Fading palette dynamically - Page 1

Hello,

I would like to make a fading on all my palettes. I can do this manually by creating my own palettes but it would be much better dynamics.

I know it is in 0x400000. For the first sprite, we read in 0x400020. 0x400020 is the transparent color. So we must modify 0x400021 to 0x400039 (for Sprite 1).

But I can't read each value to change to black/white. I always have 0 with 0x400020 and crash at 0x400021.

I tried with volMEMWORD, I use Datlib in C.
Should we send the color values such as 0x5148 at the address 0x400021?

Thanks for reading.

WORD access is even addresses only.

0x400020 isn't palette for sprite #1, sprite #1 uses whichever you want him to use for each tile.

Yes, I saying Sprite 1 for the example. But I know the palette number (and the number of palette for a sprite ) and the sprite list. And of course, the first 16 palettes may be used by fix layer.

I use the wiki page to find adresses : https://wiki.neogeodev.org/index.php?title=Palettes

But What do you say with "WORD access is even addresses" ? How do i do for read value (in C or ASM) ?

You can't read/write a word from/to an address that is odd.

Ok. I look this in the Doc of hpman.
"68000 requires even addresses when operating on word and dword (long) data. Read/write operation at an odd address for a word/long will crash the CPU."

So if i try to read odd adresses (impair like 0x400021), I have a Crash. So I'll only use 0x400020, 0x400022, 0x400024, ... Right


I try that and I have make a little nice rainbow animation with putting random value in all palettes. I use something like that : volMEMWORD(0x400200)=0x8000;
I'm more smarter now. Thanks you very much for all the information.

But now I need to read value for changing color. Can you explain me how to do that ? I try with fixprintf for printing my value without success naturally.
Like 0x8080, to 0x8040, to for finish 0x8000. Down every 3 last values to 0 for black color.

I read value with volMEMBYTE(0x400210). I have 176 in result. As byte we can read value from 0 to 255.

So I add the odd value. I have had a good masters.

volMEMBYTE(0x400210) = 255; //even
volMEMBYTE(0x400211) = 255; //odd

This give me a white palette.
The same with =0 give me black palette.

Now I need to harmonize the even and odd.

How can I lower my even and odd value ?
For example I have 128 in even and 62 in odd. I can't just reduce my values by one till 0. I have to do an operation.

=> wiki.neogeodev Do not worry about D, R0, G0 & B0 at the moment

it's incomplete but easier to understand, most fading-routines on neogeo works like this and uses only 12bit instead of 15 and darkbit because it's easier and also faster

try to master this:

1st step: you need 3 values 0..15 (0x00 ... 0x0F), use words(!)
RED 0x000F
GREEN 0x000F
BLUE 0x000F

2nd step: shift this values
RED 0x000F << 8 = 0x0F00
GREEN 0x000F << 4 = 0x00F0
BLUE 0x000F = 0x000F

3rd step: join values (simple add should work) into one word
RED + GREEN + BLUE => 0RGB => 0x0FFF

4th step: write this as word to get a white color

other colors:
0x0F00 = RED
0x0FF0 = YELLOW
0x00F0 = GREEN
0x0F0F = PURPLE
0x039F = LIGHT BLUE
0x000F = BLUE
0x00FF = CYAN

Got it?

=> read a word from palette => split this into 3 values (or 4 when using darkbit) => work with this => join => write

it's also possible to use bytes but in my opinion it's easier to work with words!

Thanks. New day, new work.

I use word now, and I can change to black.
I will do other tests to better understand the palette fading.