Tag Archives: how-to

Swing into action with an homage to Pitfall! | Wireframe #48

via Raspberry Pi

Grab onto ropes and swing across chasms in our Python rendition of an Atari 2600 classic. Mark Vanstone has the code

Whether it was because of the design brilliance of the game itself or because Raiders of the Lost Ark had just hit the box office, Pitfall Harry became a popular character on the Atari 2600 in 1982.

His hazardous attempts to collect treasure struck a chord with eighties gamers, and saw Pitfall!, released by Activision, sell over four million copies. A sequel, Pitfall II: The Lost Caverns quickly followed the next year, and the game was ported to several other systems, even making its way to smartphones and tablets in the 21st century.


Designed by David Crane, Pitfall! was released for the Atari 2600 and published by Activision in 1982

The game itself is a quest to find 32 items of treasure within a 20-minute time limit. There are a variety of hazards for Pitfall Harry to navigate around and over, including rolling logs, animals, and holes in the ground. Some of these holes can be jumped over, but some are too wide and have a convenient rope swinging from a tree to aid our explorer in getting to the other side of the screen. Harry must jump towards the rope as it moves towards him and then hang on as it swings him over the pit, releasing his grip at the other end to land safely back on firm ground.

For this code sample, we’ll concentrate on the rope swinging (and catching) mechanic. Using Pygame Zero, we can get our basic display set up quickly. In this case, we can split the background into three layers: the background, including the back of the pathway and the tree trunks, the treetops, and the front of the pathway. With these layers we can have a rope swinging with its pivot point behind the leaves of the trees, and, if Harry gets a jump wrong, it will look like he falls down the hole in the ground. The order in which we draw these to the screen is background, rope, tree-tops, Harry, and finally the front of the pathway.

Now, let’s get our rope swinging. We can create an Actor and anchor it to the centre and top of its bounding box. If we rotate it by changing the angle property of the Actor, then it will rotate at the top of the Actor rather than the mid-point. We can make the rope swing between -45 degrees and 45 degrees by increments of 1, but if we do this, we get a rather robotic sort of movement. To fix this, we add an ‘easing’ value which we can calculate using a square root to make the rope slow down as it reaches the extremes of the swing.

Our homage to the classic Pitfall! Atari game. Can you add some rolling logs and other hazards?

Our Harry character will need to be able to run backwards and forwards, so we’ll need a few frames of animation. There are several ways of coding this, but for now, we can take the x coordinate and work out which frame to display as the x value changes. If we have four frames of running animation, then we would use the %4 operator and value on the x coordinate to give us animation frames of 0, 1, 2, and 3. We use these frames for running to the right, and if he’s running to the left, we just mirror the images. We can check to see if Harry is on the ground or over the pit, and if he needs to be falling downward, we add to his y coordinate. If he’s jumping (by pressing the SPACE bar), we reduce his y coordinate.

We now need to check if Harry has reached the rope, so after a collision, we check to see if he’s connected with it, and if he has, we mark him as attached and then move him with the end of the rope until the player presses the SPACE bar and he can jump off at the other side. If he’s swung far enough, he should land safely and not fall down the pit. If he falls, then the player can have another go by pressing the SPACE bar to reset Harry back to the start.

That should get Pitfall Harry over one particular obstacle, but the original game had several other challenges to tackle – we’ll leave you to add those for yourselves.

Pitfall Python code

Here’s Mark’s code for a Pitfall!-style platformer. To get it working on your system, you’ll need to  install Pygame Zero.  And to download the full code and assets, head here.

Get your copy of Wireframe issue 48

You can read more features like this one in Wireframe issue 48, available directly from Raspberry Pi Press — we deliver worldwide.
Wireframe issue 48
And if you’d like a handy digital version of the magazine, you can also download issue 48 for free in PDF format.
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Code a Light Cycle arcade minigame | Wireframe #47

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Speed around an arena, avoiding walls and deadly trails in this Light Cycle minigame. Mark Vanstone has the code.

Battle against AI enemies in the original arcade classic.

At the beginning of the 1980s, Disney made plans for an entirely new kind of animated movie that used cutting-edge computer graphics. The resulting film was 1982’s TRON, and it inevitably sparked one of the earliest tie-in arcade machines.

The game featured several minigames, including one based on the Light Cycle section of the movie, where players speed around an arena on high-tech motorbikes, which leave a deadly trail of light in their wake. If competitors hit any walls or cross the path of any trails, then it’s game over.

Players progress through the twelve levels which were all named after programming languages. In the Light Cycle game, the players compete against AI players who drive yellow Light Cycles around the arena. As the levels progress, more AI Players are added.

The TRON game, distributed by Bally Midway, was well-received in arcades, and even won Electronic Games Magazine’s (presumably) coveted Coin-operated Game of the Year gong.

