Category : C Source Code
Archive   : XLIB06.ZIP
Filename : XCLIPPBM.ASM

;-----------------------------------------------------------------------
; MODULE XCLIPPBM
;
; This module was written by Matthew MacKenzie
; [email protected]
;
; Clipped transfer of planar bitmaps from system memory to video memory.
;
; Compile with TASM.
; C near-callable.
;
; ****** XLIB - Mode X graphics library ****************
; ****** ****************
; ****** Written By Themie Gouthas ****************
;
; [email protected]
; [email protected]
;-----------------------------------------------------------------------

include xlib.inc
include xclippbm.inc


.data

align 2

; global clipping variables
_TopBound dw (?)
_BottomBound dw (?)
_LeftBound dw (?)
_RightBound dw (?)

; VGA plane masks
ColumnMask db 011h,022h,044h,088h

; bit delay timers
LeftDelay db 0, 1, 2, 4
RightDelay db 0, 4, 2, 1


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; _x_clip_pbm
;
; C near-callable as:
;
; void x_clip_pbm (int X, int Y, int ScreenOffs, char far * Bitmap);
;
; Bitmap is a planar bitmap, in the regular Xlib format.
;
; ax, bx, cx, and dx go south.

.code

public _x_clip_pbm
align 2
_x_clip_pbm proc
ARG X:word, Y:word, ScreenOffs:word, Bitmap:dword
LOCAL left_counter, right_counter,column,clipped_height,clipped_width,screen_pos,bitmap_pos,bitmap_size,VGA_mask,width_copy,height_temp,screen_width:word=LocalStk
; Tasm 1.0 does not allow the \ line continuation
;LOCAL left_counter:word, right_counter:word, \
; column:word, clipped_height:word, clipped_width:word, \
; screen_pos:word, bitmap_pos:word, bitmap_size:word, \
; VGA_mask:word, width_copy, height_temp:word, \
; screen_width:word=LocalStk

push bp
mov bp, sp
sub sp, LocalStk
push si
push di
push ds

; sociopathic cases: are the clipping bounds out of order?
mov ax, _TopBound
cmp ax, _BottomBound
jg @@GetOut
mov ax, _LeftBound
cmp ax, _RightBound
jle @@ReasonableAndProper
@@GetOut: ; return a 1 -- no image drawn
pop ds
pop di
pop si
mov ax, 1
mov sp, bp
pop bp
ret

@@ReasonableAndProper:

; we need to use both the tables in ds and the height and width of the bitmap
les si, Bitmap

; vertical position
xor cx, cx
mov cl, byte ptr es:[si + 1] ; height of bitmap
xor ax, ax
mov al, byte ptr es:[si] ; width of bitmap
mul cx
mov bitmap_size, ax
mov ax, Y
cmp ax, _BottomBound ; top edge below clipping box?
jg @@GetOut

mov bx, cx
add bx, ax
dec bx ; bottom edge = Y + height - 1
cmp bx, _TopBound
jl @@GetOut
sub bx, _BottomBound ; bottom margin = bottom edge - BottomBound
jle @@NoBottomBound
sub cx, bx ; clip bottom margin from height
@@NoBottomBound:
mov bx, _TopBound
sub bx, ax ; top margin = TopBound - Y
jle @@NoTopBound
add ax, bx ; top edge = Y + top margin
sub cx, bx ; clip top margin from height
jmp @@KeepMargin
@@NoTopBound:
xor bx, bx
@@KeepMargin:
mov clipped_height, cx

mul _ScrnLogicalByteWidth
mov di, ax
add di, ScreenOffs ; row of upper-left corner of blit

mov cl, byte ptr es:[si] ; width of bitmap (ch is still 0 from height)
mov ax, cx
mul bx
add si, ax
add si, 2 ; starting position in bitmap

; horizontal position
mov width_copy, cx
mov dx, X
cmp dx, _RightBound
jg @@GetOut
mov dx, 0 ; unclipped value for right delay

mov ax, cx
shl ax, 2 ; width in pixels
add ax, X
dec ax ; right edge = X + width in pixels - 1
cmp ax, _LeftBound
jl @@GetOut
sub ax, _RightBound ; right margin = right edge - RightBound
jle @@NoRightBound
mov bx, ax
and bx, 3
mov dl, RightDelay[bx]
shr ax, 2
sub cx, ax ; subtract clipped bytes from width
@@NoRightBound:
mov right_counter, dx
mov dx, 0 ; unclipped value for left delay
mov ax, _LeftBound
sub ax, X ; left margin = LeftBound - X
jle @@NoLeftBound
mov bx, ax
and bx, 3
mov dl, LeftDelay[bx]
add ax, 3
shr ax, 2 ; left margin/4, rounded up
sub cx, ax ; subtract clipped bytes from width
add si, ax ; move starting position in bitmap past margin
add di, ax ; move starting position on screen past margin
@@NoLeftBound:
mov left_counter, dx
mov clipped_width, cx

mov ax, X ; add x coordinate to screen position
mov bx, ax
sar ax, 2
add di, ax

mov dx, SC_INDEX
mov al, MAP_MASK
out dx, al
inc dx

and bx, 3 ; initial mask
xor ax, ax
mov al, ColumnMask[bx]
mov VGA_mask, ax
out dx, al ; initial mask

mov column, 4
mov bitmap_pos, si
mov screen_pos, di
mov ax, _ScrnLogicalByteWidth
mov screen_width, ax ; since we move ds

