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⌂ ∞ Lander on the Acorn Archimedes

3D objects: DrawObjects (Part 3 of 3)

       Name: DrawObjects (Part 3 of 3)                               [Show more]
       Type: Subroutine
   Category: 3D objects
    Summary: Draw a destroyed object that we have found on the object map
  Deep dive: Drawing 3D objects

    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file




.dobs6

                                    \ If we get here then this is a destroyed
                                    \ object

 LDR     R14, [R11, #mainLoopCount] \ If either bit 0 or 1 of mainLoopCount are
 TST     R14, #%00000011            \ set, jump to dobs5 to draw the object and
 BNE     dobs5                      \ skip the following

                                    \ We only get here on one out of every four
                                    \ iterations around the main loop

 STMFD   R13!, {R0-R7, R9}          \ Store the registers that we want to use on
                                    \ the stack so they can be preserved

 LDR     R14, [R11, #yCamera]       \ Set R1 = R1 + yCamera
 ADD     R1, R1, R14                \         = y + yCamera
                                    \
                                    \ This reverts R1 to the altitude of the
                                    \ landscape at the object (as we subtracted
                                    \ yCamera from the altitude back in part 3)

 MOV     R0, R8                     \ Set (R0, R1, R2) = (x, y-SMOKE_HEIGHT, z)
 MOV     R2, R9                     \
 SUB     R1, R1, #SMOKE_HEIGHT      \ So this coordinate is SMOKE_HEIGHT above
                                    \ the base of the object, or 3/4 of the tile
                                    \ size (as the y-axis points downwards),
                                    \ which is where we add our smoke particles,
                                    \ one on each iteration around the main loop

 BL      AddSmokeParticleToBuffer   \ Call AddSmokeParticleToBuffer to draw a
                                    \ smoke particle rising from the destroyed
                                    \ object

 LDMFD   R13!, {R0-R7, R9}          \ Retrieve the registers that we stored on
                                    \ the stack

 B       dobs5                      \ Jump to dobs5 to draw the object