How do I add gravity to a square in my simulator in pygame?---python2.7

Question

I have no clue how to add a gravity mechanism to my square. Here is the code:

import pygame, sys
from colors import *
from random import randint
import particles

pygame.init()

#background = pygame.image.load("graphics//background.jpg")
#Background = pygame.Surface(background.get_size(), pygame.HWSURFACE)
#Background.blit(background, (0, 0))



grav_x = 2
grav_y = 2

global window, window_height, window_width, window_title
window_width, window_height = 800, 600
window_title = "particle game"
#title_icon = "graphics//icons//icon_title.jpg"
pygame.display.set_caption(window_title)
window = pygame.display.set_mode((window_width, window_height), 
pygame.HWSURFACE|pygame.DOUBLEBUF)


particle_size = 40


#class Particle(object):
    #def __init__(self, Color, xpos, ypos):
        #pygame.draw.rect(window, Color, pygame.Rect(xpos, ypos, particle_size, particle_size))


class Hydrogen:
    def __init__(self, Color, xpos, ypos):
        #Particle.__init__(self, Color, xpos, ypos)
        pygame.draw.rect(window, Color, pygame.Rect(xpos, ypos, particle_size, particle_size))

hydrogen = Hydrogen

isRunning = True

window.fill(Color.LightGray)

while isRunning:
    pygame.display.update()

    mx, my = pygame.mouse.get_pos()
    mx -= 20
    my -= 20

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            isRunning = False
        elif event.type == pygame.MOUSEBUTTONDOWN:
            hydrogen(Color.Purple, mx, my)

pygame.quit()
sys.exit()

The grav_x and grav_y are my measly attempts to create gravity.

Here is an example of my program being run down here.

---

I have tried adding gravity to my class, but it never works out, and I'm stuck brain dead.

If anyone has any ideas please tell me.

Answer 1

Here:

import pygame, sys
from random import randint

pygame.init()

#background = pygame.image.load("graphics//background.jpg")
#Background = pygame.Surface(background.get_size(), pygame.HWSURFACE)
#Background.blit(background, (0, 0))



grav_x = 2
grav_y = 2

global window, window_height, window_width, window_title
window_width, window_height = 800, 600
window_title = "particle game"
#title_icon = "graphics//icons//icon_title.jpg"
pygame.display.set_caption(window_title)
window = pygame.display.set_mode((window_width, window_height), 
pygame.HWSURFACE|pygame.DOUBLEBUF)


particle_size = 40


#class Particle(object):
    #def __init__(self, Color, xpos, ypos):
        #pygame.draw.rect(window, Color, pygame.Rect(xpos, ypos, particle_size, particle_size))


class Hydrogen:
    def __init__(self, Color, xpos, ypos, size):
        #Particle.__init__(self, Color, xpos, ypos)
        self.color = Color
        self.position = [xpos, ypos]
        self.size = size
        self.velocity = [0, 0]

    def draw(self):
        pygame.draw.rect(window, self.color, (self.position[0], self.position[1], self.size, self.size))

    def move(self):
        self.position[0] += self.velocity[0]
        self.position[1] += self.velocity[1]
        print(self.velocity)
        print(self.position)

    def gravity(self):
        self.velocity[1] += 0.1

    def floor_collide(self):
        if self.position[1] + self.size > window_height:
            self.position[1] = window_height - self.size
            self.velocity[1] = -0.5 * self.velocity[1]

hydrogen = Hydrogen((255, 255, 0), 50, 50, particle_size)

isRunning = True

clock = pygame.time.Clock()

while isRunning:
    mx, my = pygame.mouse.get_pos()
    mx -= 20
    my -= 20

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            isRunning = False

    hydrogen.gravity()
    hydrogen.floor_collide()
    hydrogen.move()

    window.fill((150, 150, 150))
    hydrogen.draw()
    pygame.display.update()
    clock.tick(60)
pygame.quit()
sys.exit() 

Some of it seems redundant now I have changed it, but I left it in. Also, since I did not have settings.py or the colors file I removed those, so you'll have to re-add them.

Answer 2

In general, what you do too implement gravity is to accelerate each particle downward on each update. I don't know pygame, but it looks like your particles don't move at all, so you should add the idea of motion and changing the position of particles repeatedly. I'd suggest setting a constant downward velocity first that is, subtract a constant from the y (or add, if the origin is at the top) and get that going. Then, gravity becomes multiplying the y velocity by 1.1 (for instance, play with it!) on each update.