026 : Collide with platform

We can add a check_platform_collisions() function that makes sure the player doesn't go below the platform.

We check to make sure that player's y-coordinate (the bottom of the player) doesn't go below the platform's y-coordinate (the top of the platform). If that ever happens, we move the player to the top of the platform and set the player's y-velocity to 0.

Right now, this platform collision detection is pretty basic - and only works with a single platform. We'll be expanding it later to make it more general.

script.js: Create the check_platform_collisions() function.

function check_input() { ... } function check_platform_collisions() { if (_player.y > _game.platform.y) { _player.y = _game.platform.y; _player.velocity_y = 0; } } // This is called ~60 times per second to update the world. function update_world() { ... }

Run your code in a browser and verify that there are no errors.

Since we'll be doing a lot more collision detection, we might as well create a check_collisions() function that will check for all the collisions that we care about in the game.

Right now, we only have platform collisions, so we only need to call check_platform_collisions(). We'll be adding more to this function later.

script.js: Create the check_collisions() function.

function check_input() { ... } function check_collisions() { check_platform_collisions(); } function check_platform_collisions() { ... }

Run your code in a browser and verify that there are no errors.

And finally, we need to call our check_collisions() function. We need to do that in update_world() so that the game checks for collisions whenever anything moves on the screen.

script.js: Add a call to check_collision() in update_world().

// This is called ~60 times per second to update the world. function update_world() { update_player(); check_collisions(); draw(); requestAnimationFrame(update_world); }

Run your code in a browser and verify that there are no errors.

Run your code and see if you can jump.

GOTO 028