Solved

256 color palette problem

Posted on 1999-01-20
2
404 Views
Last Modified: 2013-11-20

ok, i have a problem with trying to draw custom colors from a palette on a dc.  The dc is in an overridden and subclassed static box that I'm using as a window in my dialog box to draw in.


I'm creating a palette with 40 entires (shades of blue).

       LPLOGPALETTE lpPal = (LPLOGPALETTE)new BYTE[
sizeof(LOGPALETTE) + (sizeof(PALETTEENTRY) * nNumColors)];

      if (lpPal != NULL)    
      {        
            lpPal->palVersion = 0x300;
            lpPal->palNumEntries = 40;
            PALETTEENTRY *ppe = lpPal->palPalEntry;        
            for (int i=0; i<40-1; i++)
            {
                  lpPal->palPalEntry[i].peRed = 0;
                  lpPal->palPalEntry[i].peGreen = 0;
                  lpPal->palPalEntry[i].peBlue = (255-(i*5));
                  lpPal->palPalEntry[i].peFlags = 0;
            }
            bSucc = m_Pal.CreatePalette(lpPal);        
            delete [](PBYTE)lpPal;
      }


Then in the OnPaint routine, I am first Selecting in the palette to the DC

      CPalette *pPalOld = dc.SelectPalette(&m_Pal, false);

then I am realizing the pallete on the DC.

      dc.RealizePalette();

then i am setting a single pixel to a shade of blue that I have realized in the palette.

int i = 10;
dc.SetPixel( 0, 0, RGB( 0, 0, (255*(i*5)) ) );

then I am checking that pixel to see what color it actually came up with.

COLORREF p;
p = dc.GetPixel( 0, 0 );

now, at this point p should contain rgb values of 0,0,205.  But instead is contains 0,0,128 (a system color).  So what the heck is going on!!!  I know it realized the palette (or at least I think this is what it means) because when I do the following check on the palette, I examine the logpalette it returns and its got all my colors
in there no problem (although its missing all the system colors, not sure why).

CPalette *CTPal = dc.GetCurrentPalette();
tpal = (PALETTEENTRY *)malloc( sizeof(PALETTEENTRY)*256 );
memset( tpal, 0, sizeof(PALETTEENTRY) * 256 );
CTPal->GetPaletteEntries( 0, 256, tpal );
free( tpal );

the return value on GetPaletteEntries is 40 which is the correct number of colors in my custom palette.

so my question is, what the heck is going wrong here!!!!  This is driving me nuts, i've been working on this problem for 2 days now and I can't seem to figure it out.  Any help would be GREATLY appreciated.




note: I also tried using a CPen to draw the dot with.  (insert this code up where the getpixel is).

CPen *tempPen = new CPen( PS_SOLID, 1, RGB( 0, 0, 255-(i*5) ) );
CPen *oldPen = dc.SelectObject( tempPen );
dc.MoveTo(0, 0);
dc.LineTo(0,10);


it should also be noted here that when I run this test in 16 bit mode, the GetPixel comes up with %100 the right value.

0
Comment
Question by:Adept
2 Comments
 
LVL 15

Accepted Solution

by:
Tommy Hui earned 100 total points
Comment Utility
This code is wrong:

  int i = 10;
  dc.SetPixel( 0, 0, RGB( 0, 0, (255*(i*5)) ) );

it should be
  dc.SetPixel( 0, 0, RGB( 0, 0, (255-(i*5)) ) );

Note the minus sign after the 255.

But you should use SetPixel(0, 0, PALETTERGB(0, 0, 255-(i*5)));


0
 

Author Comment

by:Adept
Comment Utility

the answer you gave was correct (but I typed that part of my program wrong).  The secondary answer you gave was dead on correct though.  Using PALETTERGB instead of RGB works PERFECTLY.  Why that little nugget of information wasn't in microsofts documentation is beyond me.
0

Featured Post

Maximize Your Threat Intelligence Reporting

Reporting is one of the most important and least talked about aspects of a world-class threat intelligence program. Here’s how to do it right.

Join & Write a Comment

In this article, I'll describe -- and show pictures of -- some of the significant additions that have been made available to programmers in the MFC Feature Pack for Visual C++ 2008.  These same feature are in the MFC libraries that come with Visual …
Introduction: Database storage, where is the exe actually on the disc? Playing a game selected randomly (how to generate random numbers).  Error trapping with try..catch to help the code run even if something goes wrong. Continuing from the seve…
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

17 Experts available now in Live!

Get 1:1 Help Now