我正在使用Javascript在我的应用程序中渲染车速表示例。从现有的脚本中，范围值从0到80，我正在尝试更改速度表的范围值 - 0-240。
我可以更改文本标记值，但我无法使针指向文本标记值。
我想通过使指针找到确切的文本标记值来实现。
在drawTextMarker()方法中，我更改了以下代码以更改标记中的文本值。
iTickToPrint += 30;
请在下面找到我的代码。
/*jslint plusplus: true, sloppy: true, indent: 4 */
(function () {
"use strict";
// this function is strict...
}());
var iCurrentSpeed = 20,
iTargetSpeed = 20,
bDecrement = null,
job = null;
function degToRad(angle) {
// Degrees to radians
return ((angle * Math.PI) / 180);
}
function radToDeg(angle) {
// Radians to degree
return ((angle * 180) / Math.PI);
}
function drawLine(options, line) {
// Draw a line using the line object passed in
options.ctx.beginPath();
// Set attributes of open
options.ctx.globalAlpha = line.alpha;
options.ctx.lineWidth = line.lineWidth;
options.ctx.fillStyle = line.fillStyle;
options.ctx.strokeStyle = line.fillStyle;
options.ctx.moveTo(line.from.X, line.from.Y);
// Plot the line
options.ctx.lineTo(
line.to.X,
line.to.Y
);
options.ctx.stroke();
}
function createLine(fromX, fromY, toX, toY, fillStyle, lineWidth, alpha) {
// Create a line object using Javascript object notation
return {
from: {
X: fromX,
Y: fromY
},
to: {
X: toX,
Y: toY
},
fillStyle: fillStyle,
lineWidth: lineWidth,
alpha: alpha
};
}
function drawOuterMetallicArc(options) {
/* Draw the metallic border of the speedometer
* Outer grey area
*/
options.ctx.beginPath();
// Nice shade of grey
//options.ctx.fillStyle = "rgb(127,127,127)";
//options.ctx.fillStyle = "rgb(0,0,0)";
var my_gradient = options.ctx.createLinearGradient(0,0,20,145);
my_gradient.addColorStop(1,"purple");
my_gradient.addColorStop(0,"pink");
options.ctx.fillStyle=my_gradient;
// Draw the outer circle
options.ctx.arc(options.center.X,
options.center.Y,
options.radius-10,
0,
Math.PI,
true);
// Fill the last object
options.ctx.fill();
}
function drawInnerMetallicArc(options) {
/* Draw the metallic border of the speedometer
* Inner white area
*/
options.ctx.beginPath();
// White
options.ctx.fillStyle = "rgb(255,255,255)";
//var my_gradient = options.ctx.createLinearGradient(0,0,15,135);
//my_gradient.addColorStop(1,"purple");
//my_gradient.addColorStop(0,"brown");
//options.ctx.fillStyle=my_gradient;
// Outer circle (subtle edge in the grey)
options.ctx.arc(options.center.X,
options.center.Y,
options.radius-10,
0,
Math.PI);
options.ctx.fill();
}
function drawMetallicArc(options) {
/* Draw the metallic border of the speedometer
* by drawing two semi-circles, one over lapping
* the other with a bot of alpha transparency
*/
drawOuterMetallicArc(options);
drawInnerMetallicArc(options);
}
function drawBackground(options) {
/* Black background with alphs transparency to
* blend the edges of the metallic edge and
* black background
*/
var i = 0;
options.ctx.globalAlpha = 0.2;
//var my_gradient = options.ctx.createLinearGradient(0,0,30,220);
//my_gradient.addColorStop(0,"white");
//my_gradient.addColorStop(1,"aqua");
//options.ctx.fillStyle=my_gradient;
options.ctx.fillStyle = "rgb(255,255,255)";
// Draw semi-transparent circles
for (i = 140; i < 150; i++) {
options.ctx.beginPath();
options.ctx.arc(options.center.X,
options.center.Y,
i,
0,
Math.PI,
true);
options.ctx.fill();
}
}
function applyDefaultContextSettings(options) {
/* Helper function to revert to gauges
* default settings
*/
options.ctx.lineWidth = 2;
options.ctx.globalAlpha = 0.5;
options.ctx.strokeStyle = "rgb(255, 255, 255)";
options.ctx.fillStyle = 'rgb(255,255,255)';
}
function drawSmallTickMarks(options) {
/* The small tick marks against the coloured
* arc drawn every 5 mph from 10 degrees to
* 170 degrees.
