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CPC Memories

If we have met, you saw I am an older geek.
I’m from the Amstrad CPC Generation, I was blessed with a 6128 as my dad thought it was wasted time to watch a game load on 464 (from K7 tape).

While looking for vids of the Technimusique speech synthetizer to evaluate the gap with actual solutions, I found this video about Multiface II (which I hadnt). At 16:16 , I recognize a long forgotten familiar syntax

So here it is :

first : out &bc00, REGISTER

second out &bd00,VALUE

With the register being from this list , taken from https://cpcrulez.fr/coding_src-list-graphic-crtc-on-screen_effects_on_the_CPC464_POPU.htm

Register Function
0 Horizontal Total
1 Horizontal Displayed
2 Horizontal Sync Position
3 Sync Widths
4 Vertical Total
5 Vertical Total Adjust Vertical Displayed
7 Vertical Sync Position
8 Interlace and Skew
9 Maximum Raster Address
12 Start Address (high)
13 Start Address (low)

Messing with the registers I did two programs : a hacks and a “demo” which I share here from memory

HACK: Making sprites taller in Horizontal Beat’em up game (double dragon, vigilante, …)

How, messing with the interlacing so that there is an empty line between each real horizontal line. Needed to tweak the knob of “vertical something” at the back of the monitor.
Made my Amstrad less ridiculous compared to my friend’s Amiga

Demo: A fullscreen starfield (one layer only, no parallax) scrolling horizontally

Steps were
Paint it black : border 0, paper 0
Mode 0 ?
Draw random white dots on the screen
Mess with video register so that lines are not aligned but take full Horizontal space
Mess with video register so that lines take full Vertical space
Make a simple loop on register ?, from ? to ? and it simuletes movement

Extra layer: Add a logo to starfield.
1/ with drawing software make a logo with your nickname save it and close software
2/ Mess the video
3/Reopen drawing software load pic + ?nothing? + save it again

4/ restart computer for video reset, display pic. Must be messed, with lines shifted. Its the expected result

5/ Modify main prog to load pic

6/ Admire you name in full screen, moving indefinitely

I wonder if it would work as well on an emulator.
If you code it, capture video and share it !
Have fun.

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