Javascript 如何从控制盘获取画布的价值
如何获取画布的值。我有一个轮子,鼠标在轮子上旋转,现在我想回显它停止时的值。它正在打印整个阵列。不是车轮停在上面的那个Javascript 如何从控制盘获取画布的价值,javascript,jquery,html,canvas,Javascript,Jquery,Html,Canvas,如何获取画布的值。我有一个轮子,鼠标在轮子上旋转,现在我想回显它停止时的值。它正在打印整个阵列。不是车轮停在上面的那个 $("#canvas").mouseover(function(){ backup= ctx; alert(myData); ctx = null; }); 这是小提琴: 以下是完整的代码: var canvas=document.getElementById(“canvas”); var ctx=canvas.getContext(“2d”); var cw=
$("#canvas").mouseover(function(){
backup= ctx;
alert(myData);
ctx = null;
});
这是小提琴:
以下是完整的代码:
var canvas=document.getElementById(“canvas”);
var ctx=canvas.getContext(“2d”);
var cw=画布宽度;
var ch=画布高度;
var PI2=Math.PI*2;
var myData=[1,2,3,4,5,6,7,8,9,10,11,12];
var-cx=150;
var-cy=150;
var半径=150;
var wheel=document.createElement('canvas');
var wheelCtx=wheel.getContext('2d');
var indicator=document.createElement('canvas');
var indicatorCtx=indicator.getContext('2d');
var角度=PI2-PI2/4;
var myColor=[];
对于(var i=0;i
我将所有内容都包装在一个容器中,这样就不会有任何全局变量
需要注意的是,角度计算是:
angle = degree * Math.PI / 180;
话虽如此,您可以计算当前度数并使用以下方法对其进行规格化:
(angle * (180 / Math.PI)) % 360
我添加了一个名为getValue
的函数,该函数采用angle
参数:
function getValue(angle) {
var degree = (angle * (180 / Math.PI)) % 360,
offsetIndex = (Math.floor(degree / sweepDegree) + offset) % myData.length,
normalizedIndex = Math.abs(offsetIndex - (myData.length - 1));
return myData[normalizedIndex];
}
它基本上计算当前度数,并根据动画初始化时的初始度数(即偏移量)对其进行规格化。然后,它将度除以扫描度,在本例中为30,因为有12个项目(即,360/12===30
)并向下舍入
var sweepDegree = 360 / myData.length;
var offset = (360 - (angle * (180 / Math.PI)) % 360) / sweepDegree;
这适用于不同数量的数组项。换句话说,对于12个项目的集合长度,没有硬编码(就像在您的案例中一样),因此它应该适用于任何给定数量的项目
然后,您可以简单地使用mouseover
事件侦听器中的getValue
函数:
(函数(){
var canvas=document.getElementById(“canvas”);
var ctx=canvas.getContext(“2d”);
var cw=画布宽度;
var ch=画布高度;
var PI2=Math.PI*2;
var myData=[1,2,3,4,5,6,7,8,9,10,11,12];
var-cx=150;
var-cy=150;
var半径=150;
var wheel=document.createElement('canvas');
var wheelCtx=wheel.getContext('2d');
var indicator=document.createElement('canvas');
var indicatorCtx=indicator.getContext('2d');
var角度=PI2-PI2/4;
var sweepDegree=360/myData.length;
变量偏移=(360-(角度*(180/Math.PI))%360)/扫描角度;
var myColor=[];
对于(var i=0;i$("#canvas").mouseover(function() {
// ...