*/
var tickvalue = options.levelRadius - 8,
iTick = 0,
gaugeOptions = options.gaugeOptions,
iTickRad = 0,
onArchX,
onArchY,
innerTickX,
innerTickY,
fromX,
fromY,
line,
toX,
toY;
applyDefaultContextSettings(options);
// Tick every 20 degrees (small ticks)
for (iTick = 10; iTick < 180; iTick += 20) {
iTickRad = degToRad(iTick);
/* Calculate the X and Y of both ends of the
* line I need to draw at angle represented at Tick.
* The aim is to draw the a line starting on the
* coloured arc and continueing towards the outer edge
* in the direction from the center of the gauge.
*/
onArchX = gaugeOptions.radius - (Math.cos(iTickRad) * tickvalue);
onArchY = gaugeOptions.radius - (Math.sin(iTickRad) * tickvalue);
innerTickX = gaugeOptions.radius - (Math.cos(iTickRad) * gaugeOptions.radius);
innerTickY = gaugeOptions.radius - (Math.sin(iTickRad) * gaugeOptions.radius);
fromX = (options.center.X - gaugeOptions.radius) + onArchX;
fromY = (gaugeOptions.center.Y - gaugeOptions.radius) + onArchY;
toX = (options.center.X - gaugeOptions.radius) + innerTickX;
toY = (gaugeOptions.center.Y - gaugeOptions.radius) + innerTickY;
// Create a line expressed in JSON
line = createLine(fromX, fromY, toX, toY, "rgb(127,127,127)", 3, 0.6);
// Draw the line
drawLine(options, line);
}
}
function drawLargeTickMarks(options) {
/* The large tick marks against the coloured
* arc drawn every 10 mph from 10 degrees to
* 170 degrees.
*/
var tickvalue = options.levelRadius - 8,
iTick = 0,
gaugeOptions = options.gaugeOptions,
iTickRad = 0,
innerTickY,
innerTickX,
onArchX,
onArchY,
fromX,
fromY,
toX,
toY,
line;
applyDefaultContextSettings(options);
tickvalue = options.levelRadius - 2;
// 10 units (major ticks)
for (iTick = 20; iTick < 180; iTick += 20) {
iTickRad = degToRad(iTick);
/* Calculate the X and Y of both ends of the
* line I need to draw at angle represented at Tick.
* The aim is to draw the a line starting on the
* coloured arc and continueing towards the outer edge
* in the direction from the center of the gauge.
*/
onArchX = gaugeOptions.radius - (Math.cos(iTickRad) * tickvalue);
onArchY = gaugeOptions.radius - (Math.sin(iTickRad) * tickvalue);
innerTickX = gaugeOptions.radius - (Math.cos(iTickRad) * gaugeOptions.radius);
innerTickY = gaugeOptions.radius - (Math.sin(iTickRad) * gaugeOptions.radius);
fromX = (options.center.X - gaugeOptions.radius) + onArchX;
fromY = (gaugeOptions.center.Y - gaugeOptions.radius) + onArchY;
toX = (options.center.X - gaugeOptions.radius) + innerTickX;
toY = (gaugeOptions.center.Y - gaugeOptions.radius) + innerTickY;
// Create a line expressed in JSON
line = createLine(fromX, fromY, toX, toY, "rgb(127,127,127)", 3, 0.6);
// Draw the line
drawLine(options, line);
}
}
function drawTicks(options) {
/* Two tick in the coloured arc!
* Small ticks every 5
* Large ticks every 10
*/
drawSmallTickMarks(options);
drawLargeTickMarks(options);
}
function drawTextMarkers(options) {
/* The text labels marks above the coloured
* arc drawn every 10 mph from 10 degrees to
* 170 degrees.
*/
var innerTickX = 0,
innerTickY = 0,
iTick = 0,
gaugeOptions = options.gaugeOptions,
iTickToPrint = 0;
applyDefaultContextSettings(options);
// Font styling
options.ctx.font = 'italic 10px sans-serif';
options.ctx.textBaseline = 'top';
options.ctx.beginPath();
// Tick every 20 (small ticks)
for (iTick = 10; iTick < 180; iTick += 20) {
innerTickX = gaugeOptions.radius - (Math.cos(degToRad(iTick)) * gaugeOptions.radius);
innerTickY = gaugeOptions.radius - (Math.sin(degToRad(iTick)) * gaugeOptions.radius);
// Some cludging to center the values (TODO: Improve)
if (iTick <= 10) {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY + 5);
} else if (iTick < 50) {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX - 5,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY + 5);
} else if (iTick < 90) {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY);
} else if (iTick === 90) {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX + 4,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY);
} else if (iTick < 145) {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX + 10,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY);
} else {
options.ctx.fillStyle = 'rgb(0,0,0)';
options.ctx.fillText(iTickToPrint, (options.center.X - gaugeOptions.radius - 12) + innerTickX + 15,
(gaugeOptions.center.Y - gaugeOptions.radius - 12) + innerTickY + 5);
}
// MPH increase by 10 every 20 degrees
// iTickToPrint += Math.round(2160 / 9);
iTickToPrint += 30;
}
options.ctx.stroke();
}
function drawSpeedometerPart(options, alphaValue, strokeStyle, startPos) {
/* Draw part of the arc that represents
* the colour speedometer arc
*/
options.ctx.beginPath();
options.ctx.globalAlpha = alphaValue;
options.ctx.lineWidth = 5;
options.ctx.strokeStyle = strokeStyle;
options.ctx.arc(options.center.X,
options.center.Y,
options.levelRadius,
Math.PI + (Math.PI / 360 * startPos),
0 - (Math.PI / 360 * 10),
false);
options.ctx.stroke();
}
function drawSpeedometerColourArc(options) {
/* Draws the colour arc. Three different colours
* used here; thus, same arc drawn 3 times with
* different colours.
