Python pygame how to set the FPS

Question

I am making a python game and I don't know what should I set my FPS to. My game is stuck and not smooth. How do I know what should the FPS be?

This is my code:

http://bin.shortbin.eu:8080/x87bSUKUiN

Answer 1

After running your code I have also noticed frame rate drops which hurt the smoothness of the game.

There are two separate issues here:

1. The FPS drops

The FPS drops probably happen because of something you cannot control, like the garbage collector working. Even though you have no control of such issues, you can in general improve the performance of your game. See the following screen shot of a profiler run of your game:

You can see that the largest part of the time is spent on blit . However, a very large part of the time is also being spent in get_y_list . The get_y_list method also uses large lists which create a lot of garbage for the garbage collector to later collect, thus causing a further performance hit.

As I understand it, the get_y_list method is part of a very crude method that you're using for collision detection, one which basically takes quadratic time. Your algorithm seems to divide each object into a large amount of 2d cells, and then test collision between each pair of cells. Instead you can just test box to box intersection. If you wish to have a complicated collision shape for the objects you can use other algorithms, the internet is full of them. See this for example: https://developer.mozilla.org/en-US/docs/Games/Techniques/2D_collision_detection

Using other algorithms for collision detection will greatly improve your performance.

2. The game becoming non-smooth when there's an FPS drop.

The x and y positions of your objects are being updated like this for example: player.x -= player.vx . The physically correct method would be: player.x -= player.vx * DELTA_T . Where DELTA_T is the time elapsed since the last frame. If you don't use the time elapsed since the last frame, the speed of motion of your characters becomes dependent on FPS. Which is exactly what we're seeing.

Where do I get DELTA_T you might ask. You do it directly when calling tick:

def main():
    global DELTA_T

    finish = False
    background_x = 0
    background_y = 0
    background = pygame.image.load(BACKGROUND_IAMGE)

    while not finish:
        DELTA_T = clock.tick(REFRESH_RATE)

I tried adding the multiplication by DELTA_T but the game becomes unstable, because you assume that objects advance exactly vx 'cells' in each frame to detect collisions and floor penetrations. See my attempt below:

import pygame

pygame.init()
WINDOW_WIDTH = 700
WINDOW_HEIGHT = 500
SIZE = (WINDOW_WIDTH, WINDOW_HEIGHT)
SCREEN = pygame.display.set_mode(SIZE)
pygame.display.set_caption("Python Game")
WHITE = (255, 255, 255)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)
PINK = (255, 0, 255)
BACKGROUND_IAMGE = 'back.png'
clock = pygame.time.Clock()
REFRESH_RATE = 30
FRAMES_DELAY = 3

PLAYER_HEIGHT = 72
PLAYER_WIDTH = 40

MUSHROOM_HEIGHT = 31
MUSHROOM_WIDTH = 40

BLOCK_HEIGHT = 30
BLOCK_WIDTH = 30

FLOOR_Y = 435

DELTA_T = 0

class Player:
    def __init__(self, x, y):
        self.__images = [pygame.image.load('mario1.png'), pygame.image.load('mario2.png'),
                         pygame.image.load('mario3.png'), pygame.image.load('mario4.png'),
                         pygame.image.load('mario5.png'), pygame.image.load('mario6.png')]
        self.__current_image = self.__images[0]
        self.x = x
        self.y = y
        self.vx = 5/33.
        self.vy = 10/33.
        self.__is_mid_air = False
        self.__direction = "right"
        self.__is_jumping = False
        self.__MAX_JUMP = 20
        self.__is_walking = False
        self.__counter = 0
        self.__jump_counter = 0

    def reset_jump_counter(self):
        self.__jump_counter = 0

    def get_bottom_y(self):
        return int(self.y + PLAYER_HEIGHT)

    def set_walk(self, bol):
        self.__is_walking = bol

    def set_is_mid_air(self, bol):
        self.__is_mid_air = bol

    def is_mid_air(self):
        return self.__is_mid_air

    def get_image(self):
        if self.__is_mid_air and self.__direction == "right":
            self.__current_image = self.__images[4]
            return self.__current_image

        if self.__is_mid_air and self.__direction == "left":
            self.__current_image = self.__images[5]
            return self.__current_image

        self.__counter += 1
        if self.__counter > FRAMES_DELAY:
            self.__counter = 0

        if self.__counter == FRAMES_DELAY and self.__direction == "right":
            if self.__is_walking and self.__current_image == self.__images[0]:
                self.__current_image = self.__images[1]
            else:
                self.__current_image = self.__images[0]

