84 lines
2.1 KiB
ArmAsm
84 lines
2.1 KiB
ArmAsm
.proc circle_help ;; This is because jmp cant jump that long!
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.include "circle.inc"
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;;We have named the parts of the circle as such.
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;; |
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;; qbb | qab
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;; |
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;; qba | qaa
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;;---------------X-----------------> X
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;; qca | qda
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;; |
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;; qcb | qdb
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;; |
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;; v Y
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;; The q stands for quarter, whe have 4 quarter, and each quarter is split into 2
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draw_qaa:
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LDA byte_to_paint ;A byte containing a single 1. Coresponds to X position in the chunk.
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ORA (btp_mem_pos), Y
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STA (btp_mem_pos), Y
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draw_qda:
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;; inverted Y, this is shared with qca
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STY temp
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LDA #$07
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SEC
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SBC temp
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TAY
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LDA byte_to_paint
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ORA (btp_mem_pos_inv_y), Y
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STA (btp_mem_pos_inv_y), Y
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;LDY temp
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draw_qca: ;;mirror technique
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SEC
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;;C = 1 beacause the branching to while_x_bigger_then_y and SEC on first ittteration.
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LDA btp_mem_pos_center_two
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SBC btp_mem_pos
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STA btp_mem_pos_inv
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LDA btp_mem_pos_center_two + 1
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SBC btp_mem_pos + 1
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STA btp_mem_pos_inv + 1
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;; calculate byte_to_paint_inv 00000001 --> 10000000, 00000010 --> 01000000 ... etc
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;; uses a table!
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STX temp_
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LDX byte_to_paint
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LDA inverse_factor_value, X;; (see END.s)
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TAX ;; A is saved to x because qba use this as well
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; A = byte_to_paint_inv
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ORA (btp_mem_pos_inv), Y
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STA (btp_mem_pos_inv), Y
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;;Recover the Y value (we changed it because evrything is inverted)
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LDY temp
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draw_qba: ;;mirror_technique
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SEC
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LDA btp_mem_pos_center_two
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SBC btp_mem_pos_inv_y
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STA btp_mem_pos_inv
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LDA btp_mem_pos_center_two + 1
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SBC btp_mem_pos_inv_y + 1
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STA btp_mem_pos_inv + 1
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;STX temp_
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;LDX byte_to_paint
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;LDA inverse_factor_value, X;; (see END.s)
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TXA
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LDX temp_
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; A = byte_to_paint_inv
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ORA (btp_mem_pos_inv), Y
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STA (btp_mem_pos_inv), Y
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RTS
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.endproc
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