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Conference bulova::decw_jan-89_to_nov-90

Title:	DECWINDOWS 26-JAN-89 to 29-NOV-90
Notice:	See 1639.0 for VMS V5.3 kit; 2043.0 for 5.4 IFT kit
Moderator:	STAR::VATNE

Created:	Mon Oct 30 1989
Last Modified:	Mon Dec 31 1990
Last Successful Update:	Fri Jun 06 1997
Number of topics:	3726
Total number of notes:	19516

2376.0. "XOR and foreground color" by KAOU35::DLEROUX () Wed Feb 28 1990 11:55

    
    I have run into a small problem which I don't understand.
    
    I am trying to define an xor graphics context with the default
    foreground and background colors of the user but I don't get the
    results I anticipate.
    
    Here's what my code looks like:
    
    gcmask = GCFunction|GCLineWidth|GCBackground|GCForeground;
    gcvalues.line_width = 2;
    gcvalues.function = GXxor;
    get_something( draw_widget, DwtNforeground, value );
    				/* Does a XtGetValue */
    gcvalues.foreground = *value;
    get_something( draw_widget, DwtNbackground, value );
    gcvalues.background = *value;
    gcxor = XCreateGC( display, XtWindow( draw_widget ),
    			gcmask, &gcvalues );
    
    Then when I do my draw line routine of my small paint program it
    doesn't come out with the correct foreground color for the line.
    
    Thanks,
    		Dan

T.R	Title	User	Date	Lines
2376.1	draw_widget?	LEOVAX::TREGGIARI	`Wed Feb 28 1990 12:05`	3
	What type of widget is "draw_widget"? Leo
2376.2	Window widget	KAOU35::DLEROUX	`Wed Feb 28 1990 13:22`	6
	Sorry, draw_widget is a window widget. Isn't that the only one which can do graphics? Dan
2376.3	Xor	LEOVAX::TREGGIARI	`Wed Feb 28 1990 16:28`	13
	> Sorry, draw_widget is a window widget. Isn't that the only one which > can do graphics? It's the only one built into the widget set that can do graphics. I just wanted to determine if it was a "custom" widget. Is this on a monochrome system or multi-plane? I'm not a Xor expert, but I don't think you would get the exact same foreground color, unless the pixels you are drawing over have a value of 0 (or foreground does), since it "xor"s the pixel values. Leo
2376.4	How about black on background?	KAOU35::DLEROUX	`Thu Mar 01 1990 08:29`	12
	> ... I don't think you would get the exact same foreground color ... That's what I was beginning to suspect. How do I define a XOR GC with the user's background color and a black foreground? I tried BlackPixel as the foreground color but the resultant color on the screen was not always black depending on the user's background color. Dan
2376.5	Paint does it.	KAOU35::DLEROUX	`Thu Mar 01 1990 09:28`	12
	rep 3. You were right when you said that I would only get the correct foreground color if the background color was 0 since "xoring" the pixel values affects the resultant color. But ... Paint does obtain the correct user background and foreground color. Can anyone tell me how it does that? Dan
2376.6	Solution!!	KAOU35::DLEROUX	`Thu Mar 01 1990 09:58`	6
	For a solution to this problem check out note 706.1 in SHPLOG::DECWINDOWS_PROGRAMMING. Dan
2376.7	Look at DECW$EXAMPLES:PLAID	DECWIN::ROSENBLUM	`Fri Mar 02 1990 16:24`	4
	Also DECW$EXAMPLES:PLAID has the right sequence of events, it involves setting the plane mask to the xor of the forground and background pixel values. Mike