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  • Writer's pictureBruce

Simple Switches for your MPAGD Games

Updated: Nov 18, 2020

Switches are useful, imagine a kettle without one, sad isn't it?

Adding switches into your games opens up a bunch of new possibilities, maybe they open doors, activate a device, or spawn a nasty. Whatever you want the player to do, this simple switch code will get you started.

First let's design a switch sprite, if you are running low on available memory then maybe a single frame will do (we can use SPRITEINK to colour dependent on whether it is on or off)...alternatively have an ON and OFF frame. In this example I'll use two frames and colour.

Here's my switch sprite from 24 Hour Parsley People: Episode 1:

Once you've designed your switch, we'll need to write a little code that controls the player switching it on and off by colliding with it. When I first attempted this I got into a right mess, as the 'switching' is triggered when the player collided with it, it would alternate between ON and OFF during the collision. So the solution was to use a a sprite parameter (I used SETTINGA) to store whether there was an active collision or not - and if there was, only switch from its current state to the opposite state (ON/OFF), simple!

Here's the code in action, when the player touches the switch it will switch the electrical device on the right ON....and if it was already ON it will switch it OFF (we'll not worry about

the code for the electrical device today...just the fact that we can switch it ON or OFF)

Here's the SWITCH code:

Finally, just to ensure the switch appears smoothly and correctly when the player enters a room with a switch, let's add some rules into the SPRITE INITIALISATION event:

There you go, quick and easy switches, with a variable we can use elsewhere for what happens when the power is on. (IF E = 1 ... do really evil stuff!)

Hope this helps!

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Hello, I'm Bruce and I write games for old 8bit computers using Jonathan Cauldwell's excellent Multi-Platform Arcade Games Designer (MPAGD)

I've written a few successful* games for the Sinclair ZX Spectrum and MSX platforms that have been (largely) well received including Twenty Four Hour Parsley People scoring a 10 out of 10 on Planeta Sinclair.

In my blog I am sharing lots of the code that I wrote for my games, in a way that you can use in your own games.   I've commented it so that you'll learn some of the techniques I use to create interesting new mechanics and help your games stand out from the pack.

MPAGD includes lots of standard scripts, they're great to get you started, but if you're new (or just rusty) when it comes to writing code, hopefully my tutorials will help you get started and  turn your imagination into awesome 8 bit games!

All my code is free to use and do with as you please, but if you find them useful please feel free to buy me a coffee ...or better still - buy or download my games :)

*successful is a very relative term in 8bit computer games

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