Семафоры
Используйте семафор, который содержит состояние столкновения круга.
Таким образом, в вашем Circle.prototype будет что-то вроде этих функций и свойств
Circle.prototype = {
collided: false, // when true change color
draw() {
ctx.strokeStyle = this.collided ? "red" : "blue";
ctx.lineWidth = 3;
ctx.beginPath();
ctx.arc(this.x, this.y, this.r - 1.5, 0, Math.PI * 2);
ctx.stroke();
},
...
...
// in update
update() {
// when collision is detected set semaphore
if (collision) {
this.collided = true;
}
}
}
Счетчики
Или вы можете захотеть, чтобы изменение цвета длилось только некоторое время. Вы можете изменить семафор и использовать его как счетчик. При столкновении установите для него количество кадров, для которых нужно изменить цвет.
Circle.prototype = {
collided: 0,
draw() {
ctx.strokeStyle = this.collided ? (this.collided--, "red") : "blue";
ctx.lineWidth = 3;
ctx.beginPath();
ctx.arc(this.x, this.y, this.r - 1.5, 0, Math.PI * 2);
ctx.stroke();
},
...
...
// in update
update() {
// when collision is detected set semaphore
if (collision) {
this.collided = 60; // 1 second at 60FPS
}
}
}
Пример
Этот пример взят из другого ответа, который я сделал ранее в этом году.
Как есть много кода. Я выделил соответствующий код с помощью
/*= ANSWER CODE ==============================================================
...
=============================================================================*/
В примере используются счетчики и меняются цвета 30 кадров после столкновения с другим мячом или стеной.
Я не делал используйте семафор, так как все шары станут красными в течение секунды.
canvas.width = innerWidth -20;
canvas.height = innerHeight -20;
mathExt(); // creates some additional math functions
const ctx = canvas.getContext("2d");
const GRAVITY = 0;
const WALL_LOSS = 1;
const BALL_COUNT = 10; // approx as will not add ball if space can not be found
const MIN_BALL_SIZE = 6;
const MAX_BALL_SIZE = 30;
const VEL_MIN = 1;
const VEL_MAX = 5;
const MAX_RESOLUTION_CYCLES = 100; // Put too many balls (or too large) in the scene and the
// number of collisions per frame can grow so large that
// it could block the page.
// If the number of resolution steps is above this value
// simulation will break and balls can pass through lines,
// get trapped, or worse. LOL
const SHOW_COLLISION_TIME = 30;
const balls = [];
const lines = [];
function Line(x1,y1,x2,y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
}
Line.prototype = {
draw() {
ctx.moveTo(this.x1, this.y1);
ctx.lineTo(this.x2, this.y2);
},
reverse() {
const x = this.x1;
const y = this.y1;
this.x1 = this.x2;
this.y1 = this.y2;
this.x2 = x;
this.y2 = y;
return this;
}
}
function Ball(x, y, vx, vy, r = 45, m = 4 / 3 * Math.PI * (r ** 3)) {
this.r = r;
this.m = m
this.x = x;
this.y = y;
this.vx = vx;
this.vy = vy;
/*= ANSWER CODE ==============================================================*/
this.collided = 0;
/*============================================================================*/
}
Ball.prototype = {
update() {
this.x += this.vx;
this.y += this.vy;
this.vy += GRAVITY;
},
draw() {
/*= ANSWER CODE ==============================================================*/
ctx.strokeStyle = this.collided ? (this.collided--, "#F00") : "#00F";
ctx.lineWidth = 3;
ctx.beginPath();
