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Javascript Canvas Relative Mouse Coordinates on Rotated Rectangle?

I am trying to treat a rectangle in canvas as a piece of paper, and get the same relative coordinates returned when I hover over the same point regardless of scale, rotation, or translation of the page.
Currently I get accurate results when in portrait or inverted portrait rotations and regardless of scale/translation. However, when I switch to landscape or inverted landscape my results are off.
I've attempted to switch to rotating mouse coordinates with some trigonometric functions I found, but math is not my strong suit and it didn't work.
If someone could point me in the right direction, I would be grateful. I suspect I need to swap axis or height/width when rotating landscape but that hasn't been fruitful either.
R key rotates the "page" through 4, 90 degree changes. Coordinates of your mouse relative to the page, clamped to the page's width/height are displayed in console.
https://jsfiddle.net/2hg6u3wd/2/ (Note, JSFiddle offsets coordinates slightly for an unknown reason)
const orientation = Object.freeze({
portrait: 0,
landscape: -90,
invertedPortrait: 180,
invertedLandscape: 90
});
function CameraRotate(rotation) {
// Rotates using the center of target as origin.
ctx.translate(target.width / 2, target.height / 2);
ctx.rotate(-(currentRot * Math.PI / 180)); // Negate currentRot because ctx.rotate() is additive.
ctx.rotate(rotation * Math.PI / 180);
ctx.translate(-(target.width / 2), -(target.height / 2));
currentRot = rotation;
}
function CameraCalcRelTargetCoords(viewX, viewY) {
return {
x: clamp((viewX - ctx.getTransform().e) / ctx.getTransform().a, 0, page.width),
y: clamp((viewY - ctx.getTransform().f) / ctx.getTransform().d, 0, page.height)
};
}
function clamp(number, min, max) {
return Math.max(min, Math.min(number, max));
}
canvas.addEventListener(`mousemove`, function(e) {
console.log(CameraCalcRelTargetCoords(e.x, e.y));
});

When rotating (-)180 degrees, the scale is stored as skew since the axis are flipped. Thus you must divide by m12 and m21. This flipping also means x and y mouse coordinates need to be swapped as well.
Here is my solution:
function CameraCalcRelTargetCoords(viewX, viewY) {
// Mouse coordinates are translated to a position within the target's rectangle.
let relX, relY
if (currentRot == orientation.landscape || currentRot == orientation.invertedLandscape) {
// Landscape rotation uses skewing for scale as X/Y axis are flipped.
relX = clamp((viewY - ctx.getTransform().f) / ctx.getTransform().b, 0, target.width);
relY = clamp((viewX - ctx.getTransform().e) / ctx.getTransform().c, 0, target.height);
} else {
relX = clamp((viewX - ctx.getTransform().e) / ctx.getTransform().a, 0, target.width),
relY = clamp((viewY - ctx.getTransform().f) / ctx.getTransform().d, 0, target.height)
}
return {x: relX, y: relY};
}

Chart.js v2, remove padding/margin from radar chart

Has anyone run into the issue of removing padding (or margin?) from a chartjs chart?
Below is my code (in jsFiddle)...and image (notice the bottom? UGLY sauce).
Here's a JSFiddle that highlights the issue. Notice the padding at the bottom of the white box. https://jsfiddle.net/mre1p46x/

You can wrap a bit of logic around the fit method using the beforeFit and afterFit handlers to correct this padding when the number of labels is 3 (the fit function starts off by assuming a maximum radius of half the chart height. For a triangle, we actually have a bit more space)
All we do is scale the height property to compensate for this assumption, like so
...
options: {
scale: {
beforeFit: function (scale) {
if (scale.chart.config.data.labels.length === 3) {
var pointLabelFontSize = Chart.helpers.getValueOrDefault(scale.options.pointLabels.fontSize, Chart.defaults.global.defaultFontSize);
scale.height *= (2 / 1.5)
scale.height -= pointLabelFontSize;
}
},
afterFit: function (scale) {
if (scale.chart.config.data.labels.length === 3) {
var pointLabelFontSize = Chart.helpers.getValueOrDefault(scale.options.pointLabels.fontSize, Chart.defaults.global.defaultFontSize);
scale.height += pointLabelFontSize;
scale.height /= (2 / 1.5);
}
},
...
The scaling factor 2 / 1.5 is pretty easy to figure out
With h = distance from center of triangle to a corner
Total height of the triangle = h + distance from center of triangle to a side
= h + h * sin 30
= 1.5 h
h currently = chart height / 2
We want to scale this by r, such that
1.5 * chart height / 2 * r = chart height
This gives us
r = 2 / 1.5
Fiddle - https://jsfiddle.net/zqp525gf/

arrange div elements in square using javascript and maths

I n number of divs which are arranged in a circle using JavaScript. Right now I set the dimension of each div to 40×40. Below is what I am able to achieve so far. This is how I find X & Y of each div.
x = 100 * Math.cos(angle) + hCenter;
y = 100 * Math.sin(angle) + vCenter;
where hCenter & vCenter are center point of the screen
When there are many circles they start overlapping each other. How
can I find the height & width of each div so that they fit in circle
with a little space between each other.
How can I arrange the same circles in the square. Means animate from
circle to square. How to find new X,Y position of each div.

