364 lines
11 KiB
ArmAsm
364 lines
11 KiB
ArmAsm
; Support routines for the primary background
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_InitBG0
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lda #DIRTY_BIT_BG0_X+DIRTY_BIT_BG0_Y
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tsb DirtyBits
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rts
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; Copy a raw data file into the code field
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;
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; A=low word of picture address
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; X=high word of pixture address
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_CopyBinToField
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:srcptr equ tmp0
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:line_cnt equ tmp2
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:dstptr equ tmp3
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:col_cnt equ tmp5
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:mask equ tmp6
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:data equ tmp7
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:mask_color equ tmp8
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sta :srcptr
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stx :srcptr+2
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; Check that this is a GTERAW image and save the transparent color
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ldy #4
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:chkloop
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lda [:srcptr],y
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cmp :headerStr,y
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beq *+3
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rts
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dey
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dey
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bpl :chkloop
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; We have a valid header, now get the transparency word and load it in
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ldy #6
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lda [:srcptr],y
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sta :mask_color
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; Advance over the header
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lda :srcptr
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clc
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adc #8
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sta :srcptr
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stz :line_cnt
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:rloop
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lda :line_cnt ; get the pointer to the code field line
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asl
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tax
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lda BTableLow,x
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sta :dstptr
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lda BTableHigh,x
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sta :dstptr+2
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; ldx #162 ; move backwards in the code field
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ldy #0 ; move forward in the image data
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lda #82 ; keep a running column count
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sta :col_cnt
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:cloop
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phy
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lda [:srcptr],y ; load the picture data
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cmp :mask_color
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beq :transparent ; a value of $0000 is transparent
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jsr :toMask ; Infer a mask value for this. If it's $0000, then
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cmp #$0000
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bne :mixed ; the data is solid, otherwise mixed
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; This is a solid word
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:solid
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lda [:srcptr],y
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pha ; Save the data
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lda Col2CodeOffset,y ; Get the offset to the code from the line start
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tay
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lda #$00F4 ; PEA instruction
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sta [:dstptr],y
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iny
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pla
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sta [:dstptr],y ; PEA operand
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bra :next
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:transparent
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lda :mask_color ; Make sure we actually have to mask
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cmp #$A5A5
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beq :solid
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lda Col2CodeOffset,y ; Get the offset to the code from the line start
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tay
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lda #$B1 ; LDA (dp),y
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sta [:dstptr],y
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iny
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lda 1,s ; load the saved Y-index
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ora #$4800 ; put a PHA after the offset
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sta [:dstptr],y
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bra :next
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:mixed
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sta :mask ; Save the mask
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lda [:srcptr],y ; Refetch the screen data
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sta :data
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tyx
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lda Col2CodeOffset,y ; Get the offset into the code field
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tay
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lda #$4C ; JMP exception
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sta [:dstptr],y
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iny
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lda JTableOffset,x ; Get the address offset and add to the base address
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clc
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adc :dstptr
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sta [:dstptr],y
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ldy JTableOffset,x ; This points to the code fragment
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lda 1,s ; load the offset
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xba
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ora #$00B1
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sta [:dstptr],y ; write the LDA (--),y instruction
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iny
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iny
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iny ; advance to the AND #imm operand
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lda :mask
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sta [:dstptr],y
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iny
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iny
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iny ; advance to the ORA #imm operand
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lda :mask
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eor #$FFFF ; invert the mask to clear up the data
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and :data
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sta [:dstptr],y
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:next
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ply
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iny
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iny
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dec :col_cnt
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bne :cloop
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lda :srcptr
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clc
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adc #164
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sta :srcptr
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inc :line_cnt
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lda :line_cnt
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cmp #200
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bcs :exit
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brl :rloop
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:exit
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rts
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:toMask pha ; save original
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lda 1,s
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eor :mask_color ; only identical bits produce zero
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and #$F000
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beq *+7
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pea #$0000
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bra *+5
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pea #$F000
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lda 3,s
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eor :mask_color
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and #$0F00
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beq *+7
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pea #$0000
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bra *+5
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pea #$0F00
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lda 5,s
