateWheel() {
spinTime += 30;
if(spinTime >= spinTimeTotal) {
stopRotateWheel();
return;
}
var spinAngle = spinAngleStart - easeOut(spinTime, 0, spinAngleStart, spinTimeTotal);
startAngle += (spinAngle * Math.PI / 180);
drawSpinnerWheel();
spinTimeout = setTimeout('rotateWheel()', 30);
}
function stopRotateWheel() {
clearTimeout(spinTimeout);
var degrees = startAngle * 180 / Math.PI + 90;
var arcd = arc * 180 / Math.PI;
var index = Math.floor((360 - degrees % 360) / arcd);
ctx.save();
ctx.font = 'bold 30px Helvetica, Arial';
var text = prize_descriptions[index];
ctx.fillText(text, 250 - ctx.measureText(text).width / 2, 250 + 10);
ctx.restore();
}
function easeOut(t, b, c, d) {
var ts = (t/=d)*t;
var tc = ts*t;
return b+c*(tc + -3*ts + 3*t);
}
drawSpinnerWheel();
$("#spin").bind('click', function(e) {
e.preventDefault();
spin();
});