* TODO: Gradient possible?
*/
var startOfGreen = 10,
endOfGreen = 280,
endOfOrange = 280;
drawSpeedometerPart(options, 1.0, "rgb(82, 240, 55)", startOfGreen);
// drawSpeedometerPart(options, 0.9, "rgb(198, 111, 0)", endOfOrange);
drawSpeedometerPart(options, 0.9, "rgb(255, 0, 0)", endOfGreen);
}
function drawNeedleDial(options, alphaValue, strokeStyle, fillStyle) {
/* Draws the metallic dial that covers the base of the
* needle.
*/
var i = 0;
options.ctx.globalAlpha = alphaValue;
options.ctx.lineWidth = 3;
options.ctx.strokeStyle = strokeStyle;
options.ctx.fillStyle = fillStyle;
// Draw several transparent circles with alpha
for (i = 0; i < 25; i++) {
options.ctx.beginPath();
options.ctx.arc(options.center.X,
options.center.Y,
i,
0,
Math.PI,
true);
options.ctx.fill();
options.ctx.stroke();
}
}
function convertSpeedToAngle(options) {
/* Helper function to convert a speed to the
* equivelant angle.
*/
var iSpeed = (options.speed / 10),
iSpeedAsAngle = ((iSpeed * 20) + 10) % 180;
// Ensure the angle is within range
if (iSpeedAsAngle < 0) {
iSpeedAsAngle = iSpeedAsAngle + 180;
}else if(iSpeedAsAngle > 180) {
iSpeedAsAngle = iSpeedAsAngle - 180;
}
return iSpeedAsAngle;
}
function drawNeedle(options) {
/* Draw the needle in a nice read colour at the
* angle that represents the options.speed value.
*/
var iSpeedAsAngle = convertSpeedToAngle(options),
iSpeedAsAngleRad = degToRad(iSpeedAsAngle),
gaugeOptions = options.gaugeOptions,
innerTickX = gaugeOptions.radius - (Math.cos(iSpeedAsAngleRad) * 20),
innerTickY = gaugeOptions.radius - (Math.sin(iSpeedAsAngleRad) * 20),
fromX = (options.center.X - gaugeOptions.radius) + innerTickX,
fromY = (gaugeOptions.center.Y - gaugeOptions.radius) + innerTickY,
endNeedleX = gaugeOptions.radius - (Math.cos(iSpeedAsAngleRad) * gaugeOptions.radius),
endNeedleY = gaugeOptions.radius - (Math.sin(iSpeedAsAngleRad) * gaugeOptions.radius),
toX = (options.center.X - gaugeOptions.radius) + endNeedleX,
toY = (gaugeOptions.center.Y - gaugeOptions.radius) + endNeedleY,
line = createLine(fromX, fromY, toX, toY, "rgb(255,0,0)", 5, 0.6);
drawLine(options, line);
// Two circle to draw the dial at the base (give its a nice effect?)
drawNeedleDial(options, 0.6, "rgb(0, 0, 0)", "rgb(255,255,255)");
drawNeedleDial(options, 0.2, "rgb(0, 0, 0)", "rgb(127,127,127)");
}
function buildOptionsAsJSON(canvas, iSpeed) {
/* Setting for the speedometer
* Alter these to modify its look and feel
*/
var centerX = 170,
centerY = 170,
radius = 110,
outerRadius = 175;
// Create a speedometer object using Javascript object notation
return {
ctx: canvas.getContext('2d'),
speed: iSpeed,
center: {
X: centerX,
Y: centerY
},
levelRadius: radius - 10,
gaugeOptions: {
center: {
X: centerX,
Y: centerY
},
radius: radius
},
radius: outerRadius
};
}
function clearCanvas(options) {
options.ctx.clearRect(0, 0, 800, 600);
applyDefaultContextSettings(options);
}
function draw() {
/* Main entry point for drawing the speedometer
* If canvas is not support alert the user.
