I've setup a wiki a long time ago, not enough time to write on it thought http://wiki.megadrive.org/index.php/Main_Page
Since last week I've redo some work on megadrive so I think I'll soon update/create a lot of page on this wiki.
Sharing technical information
Moderator: BigEvilCorporation
ElBarto feel free to modify and add to your wiki if you want to. I wasnt sure how to.
Images are hosted and loaded from imageshack.us directly i think..
But if this is using up spriteminds.net bandwidth, tell me.
Anyway, i havnt written a map processor, engine, or whatever you call it yet.
But ive written some notes down, how it might be done.
I will be trying to write one in the future, in assembly, for games.
This is one project for me, it'll take a while, whole things a bit big.
These are just dev notes, abstract thinking, not much code just ways of doing stuff, "Technical Info", where do i post it.
One thing i found kinda anoying, you can only really use one 1024x1024 Plane, they take $8000 VRAM.
// Example Info
MAX MAP size V1024 H2048, thats like 4 512 planes accross.
Would be a small map for sonic, but a good size.
Plane blocks would be 32 x 32 written with block_pointers in a abstract map_sheet.
The map_sheet is an array of 8 bit block_pointers -bbbbbbb 128 different blocks, extra bit reserved.
A 2 x 4 Map_Sheet would take $800 RAM (2048 blocks) with the extra bit.
Memory stuff
Block VRAM $0000 - $3FFF
512 PLANE + window
8 Abstract planes will be written to the real_background_plane dependant on the MANXY position.
window window
MANXY player position
CHAXY player sprite position
PLANE real_background_plane
MAP map_sheet
The the window doesnt move, the PLANE does.
The MAP pattern order is the same, but segmented into planes (Easier to decode).
MAP
MAP 0
MAP 0, 1, 4, 5
All variables will be derived from MANX and MANY.
MANX = 0 (minimum X position)
CHAX = 128 (window left edge)
PLANEX = 0 (plane left edge)
MANX = 512 (X position)
CHAX = 256 (window center)
PLANEX = 350 (from window X)
The MAP needs to be loaded into the PLANE before the wait loop & before video update.
4 MAP segments mabey used at one time, this part will take alot of good program design.
All variables are derived from MANXY, to get the right patterns from the MAP to the PLANE:
Calculate Hscroll position.
Calculate Fake window position relative to the MANXY position.
In the below example you would use that fake window position and from that..
Execute a plane loader function 4 times (MAP x,y,width,height -> PLANE x,y,width,height)
MAP 0 -> PLANE
MAP 1 -> PLANE
MAP 4 -> PLANE
MAP 5 -> PLANE
Images are hosted and loaded from imageshack.us directly i think..
But if this is using up spriteminds.net bandwidth, tell me.
Anyway, i havnt written a map processor, engine, or whatever you call it yet.
But ive written some notes down, how it might be done.
I will be trying to write one in the future, in assembly, for games.
This is one project for me, it'll take a while, whole things a bit big.
These are just dev notes, abstract thinking, not much code just ways of doing stuff, "Technical Info", where do i post it.
One thing i found kinda anoying, you can only really use one 1024x1024 Plane, they take $8000 VRAM.
// Example Info
MAX MAP size V1024 H2048, thats like 4 512 planes accross.
Would be a small map for sonic, but a good size.
Plane blocks would be 32 x 32 written with block_pointers in a abstract map_sheet.
The map_sheet is an array of 8 bit block_pointers -bbbbbbb 128 different blocks, extra bit reserved.
A 2 x 4 Map_Sheet would take $800 RAM (2048 blocks) with the extra bit.
Memory stuff
Code: Select all
// DISPLAY VXX H40 2*PNT 512 $5640 USED $A9C0 MAX FREE
PNT W $1000
PNT 512 $2000
PNT 512 $2000
SAT $280 80 sprites
Hscroll $3C0
// VRAM $A000 FREE
One Pattern $20 VRAM
One Block $80 VRAM could just load visible data, but anyway
128 Blocks $4000 VRAM could load every map block ready
that would leave $6000 VRAM (blocks are for both planes)
// RAM abstract MAP
map planes 2 x 4 8 planes
block size 32 x 32 4 patterns
blocks per plane 16 x 16 256 blocks
map_sheet 32 x 64 2048 blocks $800 RAM
block bitmap 32 x 64 2048 blocks $100 RAMBlock VRAM $0000 - $3FFF
512 PLANE + window
8 Abstract planes will be written to the real_background_plane dependant on the MANXY position.
window window
MANXY player position
CHAXY player sprite position
PLANE real_background_plane
MAP map_sheet
The the window doesnt move, the PLANE does.
The MAP pattern order is the same, but segmented into planes (Easier to decode).
MAP
MAP 0
MAP 0, 1, 4, 5
All variables will be derived from MANX and MANY.
MANX = 0 (minimum X position)
CHAX = 128 (window left edge)
PLANEX = 0 (plane left edge)
MANX = 512 (X position)
CHAX = 256 (window center)
PLANEX = 350 (from window X)
The MAP needs to be loaded into the PLANE before the wait loop & before video update.
4 MAP segments mabey used at one time, this part will take alot of good program design.
All variables are derived from MANXY, to get the right patterns from the MAP to the PLANE:
Calculate Hscroll position.
Calculate Fake window position relative to the MANXY position.
In the below example you would use that fake window position and from that..
Execute a plane loader function 4 times (MAP x,y,width,height -> PLANE x,y,width,height)
MAP 0 -> PLANE
MAP 1 -> PLANE
MAP 4 -> PLANE
MAP 5 -> PLANE