BUG: PALETTEINDEX Not Working for Thin Lines on HP PaintJet

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SYMPTOMS

In a Windows 3.1 printing application, calling the PALETTEINDEX macro to select a color when drawing lines 1 pixel wide results in the printer drawing black lines no matter what color index was selected from the logical palette.

CAUSE

When the PALETTEINDEX macro is used, a COLORREF value is returned. The palette-entry index is placed in the low-order byte and a 1 is placed in the high-order byte. When a pen is created with the CreatePen function and a width of 0 (1 device unit) is placed in the nWidth field and a COLORREF value returned from PALETTEINDEX is placed in the clrref field, the pen is always black. The Hewlett-Packard (HP) PaintJet driver does not correctly handle pens with a width of 1 pixel when a color is selected with PALETTEINDEX and the high-order word of the COLORREF value is 1.

RESOLUTION

Instead of using the PALETTEINDEX macro, you can use the PALETTERGB macro to reference colors in your currently selected palette. Sometimes, this may not be desirable because you would have to know all of the RGB values of all indices in your logical palette. In that case, you could use the GetPaletteEntries() function to retrieve the RGB values of the desired logical palette index and call the PALETTERGB macro with those values.

Below is an example of how you could implement your own PALETTEINDEX function. This function performs the same function as the PALETTEINDEX macro, and works in all cases on the HP PaintJet.

   COLORREF MyPALETTEINDEX(HPALETTE hPalette, WORD wPaletteIndex)
      {
      PALETTEENTRY pe;

      GetPaletteEntries(hPalette, wPaletteIndex, 1, &pe);
      return (PALETTERGB(pe.peRed, pe.peGreen, pe.peBlue));
      }