*/
console.log('Target: ' + iTargetSpeed);
console.log('Current: ' + iCurrentSpeed);
var canvas = document.getElementById('tutorial'),
options = null;
// Canvas good?
if (canvas !== null && canvas.getContext) {
options = buildOptionsAsJSON(canvas, iCurrentSpeed);
// Clear canvas
clearCanvas(options);
// Draw the metallic styled edge
drawMetallicArc(options);
// Draw thw background
drawBackground(options);
// Draw tick marks
drawTicks(options);
// Draw labels on markers
drawTextMarkers(options);
// Draw speeometer colour arc
drawSpeedometerColourArc(options);
// Draw the needle and base
drawNeedle(options);
} else {
alert("Canvas not supported by your browser!");
}
if(iTargetSpeed == iCurrentSpeed) {
clearTimeout(job);
return;
} else if(iTargetSpeed < iCurrentSpeed) {
bDecrement = true;
} else if(iTargetSpeed > iCurrentSpeed) {
bDecrement = false;
}
if(bDecrement) {
if(iCurrentSpeed - 10 < iTargetSpeed)
iCurrentSpeed = iCurrentSpeed - 1;
else
iCurrentSpeed = iCurrentSpeed - 5;
} else {
if(iCurrentSpeed + 10 > iTargetSpeed)
iCurrentSpeed = iCurrentSpeed + 1;
else
iCurrentSpeed = iCurrentSpeed + 5;
}
job = setTimeout("draw()", 5);
}
function drawWithInputValue() {
var txtSpeed = document.getElementById('txtSpeed');
if (txtSpeed !== null) {
iTargetSpeed = txtSpeed.value;
// Sanity checks
if (isNaN(iTargetSpeed)) {
iTargetSpeed = 0;
} else if (iTargetSpeed < 0) {
iTargetSpeed = 0;
} else if (iTargetSpeed > 80) {
iTargetSpeed = 80;
}
job = setTimeout("draw()", 5);
}
}<html lang="en">
<head>
<meta charset="utf-8" />
<title>Speedometer HTML5 Canvas</title>
<script src="speedometer.js"></script>
</head>
<body>
<canvas id="tutorial" width="380" height="170">Canvas not available.</canvas>
<div>
<form id="drawTemp">
<input type="text" id="txtSpeed" name="txtSpeed"> </input>
<input type="button" value="Draw" onClick="drawWithInputValue();">
</form>
</div>
</body>
<script>
function randomIntFromInterval(min, max) {
return Math.floor(Math.random() * (max - min + 1) + min);
}
window.onload = drawsRandomValues;
function drawsRandomValues() {
//var n = 25;
// var number = Math.floor(Math.random()*n)+1;
var number = randomIntFromInterval(0,220);
document.getElementById("txtSpeed").innerHTML = number;
document.getElementById("txtSpeed").value = number;
//alert(number);
drawWithInputValue();
}
setInterval("drawsRandomValues();", 3000);
</script>
</html>
任何人都建议我在哪里更改代码以实现此目的。
PS：我从Speedometer example
找到了上述脚本答案 0 :(得分：0)
似乎是convertSpeedToAngle()的一部分：
var iSpeed = (options.speed / 10),
iSpeedAsAngle = ((iSpeed * 20) + 10) % 180;
如果你输入40，那么你得到（（（40/10）* 20）+ 10）％180 = 90的角度。他们如何想出这种想法是超出我的。
由于您知道范围是0-180度，因此您想知道当前值使用的那些度数的百分比，然后找到以度为单位的相关角度。
范围[0-1]中的小数百分比由options.speed / 240给出，因为240是您的刻度上的最大值。
取这个百分比并乘以180得到它应该在度数方面下降的位置。然后，函数非常简单（没有任何错误检查！）：
function convertSpeedToAngle(options) {
return 180 * options.speed/240;
}
尝试将其插入并查看您的问题是否仍然存在。
答案 1 :(得分：0)
感谢@Miller的想法。我尝试了你的方法，但结果在某些方面有所不同。
顺便说一下，我想出来就像从
更改下面的代码var iSpeed = (options.speed / 10),
iSpeedAsAngle = ((iSpeed * 20) + 10) % 180;
到下面的新代码
var iSpeed = (options.speed / 30), // 30 --> between tick interval range
iSpeedAsAngle = ((iSpeed * 20) + 10) ; // omitted the modulo operator of 180
convertSpeedToAngle()方法中代码的上述更改，使指针指向确切的刻度值。