bfefcbff8f
This was recomended by dicander and duunqnd because A =$ABAC
looks like one address and not 2 zero-page addresses.
83 lines
2.9 KiB
ArmAsm
83 lines
2.9 KiB
ArmAsm
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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;; petski: https://www.c64-wiki.com/wiki/File:ASCII-Codes.gif
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;;https://www.c64-wiki.com/wiki/Character_set
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;; Takes in a PETSKI-code in CODE
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;; And prints it ON X_pos, Y_pos
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;; Note that this is the real positions divided by 8
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.proc char_draw
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Character_generator_ROM = $D000
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Y_pos_offset = $F9 ; 16-bit value (uses F8), reuses from Y_pos
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X_pos_offset = $FA ; 16-bit value (uses F7)
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X_pos = $FA
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Y_pos = $F9
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charset = $FB
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code = $FE
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petski_position = $FE ; 16-bit value (uses FF),reuses code:s memory
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screen_position = $FC ; 16-bit value (uses FD)
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;#### TEMP INIT DATA ####
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LDA #$10
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STA code
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LDA #04
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STA X_pos
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LDA #02
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STA Y_pos
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;;Do arithimatic to know where to read and write bytes.
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initial:
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;We first need to clear some memory
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LDA #$00
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STA petski_position + 1
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STA Y_pos_offset + 1
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STA X_pos_offset + 1
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;;We need the relative offset for bytes to read and write.
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;; This is code *8 because 8byte is one character
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;; *8 = 2*2*2
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ASL code ;Will never owerflow, therefore 8byte
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Mult_16 petski_position, petski_position + 1
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Mult_16 petski_position, petski_position + 1
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;; Add starting position
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Add_16 petski_position, petski_position + 1, #<Character_generator_ROM , #>Character_generator_ROM, !
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;;Calculate screen_position to use
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Mov_16 screen_position, screen_position + 1, #<VIC_bank, #>VIC_bank
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;; Add the X_pos has a offset multiplier of *8 because 1 chunk = 8 addresses
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;; *8
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Mult_16 X_pos_offset, X_pos_offset + 1
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Mult_16 X_pos_offset, X_pos_offset + 1
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Mult_16 X_pos_offset, X_pos_offset + 1
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;; Add
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Add_16 screen_position, screen_position + 1, X_pos, #$00, !
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;; And Y_pos has a offset multiplier of "screen length" = 320 = (2*2 +1)*2^6
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;;Y_pos*2*2 +1 |Lets reuse X_pos for storage
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LDA Y_pos
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STA X_pos
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Add_16 Y_pos_offset, Y_pos_offset + 1, X_pos, #$00, !
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;; *2^6
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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Mult_16 Y_pos_offset, Y_pos_offset + 1
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;; Add
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Add_16 screen_position, screen_position + 1, Y_pos_offset, Y_pos_offset + 1, !
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initial_end:
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;; One character is 8 byte, move these bytes to screen
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LDY #$07
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@loop:
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LDA (petski_position), Y
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STA (screen_position), Y
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DEY
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BNE @loop
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LDA (petski_position), Y
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STA (screen_position), Y
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RTS
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.endproc
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