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⌂ ∞ ▽ Elite on the BBC Micro and NES

Drawing ships: VERTEX

[BBC Micro disc version, Ship blueprints D]

       Name: VERTEX                                                  [Show more]
       Type: Macro
   Category: Drawing ships
    Summary: Macro definition for adding vertices to ship blueprints
  Deep dive: Ship blueprints

    Context: See this macro in context in the source code
 References: This macro is used as follows:
             * SHIP_ASTEROID uses VERTEX
             * SHIP_CANISTER uses VERTEX
             * SHIP_COBRA_MK_1 uses VERTEX
             * SHIP_COBRA_MK_3 uses VERTEX
             * SHIP_DODO uses VERTEX
             * SHIP_ESCAPE_POD uses VERTEX
             * SHIP_GECKO uses VERTEX
             * SHIP_SIDEWINDER uses VERTEX
             * SHIP_SPLINTER uses VERTEX
             * SHIP_THARGOID uses VERTEX
             * SHIP_THARGON uses VERTEX
             * SHIP_VIPER uses VERTEX




 The following macro is used to build the ship blueprints:

   VERTEX x, y, z, face1, face2, face3, face4, visibility

 See the deep dive on "Ship blueprints" for details of how vertices are stored
 in the ship blueprints, and the deep dive on "Drawing ships" for information
 on how vertices are used to draw 3D wireframe ships.



 Arguments:

   x                    The vertex's x-coordinate

   y                    The vertex's y-coordinate

   z                    The vertex's z-coordinate

   face1                The number of face 1 associated with this vertex

   face2                The number of face 2 associated with this vertex

   face3                The number of face 3 associated with this vertex

   face4                The number of face 4 associated with this vertex

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



MACRO VERTEX x, y, z, face1, face2, face3, face4, visibility

 IF x < 0
  s_x = 1 << 7
 ELSE
  s_x = 0
 ENDIF

 IF y < 0
  s_y = 1 << 6
 ELSE
  s_y = 0
 ENDIF

 IF z < 0
  s_z = 1 << 5
 ELSE
  s_z = 0
 ENDIF

 s = s_x + s_y + s_z + visibility
 f1 = face1 + (face2 << 4)
 f2 = face3 + (face4 << 4)
 ax = ABS(x)
 ay = ABS(y)
 az = ABS(z)

 EQUB ax, ay, az, s, f1, f2

ENDMACRO