Smoothly Horizontal – Part 1

Drawing graphics at horizontal pixel, rather than character, positions isn’t quite as straightforward as doing it vertically.  Vertically, as each pixel row has it’s own address on the screen, we just had to find the correct address to start from, and work down from there.  Horizontally however, groups of 8 pixels are held within a single byte, using a single bit each, which makes things more complicated to know which bits to set. Continue reading

Smoothly vertical

Now that we’ve done drawing graphics at character positions, ala BASIC, lets start drawing them at pixel positions – starting with placing them vertically at any pixel row.  This is very similar to the character position code, with a couple of changes…

Firstly we need to make a pixel row address look-up table, which is simply a version of the character table, but for all 192 rows: Continue reading

Once more, with character…

And so we come to drawing graphics on the screen! (‘FINALLY!’, you all cheer)

We’ve now got a simple program where you can move a little coloured block around the screen using the joystick, but wouldn’t it be so much better if it was a smiley face instead?

The pixel display on the Spectrum is a bit… erm… ‘special’, as it’s not arranged in what you’d call a logical way (as we discovered in an earlier post when we filled some of it) and it’s a little complicated to describe, but here goes… Continue reading

Racing (and other games) at Kempston

In most games, you’ll need to provide joystick control.  The Spectrum has quite a few different types of joystick interface – Protek/Cursor, Sinclair Interface 2, and Kempston – with Kempston being the most popular.  The Kempston interface is also special as it’s the only one of those which isn’t actually keyboard-based, and so is logically separate from controlling a game via keyboard.  It’s also pretty easy to use to! Continue reading

AMA with you!

So, that’s a few posts now – how’s everybody doing?  If there’s anything I’ve covered so far which you’re not sure about, or have any queries, post up a comment and I’ll do my best to answer them.