ctx.arc(this.x, this.y, this.r - 1.5, 0, Math.PI * 2);
ctx.stroke();
/* ============================================================================*/
},
interceptLineTime(l, time) {
const u = Math.interceptLineBallTime(this.x, this.y, this.vx, this.vy, l.x1, l.y1, l.x2, l.y2, this.r);
if (u >= time && u <= 1) {
return u;
}
},
checkBallBallTime(t, minTime) {
return t > minTime && t <= 1;
},
interceptBallTime(b, time) {
const x = this.x - b.x;
const y = this.y - b.y;
const d = (x * x + y * y) ** 0.5;
if (d > this.r + b.r) {
const times = Math.circlesInterceptUnitTime(
this.x, this.y,
this.x + this.vx, this.y + this.vy,
b.x, b.y,
b.x + b.vx, b.y + b.vy,
this.r, b.r
);
if (times.length) {
if (times.length === 1) {
if(this.checkBallBallTime(times[0], time)) { return times[0] }
return;
}
if (times[0] <= times[1]) {
if(this.checkBallBallTime(times[0], time)) { return times[0] }
if(this.checkBallBallTime(times[1], time)) { return times[1] }
return
}
if(this.checkBallBallTime(times[1], time)) { return times[1] }
if(this.checkBallBallTime(times[0], time)) { return times[0] }
}
}
},
collideLine(l, time) {
/*= ANSWER CODE ==============================================================*/
this.collided = SHOW_COLLISION_TIME;
/*============================================================================*/
const x1 = l.x2 - l.x1;
const y1 = l.y2 - l.y1;
const d = (x1 * x1 + y1 * y1) ** 0.5;
const nx = x1 / d;
const ny = y1 / d;
const u = (this.vx * nx + this.vy * ny) * 2;
this.x += this.vx * time;
this.y += this.vy * time;
this.vx = (nx * u - this.vx) * WALL_LOSS;
this.vy = (ny * u - this.vy) * WALL_LOSS;
this.x -= this.vx * time;
this.y -= this.vy * time;
},
collide(b, time) { // b is second ball
/*= ANSWER CODE ==============================================================*/
this.collided = SHOW_COLLISION_TIME;
b.collided = SHOW_COLLISION_TIME;
/*============================================================================*/
const a = this;
const m1 = a.m;
const m2 = b.m;
a.x = a.x + a.vx * time;
a.y = a.y + a.vy * time;
b.x = b.x + b.vx * time;
b.y = b.y + b.vy * time;
const x = a.x - b.x
const y = a.y - b.y
const d = (x * x + y * y);
const u1 = (a.vx * x + a.vy * y) / d
const u2 = (x * a.vy - y * a.vx ) / d
const u3 = (b.vx * x + b.vy * y) / d
const u4 = (x * b.vy - y * b.vx ) / d
const mm = m1 + m2;
const vu3 = (m1 - m2) / mm * u1 + (2 * m2) / mm * u3;
const vu1 = (m2 - m1) / mm * u3 + (2 * m1) / mm * u1;
b.vx = x * vu1 - y * u4;
b.vy = y * vu1 + x * u4;
a.vx = x * vu3 - y * u2;
a.vy = y * vu3 + x * u2;
a.x = a.x - a.vx * time;
a.y = a.y - a.vy * time;
b.x = b.x - b.vx * time;
b.y = b.y - b.vy * time;
},
doesOverlap(ball) {
const x = this.x - ball.x;
const y = this.y - ball.y;
return (this.r + ball.r) > ((x * x + y * y) ** 0.5);
}
}
function canAdd(ball) {
for(const b of balls) {
if (ball.doesOverlap(b)) { return false }
}
return true;
}
function create(bCount) {
lines.push(new Line(-10, 20, ctx.canvas.width + 10, 5));
lines.push((new Line(-10, ctx.canvas.height - 2, ctx.canvas.width + 10, ctx.canvas.height - 30)).reverse());
lines.push((new Line(30, -10, 4, ctx.canvas.height + 10)).reverse());
lines.push(new Line(ctx.canvas.width - 3, -10, ctx.canvas.width - 30, ctx.canvas.height + 10));
while (bCount--) {
let tries = 100;
while (tries--) {
const dir = Math.rand(0, Math.TAU);
