我正在使用HTML5的画布和javascript制作时钟动画。它应该有三个移动的指针，但似乎只有两个渲染和工作(小时和分钟)。我没有看到任何运行时错误阻止第三个渲染。第三只手怎么了?
顺便说一句，这不是地球时钟，所以数学上可能看起来很奇怪。<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Wyrdling Clock</title>
</head>
<body onload="init();">
<div style="position: relative;">
<canvas id="clock_layer1" width="1080" height="1080" style="position: absolute; left: 0; top: 0; z-index: 0;"></canvas>
<canvas id="clock_layer2" width="1080" height="1080" style="position: absolute; left: 0; top: 0; z-index: 1;"></canvas>
<canvas id="clock_layer3" width="1080" height="1080" style="position: absolute; left: 0; top: 0; z-index: 2;"></canvas>
<canvas id="clock_layer4" width="1080" height="1080" style="position: absolute; left: 0; top: 0; z-index: 3;"></canvas>
</div>
</body>
<script>
var clock_face = null,
hour_hand = null,
minute_hand = null,
second_hand = null,
cycle_hand = null,
ctx_l1 = null,
ctx_l2 = null,
ctx_l3 = null,
ctx_l4 = null,
degrees = 0;
var WyrdTimeStarts = new Date("2019-05-22");
var HEIGHT = 1080;
var WIDTH = 1080;
var HALF_HEIGHT = HEIGHT / 2;
var HALF_WIDTH = WIDTH / 2;
var FPS = 15;
var CIRCLE_TO_HOUR_RATIO = 360 / 9;
var CIRCLE_TO_MINUTES_RATIO = 360 / 60;
var CIRCLE_TO_SECOND_RATIO = 360 / 60;
var CIRCLE_TO_CYCLE_RATIO = 360 / 3;
var CIRCLE_TO_MS_RATIO = 360 / 60000;
var DEGRESS_TO_RADIANS = Math.PI / 180;
var RADIANS_TO_DEGREES = 180 / Math.PI;
function fCleanCanvas() {
// clear canvas
ctx_l1.clearRect(0, 0, HEIGHT, WIDTH);
ctx_l2.clearRect(0, 0, HEIGHT, WIDTH);
ctx_l3.clearRect(0, 0, HEIGHT, WIDTH);
ctx_l4.clearRect(0, 0, HEIGHT, WIDTH);
} // End function fCleanCanvas
function fMinuteAngle(currentMinutes) {
// Calculate the expected angle
return Math.floor(CIRCLE_TO_MINUTES_RATIO * currentMinutes, 0);
} // End function fMinuteAngle
function fHourAngle(currentHours) {
// Calculate the expected angle
return Math.floor(CIRCLE_TO_HOUR_RATIO * currentHours, 0);
} // End function fHourAngle
function fSecondAngle(currentTime) {
// Calculate the expected angle
var secondsToMilliseconds = currentTime.getSeconds() * 1000;
var totalMilliseconds = currentTime.getMilliseconds() + secondsToMilliseconds;
return Math.floor(CIRCLE_TO_MS_RATIO * totalMilliseconds, 0);
} // End function fSecondAngle
function fDayCycleAngle(currentHours) {
// Calculate the expected angle
return Math.floor(((360/3) * (currentHours/9)),0);
} // End function fDayCycleAngle
function fDrawAsRotatedInLayer(image, angle, x) {
switch (x) {
case 1:
// Rotate around this point
ctx_l1.rotate(angle * DEGRESS_TO_RADIANS);
// Draw the image back and up
ctx_l1.drawImage(image, 0 - HALF_HEIGHT, 0 - HALF_WIDTH);
break;
case 2:
// Rotate around this point
ctx_l2.rotate(angle * DEGRESS_TO_RADIANS);
// Draw the image back and up
ctx_l2.drawImage(image, 0 - HALF_HEIGHT, 0 - HALF_WIDTH);
break;
case 3:
// Rotate around this point
ctx_l3.rotate(angle * DEGRESS_TO_RADIANS);
// Draw the image back and up
ctx_l3.drawImage(image, 0 - HALF_HEIGHT, 0 - HALF_WIDTH);
break;
case 3:
// Rotate around this point
ctx_l4.rotate(angle * DEGRESS_TO_RADIANS);
// Draw the image back and up
ctx_l4.drawImage(image, 0 - HALF_HEIGHT, 0 - HALF_WIDTH);
break;
default:
break;
}
} // End function fDrawAsRotatedInLayer
function draw() {
var currentTime = new Date();
var today = new Date();
var diffMs = (today - WyrdTimeStarts); // milliseconds in the Wyrd so far