alert(getValue(angle));
});
<canvas id="canvas" width="310" height="310" style="background-color:#ffff">
</canvas>
<div id="counterBox">
<label>Counter:</label>
<span></span>
</div>
<div id="countBox">
<label>Index:</label>
<span></span>
</div>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var cw = canvas.width;
var ch = canvas.height;
var PI2 = Math.PI * 2;
var myData = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
var cx = 150;
var cy = 150;
var radius = 150;
var wheel = document.createElement('canvas');
var wheelCtx = wheel.getContext('2d');
var indicator = document.createElement('canvas');
var indicatorCtx = indicator.getContext('2d');
var currentSelection = 12;
var counter = 360;
var angle = PI2 - PI2 / 4;
var myColor = [];
for (var i = 0; i < myData.length; i++) {
myColor.push(randomColor());
}
makeWheel();
makeIndicator();
requestAnimationFrame(animate);
function makeWheel() {
wheel.width = wheel.height = radius * 2 + 2;
wheelCtx.lineWidth = 1;
wheelCtx.font = '40px Pacifico, cursive';
wheelCtx.textAlign = 'center';
wheelCtx.textBaseline = 'middle';
var cx = wheel.width / 2;
var cy = wheel.height / 2;
var sweepAngle = PI2 / myData.length;
var startAngle = 0;
for (var i = 0; i < myData.length; i++) {
// calc ending angle based on starting angle
var endAngle = startAngle + sweepAngle;
// draw the wedge
wheelCtx.beginPath();
wheelCtx.moveTo(cx, cy);
wheelCtx.arc(cx, cy, radius, startAngle, endAngle, false);
wheelCtx.closePath();
wheelCtx.fillStyle = myColor[i];
wheelCtx.strokeStyle = 'black';
wheelCtx.fill();
wheelCtx.stroke();
// draw the label
var midAngle = startAngle + (endAngle - startAngle) / 2;
var labelRadius = radius * .85;
var x = cx + (labelRadius) * Math.cos(midAngle);
var y = cy + (labelRadius) * Math.sin(midAngle);
wheelCtx.fillStyle = 'gold';
wheelCtx.fillText(myData[i], x, y);
wheelCtx.strokeText(myData[i], x, y);
// increment angle
startAngle += sweepAngle;
}
}
function makeIndicator() {
indicator.width = indicator.height = radius + radius / 10;
indicatorCtx.font = '40px Georgia';
indicatorCtx.textAlign = 'center';
indicatorCtx.textBaseline = 'middle';
indicatorCtx.fillStyle = 'skyblue';
indicatorCtx.strokeStyle = 'blue';
indicatorCtx.lineWidth = 1;
var cx = indicator.width / 2;
var cy = indicator.height / 2;
indicatorCtx.beginPath();
indicatorCtx.moveTo(cx - radius / 8, cy);
indicatorCtx.lineTo(cx, cy - indicator.height / 2);
indicatorCtx.lineTo(cx + radius / 8, cy);
indicatorCtx.closePath();
indicatorCtx.fillStyle = 'skyblue'
indicatorCtx.fill();
indicatorCtx.stroke();
indicatorCtx.beginPath();
indicatorCtx.arc(cx, cy, radius / 3, 0, PI2);
indicatorCtx.closePath();
indicatorCtx.fill();
indicatorCtx.stroke();
indicatorCtx.fillStyle = 'blue';
indicatorCtx.fillText('Prizes', cx, cy);
}
var lastloop = new Date;
var thisloop = new Date;
var fps = 0;
function animate(time) {
ctx.clearRect(0, 0, cw, ch);
ctx.translate(cw / 2, ch / 2);
ctx.rotate(angle);
ctx.drawImage(wheel, -wheel.width / 2, -wheel.height / 2);
ctx.rotate(-angle);
ctx.translate(-cw / 2, -ch / 2);
ctx.drawImage(indicator, cw / 2 - indicator.width / 2, ch / 2 - indicator.height / 2)
angle += PI2 / 360;
thisloop = new Date;
fps = 1000 / (thisloop - lastloop);
lastloop = thisloop;
counter--;
if (counter < 1) {
counter = 360;
}
$("#counterBox span").html(counter);
var index = counter / 30;
$("#countBox span").html(Math.round(index));
//$("#fpsBox span").html(fps);
requestAnimationFrame(animate);
}
function randomColor() {
return ('#' + Math.floor(Math.random() * 16777215).toString(16));
}
var backup = null;
$("#canvas").mouseover(function() {
backup = ctx;
alert(myData[Math.round(counter / 30)-1]);
ctx = null;
});
$("#canvas").mouseout(function() {
// backup= ctx;
ctx = backup;
animate();
});
counter--;
if (counter == 0) {
counter = 360;
}
$("#counterBox span").html(counter);
if (counter % 30 === 0) {
index--;
}
$("#countBox span").html(Math.round(index));
if (index === 0) {
index = 12;
}
$("#canvas").mouseover(function() {
backup = ctx;
alert(index);
ctx = null;
});