Drawing ships: EDGE

       Name: EDGE                                                    [Show more]
       Type: Macro
   Category: Drawing ships
    Summary: Macro definition for adding edges to ship blueprints
  Deep dive: Ship blueprints
             Drawing ships
    Context: See this macro in context in the source code
 References: This macro is used as follows:
             * SHIP_CANISTER uses EDGE
             * SHIP_COBRA_MK_3 uses EDGE
             * SHIP_CONSTRICTOR uses EDGE
             * SHIP_KRAIT uses EDGE
             * SHIP_PYTHON uses EDGE
             * SHIP_SHUTTLE uses EDGE
             * SHIP_TRANSPORTER uses EDGE
             * SHIP_VIPER uses EDGE


 The following macro is used to build the ship blueprints:

   EDGE vertex1, vertex2, face1, face2, visibility

 When stored in memory, bytes #2 and #3 contain the vertex numbers multiplied
 by 4, so we can use them as indices into the heap at XX3 to fetch the screen
 coordinates for each vertex, as they are stored as four bytes containing two
 16-bit numbers (see part 10 of the LL9 routine for details).


 Arguments:

   vertex1              The number of the vertex at the start of the edge

   vertex1              The number of the vertex at the end of the edge

   face1                The number of face 1 associated with this edge

   face2                The number of face 2 associated with this edge

   visibility           The visibility distance, beyond which the edge is not
                        shown


MACRO EDGE vertex1, vertex2, face1, face2, visibility

 f = face1 + (face2 << 4)
 EQUB visibility, f, vertex1 << 2, vertex2 << 2

ENDMACRO