Graphics Hardware Interface (GHI)

The entry point and functions supported by a GRADD are referred to as the 
Graphics Hardware Interface (GHI). The differences between the VMAN 
protocol (VMI) and the protocol for the GRADDs GHI include the following: 

   *  The GHI is a subset of the VMI. 
   *  The ulFunction parameter value changes to the appropriate GHI_CMD_ 
      function name. 
 

 Each GRADD has an exported function, called HWEntry, which is the same 
 function type as VMIEntry in VMAN. 

 HWEntry receives all of the operations from VMAN. 

 In the GRADD model, the GRADDs are the only components that have direct 
 access to the video hardware. GRADD code uses the accelerated features of 
 a graphics adapter.  By returning RC_SIMULATE for a graphics operation, 
 the GRADD gives the SOFTDRAW component permission to draw directly to the 
 video memory of the hardware.  The serialization of video memory is 
 handled by the Video Manager through the the GHI_CMD_REQUESTHW function. 

 Each GRADD must process the following GHI_CMD_ functions: 

   *  GHI_CMD_INIT 
   *  GHI_CMD_QUERYCAPS 
   *  GHI_CMD_QUERYMODES 
   *  GHI_CMD_SETMODE 
   *  GHI_CMD_PALETTE 

      * This function is mandatory only when a 256-color mode has been 
      chosen. 
 

 The following GHI functions can return RC_SIMULATE and let VMAN handle 
 the operations: 

   *  GHI_CMD_BANK 
   *  GHI_CMD_BITBLT 
   *  GHI_CMD_LINE 
   *  GHI_CMD_MOVEPTR 
   *  GHI_CMD_SETPTR 
   *  GHI_CMD_SHOWPTR 
   *  GHI_CMD_TEXT 
 

 The GHI function numbers are assigned in such a way that they can be used 
 as a zero-based index into a function jump table.