Although the arcade game wasn’t ported to home computers at the time, several similar games – and outright clones – emerged, such as the unsubtly named Light Cycle for the BBC Micro, Oric, and ZX Spectrum.

The Light Cycle minigame is essentially a variation on Snake, with the player leaving a trail behind them as they move around the screen. There are various ways to code this with Pygame Zero.

In this sample, we’ll focus on the movement of the player Light Cycle and creating the trails that are left behind as it moves around the screen. We could use line drawing functions for the trail behind the bike, or go for a system like Snake, where blocks are added to the trail as the player moves.

In this example, though, we’re going to use a two-dimensional list as a matrix of positions on the screen. This means that wherever the player moves on the screen, we can set the position as visited or check to see if it’s been visited before and, if so, trigger an end-game event.

Our homage to the TRON Light Cycle classic arcade game.

For the main draw() function, we first blit our background image which is the cross-hatched arena, then we iterate through our two-dimensional list of screen positions (each 10 pixels square) displaying a square anywhere the Cycle has been. The Cycle is then drawn and we can add a display of the score.

The update() function contains code to move the Cycle and check for collisions. We use a list of directions in degrees to control the angle the player is pointing, and another list of x and y increments for each direction. Each update we add x and y coordinates to the Cycle actor to move it in the direction that it’s pointing multiplied by our speed variable.

We have an on_key_down() function defined to handle changing the direction of the Cycle actor with the arrow keys. We need to wait a while before checking for collisions on the current position, as the Cycle won’t have moved away for several updates, so each screen position in the matrix is actually a counter of how many updates it’s been there for.

We can then test to see if 15 updates have happened before testing the square for collisions, which gives our Cycle enough time to clear the area. If we do detect a collision, then we can start the game-end sequence.

We set the gamestate variable to 1, which then means the update() function uses that variable as a counter to run through the frames of animation for the Cycle’s explosion. Once it reaches the end of the sequence, the game stops.

We have a key press defined (the SPACE bar) in the on_key_down() function to call our init() function, which will not only set up variables when the game starts but sets things back to their starting state.

Here’s Mark’s code for a TRON-style Light Cycle minigame. To get it working on your system, you’ll need to install Pygame Zero. And to download the full code and assets, head here.

So that’s the fundamentals of the player Light Cycle movement and collision checking. To make it more like the original arcade game, why not try experimenting with the code and adding a few computer-controlled rivals?

Get your copy of Wireframe issue 47

You can read more features like this one in Wireframe issue 47, available directly from Raspberry Pi Press — we deliver worldwide.

And if you’d like a handy digital version of the magazine, you can also download issue 47 for free in PDF format.

The post Code a Light Cycle arcade minigame | Wireframe #47 appeared first on Raspberry Pi.

Code your own Pipe Mania puzzler | Wireframe #46

via Raspberry Pi

Create a network of pipes before the water starts to flow in our re-creation of a classic puzzler. Jordi Santonja shows you how.

A screen grab of the game in motion
Pipe Mania’s design is so effective, it’s appeared in various guises elsewhere – even as a minigame in BioShock.

Pipe Mania, also called Pipe Dream in the US, is a puzzle game developed by The Assembly Line in 1989 for Amiga, Atari ST, and PC, and later ported to other platforms, including arcades. The player must place randomly generated sections of pipe onto a grid. When a counter reaches zero, water starts to flow and must reach the longest possible distance through the connected pipes.

Let’s look at how to recreate Pipe Dream in Python and Pygame Zero. The variable start is decremented at each frame. It begins with a value of 60*30, so it reaches zero after 30 seconds if our monitor runs at 60 frames per second. In that time, the player can place tiles on the grid to build a path. Every time the user clicks on the grid, the last tile from nextTiles is placed on the play area and a new random tile appears at the top of the next tiles. randint(2,8) computes a random value between 2 and 8.

Our Pipe Mania homage. Build a pipeline before the water escapes, and see if you can beat your own score.

grid and nextTiles are lists of tile values, from 0 to 8, and are copied to the screen in the draw function with the screen.blit operation. grid is a two-dimensional list, with sizes gridWidth=10 and gridHeight=7. Every pipe piece is placed in grid with a mouse click. This is managed with the Pygame functions on_mouse_move and on_mouse_down, where the variable pos contains the mouse position in the window. panelPosition defines the position of the top-left corner of the grid in the window. To get the grid cell, panelPosition is subtracted from pos, and the result is divided by tileSize with the integer division //. tileMouse stores the resulting cell element, but it is set to (-1,-1) when the mouse lies outside the grid.

The images folder contains the PNGs with the tile images, two for every tile: the graphical image and the path image. The tiles list contains the name of every tile, and adding to it _block or _path obtains the name of the file. The values stored in nextTiles and grid are the indexes of the elements in tiles.