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eor :mask_color
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and #$00F0
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beq *+7
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pea #$0000
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bra *+5
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pea #$00F0
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lda 7,s
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eor :mask_color
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and #$000F
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beq *+7
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lda #$0000
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bra *+5
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lda #$000F
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ora 1,s
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sta 1,s
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pla
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ora 1,s
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sta 1,s
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pla
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ora 1,s
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sta 1,s
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pla
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sta 1,s ; pop the saved word
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pla
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rts
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:headerStr asc 'GTERAW'
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; Copy a loaded SHR picture into the code field
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;
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; A=low word of picture address
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; X=high workd of pixture address
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;
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; Picture must be within one bank
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_CopyPicToField
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:srcptr equ tmp0
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:line_cnt equ tmp2
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:dstptr equ tmp3
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:col_cnt equ tmp5
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:mask equ tmp6
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:data equ tmp7
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sta :srcptr
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stx :srcptr+2
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stz :line_cnt
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:rloop
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lda :line_cnt ; get the pointer to the code field line
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asl
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tax
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lda BTableLow,x
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sta :dstptr
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lda BTableHigh,x
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sta :dstptr+2
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; ldx #162 ; move backwards in the code field
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ldy #0 ; move forward in the image data
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lda #80 ; keep a running column count
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; lda #82 ; keep a running column count
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sta :col_cnt
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:cloop
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phy
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lda [:srcptr],y ; load the picture data
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beq :transparent ; a value of $0000 is transparent
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jsr :toMask ; Infer a mask value for this. If it's $0000, then
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bne :mixed ; the data is solid, otherwise mixed
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; This is a solid word
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lda [:srcptr],y
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pha ; Save the data
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lda Col2CodeOffset,y ; Get the offset to the code from the line start
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tay
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lda #$00F4 ; PEA instruction
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sta [:dstptr],y
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iny
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pla
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sta [:dstptr],y ; PEA operand
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bra :next
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:transparent
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lda Col2CodeOffset,y ; Get the offset to the code from the line start
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tay
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lda #$B1 ; LDA (dp),y
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sta [:dstptr],y
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iny
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lda 1,s ; load the saved Y-index
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ora #$4800 ; put a PHA after the offset
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sta [:dstptr],y
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bra :next
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:mixed
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sta :mask ; Save the mask
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lda [:srcptr],y ; Refetch the screen data
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sta :data
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tyx
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lda Col2CodeOffset,y ; Get the offset into the code field
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tay
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lda #$4C ; JMP exception
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sta [:dstptr],y
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iny
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lda JTableOffset,x ; Get the address offset and add to the base address
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clc
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adc :dstptr
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sta [:dstptr],y
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ldy JTableOffset,x ; This points to the code fragment
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lda 1,s ; load the offset
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xba
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ora #$00B1
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sta [:dstptr],y ; write the LDA (--),y instruction
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iny
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iny
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iny ; advance to the AND #imm operand
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lda :mask
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sta [:dstptr],y
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iny
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iny
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iny ; advance to the ORA #imm operand
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lda :data
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sta [:dstptr],y
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:next
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ply
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; dex
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; dex
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iny
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iny
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dec :col_cnt
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bne :cloop
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lda :srcptr
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clc
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; adc #164
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adc #160
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sta :srcptr
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inc :line_cnt
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lda :line_cnt
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; cmp #208
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cmp #200
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bcs :exit
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brl :rloop
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:exit
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rts
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:toMask bit #$F000
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beq *+7
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and #$0FFF
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bra *+5
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ora #$F000
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bit #$0F00
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beq *+7
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and #$F0FF
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bra *+5
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ora #$0F00
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bit #$00F0
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beq *+7
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and #$FF0F
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bra *+5
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ora #$00F0
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bit #$000F
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beq *+7
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and #$FFF0
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bra *+5
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ora #$000F
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rts
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