125 lines
3.3 KiB
ArmAsm
125 lines
3.3 KiB
ArmAsm
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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.proc circle
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.include "circle.inc"
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;; We use the algorithm jerkos method
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;; git
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;; X_rel = radius (share the same address)
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;;Y_rel =0
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LDA #$00
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STA Y_rel
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;; t1 = radius >> 4
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LDA radius
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LSR
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LSR
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LSR
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LSR
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STA t1
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draw_center_px_in_circle:
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JSR pixel_draw
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LDA btp_mem_pos
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STA btp_mem_pos_center
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LDA btp_mem_pos + 1
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STA btp_mem_pos_center + 1
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;; btp_mem_pos_center_two = 2*btp_mem_pos_center | used later for calculating btp_mem_pos_inv
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Mult_16 btp_mem_pos_center, btp_mem_pos_center + 1
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;; fix offset of 8 bytes, idk why this is needed
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Sub_16 btp_mem_pos_center, btp_mem_pos_center + 1, #$40, #$01 ;-320
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draw_lower_px_in_circle:
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CLC
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LDA Y_pos
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STA temp
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ADC radius
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STA Y_pos
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JSR pixel_draw
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LDA btp_mem_pos
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STA btp_mem_pos_qcb
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STA btp_mem_pos_qdb
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LDA btp_mem_pos + 1
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STA btp_mem_pos_qdb + 1
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STA btp_mem_pos_qcb + 1
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;; fix offset of 8 bytes, idk why this is needed
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Sub_16 btp_mem_pos_qcb, btp_mem_pos_qcb + 1, #$40, #$01 ;-320
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Sub_16 btp_mem_pos_qdb, btp_mem_pos_qdb + 1, #$40, #$01 ;-320
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LDA temp
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STA Y_pos
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draw_right_px_in_circle:
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CLC
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LDA X_pos
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ADC radius
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STA X_pos
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;; We only draw the first pixel using absolute position.
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;; After that we use relative position.
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JSR pixel_draw
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;; This sets byte_to_paint, btp_mem_pos and Y
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LDA btp_mem_pos
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STA btp_mem_pos_qda
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LDA btp_mem_pos + 1
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STA btp_mem_pos_qda + 1
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;; fix offset of 8 bytes, idk why this is needed
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Sub_16 btp_mem_pos_qda, btp_mem_pos_qda + 1, #$40, #$01 ;-320
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while_x_bigger_then_y:
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;;Draw pixels and does the ypos incrementation logic
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;; WARNING expects C=1 before and C =0 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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JSR circle_help
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;;t1 += y
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; C==0 from circle_help
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LDA t1
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ADC Y_rel
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STA t1
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;; t2 = t1 - x
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SEC
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SBC X_rel
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STA t2
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;; if t2 < 0 then skip to endif
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;; we can skipp CMP #$00 because SBC above do the same
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BMI endif
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if:
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decrement_x_pos:
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DEC X_rel
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ASL byte_to_paint
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BCC decrement_x_pos_end
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move_8px_left:
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;; Next chunk is 8 addresses away. Look in pixel_draw for more detail.
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;; -8.
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;; C = 1 because branching
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Sub_16 btp_mem_pos, btp_mem_pos + 1, #$08, #$00, ! ;+8
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;; Y is inverted
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Sub_16 btp_mem_pos_qda, btp_mem_pos_qda + 1, #$08, #$00, ! ;+8
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;; X and Y has swoped
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Sub_16 btp_mem_pos_qcb, btp_mem_pos_qcb + 1, #$40, #$01, ! ;-320
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;; X and Y has swoped and Y has inverted
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Sub_16 btp_mem_pos_qdb, btp_mem_pos_qdb +1, #$40, #$01, ! ;+320
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;; Restores byte to paint
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LDX #%00000001
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STX byte_to_paint
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LDA t2
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decrement_x_pos_end:
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STA t1 ; t1 = t2
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endif:
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;; repeat if X > Y
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LDA X_rel
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CMP Y_rel
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BCS while_x_bigger_then_y
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RTS
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.include "routines/circle/circle_help.s"
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.endproc
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