070 : Adding more platforms

Before we can add more platforms, we'll first need to fixup the _player.platform variable.

Why? What's wrong with it?

Well, when we only had a single platform along the bottom of the screen, a simple boolean (true or false) value was good enough. But now that we're adding more platforms, we'll want to know **which** platform the player is standing on.

We can update _player.platform by initializing it to null (instead of false) and setting it to the platform (instead of true) when the player collides with a platform.

The null value simply means that there is no object stored in the variable - in our case, it means that there is no platform associated with the player.

script.js: Initializing the platform variable to null.

function init_player() { ... _player.origin_x = _player.width / 2; _player.origin_y = _player.height; _player.platform = false; _player.platform = null; _player.velocity_x = 0; _player.velocity_x_delta = 0.8; ... }

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

Fortunately we can still use _player.platform in the if statement in check_input() because (in JavaScript) a null value will be interpreted as false. Any non-null value will be interpreted as true.

script.js: Updating platform to null.

function check_input() { ... // Up arrow, 'w' and spacebar to jump. if (_game.keymap[38] || _game.keymap[87] || _game.keymap[32]) { // Only allow jumps if the player is on a platform. if (_player.platform) { _player.platform = false; _player.platform = null; _player.velocity_y = _player.velocity_y_jump; } } ... }

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

The last place to fixup is the check_platform_collisions() function.

function check_platform_collisions() { _player.platform = false; _player.platform = null; if (collide(_game.platform, _player)) { _player.platform = true; _player.platform = _game.platform; _player.y = _game.platform.y; _player.velocity_y = 0; } }

Now that the _player.platform variable has been updated, we can start adding more platforms.

GOTO 077 if you already have the Monster I - Stationary badge.

GOTO 076