        if self.__counter == FRAMES_DELAY and self.__direction == "left":
            if self.__is_walking and self.__current_image == self.__images[2]:
                self.__current_image = self.__images[3]
            else:
                self.__current_image = self.__images[2]

        return self.__current_image

    def stand_still(self):
        if self.__direction == "right":
            self.__current_image = self.__images[0]
        if self.__direction == "left":
            self.__current_image = self.__images[2]

    def set_jump(self, bol):
        self.__is_jumping = bol
        if not bol:
            self.reset_jump_counter()

    def check_jump(self):
        if self.__jump_counter != self.__MAX_JUMP and self.__is_jumping:
            self.y -= self.vy * DELTA_T
            self.__jump_counter += 1
        if self.__jump_counter >= self.__MAX_JUMP:
            self.__is_jumping = False
            self.__jump_counter = 0

    def is_jumping(self):
        return self.__is_jumping

    def fall(self):
        if not self.__is_jumping:
            self.y += self.vy * DELTA_T

    def get_direction(self):
        return self.__direction

    def turn_around(self):
        if self.__direction == "right":
            self.__direction = "left"
        elif self.__direction == "left":
            self.__direction = "right"

    def get_x_list(self):
        result = []
        for i in range(PLAYER_WIDTH + 1):
            result.append(self.x + i)
        return result

    def get_y_list(self):
        result = []
        for i in range(PLAYER_HEIGHT + 1):
            result.append(self.y + i)
        return result

    def get_right_x(self):
        return self.x + PLAYER_WIDTH

    def is_crash(self, obj):
        is_x_equals = False
        for i in range(int(self.vx * DELTA_T+0.5)):
            if self.x + PLAYER_WIDTH + i in obj.get_x_list():
                is_x_equals = True
            if self.x - i in obj.get_x_list():
                is_x_equals = True

        is_y_equals = False
        for i in range(int(self.vy*DELTA_T+0.5)):
            if self.y + PLAYER_HEIGHT + i in obj.get_y_list():
                is_y_equals = True
            if self.y - i in obj.get_y_list():
                is_y_equals = True

        return is_x_equals and is_y_equals

class Monster:
    def __init__(self, x, y, vx, vy, monster_type):
        self.__images = [pygame.image.load(monster_type + '1.png').convert(),
                         pygame.image.load(monster_type + '2.png').convert()]
        if monster_type == "mushroom":
            self.__width = MUSHROOM_WIDTH
            self.__height = MUSHROOM_HEIGHT

        self.__current_image = self.__images[0]
        self.__FIRST_X = x
        self.__FIRST_Y = y
        self.__x = x
        self.__y = y
        self.__vx = vx
        self.__vy = vy
        self.__direction = "left"
        self.__monster_type = monster_type
        self.__counter = 0

    def get_image(self):
        self.__counter += 1
        if self.__counter > FRAMES_DELAY:
            self.__counter = 0

        if self.__monster_type == "mushroom" and self.__counter == FRAMES_DELAY:
            if self.__current_image == self.__images[1]:
                self.__current_image = self.__images[0]
                self.__current_image.set_colorkey(PINK)
            else:
                self.__current_image = self.__images[1]
                self.__current_image.set_colorkey(PINK)
            return self.__current_image
        elif self.__monster_type == "mushroom" and self.__counter != FRAMES_DELAY:
            self.__current_image.set_colorkey(PINK)
            return self.__current_image

    def get_x(self):
        return self.__x

    def get_vx(self):
        return self.__vx

    def get_vy(self):
        return self.__vx

    def get_y(self):
        return self.__y

    def step(self):
        if self.__direction == "right":
            self.__x += self.__vx * DELTA_T
        elif self.__direction == "left":
            self.__x -= self.__vx * DELTA_T

    def get_direction(self):
        return self.__direction

    def turn_around(self):
        if self.__direction == "right":
            self.__direction = "left"
        elif self.__direction == "left":
            self.__direction = "right"

    def get_x_list(self):
        result = []
        for i in range(MUSHROOM_WIDTH + 1):
            result.append(self.__x + i)
        return result

    def get_y_list(self):
        result = []
        for i in range(MUSHROOM_HEIGHT + 1):
            result.append(self.__y + i)
        return result

    def is_crash(self, obj):
        is_x_equals = False
        for i in range(int(self.__vx * DELTA_T+0.5)):
            if self.__x + self.__width + i in obj.get_x_list():
                is_x_equals = True
            if self.__x - i in obj.get_x_list():
                is_x_equals = True

        is_y_equals = False
        for i in range(int(self.__vy * DELTA_T+0.5)):
            if self.__y + self.__height + i in obj.get_y_list():
                is_y_equals = True
            if self.__y - i in obj.get_y_list():
                is_y_equals = True