var diffDays = Math.floor(diffMs / 97200000); // Wyrd days
var diffHrs = (diffMs % 97200000) / 3600000; // hours
var diffMins = ((diffMs % 97200000) % 3600000) / 60000; // minutes
fCleanCanvas();
// Draw the clock background onto canvas layer 1
ctx_l1.drawImage(clock_face_base, 0, 0);
// Save canvas layer 1's drawing state
ctx_l1.save();
// Move to center point for rotation of hour hand
ctx_l1.translate(HALF_HEIGHT, HALF_WIDTH);
fDrawAsRotatedInLayer(hour_hand, fHourAngle(diffHrs), 1);
// Restore canvas layer 1's previous drawing state
ctx_l1.restore();
// Draw the clock's middle layer onto canvas layer 2
ctx_l2.drawImage(clock_face_mid, 0, 0);
// Save canvas layer 2's drawing state
ctx_l2.save();
// Move to center point for rotation of minute hand
ctx_l2.translate(HALF_HEIGHT, HALF_WIDTH);
fDrawAsRotatedInLayer(minute_hand, fMinuteAngle(diffMins), 2);
// Restore canvas layer 2's previous drawing state
ctx_l2.restore();
// Save canvas layer 3's drawing state
ctx_l3.save();
// Move to center point for rotation of day cycle (shows which 9 hour segment of the 27 hour day is it)
ctx_l3.translate(HALF_HEIGHT, HALF_WIDTH);
fDrawAsRotatedInLayer(cycle_hand, fDayCycleAngle(diffHrs), 3);
// Restore canvas layer 3's previous drawing state
ctx_l3.restore();
// Draw the clock's cap onto canvas layer 4
ctx_l4.drawImage(clock_face_top, 0, 0);
// Save canvas layer 4's drawing state
ctx_l4.save();
// Move to center point for rotation of second hand
ctx_l4.translate(HALF_HEIGHT, HALF_WIDTH);
fDrawAsRotatedInLayer(second_hand, fSecondAngle(currentTime), 4);
// Restore canvas layer 4's previous drawing state
ctx_l4.restore();
window.requestAnimationFrame(draw, 1000 / FPS);
} // End function draw
function imgLoaded() {
// Image loaded event complete. Start the timer
window.requestAnimationFrame(draw, 1000 / FPS);
} // End function imgLoaded
function init() {
// Grab the clock element
var canvas1 = document.getElementById('clock_layer1');
var canvas2 = document.getElementById('clock_layer2');
var canvas3 = document.getElementById('clock_layer3');
var canvas4 = document.getElementById('clock_layer4');
// Canvas supported?
if(canvas1.getContext('2d')) {
ctx_l1 = canvas1.getContext('2d');
ctx_l2 = canvas2.getContext('2d');
ctx_l3 = canvas3.getContext('2d');
ctx_l4 = canvas4.getContext('2d');
// Load the hour hand image
hour_hand = new Image();
hour_hand.src = 'Wyrdling Clock - hand 1.png';
// Load the minute hand image
minute_hand = new Image();
minute_hand.src = 'Wyrdling Clock - hand 2.png';
// Load the cycle hand image
cycle_hand = new Image();
cycle_hand.src = 'Wyrdling Clock - hand 3.png';
// Load the second hand image
second_hand = new Image();
second_hand.src = 'Wyrdling Clock - hand 4.png';
// Load the clock face part 2 image
clock_face_mid = new Image();
clock_face_mid.src = 'Wyrdling Clock - face 2.png';
// Load the clock face part 3 image
clock_face_top = new Image();
clock_face_top.src = 'Wyrdling Clock - face 3.png';
// Load the clock face base image
clock_face_base = new Image();
clock_face_base.src = 'Wyrdling Clock - face 1.png';
clock_face_base.onload = imgLoaded;
} else {
alert("Canvas not supported!");
} // End if(canvas1.getContext('2d'))
} // End function init
</script>
</html>
一旦你看到它，你会后悔的。
看fDrawAsRotatedInLayer的开关，你有2倍的case 3:。它永远不会进入秒句柄