searchProc
Custom Search and Complement Procedures
Custom search and complement procedures allow an application to override
the inverse table matching code. The desired color is specified in the RGBColor field of a ColorSpec record and passed via a pointer on the stack; the procedure returns the corresponding pixel value in the value field of the ColorSpec. A custom search procedure can provide its own matching rules. For instance,
you might want to map all levels of green to a single green on a monitor. To do
this, you could write and install a custom search procedure that is passed the
RGB under question by the Color Manager. It can then analyze the color, and if it decides to act on this color, it can return the index of the desired shade of
green. Otherwise, it can pass the color back to the Color Manager for matching, using the normal inverse table routine.
Many applications can share the same graphics device, each with its own
custom procedure. The prodedures are chain elements in a linked list made up
of elements of type SProcHndl. The list begins in the gdSearchProc field of the The interface is as follows:
Note: There is an error in Inside Macintosh in the Pascal definition of this
function. The rgb parameter should be a VAR parameter. So if you are writing a searchProc in Pascal, the interface should be:
FUNCTION SearchProc (VAR rgb: RGBColor; VAR position: LONGINT): When attempting to approximate a color, the Color Manager calls each search procedure in the list until the Boolean value returns TRUE. The index value of the closest match is returned by the position parameter. If no search
the default search procedure.
The application can also supply a custom complement procedure to find the
complement of a specified color. Complement procedures work the same as
search procedures, and are kept in a list made up of elements of type
CProcHndl beginning in the gdCompProc field of the gDevice. The default complement procedure simply uses the 1's complement of the RGB
color components before looking them up in the inverse table. The interface is
as follows: