Gravity and platforms

Programming Questions

alvar.0

in Programming Questions • 4 months ago

Hello everyone, I have a little question about basic gravity and platforms.

In my programs, there's two squares : player and enemy. There is also a bunch of platforms, "solid" structures that no object is supposed to pass by.

Here are my problems :

- I just don't know how to come up with a basic gravity feature. I guess there is a force that pulls down the objets and jumping, for example, is just "going against" that force?

- I managed to "detect" if one square is over a platform, but I don't know how to make the platform "solid" as in : the animated objets cannot go into that part of the screen.

Here's my code, I hope you guys can help me.

Also, any comment on my code or problems with it will be more than welcome.

Thanks!

The code is divided in two parts. Main and Classes.

Player myPlayer;
Enemy myEnemy;
Platform [] myPlats = new Platform [6];
void setup() {
//boolean lost = false;
noSmooth();
size(600, 600);
frameRate(60);
background(255);
myPlayer = new Player(300, 570);
myEnemy = new Enemy(100, 100, 20, 20);
myPlats [0] = new Platform(0, 170, 220, 10);
myPlats [1] = new Platform(380, 170, 220, 10);
myPlats [2] = new Platform(150, 290, 300, 10);
myPlats [3] = new Platform(0, 410, 220, 10);
myPlats [4] = new Platform(380, 410, 220, 10);
myPlats [5] = new Platform(0, 590, 600, 10);
}
void draw() {
background(255);
for (int i = 0; i < myPlats.length; i++) {
myPlats[i].drawPlatform();
}
myEnemy.run();
myPlayer.run();
}
//Classes
//Classes
//The Player and the enemy are a class
float posX = 0;
float posY = 0;
float wX = 20;
float hX = 20;
float speed = 5;
float gravity = 0.2;
class Player {
//GLOBAL VARIABLES
//CONSTRUCTOR
Player(float _posX, float _posY) {
posX = _posX;
posY = _posY;
}
//FUNCTIONS
void run() {
display();
//collision();
//vibration();
System();
pMovement();
}
void display() {
noStroke();
fill(0);
rect(posX, posY, wX, hX);
}
//Ugghh...
void vibration() {
if (!keyPressed) {
posY = posY + random(-1, 1);
}
}
void pMovement() {
//First condition, not sure about it
// if ((((posX <=width) && posX >= 0)) && ((posY <=height) && (posY >=0))) {
{
if (keyPressed && keyCode == LEFT) {
posX = (constrain(posX-speed, 0, 600));
}
if (keyPressed && keyCode == RIGHT) {
posX = (constrain(posX+speed, 0, 580));
}
}
}
// }
void System() {
boolean collision = rectangle_collision(posX, posY, wX, hX, posEx, posEy, wEx, hEy);
if (collision) {
posX +=random(-3, 3);
fill(255, 0, 0, 125);
rect(0, 0, 1000, 1000);
fill(255);
stroke(255);
text("---------------------", width/2, height/2, 100, 100);
;
}
}
boolean rectangle_collision(float posX, float posY, float wX, float hX, float posEx, float posEy, float wEx, float hEy)
{
return !(posX > posEx+wX || posX+wX < posEx || posY > posEy+hEy || posY+hX < hEy);
}
}

//Enemy
float posEx = 0;
float posEy = 150;
float wEx = 20;
float hEy = 20;
class Enemy {
// Constructor
Enemy(float _posEx, float _posEy, float _wEx, float _hEy) {
posEx = _posEx;
posEy = _posEy;
wEx = _wEx;
hEy = _hEy;
}
float enSpeed = 5;
float gravity = 1;
void run() {
display();
movement();
// gravity();
}
void display() {
fill(255, 20, 20);
rect(posEx, posEy, 20, 20);
}
void movement() {
gravity();
posEx += enSpeed;
if ((((posEx >=585) || posEx <= 0)))
enSpeed = 0;
if (((posEy >=570) || (posEy <=0))) {
enSpeed = 0;
}
}
void gravity() {
posEy += gravity;
}
}
//Controls of enemy, if needed
/*
if (keyPressed && keyCode == LEFT) {
posEx = (constrain(posEx-enSpeed, 0, 600));
}
if (keyPressed && keyCode == RIGHT) {
posEx = (constrain(posEx+enSpeed, 0, 580));}
if (keyPressed && keyCode == UP) {
posEy = posEy-enSpeed;}
if (keyPressed && keyCode == DOWN) {
posEy = posEy+enSpeed;}
*/
// CHANGE CONTROLS FOR ENEMY.
// CHECK BOUNDERIES, SINCE THEY'RE NOT WORKING AT ALL FOR ENEMY
class Platform {
float xPos;
float yPos;
float platWidth;
float platHeight;
Platform(float x, float y, float w, float h) {
xPos = x;
yPos = y;
platWidth = w;
platHeight = h;
}
void drawPlatform() {
collisionEn();
displayPlat();
// collisionPlay();
}
void displayPlat() {
fill(0);
rect(xPos, yPos, platWidth, platHeight);
}
void collisionEn() {
for (int i = 0; i < myPlats.length; i++) {
if (posEx > myPlats[i].xPos
&& posEx+wEx > myPlats[i].xPos
&& posEx+wEx < myPlats[i].xPos + myPlats[i].platWidth
&& posEx < myPlats[i].xPos + myPlats[i].platWidth
&& posEy > myPlats[i].yPos
&& posEy < myPlats[i].yPos + myPlats[i].platHeight
&& posEy+hEy > myPlats[i].yPos
&& posEy+hEy < myPlats[i].yPos + myPlats[i].platHeight)
rect(0, 0, 1000, 1000);
}
}
// void collisionPlay(){
// for (int i = 0; i < myPlats.length; i++) {
// if (((posX > myPlats[i].xPos) && (posX < myPlats[i].xPos + myPlats[i].platWidth)) && ((posY > myPlats[i].yPos) && (posY < myPlats[i].yPos + myPlats[i].platHeight)))
// rect(0,0,1000,1000);}}
}

