90 lines
2.2 KiB
ArmAsm
90 lines
2.2 KiB
ArmAsm
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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;;drawing line from 2 cordinates
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;;# (X_pos, Y_pos) #
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;;# * #
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;;# * #
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;;# * #
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;;# (X_end, Y_end) #
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;;NOTE THAT X_pos <= X_end, Y_pos <= Y_end. Min 45deg!
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.proc line_down_inv
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;; Look at line_down for referense
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.include "line.inc"; Defines memory positions, ex X_pos
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LDA #$00
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STA V + 1
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STA dx_2 + 1
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SEC
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LDA dy
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SBC dx
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Mult_16 A, V + 1
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STA V
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Mult_16 dx_2, dx_2 + 1
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;; D = dx_2 - dy. (signed 16-bit)
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SEC
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LDA dx_2
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SBC dy
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STA D
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LDA dx_2 + 1
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SBC #$00
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STA D + 1
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;; because C flag is wrong value we let dy_2 be 1 to small
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Sub_16 dx_2, dx_2 +1, #$01,#$00
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selfmod:
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LDA dx_2
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STA case_2 + 1
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LDA dx_2 + 1
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STA case_2 + 7
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LDA V
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STA case_1 + 3
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LDA V + 1
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STA case_1 + 9
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end_selfmod:
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LDA X_end
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STA X_pos
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LDA Y_end
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STA Y_pos
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JSR pixel_calc ;;only used first pixel. after this relative position is abused
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STA byte_to_paint
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INY
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Sub_16 btp_mem_pos, btp_mem_pos + 1, #$00, #$00, !
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LDX dy
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CLC
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for_y: ; C =0
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LDA byte_to_paint
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ORA (btp_mem_pos), Y
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STA (btp_mem_pos), Y
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increment_y_pos:
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DEY
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BNE increment_y_pos_end
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move_8px_down:
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LDY #$08
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Sub_16 btp_mem_pos, btp_mem_pos + 1, #$3f ,#$01, !
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increment_y_pos_end:
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DEX
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BEQ end
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;Lag_16 D, D + 1, #$00, #$02, case_2
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LDA D + 1
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BMI case_2
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case_1:
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Sub_16 D, D + 1, #V, #V + 1, !
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increment_pixel_x:
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ASL byte_to_paint
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BCC for_y
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move_8px_left:
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Sub_16 btp_mem_pos, btp_mem_pos + 1, #$08, #$00,!
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ROL byte_to_paint
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JMP for_y
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case_2:
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Add_16 D, D + 1, #dx_2, #dx_2 + 1,! ;D = D + 2*dx
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CLC ; for_y shall always have C = 1
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JMP for_y
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end:
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RTS
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.endproc
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