ReC98/th04/spark_render.asm

65 lines
1.4 KiB
NASM

; Draws the hardcoded spark sprite with the given ID, with ([x], [vram_y])
; pointing to the top-left point. Assumptions:
; • ES is already be set to the beginning of a VRAM segment
; • The GRCG is active, and set to the intended color
; void near fastcall spark_render(int x, int vram_y, int sprite_id);
public @spark_render
@spark_render proc near
push si
push di
mov si, ax ; SI = [x]
mov bx, dx ; BX = [vram_y]
sar ax, 3 ; x / 8
shl dx, 6 ; [vram_y] * 64
add ax, dx
shr dx, 2 ; (([vram_y] * 64) / 4) = [vram_y] * 16
add ax, dx
mov di, ax ; ([vram_y] * 64) + ([vram_y] * 16) = [vram_y * ROW_SIZE]
and si, 7 ; [x] & 7
mov ax, si
shl si, 7 ; *= SPARK_SIZE * SPARK_SPRITES (offset of X-shifted sprite)
add si, offset sSPARKS
and cx, 7 ; & (SPARK_SPRITES - 1)
shl cx, 4 ; * SPARK_SIZE
add si, cx
cmp bx, RES_Y - SPARK_H
ja short @@ywrap_needed
mov cx, SPARK_H ; CX = # of rows copied *before* Y wrap
xor bx, bx ; BX = # of rows copied *after* Y wrap
jmp short @@blit_loop
@@ywrap_needed:
mov cx, RES_Y
sub cx, bx
mov bx, SPARK_H
sub bx, cx
@@blit_loop:
lodsw
or ah, ah
jz short @@8px
mov es:[di], ax
jmp short @@next_row
@@8px:
or al, al
jz short @@next_row
mov es:[di], al
@@next_row:
add di, ROW_SIZE
loop @@blit_loop
or bx, bx
jz short @@ret
sub di, PLANE_SIZE
xchg cx, bx
jmp short @@blit_loop
@@ret:
pop di
pop si
retn
@spark_render endp
even