Replies(11)

Mushussu

Re: Gravity and platforms

4 months ago

Hello,

You have to read the handsome book of Daniel Shiffman :

http://natureofcode.com/book/chapter-2-forces/

You can use the Box2D library if you do not want to create all a physic world.

PhiLho

Some people, when confronted with a programming problem, think: "I know, I will use a library". Now, they have two problems...

Just joking, Mushussu's suggestion isn't bad, but mastering Box2D isn't trivial, and solving this little problem, already quite advanced, can be an interesting programming challenge (and it isn't that hard in itself).

Gravity: there is bouncing ball example sketch coming with Processing (the one bouncing on the ground). Also several topics on it on this forum. A little search and study can help. You have to manage acceleration of gravity, and perhaps rebounds with loss of energy (or not, for a player: no elasticity).
Solid platform: they are like the ground. Just stop movement when you check a rectangle collision (search the wiki or the site).

alvar.0

Re: Gravity and platforms

4 months ago

Seems like I have to get into vectors, right, PhiLho?

I will look at some tutorials and read on the topic. Seems kind of complicated to be honest, but I'll try to wrap my head around it.

v.k.

Re: Gravity and platforms

4 months ago

maybe you should try with one platform and one shape first...

alvar.0

Re: Re: Gravity and platforms

4 months ago

Exactly what I'm doing right now. I am working on one thing at a time on separate projects and then I'll put them all together.

v.k.

Re: Gravity and platforms

4 months ago

have you seen this already?

http://wiki.processing.org/w/Rect-Rect_intersection

alvar.0

Re: Gravity and platforms

4 months ago

Yes, I understand that. I can manage to not let a rect() go into another one in a simple program. But when I'm using an array to generate the platforms and classes for the Player and the Enemy it gets a little bit more complicated.

Also, I can manage to simulate gravity when I do something simple. Like, something appears on the screen and then it goes down. But on KeyPressed I cannot seem to make it work. I am working around it, I'll figure it out soon I hope.

From what I've tried until now, my function in which I define that pressing up makes the player go up seems to do just that : it goes up. It does not go down.

v.k.

Re: Gravity and platforms

4 months ago

Well I don't really understand what is going wrong or your goal, but I would try something in this way... Just a raw start maybe...

Platform[] pts = new Platform [10];
Enemy e;
void setup() {
size(300, 300);
for (int i=0; i< pts.length; i++) {
pts[i] = new Platform(random(width), random(height), 60, 10);
}
e = new Enemy(width/2, height/2, 15, 15);
}
void draw() {
background(255);
for (int i=0; i< pts.length; i++) {
pts[i].display();
}
e.display();
}
void keyPressed() {
if (key == CODED) {
switch (keyCode) {
case UP :
e.moveUp();
break;
case DOWN :
e.moveDown();
break;
case LEFT :
e.moveLeft();
break;
case RIGHT :
e.moveRight();
break;
}
}
}
class Platform {
float x, y, w, h;
Platform( float _x, float _y, float _w, float _h) {
x = _x;
y = _y;
w = _w;
h = _h;
}
void display() {
if (isColiding(e))
fill(170);
else
fill(10);
noStroke();
rect(x, y, w, h);
}
boolean isColiding(Enemy e)
{
return !(e.x > x+w || e.x + e.w < x || e.y > y+h || e.y + e.h < y);
}
}
class Enemy {
float x, y, w, h;
Enemy( float _x, float _y, float _w, float _h) {
x = _x;
y = _y;
w = _w;
h = _h;
}
void display() {
fill(255, 240, 20);
stroke(100, 10, 100);
rect(x, y, w, h);
}
void moveUp() {
y-=4;
}
void moveDown() {
y+=4;
}
void moveLeft() {
x-=4;
}
void moveRight() {
x+=4;
}
}

alvar.0

Re: Gravity and platforms

4 months ago

It is true that my description was pretty obscure. What I meant is that pressing up would result in a "jump".

v.k.

Re: Gravity and platforms

4 months ago

Sorry i didn't get you right. Ignore my previous answer. You may want to look for mario in the forum and openProcessing. Also there is this great tutorial about vectors by Daniel Shiffman if you want.

alvar.0

Re: Gravity and platforms

4 months ago

Thanks v.k., I was reading that page ( Mushussu recommended it earlier).

I am checking different samples and the methods change a lot depending on who made the program.

For instance, some programmers use a boolean to do the jumping thing I was trying to do. Others don't even use vectors if I understood their code correctly. Some examples allow me to do what I want but they do it without using classes to generate the objets, which I do, and I cannot figure out how to mix the two.

I feel like I'm at a hard part of the learning process, but I have to get through this to be able to achieve my programming goals!

These are two programs I've been studying to understand how to build mine :

http://www.openprocessing.org/sketch/72711

http://www.openprocessing.org/sketch/72713

Thanks for your help.

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