You can manipulate single pels in a bit map by using GpiSetPel and GpiQueryPel. GpiSetPel sets the pel at the specified point (in world coordinates) to the current line color. This function is independent of the current drawing mode, and its effect is immediate. It is, however, a device-dependent function. The CAPS_RASTER_CAPS option of DevQueryCaps indicates if GpiSetPel is supported on the current device.