[GEM Development] Today I Learned

[Thomas Clayton]

John,

 I understand, I hope.

I'm thinking that the function-call will (would) have to be made "lower" in the system, so ALL windows would see the same palette. This implies some  fundamental programming changes with-in GEM. 

(Now, let me show my ignorance: this would be changing the call from the AES to the VDI ?? )

Thomas Clayton





--- On Sat, 2/25/12, John Elliott <jce at seasip.demon.co.uk> wrote:

From: John Elliott <jce at seasip.demon.co.uk>
Subject: Re: [GEM Development] Today I Learned
To: gem-dev at simpits.org
Date: Saturday, February 25, 2012, 4:25 PM

> For 16 color (or colour(?), in UK English) modes, I thought there was one, > and only one, set of 16 for ALL computers - not JUST versions of GEM. Those>  16 were THE same established ones for TI-99/4a, Apple II's., IBM CGA, EGA,>  and VGA, AND Macintoshes. (It was something like "native" choices. They MI> GHT not LOOK the same (or be) BUT the video chip WOULD BE making THE same a> ssignments for ANY system.)
> 
> It was when one 'went to' 256 colors that "variety" became an "issue". Is T> HIS what you're commenting upon? 

  No. This behaviour is present in any driver where the red/green/blue 
assignments of the colours onscreen can be changed. For example, EGA 640x200
mode has a palette of 16 colours and all 16 can be displayed on the screen. 
But because the EGA has palette registers of a sort, it's possible to use 
vs_color() to make all red pixels on the screen go green with one function 
call:

    WORD rgb[] = { 0, 1000, 0 };
    vs_color(vdi_handle, RED, rgb);

  The problem is that if this change is made by one program, and a second
program then asks 'what RGB values does the RED pen have?' the values 
returned will be { 1000, 0, 0 } not { 0, 1000, 0 }.

-- 
John Elliott
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