# The basics of infinite terrain generation for a horizontal endless runner – discretizing the terrain with Simplify.js library and adding Matter physics

If you enjoyed the post about infinite terrain generation for a horizontal endless runner, and tried to build a physics terrain out of the example I published, you probably faced these issues:

1 – With a 750 pixels wide game, you absolutely can’t build 750 bodies to turn a cosine-generated terrain into a physics terrain.

2 – 750 points are too many even to draw the terrain using grahpics objects.

So we have to find a way to keep our terrain smooth while dramatically reduce the points needed to draw it. Less points mean less bodies.

Here comes into play the Ramerâ€“Douglasâ€“Peucker algorithm: the purpose of the algorithm is, given a curve composed of line segments, to find a similar curve with fewer points. The algorithm defines “dissimilar” based on the maximum distance between the original curve and the simplified curve. The simplified curve consists of a subset of the points that defined the original curve.

Coding the Ramer-Douglas-Peucker algorithm is quite easy, but why should we reinvent the wheel when we can use Simplify.js library by Vladimir “mourner” Agafonkin?

In this example, we have a randomly generated terrain made of more than 1300 points usually reduced – but perfectly working – to less than 50 physics bodies.

There is no interactivity: a terrain is generated, then 60 random polygons fall down, then a new terrain is generated, and so on.

It’s amazing how you can have a perfectly working terrain using less of 4% the original points.

Look at the source code:

```var game;

var gameOptions = {
startTerrainHeight: 0.5,
amplitude: 300,
slopeLength: [100, 350],
}
let gameConfig = {
type: Phaser.AUTO,
backgroundColor: 0x75d5e3,
scale: {
mode: Phaser.Scale.FIT,
autoCenter: Phaser.Scale.CENTER_BOTH,
parent: "thegame",
width: 1334,
height: 750
},
physics: {
default: "matter",
matter: {
debug: true,
debugBodyColor: 0x000000
}
},
scene: playGame
}
game = new Phaser.Game(gameConfig);
window.focus();
}
class playGame extends Phaser.Scene{
constructor(){
super("PlayGame");
}
create(){
this.sliceStart = new Phaser.Math.Vector2(0, Math.random());
this.drawTerrain(this.slopeGraphics, this.sliceStart);
}
drawTerrain(graphics, sliceStart){
let slopePoints = [];
let slopes = 0;
let slopeStart = 0;
let slopeStartHeight = sliceStart.y;
let currentSlopeLength = Phaser.Math.Between(gameOptions.slopeLength[0], gameOptions.slopeLength[1]);
let slopeEnd = slopeStart + currentSlopeLength;
let slopeEndHeight = Math.random();
let currentPoint = 0;
while(currentPoint < game.config.width){
if(currentPoint == slopeEnd){
slopes ++;
slopeStartHeight = slopeEndHeight;
slopeEndHeight = Math.random();
var y = game.config.height * gameOptions.startTerrainHeight + slopeStartHeight * gameOptions.amplitude;
slopeStart = currentPoint;
currentSlopeLength = Phaser.Math.Between(gameOptions.slopeLength[0], gameOptions.slopeLength[1]);
slopeEnd += currentSlopeLength;
}
else{
var y = (game.config.height * gameOptions.startTerrainHeight) + this.interpolate(slopeStartHeight, slopeEndHeight, (currentPoint - slopeStart) / (slopeEnd - slopeStart)) * gameOptions.amplitude;
}
slopePoints.push(new Phaser.Math.Vector2(currentPoint, y))
currentPoint ++ ;
}
let simpleSlope = simplify(slopePoints, 1, true);
graphics.x = sliceStart.x;
graphics.clear();
graphics.moveTo(0, game.config.height);
graphics.fillStyle(0x654b35);
graphics.beginPath();
simpleSlope.forEach(function(point){
graphics.lineTo(point.x, point.y);
}.bind(this))
graphics.lineTo(currentPoint, game.config.height);
graphics.lineTo(0, game.config.height);
graphics.closePath();
graphics.fillPath();
graphics.lineStyle(16, 0x6b9b1e);
graphics.beginPath();
simpleSlope.forEach(function(point){
graphics.lineTo(point.x, point.y);
})
graphics.strokePath();
for(let i = 1; i < simpleSlope.length; i++){
let line = new Phaser.Geom.Line(simpleSlope[i - 1].x, simpleSlope[i - 1].y, simpleSlope[i].x, simpleSlope[i].y);
let distance = Phaser.Geom.Line.Length(line);
let center = Phaser.Geom.Line.GetPoint(line, 0.5);
let angle = Phaser.Geom.Line.Angle(line)
isStatic: true,
angle: angle
})
}
this.add.text(0, game.config.height - 60, "Bodies to generate terrain: " + simpleSlope.length, {
fontFamily: "Arial",
fontSize: 64,
color: "#00ff00"
});
this.polygons = 0;
delay: 500,
callbackScope: this,
callback: function(){
this.matter.add.polygon(Phaser.Math.Between(0, game.config.width), -50, Phaser.Math.Between(3, 10), Phaser.Math.Between(10, 40));
this.polygons ++;
if(this.polygons > 60){
this.scene.start("PlayGame");
}
},
loop: true
});
}
interpolate(vFrom, vTo, delta){
let interpolation = (1 - Math.cos(delta * Math.PI)) * 0.5;
return vFrom * (1 - interpolation) + vTo * interpolation;
}
}
```

What about re-introducing the scrolling and adding a car? Wait for next tutorial to see a complete game prototype, meanwhile download the source code and enjoy.

215 GAME PROTOTYPES EXPLAINED WITH SOURCE CODE
// 1+2=3
// 10000000
// 2 Cars
// 2048
// Avoider
// Ballz
// Block it
// Blockage
// Bloons
// Boids
// Bombuzal
// Breakout
// Bricks
// Columns
// CubesOut
// Dots
// DROP'd
// Dudeski
// Eskiv
// Filler
// Fling
// Globe
// HookPod
// Hundreds
// InkTd
// Iromeku
// Lumines
// Magick
// MagOrMin
// Maze
// Memdot
// Nano War
// Nodes
// o:anquan
// Ononmin
// Pacco
// Phyballs
// Platform
// Poker
// Pool
// Poux
// Pudi
// qomp
// Racing
// Renju
// SameGame
// Security
// Sling
// Slingy
// Sokoban
// Splitter
// Sproing
// Stack
// Stairs
// Stringy
// Sudoku
// Tetris
// Threes
// Toony
// Turn
// TwinSpin
// vvvvvv
// Wordle
// Worms
// Yanga
// Zhed
// zNumbers