Scrolling Milestone... one way!

[DanielAllsopp]

Good afternoon! Hope you're all well!

So, I've managed to fudge my way through repeating my background sprites (they don't move yet though!) and started on trying to get the scrolling working, which seems to be working but only in one direction.

I'm following the instructions for Scroller_XLimited in this archive on Aminet by Georg Steger:

http://aminet.net/package/dev/src/ScrollingTrick

I'm smooth scrolling using BPLCON1, i.e. subtracting $11 and moving my bitplane pointers by 2 bytes after blitting into the hidden right hand column.

That seems to work.

In this example, after I've moved 5 columns and then I switch the scrolling in the opposite direction, by adding $11 to the value in BPLCON1 but something weird happens:



From looking at that weird effect, any immediate pointers as to why that would do that?

Anyway, I'm getting there with this ASM malarky and I'm extremely grateful for the help and encouragement that I get from this board. You're all marvellous and very patient individuals so thanks

[Galahad/FLT]

Originally Posted by DanielAllsopp

Good afternoon! Hope you're all well!

So, I've managed to fudge my way through repeating my background sprites (they don't move yet though!) and started on trying to get the scrolling working, which seems to be working but only in one direction.

I'm following the instructions for Scroller_XLimited in this archive on Aminet by Georg Steger:

http://aminet.net/package/dev/src/ScrollingTrick

I'm smooth scrolling using BPLCON1, i.e. subtracting $11 and moving my bitplane pointers by 2 bytes after blitting into the hidden right hand column.

That seems to work.

In this example, after I've moved 5 columns and then I switch the scrolling in the opposite direction, by adding $11 to the value in BPLCON1 but something weird happens:



From looking at that weird effect, any immediate pointers as to why that would do that?

Anyway, I'm getting there with this ASM malarky and I'm extremely grateful for the help and encouragement that I get from this board. You're all marvellous and very patient individuals so thanks

Presumably you're now adding $11 to BPLCON1, and once you get to $ff or $00 (whichever is your default restart), you're then subtracting 2 from your bitplane pointers and restarting on BPLCON1?

[DanielAllsopp]

Originally Posted by Galahad/FLT

Presumably you're now adding $11 to BPLCON1, and once you get to $ff or $00 (whichever is your default restart), you're then subtracting 2 from your bitplane pointers and restarting on BPLCON1?

Boom, that'll be it! How did I miss that God-damn it?! I'm not decreasing the bitplane pointers.

Code's getting a bit messy so I'm gonna tidy that up first and then put this change in. Thanks Galahad.

[DanScott]

Rather than adding/subtracting $11 from BPLCON1, it might be better to store your X scroll position in a variable.

Then you can calculate your BPLCON1 value and bitplane offsets from that value. It will allow you to scroll at different speeds etc... you just add and subtract from that variable, and then calculate the correct BPLCON1 and offset from that value

[DanielAllsopp]

Originally Posted by DanScott

Rather than adding/subtracting $11 from BPLCON1, it might be better to store your X scroll position in a variable.

Then you can calculate your BPLCON1 value and bitplane offsets from that value. It will allow you to scroll at different speeds etc... you just add and subtract from that variable, and then calculate the correct BPLCON1 and offset from that value

That's a canny idea, I already have a scroll counter, but it counts up by the number 16 pixel blocks I've moved, i.e. it increments by one when the BPLCON1 value is reset.

I'll have a think how best to adjust my code. Might be easier to do with some sort of user input like a joystick or keypresses so I'll see if I can get something together to read that first.

Thanks for the tips!

[Galahad/FLT]

Originally Posted by DanielAllsopp

Boom, that'll be it! How did I miss that God-damn it?! I'm not decreasing the bitplane pointers.

Code's getting a bit messy so I'm gonna tidy that up first and then put this change in. Thanks Galahad.

[Tigerskunk]

Nice, always good seeing more game developers for OCS...

(or AGA, or whatever you are doing. Just please don't do a SHMUP.. )