Creation of a platform game with Flash - step 1

November 3rd update: part 2 released.

Back from my holidays, here I come with a brand new tutorial serial.

This time I will talk about platform games.

"Platform game, or platformer, is a video game genre characterized by jumping to and from suspended platforms or over obstacles. It must be possible to control these jumps and to fall from platforms or miss jumps. The most common unifying element to these games is a jump button."

This is the beginning of a very interesting article taken from Wikipedia.

I strongly recommend you to read it... all in all it's a piece of our history.

I think we can develop interesting Flash platform games.

The very first step is introducing the level. I decided to code the level as a tile-based level, so you should read How to load levels in a Flash tile based game tutorial before all.

Level creation

In this example I am going to use the array method.

In the first frame write the actionscript:

Line 1: Defining a new array called level that will contain the level data

Line 2: Creating a new empty movie clip that will contain the level

Lines 3-17: Populating the array with more arrays to design the level. We will have a zero for an empty spot or a one for a platform/wall

Lines 18-19: Loops that scan the entire array and sub-arrays

Lines 20-23: If the array at position (y,x) is different than zero (in this case it can only be one but this will be useful when we will introduce different types of platforms) then attach a movie previously created and linkaged as "block" in the right position according to y and x array position. The gotoAndStop instruction will be useful when we will have more platform tiles, one per frame in the same movieclip.

Now the level is complete, time to add the hero.

The Player

I linkaged another movieclip as player. In this first example, you should design your hero smaller than any other platform. We'll see in further tutorials how this won't be so important once the game engine will be finished, but at the moment it's very important.

The new actionscript is:

Line 1: Initializing yspeed variable at zero. This is the vertical speed of the player

Line 2: Initializing max_yspeed variable at 16. This is the maximum vertical speed of the player. You will know what I mean in a minute or two.

Line 3: Initializing gravity variable at 1. This represents the gravity of the game.

Here I have to make a consideration: there should be two types of platforms: one with a so called "gravity" and one without it.
If you make a platform game with gravity, when the player steps off a platform, he will start falling down at increasing speed, just like in the real world. If you make the game without gravity, when the player steps off a platform, he will simply "move down" at a constant speed.

If you want the player to fall down at an increasing speed, use a low gravity value and a high max_yspeed value, like in my example. You will have to put a limit to yspeed anyway for a playability reason.

If you want the player to fall down at a constant speed, use a mid gravity value, such as 4 or 5 and do the same for the max_yspeed value. In this case, I suggest to set both values equals to the walking speed you will learn later.

Line 29: Putting the player on the stage, in a high place. You may need to reload the page to watch him fall.

Line 30: Routine to be executed at every frame

Line 31: yspeed variable is increased by gravity value

Lines 32-34: Checking if yspeed value exceeds max_yspeed value and if true, set yspeed value to max_yspeed value

Lines 35-37: These are the core lines for gravity management. Look: I perform an hit test between the platforms and the "feet" of the player plus yspeed value. In other words, I forecast next player's position as if there was no walls. Then, I check if there is a wall in that position. If there is a wall, I decrease yspeed value and repeat the whole operation.

This picture will explain how does it work.

Line 38: Adding yspeed to _y position. As explained, yspeed can be zero if the player is already on a platform

Now we have a static player on the stage. Time to move him!

The moving player

We want now the player to move left and right