const vel = Math.rand(VEL_MIN, VEL_MAX);
const ball = new Ball(
Math.rand(MAX_BALL_SIZE + 30, canvas.width - MAX_BALL_SIZE - 30),
Math.rand(MAX_BALL_SIZE + 30, canvas.height - MAX_BALL_SIZE - 30),
Math.cos(dir) * vel,
Math.sin(dir) * vel,
Math.rand(MIN_BALL_SIZE, MAX_BALL_SIZE),
);
if (canAdd(ball)) {
balls.push(ball);
break;
}
}
}
}
function resolveCollisions() {
var minTime = 0, minObj, minBall, resolving = true, idx = 0, idx1, after = 0, e = 0;
while (resolving && e++ < MAX_RESOLUTION_CYCLES) { // too main ball may create very lone resolution cycle. e limits this
resolving = false;
minObj = undefined;
minBall = undefined;
minTime = 1;
idx = 0;
for (const b of balls) {
idx1 = idx + 1;
while (idx1 < balls.length) {
const b1 = balls[idx1++];
const time = b.interceptBallTime(b1, after);
if (time !== undefined) {
if (time <= minTime) {
minTime = time;
minObj = b1;
minBall = b;
resolving = true;
}
}
}
for (const l of lines) {
const time = b.interceptLineTime(l, after);
if (time !== undefined) {
if (time <= minTime) {
minTime = time;
minObj = l;
minBall = b;
resolving = true;
}
}
}
idx ++;
}
if (resolving) {
if (minObj instanceof Ball) {
minBall.collide(minObj, minTime);
} else {
minBall.collideLine(minObj, minTime);
}
after = minTime;
}
}
}
create(BALL_COUNT);
mainLoop();
function mainLoop() {
ctx.clearRect(0,0,ctx.canvas.width, ctx.canvas.height);
resolveCollisions();
for (const b of balls) { b.update() }
for (const b of balls) { b.draw() }
ctx.lineWidth = 1;
ctx.strokeStyle = "#000";
ctx.beginPath();
for(const l of lines) { l.draw() }
ctx.stroke();
requestAnimationFrame(mainLoop);
}
function mathExt() {
Math.TAU = Math.PI * 2;
Math.rand = (min, max) => Math.random() * (max - min) + min;
Math.randI = (min, max) => Math.random() * (max - min) + min | 0; // only for positive numbers 32bit signed int
Math.randItem = arr => arr[Math.random() * arr.length | 0]; // only for arrays with length < 2 ** 31 - 1
// contact points of two circles radius r1, r2 moving along two lines (a,e)-(b,f) and (c,g)-(d,h) [where (,) is coord (x,y)]
Math.circlesInterceptUnitTime = (a, e, b, f, c, g, d, h, r1, r2) => { // args (x1, y1, x2, y2, x3, y3, x4, y4, r1, r2)
const A = a * a, B = b * b, C = c * c, D = d * d;
const E = e * e, F = f * f, G = g * g, H = h * h;
var R = (r1 + r2) ** 2;
const AA = A + B + C + F + G + H + D + E + b * c + c * b + f * g + g * f + 2 * (a * d - a * b - a * c - b * d - c * d - e * f + e * h - e * g - f * h - g * h);
const BB = 2 * (-A + a * b + 2 * a * c - a * d - c * b - C + c * d - E + e * f + 2 * e * g - e * h - g * f - G + g * h);
const CC = A - 2 * a * c + C + E - 2 * e * g + G - R;
return Math.quadRoots(AA, BB, CC);
}
Math.quadRoots = (a, b, c) => { // find roots for quadratic
if (Math.abs(a) < 1e-6) { return b != 0 ? [-c / b] : [] }
b /= a;
var d = b * b - 4 * (c / a);
if (d > 0) {
d = d ** 0.5;
return [0.5 * (-b + d), 0.5 * (-b - d)]
}
return d === 0 ? [0.5 * -b] : [];
}
Math.interceptLineBallTime = (x, y, vx, vy, x1, y1, x2, y2, r) => {
const xx = x2 - x1;
const yy = y2 - y1;
const d = vx * yy - vy * xx;
if (d > 0) { // only if moving towards the line
const dd = r / (xx * xx + yy * yy) ** 0.5;
const nx = xx * dd;
const ny = yy * dd;
return (xx * (y - (y1 + nx)) - yy * (x -(x1 - ny))) / d;
}
}
}
<canvas id="canvas"></canvas>