Many of the color presentation parameters come in pairs. For example, the background color of a window can be set using either PP_BACKGROUNDCOLOR, which takes an RGB color value (for example, RGB_RED), or PP_BACKGROUNDCOLORINDEX, which takes a color index (for example, CLR_RED). The newer presentation parameters do not have a color index equivalent, so it is recommended that you use RGB values wherever possible. RGB presentation parameters will also work with SYSCLR_ index values and negative CLR_ indexes (for example, CLR_BLACK).
WinQueryPresParam can be used to query a pair of color presentation parameters at once. The first parameter takes precedence over the second, and should normally be the RGB presentation parameter. The color index should be the second. If you are querying a color index presentation parameter and you want the color value to be returned as an RGB value, you can specify either QPF_ID1COLORINDEX or QPF_ID2COLORINDEX to convert a color index value to an RGB value.
If a window does not have a presentation parameter set for a particular color, the window must select a default color to use. For example, if there is no value set for PP_FOREGROUNDCOLOR or PP_FOREGROUNDCOLORINDEX, the window has to choose a default foreground color when it paints. The usual practice is to select a corresponding system color (for example, SYSCLR_WINDOWTEXT) and use that to paint the foreground of the window.
The decision of which system color to use is an important one, as system colors can be changed by the user with a Scheme Palette. Your choice should always be appropriate to the functionality of the window. If the user does change a system color, your window will receive a WM_SYSCOLORCHANGED message to notify you that your default colors might have been changed.
If there is no appropriate system color available, you will need to select a hard-coded color value as the default instead.
/****************************************************************/
/* Query presentation parameter value for background color */
/****************************************************************/
if (WinQueryPresParam(
hwndMain, /* Window handle */
PP_BACKGROUNDCOLOR, /* Background presparam (RGB) */
PP_BACKGROUNDCOLORINDEX, /* Background presparam (Index)*/
NULL,
sizeof(lColor), /* Length of data buffer */
&lColor, /* Data buffer returned */
QPF_ID2COLORINDEX) == 0) /* Convert 2nd presparam to RGB*/
{
/*************************************************************/
/* No presparam found - query default background color */
/*************************************************************/
lColor = WinQuerySysColors(
HWND_DESKTOP, /* Desktop window handle */
SYSCLR_BACKGROUND, /* System default background */
0); /* Reserved */
}
GpiSetBackColor(hps, lColor);