60 lines
1.1 KiB
ArmAsm
60 lines
1.1 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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;; https://schwarzers.com/algorithms/
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LDY Y_pos
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LDX X_pos
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;; X_pos = X_pos + r (hack, should fix later ( xpos == ypos is not always true))
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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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;; 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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while_x_bigger_then_y:
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STY Y_pos
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STX X_pos
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STA temp
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jsr pixel_draw
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LDY Y_pos
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LDX X_pos
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LDA temp
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INY ; y++
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;;t1 += y
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CLC
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LDA t1
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STY temp
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ADC temp
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STA t1
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;; t2 = t1 -x
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SEC
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STX temp
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SBC temp
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;; if t2 < 0 then skip to endif
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CMP #$00
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BMI endif
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if:
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DEX; x--
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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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STX temp
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TYA
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CMP temp
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JMP while_x_bigger_then_y
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BEQ while_x_bigger_then_y
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.endproc
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