132 lines
2.1 KiB
ArmAsm
132 lines
2.1 KiB
ArmAsm
; Draws a filled trapezoid in the screen
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; note it is blocky (even/odd Y always set) for simplicity
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; TODO: use 5.3 fixed point rather than 8.8?
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; called pointing INL/INH to data structure:
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; .byte LEFT_SLOPE_H,LEFT_SLOPE_L
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; .byte RIGHT_SLOPE_H,RIGHT_SLOPE_L
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; .byte START_X_H,START_X_L
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; .byte END_X_H,END_X_L
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; .byte END_Y,START_Y
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; if START_Y=$ff then draw bullet-hole on background at left_slopeh/l
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; color is trapezoid_color_smc+1, usually it's going to be #$11 (red)
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; 10 bytes/trapezoid? Much smaller than a say 10x5 sprite
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draw_trapezoid:
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; FIXME: make this a loop
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ldy #0
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trapezoid_load_loop:
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lda (INL),Y
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sta trapezoid_left_slope,Y
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iny
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cpy #8
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bne trapezoid_load_loop
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lda (INL),Y
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sta trapezoid_endy_smc+1
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iny
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lda (INL),Y
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tay
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bmi draw_bullethole
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draw_trapezoid_loop:
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lda gr_offsets,Y
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sta trapezoid_draw_loop_smc+1
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lda gr_offsets+1,Y
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clc
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adc DRAW_PAGE
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sta trapezoid_draw_loop_smc+2
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trapezoid_color_smc:
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lda #$11
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ldx trapezoid_x_start
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bmi trap_clamp0
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cpx #40
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bcc trapezoid_draw_loop ; blt
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ldx #39
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jmp trapezoid_draw_loop
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trap_clamp0:
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ldx #0
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jmp trapezoid_draw_loop
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trapezoid_draw_loop:
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trapezoid_draw_loop_smc:
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sta $c00,X
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inx
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cpx trapezoid_x_end
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bne trapezoid_draw_loop
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; add in 8.8 fixed point (should we make this 6.2 or 5.3 instead?)
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clc
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lda trapezoid_x_start+1
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adc trapezoid_left_slope+1
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sta trapezoid_x_start+1
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lda trapezoid_x_start
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adc trapezoid_left_slope
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sta trapezoid_x_start
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clc
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lda trapezoid_x_end+1
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adc trapezoid_right_slope+1
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sta trapezoid_x_end+1
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lda trapezoid_x_end
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adc trapezoid_right_slope
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sta trapezoid_x_end
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dey
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dey
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trapezoid_endy_smc:
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cpy #0
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bne draw_trapezoid_loop
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rts
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draw_bullethole:
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ldy trapezoid_left_slope+1 ; get Y value
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lda gr_offsets,Y
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clc
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adc trapezoid_left_slope
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sta bullethole_draw_loop_smc+1
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lda gr_offsets+1,Y
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clc
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adc #$8 ; to background page $c00?
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sta bullethole_draw_loop_smc+2
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bullethole_draw:
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ldy #3
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bullethole_draw_loop:
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lda #$66
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bullethole_draw_loop_smc:
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sta $c00,Y
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dey
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bne bullethole_draw_loop
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rts
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trapezoid_left_slope:
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.byte 0,0
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trapezoid_right_slope:
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.byte 0,0
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trapezoid_x_start:
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.byte 0,0
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trapezoid_x_end:
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.byte 0,0
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