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60 lines
1.6 KiB
ArmAsm
60 lines
1.6 KiB
ArmAsm
; Driver to restore the screen using all the saved data.
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;
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; The backing store is a stack that grows downward in order to restore the
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; chunks in reverse order that they were saved. Each entry in the stack
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; includes:
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;
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; 2 bytes: address of restore routine
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; 1 byte: x coordinate
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; 1 byte: y coordinate
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; nn: x * y bytes of data, in lists of rows
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;
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; Note that sprites of different sizes will have different sized entries
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; in the stack, so the entire list has to be processed in order. But you want
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; that anyway, so it's not a big deal.
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;
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; The global variable 'bgstore' is used as the stack pointer. It musts be
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; initialized to a page boundary, the stack grows downward from there.
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; starting from the last byte on the previous page. E.g. if the initial
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; value is $c000, the stack grows down using $bfff as the highest address,
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; the initial bgstore value must point to 1 + the last usable byte
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;
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; All registers are clobbered because there's no real need to save them since
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; this will be called from the main game loop.
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restorebg_init
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lda #0 ; init backing store to end of free memory, $c000
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sta bgstore
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lda #BGTOP
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sta bgstore+1
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rts
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restorebg_driver
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ldy #0
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lda (bgstore),y
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sta restorebg_jsr+1
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iny
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lda (bgstore),y
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sta restorebg_jsr+2
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iny
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lda (bgstore),y
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sta PARAM0
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iny
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lda (bgstore),y
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sta PARAM1
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iny
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restorebg_jsr
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jsr $ffff
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clc
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tya ; y contains the number of bytes processed
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adc bgstore
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sta bgstore
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lda bgstore+1
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adc #0
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sta bgstore+1
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cmp #BGTOP
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bcc restorebg_driver
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rts
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