The AddShipExplosionToBuffer subroutine - Lander on the Acorn Archimedes

       Name: AddShipExplosionToBuffer                                [Show more]
       Type: Subroutine
   Category: Particles
    Summary: An unused routine that adds a 50-cluster explosion cloud to the
             particle data buffer, just front of the player's ship
  Deep dive: Unused code in Lander
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


.AddShipExplosionToBuffer

 STMFD   R13!, {R14}                \ Store the registers that we want to use on
                                    \ the stack so they can be preserved

 MOV     R8, #50                    \ Set R8 = 50 so the explosion contains 50
                                    \ clusters of four particles

                                    \ Now we add an explosion to the particle
                                    \ buffer at coordinates (R0, R1, R2), which
                                    \ are set to PLAYER_FRONT_Z tiles forwards
                                    \ from the camera coordinates, so that's
                                    \ just in front of the ship (when the ship
                                    \ is not close to the ground, in which case
                                    \ the explosion would be above the ship as
                                    \ the ship moves down the screen)

 LDR     R0, [R11, #xCamera]        \ Set R0 = xCamera

 MOV     R1, #0                     \ Set R1 = 0

 LDR     R2, [R11, #zCamera]        \ Set R2 = zCamera - PLAYER_FRONT_Z
 SUB     R2, R2, #PLAYER_FRONT_Z

 BL      AddExplosionToBuffer       \ Add an explosion into the particle data
                                    \ buffers

 LDMFD   R13!, {PC}                 \ Retrieve the registers that we stored on
                                    \ the stack and return from the subroutine

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Subroutine AddExplosionToBuffer (category: Particles)

Create a big explosion of particles and add it to the particle data buffer

[X]

Configuration variable PLAYER_FRONT_Z = (TILES_Z - 5) * TILE_SIZE

The distance along the z-axis between the tile in front of the player and the camera, which is where we spawn explosions and falling rocks (set to six tiles forwards from the camera)

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Configuration variable xCamera = &13C

The 3D x-coordinate of the camera position (though note that the camera position is actually at the back of the on-screen landscape, not the front)

[X]

Configuration variable zCamera = &144

The 3D z-coordinate of the camera position (though note that the camera position is actually at the back of the on-screen landscape, not the front, so the camera's z-coordinate is larger than it would be for a more traditional camera position; it is more like the camera's focal point than position, in a sense)