Upgrade Guide - Prolifics

Table A-1 The altsc_t structure (Continued)Member name Description Typelen Length of the occurrence unsigned charattr Occurrence attributes attributevalids[AS_VAL] Occurrence validation bits unsigned char*text Occurrence data unsigned charOther parameters:number Integer parameter intvptr Pointer parameter–currently not used. VOIDPTR*This information is supplied on all calls except for INIT and RESET.The altsc_t structure serves two purposes:! Lets the scrolling driver save information about an array between calls.! Acts as a vehicle for passing data between the driver and Panther.A scrolling driver can manage several arrays at once. The scrolldata member of thealtsc_t structure serves the purpose of keeping tract of data for each array. When thedriver is called to AS_INIT_FUNC, the driver should store a pointer in the scrolldatamember, usually to an internal structure. Panther assumes that the driver uses thepointer in scrolldata to access the offscreen data. The scrolldata pointer can onlybe changed during the INIT call; all other calls pass back the same pointer saved fromthe INIT call.The altsc_t structure also passes data into and out of the driver. The scrollinginformation parameters–luid, max_items, and shs–are passed so the driver knowsthe size of the array, current and potential. However, the luid and shs parameters areonly completely accurate for the AS_INSRT_FUNC and AS_DEL_FUNC calls; otherwise,they are approximate. The occurrence information parameters–item, len, attr, valids,and text–are used to pass information about specific occurrences into and out of thedriver. The other parameters –number, vptr–are used only for specific calls.Thesemembers are discussed later in the description of each action.A-4 JAM Documentation: Alternative Scrolling