Here’s Jordi’s code for a Pipemania-style puzzler. To get it working on your system, you’ll need to install Pygame Zero. And to download the full code and assets, head here.

The image waterPath isn’t shown to the user, but it stores the paths that the water is going to follow. The first point of the water path is located in the starting tile, and it’s stored in currentPoint. update calls the function CheckNextPointDeleteCurrent, when the water starts flowing. That function finds the next point in the water path, erases it, and adds a new point to the waterFlow list. waterFlow is shown to the user in the draw function.

pointsToCheck contains a list of relative positions, offsets, that define a step of two pixels from currentPoint in every direction to find the next point. Why two pixels? To be able to define the ‘cross’ tile, where two lines cross each other. In a ‘cross’ tile the water flow must follow a straight line, and this is how the only points found are the next points in the same direction. When no next point is found, the game ends and the score is shown: the number of points in the water path, playState is set to 0, and no more updates are done.

Get your copy of Wireframe issue 46

You can read more features like this one in Wireframe issue 46, available directly from Raspberry Pi Press — we deliver worldwide.


And if you’d like a handy digital version of the magazine, you can also download issue 46 for free in PDF format.

The post Code your own Pipe Mania puzzler | Wireframe #46 appeared first on Raspberry Pi.

Powering up an HP YIG tuned oscillator

via Dangerous Prototypes

Kwong explained the operation principle of an YIG tuned oscillator and demonstrated the tuning characteristics:

I was going through some of the components I accumulated over the years and stumbled upon a Hewlett Packard YIG tuned oscillator (part number 5086-7023) that I bought a while back. This YIG oscillator was made for a frequency extension module for the HP 8660C synthesized signal generator and has a tunable range of between 2.7 to 4.2 GHz.

More details on Kerry Wong’s blog.

Check out the video after the break.

Code your own Artillery-style tank game | Wireframe #44

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Fire artillery shells to blow up the enemy with Mark Vanstone’s take on a classic two-player artillery game

Artillery Duel was an early example of the genre, and appeared on such systems as the Bally Astrocade and Commodore 64 (pictured).

To pick just one artillery game is difficult since it’s a genre in its own right. Artillery simulations and games have been around for almost as long as computers, and most commonly see two players take turns to adjust the trajectory of their tank’s turret and fire a projectile at their opponent. The earliest versions for microcomputers appeared in the mid-seventies, and the genre continued to develop; increasingly complex scenarios appeared involving historical settings or, as we saw from the mid-90s on, even offbeat ideas like battles between factions of worms.

To code the basics of an artillery game, we’ll need two tanks with turrets, a landscape, and some code to work out who shot what, in which direction, and where said shot landed. Let’s start with the landscape. If we create a landscape in two parts – a backdrop and foreground – we can make the foreground destructible so that when a missile explodes it damages part of the landscape. This is a common effect used in artillery games, and sometimes makes the gameplay more complicated as the battle progresses. In our example, we have a grass foreground overlaid on a mountain scene. We then need a cannon for each player. In this case, we’ve used a two-part image, one for the base and one for the turret, which means the latter can be rotated using the up and down keys.

Our homage to the artillery game genre. Fire away at your opponent, and hope they don’t hit back first.

For this code example, we can use the Python dictionary to store several bits of data about the game objects, including the Actor objects. This makes the data handling tidy and is quite similar to the way that JSON is used in JavaScript. We can use this method for the two cannons, the projectile, and an explosion object. As this is a two-player game, we’ll alternate between the two guns, allowing the arrow keys to change the angle of the cannon. When the SPACE bar is pressed, we call the firing sequence, which places the projectile at the same position as the gun firing it. We then move the missile through the air, reducing the speed as it goes and allowing the effects of gravity to pull it towards the ground.

We can work out whether the bullet has hit anything with two checks. The first is to do a pixel check with the foreground. If this comes back as not transparent, then it has hit the ground, and we can start an explosion. To create a hole in the foreground, we can write transparent pixels randomly around the point of contact and then set off an explosion animation. If we test for a collision with a gun, we may find that the bullet has hit the other player and after blowing up the tank, the game ends. If the impact only hit the landscape, though, we can switch control over to the other player and let them have a go.

So that’s your basic artillery game. But rest assured there are plenty of things to add – for example, wind direction, power of the shot, variable damage depending on proximity, or making the tanks fall into holes left by the explosions. You could even change the guns into little wiggly creatures and make your own homage to Worms.

Here’s Mark’s code for an artillery-style tank game. To get it working on your system, you’ll need to install Pygame Zero. And to download the full code and assets, head here.

Get your copy of Wireframe issue 44

You can read more features like this one in Wireframe issue 44, available directly from Raspberry Pi Press — we deliver worldwide.

And if you’d like a handy digital version of the magazine, you can also download issue 44 for free in PDF format.

Wireframe #44, bringing the past and future of Worms to the fore.

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