Is there a better way of writing this data structure in Dart? - dictionary

Question

Map in Dart is an hash table, am I right?
Map starsData = {
'stars':{
'star1': {'x': 0, 'y': 10},
'star2': {'x': 0, 'y': 10}
}
};
This object below in JavaScript can be accessed as an hash table, faster!! I just want to do the some in Dart, but I am not sure if the best way is using Map.
const starsData = {
stars:{
'star1': {'x': 0, 'y': 10},
'star2': {'x': 0, 'y': 10}
}
};

Answer 1

I have rewritten your JavaScript implementation (based on the project your linked: https://github.com/ToniCalfim/fallingstars/blob/master/index.js) in Dart:
Can also be tested with:
https://dartpad.dev/900989f4e35e5a61200e4ad04ecd399a
import 'dart:html';
import 'dart:math' as math;
const starsDiameter = 1.25;
const colorPallete = [
'white',
'yellow',
'blue',
'red',
'orange',
'turquoise',
'purple',
'green',
'lightblue',
'lightyellow',
'lightgreen',
'darkred',
'darkblue',
'darkorange',
'darkturquoise',
'darkgreen'
];
final math.Random _rnd = math.Random();
int getRandomNumber(int min, int max) => min + _rnd.nextInt(max - min);
class Star {
int x, y;
int positionX = getRandomNumber(2, 650);
int positionY = getRandomNumber(3, 125);
double diameter = starsDiameter;
int pulsing = 0;
int blinking = 0;
int timeToFall = getRandomNumber(0, 7500);
int velocityToFall = getRandomNumber(1, 5);
int directionToFall = getRandomNumber(-1, 1);
String color = colorPallete[getRandomNumber(0, colorPallete.length)];
Star() {
x = positionX;
y = positionY;
}
}
final List<Star> stars = List.generate(175, (_) => Star());
void update() {
for (final currentStar in stars) {
final currentTimeToFall = currentStar.timeToFall;
if (currentTimeToFall != 0) {
currentStar.timeToFall = currentTimeToFall - 1;
} else {
final currentVelocityToFall = currentStar.velocityToFall;
final currentAngleToFall = currentStar.directionToFall;
final currentPositionX = currentStar.x;
final currentPositionY = currentStar.y;
currentStar.x = currentPositionX + 1 * currentAngleToFall;
currentStar.y = currentPositionY + currentVelocityToFall;
}
}
}
final CanvasElement canvas = querySelector('#canvas') as CanvasElement;
final CanvasRenderingContext2D context2D = canvas.context2D;
void drawStars() {
context2D.clearRect(
0, 0, context2D.canvas.width, context2D.canvas.height); // Clear canvas
for (final currentStar in stars) {
context2D.beginPath();
context2D.fillStyle = currentStar.color;
context2D.arc(currentStar.x, currentStar.y, starsDiameter, 0, 2 * math.pi);
context2D.fill();
context2D.closePath();
}
}
void animateLoop([num highResTime]) {
update();
drawStars();
window.requestAnimationFrame(animateLoop);
}
void main() {
animateLoop();
}
By looking at your code I could not see any reason why the stars should be saved in a Map or other Hash tables related structure. You are using the stars in two ways: draw and update. In both cases your are just going through all the stars which can be done by using a simple list and iterate over all elements.
I should add that I am not a front-end programmer and I cannot really judge if the way your are drawing the 2D canvas is the most efficient way to do that. My converted code are only are attempt to show how the data could be structured in Dart.