Re: [colorforth] Setting a pixel on the screen

[Jason Kemp <jason.kemp@xxxxxxxxxxxxxxxx>]

Hi Ray,

Thanks for all the encouragement.  I cracked it on Friday and was 
intending to reply, but I'm trying not to touch the computer over the 
weekends now and Monday was a bank holiday too!

: pixel show black screen ffff 400 400 1024 * + 2* 1e80000 + 2/ 2/ ! 
keyboard ;

It needs a 2/ 2/ because ! multiplies the address it is given by 4.  
This must be something to do with addressing doublewords as opposed to 
bytes--I'm sure it's something quite obvious to most but it's taking me 
a long time to build up a picture of what's going on here.  Are 
addresses in colorforth stored as the count of doublewords rather than a 
true address?

Jason




Ray St. Marie said the following on 27/05/2008 20:23:
> rethinking my previous post to this question...
> Hi Jason,
> Ray here
>
> On Tue, May 20, 2008 at 4:41 PM, Jason Kemp <jason.kemp@xxxxxxxxxxxxxxxx> wrote:
>   
> > Good evening all,
> >
> > I have been attempting to set a pixel on the screen to white.  Please show
> > me what I am doing wrong:
> >
> > : ohno show black screen ffff 400 400 1024 * + 2* 1e80000 + ! keyboard ;>
> > Only the ffff and the 1e80000 are in hex.  The screen is 1024x768, 16-bit,
> > VESA 117h.
> >
> > Thanks,
> > Jason
> >
> >     
>
> Jason, have you tried the word color after ffff, to set the color, as in...
>
> : ohno show black screen ffff COLOR 400 400 1024 * + 2* 1e80000 + ! keyboard ;
>
> I happened to be looking in an old source and reading the word SWITCH.
> In the top of the word we see an example of writeing to AGP before
> switching to keyboard.
>
> Karig has a nice look at it :
>
> http://www.karig.net/os/cf/g.htm
>
> Halfway down the page. All of the rest of that page are examples of
> 'emit'ing pixels to the page.
>
> Good luck with this, Jason. Please keep me in the loop, your
> experiments, as I'd like to try them out as well. :-)
>
> All the best,
> Ray
>
>   


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