[plt-scheme] help : White color and "get-pixel" on Viewport graphics.

What platofmr are you using? It works correctly for me on macos x.

One thing to try is replacing "white" with:

  (make-rgb 1 1 1)

Does that help?

Robby

At Sat, 12 Apr 2003 12:35:44 -0700 (PDT), "A.Pasquino" wrote:
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> 
> Hi all ,
> 
> (this is my first post) 
> 
> I'm doing some little tests with the Viewport library,
> 
> I have a little problem at using the "get-pixel"
> operation.
> 
> In particular when I call this function on a white
> pixel the result is '1' (but according to the manual
> it should be '0'). 
> 
> I noticed that when I draw a white pixel the values of
> the RGB colors are R=248/255 G=84/85 B=248/255, maybe
> the "get-pixel" actually tests for a 255/255 R/G/B
> value and so it replies 1?
> (you can get the same values from an empty window
> without drawing a white pixel with the "draw-pixel"). 
> 
> How can I set a 'true' white in order to get
> a 0 from the 'get-pixel' function? 
> Maybe I misunderstood how to use these functions? 
> Any help is welcome, Thank you in advance.
> 
> Alex. 
> 
> PS: thank you to the PLT team for your Great
> Environment! 
> 
> This is my test code: 
> 
> it should open a 10x10 pixels window and draw a white
> pixel in the center, position (4,4)
> (actually the "draw-pixel" is not necessary). 
> 
> (require (lib "graphics.ss" "graphics")) 
> (define (test)
>   (open-graphics)   
> 
>   (let ((my-port (open-viewport "rgb-test" 10 10))
>         (position (make-posn 4 4)))
>     ((draw-pixel my-port) position "white")
>     (display ((get-pixel my-port) position))
> 
>     (let ((pix-color ((get-color-pixel my-port)
> position)))
>       (newline)
>       (display (rgb-red pix-color))(display " ")
>       (display (rgb-green pix-color))(display " ")
>       (display (rgb-blue pix-color))(display " "))
>     (close-viewport my-port)
>     )
>   (close-graphics)
>   )
>    
> >(test)
> 1
> 248/255 84/85 248/255
> 
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