circle rotated rectangle collision detection - html5-canvas

Question

I am trying to implement the collision detection between rotated rectangle and circle by following this http://www.migapro.com/circle-and-rotated-rectangle-collision-detection/
I have added the code in jsfiddle here http://jsfiddle.net/Z6KSX/2/.
What am i missing here ?
function check_coll ( circle_x,circle_y, rect_x, rect_y, rect_width, rect_height, rect_angle)
{
// Rotate circle's center point back
var rect_centerX = rect_x /2 ;
var rect_centerY = rect_y /2 ;
var cx = (Math.cos(rect_angle) * (circle_x - rect_centerX)) - (Math.sin(rect_angle) * (circle_y - rect_centerY)) + rect_centerX;
var cy = (Math.sin(rect_angle) * (circle_x - rect_centerX)) + (Math.cos(rect_angle) * (circle_y - rect_centerY)) + rect_centerY;
// Closest point
var x, y;
// Find the unrotated closest x point from center of unrotated circle
if (cx < rect_x) {
x = rect_x;
}
else if (cx > rect_x + rect_width){
x = rect_x + rect_width;
}
else{
x = cx;
}
// Find the unrotated closest y point from center of unrotated circle
if (cy < rect_y){
y = rect_y;
}
else if (cy > rect_y + rect_height) {
y = rect_y + rect_height;
}
else {
y = cy;
}
// Determine collision
var collision = false;
var c_radius = 5;
var distance = findDistance(cx, cy, x, y);
if (distance < c_radius) {
collision = true; // Collision
}
else {
collision = false;
}
return collision;
}
function findDistance (x1, y1, x2, y2) {
var a = Math.abs(x1 - x2);
var b = Math.abs(y1 - y2);
var c = Math.sqrt((a * a) + (b * b));
return c;
}

Answer 1

Hehe, I find this amusing as I somewhat recently solved this for myself after spending a large amount of time going down the wrong path.
Eventually I figured out a way:
1.) Simply rotate the point of the center of the circle by the Negative amount the rectangle has been rotated by. Now the point is 'aligned' with the rectangle (in the rectangles relative coordinate space).
2.) Solve for circle vs. AABB. The way I solved it gave me a point on the rectangle that is closest to the circle's center.
3.) Rotate the resulting point from by the Positive amount the rectangle has been rotated by. Continue solving as usual (checking if the distance between that point and the circle center is within the circle's radius)
From a very quick glance at your code, it seems like maybe you are doing the same thing, but missing the last step? I suggest drawing out your point on the rectangle from step 2 to see exactly where it is to help debug.

Answer 2

I was able to figure this out . The issue in the code was, I was using the wrong radius and had missed the center of rect_x and rect_y
var rect_centerX = rect_x + (rect_width / 2);
var rect_centerY = rect_y + (rect_height /2);
When dealing with rotation on the canvas we will need to add the translate values to the corresponding x and y values used in createrect.

Answer 3

I also use this code for my project and it's working. The only thing you need to do is use -angle instead of the angle.
Here is my code link
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const rectX = 100;
const rectY = 100;
const rectWidth = 200;
const rectHeight = 100;
const circleRadius = 2;
const rectMidPointX = rectX + rectWidth / 2;
const rectMidPointY = rectY + rectHeight / 2;
const angle = Math.PI / 4;
let circleX;
let circleY;
canvas.addEventListener('mousemove', (e) => {
circleX = e.clientX;
circleY = e.clientY;
ctx.save();
ctx.beginPath();
ctx.fillStyle = '#fff';
ctx.arc(circleX, circleY, circleRadius, 0, 2 * Math.PI);
ctx.fill();
ctx.stroke();
ctx.restore();
calculateIntersection();
})
ctx.save();
//ctx.fillRect(100, 100, 100, 100);
ctx.strokeStyle = 'black';
ctx.translate(rectMidPointX, rectMidPointY);
ctx.rotate(angle);
ctx.translate(-rectMidPointX, -rectMidPointY);
ctx.strokeRect(rectX, rectY, rectWidth, rectHeight);
ctx.restore();
// Determine collision
let collision = false;
const findDistance = (fromX, fromY, toX, toY) => {
const a = Math.abs(fromX - toX);
const b = Math.abs(fromY - toY);
return Math.sqrt((a * a) + (b * b));
};
function calculateIntersection() {
// Rotate circle's center point back
const unrotatedCircleX = Math.cos(-angle) * (circleX - rectMidPointX) -
Math.sin(-angle) * (circleY - rectMidPointY) + rectMidPointX;
const unrotatedCircleY = Math.sin(-angle) * (circleX - rectMidPointX) +
Math.cos(-angle) * (circleY - rectMidPointY) + rectMidPointY;
// Closest point in the rectangle to the center of circle rotated backwards(unrotated)
let closestX, closestY;
// Find the unrotated closest x point from center of unrotated circle
if (unrotatedCircleX < rectX)
closestX = rectX;
else if (unrotatedCircleX > rectX + rectWidth)
closestX = rectX + rectWidth;
else
closestX = unrotatedCircleX;
// Find the unrotated closest y point from center of unrotated circle
if (unrotatedCircleY < rectY)
closestY = rectY;
else if (unrotatedCircleY > rectY + rectHeight)
closestY = rectY + rectHeight;
else
closestY = unrotatedCircleY;
const distance = findDistance(unrotatedCircleX, unrotatedCircleY, closestX, closestY);
if (distance < circleRadius)
collision = true; // Collision
else
collision = false;
console.log('collision', collision);
}
<canvas id="canvas" width="400px" height="400px" />