How can I find the height & width of each div so that they fit in circle with a little space between each other.
The width and height of each circle are the same as its diameter, which (plus the little splace) is equivalent to the length of the sides of the polygon formed by their positions. You know the size ("diameter") of the large square/circle in which the are arranged, so you can easily compute the length of the sides from that and the number of items. Then subtract a small constant or factor, and you've got your result.
How to find new X,Y position of each div so that they are arranged in a square?
Compute from the angle on which side of the square they will sit. You've got your first coordinate. Then, use sin/cos to compute the position on that side.
var dir = Math.round(angle / Math.PI * 2) % 4,
dis = dir<2 ? 100 : -100;
if (dir % 2 == 0) {
x = hCenter + dis;
y = vCenter + dis * Math.tan(angle);
} else {
x = hCenter + dis / Math.tan(angle);
y = vCenter + dis;
}

Raphael custom attribute (Arc) results in deformed circle

I am working on a progress bar plugin for jQuery that utilizes Raphael for smooth graphics.
I tried to transform the attribute function provided by this Raphael example (polar clock).
The problem is, that at first I didn't notice that the Raphael example also has the deformation error there. Relatively larger circles just mitigate it. Looking at smaller ones, it is noticeable.
And yes, I have basicly copy-pasted the function with some minor tweaks, but the end result sport the same error.
I have set up a JSBin where I've added reference circles to my scene, so it's easier to spot the issue: http://jsbin.com/ekovir/1
How do I tune the Arc function to draw proper circle?

I think it's a bug in Chrome's SVG rendering implementation. At least in FireFox and Safari it looks much better.
Also, when selecting the arc-to point, I think it's better to use (center.x + radius * cos(a-0.01), center.y + radius * sin(a-0.01)), instead of (center.x + radius * cos(a) - 0.01, center.y + radius * sin(a)), otherwise the center may shift a bit.
As a workaround, I suggest creating one set of segments for the progress bar and then changing their color as the work is done, instead of drawing new ones over the old. This should look fine in any browser, and I don't think the defects are easy to spot without the contrasting background circle.

I have found what caused the circle to be deformed.
I used stroke-width to set the "fatness" / "cap" of the circle, and the larger it gets, the more it deforms.
At least, those are my observations, it could as well technically be caued by something else.
Anyways, in order to get proper donut, I ended up with this method:
/**
* Donut circle drawing
*
* #param integer start Percentage to start with
* #param float diameter
* #param float fat How fat should the circle bar be
* #return object
*/
var fatDonutArc = function (start, diameter, fat)
{
var center = diameter / 2;
var outerRadius = center;
var innerRadius = center - fat; // subtract fat
var alpha = 360 / 100 * start;
var a = (90 - alpha) * Math.PI / -180; // -180 starts to draw from 12 o'clock
// calculate outer ring point coordinates
var outerX = center + outerRadius * Math.cos(a);
var outerY = center + outerRadius * Math.sin(a);
// calculate inner ring point coordinates
var innerX = center + innerRadius * Math.cos(a);
var innerY = center + innerRadius * Math.sin(a);
// path cache
var path;
if (start !== 100)
{
path = [
// move to start point of inner ring
[
"M",
center,
center - innerRadius
],
// draw a line to outer ring
[
"L",
center,
center - outerRadius
],
// arc to outer ring end
[
"A",
outerRadius,
outerRadius,
0,
+(alpha > 180),
1,
outerX,
outerY
],
// move to inner ring end
[
"L",
innerX,
innerY
],
// arc to inner ring start
[
"A",
innerRadius,
innerRadius,
0,
+(alpha > 180),
0,
center,
center - innerRadius
]
];
}
else
{
path = [
// move to outer ring start
[
"M",
center,
center - outerRadius
],
// arc around the clock
[
"A",
outerRadius,
outerRadius,
0,
+(alpha > 180),
1,
outerX - .1, // subtract, otherwise the path becomes "reset"
outerY
],
// connect
[
"z"
],
// move to inner circle start
[
"M",
innerX,
innerY
],
// arc around the clock
[
"A",
innerRadius,
innerRadius,
0,
+(alpha > 180),
0,
innerX + .1, // subtract, otherwise the path becomes "reset"
innerY
],
// and connect
[
"z"
]
];
}
return {
path : path
};
};
That's a mashup of: raphael.js - converting pie graph to donut graph + http://raphaeljs.com/polar-clock.html
Here I have set up an example, to see it in action: http://jsbin.com/erusos/1
There still is one unanswered question: In Chrome, is it the CSS renderer, that doesn't fully round the circle, or is it the SVG?
Enjoy!

