Landing on Platforms

Part of the Worlds section of Coddy's Pygame journey. Lesson 16 of 35.

Now let walls hold the player up. After the sideways move is fixed, move along y and fix that move the same way: if the player overlaps a wall while falling, put its feet on the wall's top.

vel_y = min(vel_y + GRAVITY, MAX_FALL)
player.y += vel_y
on_ground = False
for wall in walls:
    if player.colliderect(wall):
        if vel_y > 0:
            player.bottom = wall.top
            vel_y = 0
            on_ground = True

on_ground starts each frame False and only a landing makes it True. Walk off a ledge, and the next frame finds nothing under the player, so it falls and cannot jump in the air.

This replaces the FLOOR line: the bottom row of the map is ground like any other wall. Gravity pulls the player 1 pixel into the ground every frame, and the landing test lifts it back, so it stands still.

Challenge

Medium

Remove the FLOOR line test.
After player.y += vel_y, set on_ground = False, then loop over walls.
For each wall the player collides with while vel_y > 0: player.bottom = wall.top, vel_y = 0, on_ground = True.

Try it yourself

import pygame

TILE = 36
SPEED = 4
GRAVITY = 1
JUMP = -15
MAX_FALL = 12
FLOOR = 324

LEVEL = [
    "................",
    "................",
    "................",
    "....P.....###...",
    "................",
    "................",
    "...####.........",
    "............#...",
    "#.......#...#..#",
    "################",
]

pygame.init()
screen = pygame.display.set_mode((576, 360))
pygame.display.set_caption("Landing")
clock = pygame.time.Clock()

background = pygame.image.load("assets/backgrounds/clouds.png").convert_alpha()
block_img = pygame.image.load("assets/images/block.png").convert_alpha()
player_img = pygame.image.load("assets/images/player.png").convert_alpha()

walls = []
for row, line in enumerate(LEVEL):
    for col, char in enumerate(line):
        if char == "#":
            walls.append(pygame.Rect(col * TILE, row * TILE, TILE, TILE))
        elif char == "P":
            start = (col * TILE + TILE // 2, row * TILE + TILE)

player = player_img.get_rect(midbottom=start)
vel_y = 0
on_ground = False

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN and event.key in (pygame.K_SPACE, pygame.K_UP):
            if on_ground:
                vel_y = JUMP
        elif event.type == pygame.KEYUP and event.key in (pygame.K_SPACE, pygame.K_UP):
            if vel_y < -4:
                vel_y = -4

    keys = pygame.key.get_pressed()
    dx = 0
    if keys[pygame.K_LEFT]:
        dx -= SPEED
    if keys[pygame.K_RIGHT]:
        dx += SPEED

    player.x += dx
    for wall in walls:
        if player.colliderect(wall):
            if dx > 0:
                player.right = wall.left
            elif dx < 0:
                player.left = wall.right

    vel_y = min(vel_y + GRAVITY, MAX_FALL)
    player.y += vel_y
    on_ground = False
    if player.bottom > FLOOR:
        player.bottom = FLOOR
        vel_y = 0
        on_ground = True

    for y in range(0, 360, 72):
        for x in range(0, 576, 72):
            screen.blit(background, (x, y))
    for wall in walls:
        screen.blit(block_img, wall)
    screen.blit(player_img, player)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()