To implement support for a presentation parameter in a window, you need to find out what its value is and when that value has been changed. To query a presentation parameter's value use WinQueryPresParam, passing in the index of the presentation parameter and a buffer large enough for the value to be returned in. For presentation parameters that have string values, the buffer should be large enough to include the null termination character.
The flag QPF_NOINHERIT can be specified if the presentation parameter should not be inherited from the window's owner. Otherwise the system looks up the window's owner chain until it finds an occurrence of the same presentation parameter index.
When a presentation parameter is set or changed, the window receives a WM_PRESPARAMCHANGED message. If only one value is changed, that presentation parameter's index is passed with the message. If more than one value is changed, zero is passed. In the latter case, the window must query all its presentation parameters to find out which ones have changed. In response to the WM_PRESPARAMCHANGED message, the receiving window should repaint itself according to the new values received. It is not possible to reject a presentation parameter change; the new value has already been set by the time the notification message has been received.
WinRemovePresParam is available for removing a presentation parameter from a window.
/*******************************************************************/
/* Set the background color of the window */
/*******************************************************************/
lColor = RGB_RED; /* RGB color value */
WinSetPresParam(hwndMain, /* window handle */
PP_BACKGROUNDCOLOR, /* background pres param */
sizeof(lColor), /* length of pres param */
&lColor); /* pres param value */
---------------------------------------------------------------------
... in window procedure for hwndMain ...
case WM_PRESPARAMCHANGED:
/****************************************************************/
/* Message received when a presparam has been changed. */
/* Invalidate the window to repaint with new color. */
/****************************************************************/
WinInvalidateRect(hwndMain, NULL, FALSE);
break;
case WM_PAINT:
/****************************************************************/
/* Repaint the window */
/****************************************************************/
hps = WinBeginPaint(hwndMain, NULLHANDLE, NULL);
/****************************************************************/
/* Put presentation space into RGB mode */
/****************************************************************/
GpiCreateLogColorTable(hps, 0, LCOLF_RGB, 0, 0, NULL);
/****************************************************************/
/* Query presentation parameter value for background color */
/****************************************************************/
WinQueryPresParam(hwndMain, /* Window handle */
PP_BACKGROUNDCOLOR, /* Background presparam */
0,
NULL,
sizeof(lColor), /* Length of data buffer */
&lColor, /* Data buffer returned */
0);
/****************************************************************/
/* Fill window with background color retrieved from presparam */
/****************************************************************/
WinQueryWindowRect(hwndMain, &rectMain);
WinFillRect(hps, &rectMain, lColor);
... rest of painting code ...
WinEndPaint(hps);
break;