Calculate the bounding box's X, Y, Height and Width of a rotated element via JavaScript

Basically I'm asking this question for JavaScript: Calculate Bounding box coordinates from a rotated rectangle
In this case:
iX = Width of rotated (blue) HTML element
iY = Height of rotated (blue) HTML element
bx = Width of Bounding Box (red)
by = Height of Bounding Box (red)
x = X coord of Bounding Box (red)
y = Y coord of Bounding Box (red)
iAngle/t = Angle of rotation of HTML element (blue; not shown but
used in code below), FYI: It's 37 degrees in this example (not that it matters for the example)
How does one calculate the X, Y, Height and Width of a bounding box (all the red numbers) surrounding a rotated HTML element (given its width, height, and Angle of rotation) via JavaScript? A sticky bit to this will be getting the rotated HTML element (blue box)'s original X/Y coords to use as an offset somehow (this is not represented in the code below). This may well have to look at CSS3's transform-origin to determine the center point.
I've got a partial solution, but the calculation of the X/Y coords is not functioning properly...
var boundingBox = function (iX, iY, iAngle) {
var x, y, bx, by, t;
//# Allow for negetive iAngle's that rotate counter clockwise while always ensuring iAngle's < 360
t = ((iAngle < 0 ? 360 - iAngle : iAngle) % 360);
//# Calculate the width (bx) and height (by) of the .boundingBox
//# NOTE: See https://stackoverflow.com/questions/3231176/how-to-get-size-of-a-rotated-rectangle
bx = (iX * Math.sin(iAngle) + iY * Math.cos(iAngle));
by = (iX * Math.cos(iAngle) + iY * Math.sin(iAngle));
//# This part is wrong, as it's re-calculating the iX/iY of the rotated element (blue)
//# we want the x/y of the bounding box (red)
//# NOTE: See https://stackoverflow.com/questions/9971230/calculate-rotated-rectangle-size-from-known-bounding-box-coordinates
x = (1 / (Math.pow(Math.cos(t), 2) - Math.pow(Math.sin(t), 2))) * (bx * Math.cos(t) - by * Math.sin(t));
y = (1 / (Math.pow(Math.cos(t), 2) - Math.pow(Math.sin(t), 2))) * (-bx * Math.sin(t) + by * Math.cos(t));
//# Return an object to the caller representing the x/y and width/height of the calculated .boundingBox
return {
x: parseInt(x), width: parseInt(bx),
y: parseInt(y), height: parseInt(by)
}
};
I feel like I am so close, and yet so far...
Many thanks for any help you can provide!
TO HELP THE NON-JAVASCRIPTERS...
Once the HTML element is rotated, the browser returns a "matrix transform" or "rotation matrix" which seems to be this: rotate(Xdeg) = matrix(cos(X), sin(X), -sin(X), cos(X), 0, 0); See this page for more info.
I have a feeling this will enlighten us on how to get the X,Y of the bounding box (red) based solely on the Width, Height and Angle of the rotated element (blue).
New Info
Humm... interesting...
Each browser seems to handle the rotation differently from an X/Y perspective! FF ignores it completely, IE & Opera draw the bounding box (but its properties are not exposed, ie: bx & by) and Chrome & Safari rotate the rectangle! All are properly reporting the X/Y except FF. So... the X/Y issue seems to exist for FF only! How very odd!
Also of note, it seems that $(document).ready(function () {...}); fires too early for the rotated X/Y to be recognized (which was part of my original problem!). I am rotating the elements directly before the X/Y interrogation calls in $(document).ready(function () {...}); but they don't seem to update until some time after(!?).
When I get a little more time, I will toss up a jFiddle with the example, but I'm using a modified form of "jquery-css-transform.js" so I have a tiny bit of tinkering before the jFiddle...
So... what's up, FireFox? That ain't cool, man!
The Plot Thickens...
Well, FF12 seems to fix the issue with FF11, and now acts like IE and Opera. But now I am back to square one with the X/Y, but at least I think I know why now...
It seems that even though the X/Y is being reported correctly by the browsers for the rotated object, a "ghost" X/Y still exists on the un-rotated version. It seems as though this is the order of operations:
Starting with an un-rotated element at an X,Y of 20,20
Rotate said element, resulting in the reporting of X,Y as 15,35
Move said element via JavaScript/CSS to X,Y 10,10
Browser logically un-rotates element back to 20,20, moves to 10,10 then re-rotates, resulting in an X,Y of 5,25
So... I want the element to end up at 10,10 post rotation, but thanks to the fact that the element is (seemingly) re-rotated post move, the resulting X,Y differs from the set X,Y.
This is my problem! So what I really need is a function to take the desired destination coords (10,10), and work backwards from there to get the starting X,Y coords that will result in the element being rotated into 10,10. At least I know what my problem is now, as thanks to the inner workings of the browsers, it seems with a rotated element 10=5!

