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<canvas id="surface" width="600" height="400"></canvas> |
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import 'dart:html'; | |
import 'dart:math' show pi; | |
CanvasElement canvas; | |
CanvasRenderingContext2D ctx; | |
const double RADIUS = 15.0; | |
class Ball { | |
double radius; | |
double startX = 50; | |
double startY = 50; | |
double velocityX = 0; | |
double velocityY = 0; | |
Ball(this.radius); | |
} | |
void main() { | |
canvas = querySelector('#surface'); | |
ctx = canvas.getContext('2d'); | |
var ball = new Ball(RADIUS); | |
void doMouseDown(event) { | |
ball.startX = event.page.x; | |
ball.startY = event.page.y; | |
} | |
canvas.onMouseDown.listen(doMouseDown); | |
void draw(num time) { | |
ctx.save(); | |
ctx.fillStyle = "rgba(200, 0, 200, .3)"; | |
ctx.fillRect(0, 0, canvas.width, canvas.height); | |
ctx.restore(); | |
ball.startX += ball.velocityX; | |
ball.startY += ball.velocityY; | |
ball.velocityX *= .99; | |
ball.velocityY *= .99; | |
ball.velocityY += .25; | |
ball.velocityX += .25; | |
if (ball.startY + ball.radius > canvas.height) { | |
ball.startY = canvas.height - ball.radius; | |
ball.velocityY = -(ball.velocityY).abs(); | |
} | |
; | |
if (ball.startX + ball.radius > canvas.width) { | |
ball.startX = canvas.width - ball.radius; | |
ball.velocityX = -(ball.velocityX).abs(); | |
} | |
; | |
ctx.save(); | |
ctx.translate(ball.startX, ball.startY); | |
ctx.fillStyle = "#ffff00"; | |
ctx.beginPath(); | |
ctx.arc(0, 0, ball.radius, 0, pi * 2, true); | |
ctx.closePath(); | |
ctx.fill(); | |
ctx.restore(); | |
window.requestAnimationFrame(draw); | |
}; | |
window.requestAnimationFrame(draw); | |
} |
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