dos33fsprogs/games/ootw/gr_trapezoid.s
Vince Weaver b1238af49d re-arranged the entire directory structure
this will probably upset people
2021-01-05 15:29:31 -05:00

132 lines
2.1 KiB
ArmAsm

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