I know this is a bit late, but I've written a fiddle for exactly this problem, on an HTML5 canvas:
http://jsfiddle.net/oscarpalacious/ZdQKg/
I hope somebody finds it useful!
I'm actually not calculating your x,y for the upper left corner of the container. It's calculated as a result of the offset (code from the fiddle example):
this.w = Math.sin(this.angulo) * rotador.h + Math.cos(this.angulo) * rotador.w;
this.h = Math.sin(this.angulo) * rotador.w + Math.cos(this.angulo) * rotador.h;
// The offset on a canvas for the upper left corner (x, y) is
// given by the first two parameters for the rect() method:
contexto.rect(-(this.w/2), -(this.h/2), this.w, this.h);
Cheers

Have you tried using getBoundingClientRect() ?
This method returns an object with current values of "bottom, height, left, right, top, width" considering rotations

Turn the four corners into vectors from the center, rotate them, and get the new min/max width/height from them.
EDIT:
I see where you're having problems now. You're doing the calculations using the entire side when you need to be doing them with the offsets from the center of rotation. Yes, this results in four rotated points (which, strangely enough, is exactly as many points as you started with). Between them there will be one minimum X, one maximum X, one minimum Y, and one maximum Y. Those are your bounds.

My gist can help you
Bounding box of a polygon (rectangle, triangle, etc.):
Live demo https://jsfiddle.net/Kolosovsky/tdqv6pk2/
let points = [
{ x: 125, y: 50 },
{ x: 250, y: 65 },
{ x: 300, y: 125 },
{ x: 175, y: 175 },
{ x: 100, y: 125 },
];
let minX = Math.min(...points.map(point => point.x));
let minY = Math.min(...points.map(point => point.y));
let maxX = Math.max(...points.map(point => point.x));
let maxY = Math.max(...points.map(point => point.y));
let pivot = {
x: maxX - ((maxX - minX) / 2),
y: maxY - ((maxY - minY) / 2)
};
let degrees = 90;
let radians = degrees * (Math.PI / 180);
let cos = Math.cos(radians);
let sin = Math.sin(radians);
function rotatePoint(pivot, point, cos, sin) {
return {
x: (cos * (point.x - pivot.x)) - (sin * (point.y - pivot.y)) + pivot.x,
y: (sin * (point.x - pivot.x)) + (cos * (point.y - pivot.y)) + pivot.y
};
}
let boundingBox = {
x1: Number.POSITIVE_INFINITY,
y1: Number.POSITIVE_INFINITY,
x2: Number.NEGATIVE_INFINITY,
y2: Number.NEGATIVE_INFINITY,
};
points.forEach((point) => {
let rotatedPoint = rotatePoint(pivot, point, cos, sin);
boundingBox.x1 = Math.min(boundingBox.x1, rotatedPoint.x);
boundingBox.y1 = Math.min(boundingBox.y1, rotatedPoint.y);
boundingBox.x2 = Math.max(boundingBox.x2, rotatedPoint.x);
boundingBox.y2 = Math.max(boundingBox.y2, rotatedPoint.y);
});
Bounding box of an ellipse:
Live demo https://jsfiddle.net/Kolosovsky/sLc7ynd1/
let centerX = 350;
let centerY = 100;
let radiusX = 100;
let radiusY = 50;
let degrees = 200;
let radians = degrees * (Math.PI / 180);
let radians90 = radians + Math.PI / 2;
let ux = radiusX * Math.cos(radians);
let uy = radiusX * Math.sin(radians);
let vx = radiusY * Math.cos(radians90);
let vy = radiusY * Math.sin(radians90);
let width = Math.sqrt(ux * ux + vx * vx) * 2;
let height = Math.sqrt(uy * uy + vy * vy) * 2;
let x = centerX - (width / 2);
let y = centerY - (height / 2);