Version analysis of LL9 (Part 11 of 12)

This code appears in the following versions (click to see it in the source code):

Cassette, Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron

Code variations between these versions are shown below.

       Name: LL9 (Part 11 of 12)
       Type: Subroutine
   Category: Drawing ships

Code variation 1 of 8A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
    Summary: Draw ship: Add all visible edges to the ship line heap
    Summary: Draw ship: Loop back for the next edge

  Deep dive: Drawing ships

Code variation 2 of 8A variation in the comments only

This variation is blank in the Master version.

Cassette, Flight, Docked, 6502SP, Electron
 This part adds all the visible edges to the ship line heap, so we can draw
 them in part 12.

 Other entry points:

   LL81+2               Draw the contents of the ship line heap, used to draw
                        the ship as a dot from SHPPT

Code variation 3 of 8Related to the Master version

The cassette, disc and 6502SP versions add all the lines in a ship to the heap and then draw them all in one go, whereas the Master version erases and draws lines as they are added to the ship line heap.

See below for more variations related to this code.

This variation is blank in the Master version.

Cassette, Flight, Docked, 6502SP, Electron
.LL80

 LDY U                  \ Fetch the ship line heap pointer, which points to the
                        \ next free byte on the heap, into Y

 LDA XX15               \ Add X1 to the end of the heap
 STA (XX19),Y

 INY                    \ Increment the heap pointer

 LDA XX15+1             \ Add Y1 to the end of the heap
 STA (XX19),Y

 INY                    \ Increment the heap pointer

 LDA XX15+2             \ Add X2 to the end of the heap
 STA (XX19),Y

 INY                    \ Increment the heap pointer

 LDA XX15+3             \ Add Y2 to the end of the heap
 STA (XX19),Y

 INY                    \ Increment the heap pointer

 STY U                  \ Store the updated ship line heap pointer in U

 CPY T1                 \ If Y >= T1 then we have reached the maximum number of
 BCS LL81               \ edge lines that we can store in the ship line heap, so
                        \ skip to LL81 so we don't loop back for the next edge

.LL78

Code variation 4 of 8Related to the Master version

See variation 3 above for details.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 INC XX17               \ Increment the edge counter to point to the next edge

 LDY XX17               \ If Y >= XX20, which contains the number of edges in
 CPY XX20               \ the blueprint, jump to LL81 as we have processed all
 BCS LL81               \ the edges and don't need to loop back for the next one

 LDY #0                 \ Set Y to point to byte #0 again, ready for the next
                        \ edge
 LDA LSNUM              \ If LSNUM >= CNT, skip to LL81 so we don't loop back
 CMP CNT                \ for the next edge (CNT was set to the maximum heap
 BCS LL81               \ size for this ship in part 10, so this checks whether
                        \ we have just run out of space in the ship line heap,
                        \ and stops drawing edges if we have)

Code variation 5 of 8Minor and very low-impact

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 LDA V                  \ Increment V by 4 so V(1 0) points to the data for the
 ADC #4                 \ next edge
 STA V

 BCC ll81               \ If the above addition didn't overflow, jump to ll81 to
                        \ skip the following instruction

 INC V+1                \ Otherwise increment the high byte of V(1 0), as we
                        \ just moved the V(1 0) pointer past a page boundary

.ll81
 LDA V                  \ Increment V by 4 so V(1 0) points to the data for the
 CLC                    \ next edge
 ADC #4
 STA V

 BCC P%+4               \ If the above addition didn't overflow, skip the
                        \ following instruction

 INC V+1                \ Otherwise increment the high byte of V(1 0), as we
                        \ just moved the V(1 0) pointer past a page boundary

Code variation 6 of 8Related to the Master version

See variation 3 above for details.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
 JMP LL75               \ Loop back to LL75 to process the next edge
 INC XX17               \ Increment the edge counter to point to the next edge

 LDY XX17               \ If Y < XX20, which contains the number of edges in
 CPY XX20               \ the blueprint, loop back to LL75 to process the next
 BCC LL75               \ edge

.LL81

Code variation 7 of 8Related to the Master version

See variation 3 above for details.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Electron
Master
                        \ We have finished adding lines to the ship line heap,
                        \ so now we need to set the first byte of the heap to
                        \ the number of bytes stored there

 LDA U                  \ Fetch the ship line heap pointer from U into A, which
                        \ points to the end of the heap, and therefore contains
                        \ the heap size
 JMP LSCLR              \ Jump down to part 12 below to draw any remaining lines
                        \ from the old ship that are still in the ship line heap

Code variation 8 of 8Minor and very low-impact

This variation is blank in the Master version.

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, Electron
6502SP
 LDY #0                 \ Store A as the first byte of the ship line heap, so
 STA (XX19),Y           \ the heap is now correctly set up
 STA (XX19)             \ Store A as the first byte of the ship line heap, so
                        \ the heap is now correctly set up