VDI color indices for 256 color mode ?
Janka Gerhard
Can anybody tell me the color register indices for VDI for 256 color
mode ? All the books I have only list indices for up to 16 colors
since they obviously were written in pre Falcon times.
BTW, I always wondered what reason could be behind mixing the colors
as it is done at outputs via VDI. Anyway It would be nice if
somebody could help, and spare me the task of writing a test program
to find out about VDI and 256 color mode indices.
Thanks
Gerhard
Philipp Donze
> All the books I have only list indices for up to 16 colors
> since they obviously were written in pre Falcon times.
As far as I know there is no standard palette for 256 colors.
Atari never defined something like "VDI color 154 is light red
(=red 900, green 700, blue 700)".
So you can't assume that an index has the color representation
which it has on your Falcon. But I think most of the people
use the standard palette if the Atari VDI or the new (better)
palette from NVDI.
I think Atari defined only the first 16 colors because the user
interface (=GEM) only uses the first 16 colors. The other 246
colors can be changed by the applications.
This approach gives us a strange looking screen in a multitasking
environment in which more than one program uses more than 256
colors. (=the windows in the background use also the current
palette in the 256 color mode)
So it's not "nice".
Regards
Philipp
Janka Gerhard
Sorry, it seems I didn't make my problem clear enough. My problem is
not about the RGB values of certain VDI color indices but the shifting
of color indices VDI ( and NVDI too ) does. For example when I make
my program read a picture with 16 colors and display it on screen,
when using VDI functions to set the colors according to the picture
palette, I have to use a color index different from the index in the
picture palette, using certain rules that can be found in books like
e.g. the Atari Compendium etc., e.g. 2->3, 15->13 etc. to get the right
colors on screen. Now for 256 color pictures these color index shifting
rules seem to be similar than for 16 colors but not exactly the same.
Color indices from 16 to 254 seem to be identical in picture and VDI
palette but at least index 255 has to be changed ( to 1 ? ) which
causes changes in the others between 0 and 15.
regards
Gerhard
baldrick
Janka Gerhard wrote in message <3CF227E1...@siemens.at>...
>Sorry, it seems I didn't make my problem clear enough. My problem is
>not about the RGB values of certain VDI color indices but the shifting
>of color indices VDI ( and NVDI too ) does. For example when I make
>my program read a picture with 16 colors and display it on screen,
>when using VDI functions to set the colors according to the picture
>palette, I have to use a color index different from the index in the
>picture palette, using certain rules that can be found in books like
>e.g. the Atari Compendium etc., e.g. 2->3, 15->13 etc. to get the right
>colors on screen. Now for 256 color pictures these color index shifting
>rules seem to be similar than for 16 colors but not exactly the same.
>Color indices from 16 to 254 seem to be identical in picture and VDI
>palette but at least index 255 has to be changed ( to 1 ? ) which
>causes changes in the others between 0 and 15.
>
I have this table in the ximgload.c file in boinkout2's source code.
The short answer is it's 1 to 1 excet for the changes for 16 color modes and
1 = 255
255 = 15
so it's
0,255,1,2,4,6,3,5,7,8,9,10,12,14,11,13,16,17,18,19,20....
...251,252,253,254,15
Dan
aka baldrick
Janka Gerhard
So that's why the games I wrote before seemed to work okay when I
used the same changes as for 16 color mode.
Many thanks
Gerhard