BBC Mode 2 sprites

bbc micro/electron/atom/risc os coding queries and routines
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wnmderek
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BBC Mode 2 sprites

Post by wnmderek »

I am trying to create a sprite routine that works in Mode 2. As I am just starting, and drawing sources from various places, I have a sprite routine that draws each line of the sprite on the same line. If I try to add to get to the next screen line for the next row of relevant data, it appears anywhere but underneath the last row drawn above it.

Also if I try to start the sprite at other screen locations then the draw routine messes up too.

I know it has to do with the strange way the video memory is drawn, I am just not sure how to get around it.

I am trying initially to create a sprite routine that I pass by whatever means sprite screen memory location (ill convert x/y to screen later if I ever get that far!) and lo/hi of the sprite data.

Has anyone done this or be able to offer any suggestions please?
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richardtoohey
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Re: BBC Mode 2 sprites

Post by richardtoohey »

Welcome. :D

I've moved your question into this forum because I think it's probably better in here.

If you have a look down the topics there may be something that helps already (e.g. the Kevin Edwards magazine articles).

Good luck!
RobC
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Re: BBC Mode 2 sprites

Post by RobC »

There's this.

I found Neil Beresford's shell a good starting point when developing my Bomb Jack game in Swift.

If you need something that restores the background as the sprite moves in mode 2, let me know and I'll post my sprite code.
Last edited by RobC on Mon Oct 15, 2018 10:54 am, edited 1 time in total.
wnmderek
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Re: BBC Mode 2 sprites

Post by wnmderek »

Hi thanks. I will take a look. If you have any code that may help please paste if possible?
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sydney
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Re: BBC Mode 2 sprites

Post by sydney »

There is some example code over at the old retrosoftware site:
http://www.retrosoftware.co.uk/wiki/ind ... te_plotter
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Andrew_Waite
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Re: BBC Mode 2 sprites

Post by Andrew_Waite »

This thread might help. It describes how I built the sprite engine for the rocketman in my 'Planet Nubium' game, with lots of helpful pointers from other folk along the way (Thanks again!).

The game uses Mode 1, but it should be possible to convert the code to the other 20Kbyte modes.

viewtopic.php?f=54&t=13053
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