        return is_x_equals and is_y_equals

class Block:
    def __init__(self, x, y, width=1, height=1):
        self.__image = pygame.image.load("block.png")
        self.__x = x
        self.__y = y
        self.__width = width
        self.__height = height

    def load_image(self, background_x):
        for i in range(self.__width):
            for j in range(self.__height):
                SCREEN.blit(self.__image, (self.__x + (i * BLOCK_WIDTH) + background_x, self.__y + (j * BLOCK_HEIGHT)))

    def get_x_list(self):
        result = []
        for i in range(BLOCK_WIDTH * self.__width + 1):
            result.append(self.__x + i)
        return result

    def get_y_list(self):
        result = []
        for i in range(BLOCK_HEIGHT * self.__height + 1):
            result.append(self.__y + i)
        return result

    def get_y(self):
        return self.__y

    def get_x(self):
        return self.__x

    def get_width(self):
        return self.__width

    def get_height(self):
        return self.__height

    def get_bottom_y(self):
        return self.__y + (BLOCK_HEIGHT * self.__height)

    def get_right_x(self):
        return self.__x + self.__width * BLOCK_WIDTH

player = Player(140, FLOOR_Y - PLAYER_HEIGHT)
blocks = [Block(270, 280, 1, 1), Block(301, FLOOR_Y - BLOCK_HEIGHT * 8, 1, 8),
          Block(600, FLOOR_Y - BLOCK_HEIGHT * 8, 2, 8)]
monsters = [Monster(380, FLOOR_Y - MUSHROOM_HEIGHT, 3/33., 3/33., "mushroom")]

def main():
    global DELTA_T

    finish = False
    background_x = 0
    background_y = 0
    background = pygame.image.load(BACKGROUND_IAMGE)

    while not finish:
        DELTA_T = clock.tick(REFRESH_RATE)
        SCREEN.blit(background, (background_x, background_y))
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                finish = True

        block_on_right = False
        block_on_left = False
        is_player_on_block = False
        for block in blocks:
            block.load_image(background_x)
            for i in range(int(player.vy * DELTA_T+0.5)):
                for x in player.get_x_list():
                    if player.get_bottom_y() + i == block.get_y() and x in block.get_x_list():
                        is_player_on_block = True
                        player.y += i
                    if player.y - i == block.get_bottom_y() and x in block.get_x_list():
                        player.set_jump(False)
                        player.y -= i

            for i in range(int(player.vx*DELTA_T+0.5)):
                for y in player.get_y_list():
                    if player.get_right_x() + i == block.get_x() and y in block.get_y_list():
                        block_on_right = True
                        player.x += (i - 1)
                        background_x -= (i - 1)
                    if player.x - i == block.get_right_x() and y in block.get_y_list():
                        block_on_left = True
                        player.x -= (i - 1)
                        background_x += (i - 1)
            for monster in monsters:
                if monster.is_crash(block):
                    monster.turn_around()

        keys = pygame.key.get_pressed()

        if (keys[pygame.K_UP] or keys[pygame.K_SPACE] or keys[pygame.K_w]) and not player.is_mid_air():
            player.set_jump(True)

        if (keys[pygame.K_RIGHT] or keys[pygame.K_d]) and not block_on_right:
            if player.get_direction() != "right":
                player.turn_around()
            player.set_walk(True)

            background_x -= player.vx * DELTA_T
            player.x += player.vx * DELTA_T

        if (keys[pygame.K_LEFT] or keys[pygame.K_a]) and not block_on_left:
            if player.get_direction() != "left":
                player.turn_around()
            player.set_walk(True)

            if background_x != 0:
                background_x += player.vx * DELTA_T
                player.x -= player.vx * DELTA_T

        if not any(keys):
            player.stand_still()
            player.set_walk(False)

        for monster in monsters:
            monster.step()
            SCREEN.blit(monster.get_image(), (background_x + monster.get_x(), monster.get_y()))

        is_player_on_ground = False
        for i in range(int(player.vy * DELTA_T+0.5)):
            if player.get_bottom_y() + i == FLOOR_Y:
                player.y += i
                is_player_on_ground = True

        if is_player_on_block or is_player_on_ground:
            player.set_is_mid_air(False)
        else:
            player.set_is_mid_air(True)
            player.fall()

        player.check_jump()

        player_image = player.get_image().convert()
        player_image.set_colorkey(PINK)

        SCREEN.blit(player_image, (player.x + background_x, player.y))
        pygame.display.flip()

    pygame.quit()

if __name__ == '__main__':
    main()