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roipeker/ball.dart

Created Nov 27, 2020
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graphx, balls vs lines collisions
class Ball extends Shape {
double radius, vx, vy;
Color color;
Ball({double x, double y, this.radius, this.vx, this.vy, this.color}) {
this.x = x;
this.y = y;
graphics
.beginFill(color.value, .8)
.lineStyle(6, 0x0)
.drawCircle(0, 0, radius)
.endFill()
.beginFill(Colors.black.value, .9)
.drawCircle(0, 0, 3)
.endFill();
}
}
/// roipeker2020
///
/// As other samples, use the `SceneBuilderWidget`.
///
/// web demo: https://roi-graphx-balls-collision.surge.sh/#/
class DemoBallLineCollision extends Sprite {
/// lazy with the types :P
var lines = [];
var points = <List<double>>[];
var balls = <Ball>[];
double maxAge = 200;
@override
void addedToStage() {
final random = GameUtils.rndRange;
List.generate(10, (index) {
var ball = Ball(
x: random(0, sw),
y: random(-50, -200),
radius: random(20, 50),
vx: random(-5, 5),
vy: 0,
color: GameUtils.rndFromList(Colors.primaries),
);
addChild(ball);
balls.add(ball);
});
stage.onMouseDown.add(_onMouseDown);
}
void _onMouseDown(input) {
stage.onMouseUp.addOnce((input) => stage.onMouseMove.removeAll());
stage.onMouseMove.add((input) => points.add([mouseX, mouseY, 0.0]));
points = [
[mouseX, mouseY, 0.0]
];
lines.add(points);
}
@override
void update(t) {
balls.forEach((b) => updateBall(b));
graphics.clear();
for (var i = 0; i < lines.length; i++) {
graphics.lineStyle(3, 0x212121);
var line = lines[i];
for (int j = 0; j < line.length; j++) {
var p = line[j];
p[2]++;
if (j == 0) {
graphics.moveTo(p[0], p[1]);
} else {
graphics.lineTo(p[0], p[1]);
}
}
/// remove empty points.
while (line.isNotEmpty && line[0][2] > maxAge) {
line.removeAt(0);
}
}
/// remove empty lines.
while (lines.length > 0 && lines[0].length == 0) {
lines.removeAt(0);
}
}
void updateBall(Ball ball) {
ball.vy += 0.1;
ball.x += ball.vx;
ball.y += ball.vy;
/// make it bounce back if it hits and goes up
if (ball.y < -200) {
ball.y = -200;
ball.vy *= -1;
}
/// if it went down the windows size, reset position and speed.
if (ball.y - ball.radius > sh) {
ball.x = GameUtils.rndRange(0, sw);
ball.y = -100;
ball.vy = ball.vx = 0;
}
/// make it hit the wall on the right side.
if (ball.x + ball.radius > sw) {
ball.x = sw - ball.radius;
ball.vx *= -1;
}
/// make it hit the wall on the left side.
if (ball.x - ball.radius < 0) {
ball.x = ball.radius;
ball.vx *= -1;
}
for (var i = 0; i < lines.length; i++) {
var line = lines[i];
for (var j = 0; j < line.length; j++) {
var p = line[j];
var px = p[0];
var py = p[1];
var dx = ball.x - px;
var dy = ball.y - py;
var dist = sqrt(dx * dx + dy * dy);
/// check if the distance between the circle and the points is less than
/// the circle radius, is a collision.
if (dist < ball.radius) {
/// move the ball along the line...
var nx = px + dx / dist * ball.radius;
var ny = py + dy / dist * ball.radius;
ball.vx += (nx - ball.x) * 2;
ball.vy += (ny - ball.y) * 2;
ball.x = nx;
ball.y = ny;
}
}
}
}
}
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