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我很努力地理解爲什麼我的角度正在返回怪異的角度，如果任何東西比正確的角度繪製。我在HTML5中使用Canvas繪製了一個基本的三角形。試圖找到兩個向量（三角形）之間的角度（HTML5帆布）
我有html代碼和js代碼粘貼在這裏：請有人告訴我爲什麼只有這些直角加起來180度。我已經設置了js代碼來輸出角度和它們的總和到控制檯...所以你可以看到我在說什麼。
您可以修改繪圖函數代碼來設置其中一個點的位置以形成直角。然後您將看到180度和角度是正確的。
我在互聯網上搜索瞭解釋並檢查了我的公式。不能似乎找出這一個。
非常感謝您對您可以提供任何幫助..
--- CODE FOR HTML ---
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Canvas - Triangle experiment</title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"></script>
<script src="js/drawShapes.js"></script>
<style>
* { margin: 0; }
* { padding: 0; }
span.markings {
position: absolute;
}
div.drawingArea {
margin: 50px 0 0 10px;
padding: 0;
width: 500px;
height: 500px;
position: relative;
background: #ccc;
}
.coords { position: absolute; top: 0; left: 200px; }
.coords p { position: relative; }
.xcoord, .ycoord { font-weight: bold; color: red; }
#myCanvas { background: #eee; }
</style>
</head>
<body>
<div class="coords"><p>X: <span class="xcoord"></span></p><p>Y: <span class="ycoord"></span></p></div>
<div class="drawingArea">
<span class="markings A"></span>
<span class="markings B"></span>
<span class="markings C"></span>
<canvas id="myCanvas" width="410" height="410">Your browser does not have support for Canvas. You should see:</canvas>
</div>
</body>
</html>
--- CODE FOR JS ---
$(document).ready(function(){
// Just for dev purposes.. show X and Y coords when inside drawingArea
$('.drawingArea').mousemove(function(e){
$('.xcoord').html(e.pageX -10); // subtract 10 for margin left is 10
$('.ycoord').html(e.pageY -50); // subtract 40 bc margin top is 40
});
draw();
function draw()
{
// Initialize context
createContext('2d');
// Set the style properties.
context.fillStyle = '#fff';
context.strokeStyle = '#FF9900';
context.lineWidth = 5;
// Set initial positions and lengths
pts = {};
pts.AXLoc = 60;
pts.AYLoc = 40;
pts.BXLoc = 360;
pts.BYLoc = 40;
pts.CXLoc = 100;
pts.CYLoc = 340;
// Get difference between points
vector = {};
vector.Ax = Math.abs(pts.AXLoc-pts.BXLoc);
vector.Ay = Math.abs(pts.AYLoc-pts.BYLoc);
vector.Bx = Math.abs(pts.BXLoc-pts.CXLoc);
vector.By = Math.abs(pts.BYLoc-pts.CYLoc);
vector.Cx = Math.abs(pts.CXLoc-pts.AXLoc);
vector.Cy = Math.abs(pts.CYLoc-pts.AYLoc);
console.log(vector.Ax);
console.log(vector.Ay);
console.log(vector.Bx);
console.log(vector.By);
console.log(vector.Cx);
console.log(vector.Cy);
// Find the magnitude of each vector
vector.magA = Math.sqrt(Math.pow(vector.Ax, 2) + Math.pow(vector.Ay, 2));
vector.magB = Math.sqrt((Math.pow((vector.Bx), 2) + Math.pow((vector.By), 2)));
vector.magC = Math.sqrt((Math.pow((vector.Cx), 2) + Math.pow((vector.Cy), 2)));
// Cos A = (A.C)/sqrt(magnitude of A) x (magnited of C)
// This should return radian which is then converted to degrees
// Create function once code works!
vector.angleA = ((vector.Ax * vector.Cx) + (vector.Ay * vector.Cy))/(vector.magA * vector.magC);
vector.angleA = Math.acos(vector.angleA) * (180/Math.PI);
vector.angleB = ((vector.Ax * vector.Bx) + (vector.Ay * vector.By))/(vector.magA * vector.magB);
vector.angleB = Math.acos(vector.angleB) * (180/Math.PI);
vector.angleC = ((vector.Bx * vector.Cx) + (vector.By * vector.Cy))/(vector.magB * vector.magC);
vector.angleC = Math.acos(vector.angleC) * (180/Math.PI);
// Output test data
console.log('angle a = ' + vector.angleA);
console.log('angle b = ' + vector.angleB);
console.log('angle c = ' + vector.angleC);
vector.allangles = vector.angleA + vector.angleB + vector.angleC;
console.log('All angles = ' +vector.allangles); // only adds up to 180deg if right angle??!!
// Begin drawing
context.beginPath();
// Start from the top-left point.
context.moveTo(pts.AXLoc, pts.AYLoc); // give the (x,y) coordinates
context.lineTo(pts.BXLoc, pts.BYLoc);
context.lineTo(pts.CXLoc, pts.CYLoc);
//context.lineTo(pts.AXLoc, pts.AYLoc); // closes the origin point? alternate way of closing???
context.lineJoin = 'mitre';
context.closePath(); // closes the origin point? good for strokes
// Done! Now fill the shape, and draw the stroke.
// Note: your shape will not be visible until you call any of the two methods.
context.fill();
context.stroke();
context.closePath();
// Set position of markings (spans)
$('span.markings.A').css({
'top' : pts.AYLoc -30,
'left' : pts.AXLoc -5
});
$('span.markings.B').css({
'top' : pts.BYLoc -5,
'left' : pts.BXLoc +10
});
$('span.markings.C').css({
'top' : pts.CYLoc -5,
'left' : pts.CXLoc -25
});
// Write markings onto canvas (degrees and lengths)
$('span.markings.A').html('A');
$('span.markings.B').html('B');
$('span.markings.C').html('C');
}
function createContext(contextType)
{
// Get the canvas element.
var elem = document.getElementById('myCanvas');
if (!elem || !elem.getContext) {
return;
}
// Get the canvas 2d context.
context = elem.getContext(contextType);
if (!context) {
return;
}
}
});
好的謝謝Manishie！我會嘗試這個 – Rogelio
Manishie，所以我有點糊塗，但...這是我用信公式，所以不知道你是如何得出你的。儘管如此，我欠你。非常感謝。 http://www.youtube.com/watch?v=4WxniMJYySc&feature=plcp – Rogelio
沒問題！ :-)我從25年前的一本數學書籍中得到了我的解答！ – manishie