; we've used all our tables, so we can change ds to point to the bitmap,
; and es to point to the screen
mov ds, word ptr [Bitmap + 2]
mov ax, SCREEN_SEG
mov es, ax

cld ; strings go forward
mov bx, width_copy
sub bx, clipped_width ; bytes to advance one line in bitmap

; let's actually draw something for a change
@@WritePlane:
mov ax, clipped_height
mov height_temp, ax
mov dx, screen_width
sub dx, clipped_width ; bytes to advance one line across screen

@@WriteLine:
mov cx, clipped_width
shr cx, 1
rep movsw ; in they went, two by two...
adc cx, 0
rep movsb ; catch stray last byte, if it's there
add si, bx ; advance one bitmap line
add di, dx ; advance one screen line

dec height_temp
jnz @@WriteLine

dec column
jz @@OuttaHere ; only four columns per customer, please
mov dx, SC_INDEX + 1
rol byte ptr VGA_mask, 1
adc screen_pos, 0 ; add to location if we've wrapped to plane 0
mov al, byte ptr VGA_mask
out dx, al ; set VGA for next column

shr right_counter, 1
jnc @@NoRightCounter
dec clipped_width ; cut off right edge for later planes
inc bx
@@NoRightCounter:
shr left_counter, 1
jnc @@NoLeftCounter
inc clipped_width ; add to left edge for later planes
dec bx
dec bitmap_pos
dec screen_pos
@@NoLeftCounter:
mov si, bitmap_pos
add si, bitmap_size
mov bitmap_pos, si
mov di, screen_pos
jmp @@WritePlane

@@OuttaHere: ; return a 0 -- something was inside the boundary
pop ds
pop di
pop si
mov ax, 0
mov sp, bp
pop bp
ret
_x_clip_pbm endp


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; _x_clip_masked_pbm
;
; C near-callable as:
;
; void x_clip_masked_pbm (int X, int Y, int ScreenOffs, char far * Bitmap);
;
; Bitmap is a planar bitmap, in the regular Xlib format.
; The width of the bitmap cannot be greater than 90 bytes, however.
; Ain't that just criminal?
;
; ax, bx, cx, and dx go south.


; one branch per pixel is more than enough -- we'll unroll the line-writing
; loop all the way to try to get a little speed (at the expense, as usual,
; of a chunk of memory)

MaskedPoint macro offset
mov al, [si + offset]
or al, al
jz $+6
mov es:[di + offset], al
endm

MaskedPointSize equ 11

public _x_clip_masked_pbm
align 2
_x_clip_masked_pbm proc
ARG X:word, Y:word, ScreenOffs:word, Bitmap:dword
; Tasm 1.0 does not allow the \ line continuation
LOCAL left_counter,right_counter,column:word,clipped_height,screen_pos,bitmap_pos,bitmap_size,VGA_mask,width_copy,height_temp,screen_width:word=LocalStk
;LOCAL left_counter:word, right_counter:word, \
; column:word, clipped_height:word, \
; screen_pos:word, bitmap_pos:word, bitmap_size:word, \
; VGA_mask:word, width_copy, height_temp:word, \
; screen_width:word=LocalStk
push bp
mov bp, sp
sub sp, LocalStk
push si
push di
push ds

; sociopathic cases: are the clipping bounds out of order?
mov ax, _TopBound
cmp ax, _BottomBound
jg @@GetOut
mov ax, _LeftBound
cmp ax, _RightBound
jle @@ReasonableAndProper
@@GetOut: ; return a 1 -- no image drawn
pop ds
pop di
pop si
mov ax, 1
mov sp, bp
pop bp
ret

@@ReasonableAndProper:

; we need to use both the tables in ds and the height and width of the bitmap
les si, Bitmap

; vertical position
xor cx, cx
mov cl, byte ptr es:[si + 1] ; height of bitmap
xor ax, ax
mov al, byte ptr es:[si] ; width of bitmap
mul cx
mov bitmap_size, ax
mov ax, Y
cmp ax, _BottomBound ; top edge below clipping box?
jg @@GetOut

mov bx, cx
add bx, ax
dec bx ; bottom edge = Y + height - 1
cmp bx, _TopBound
jl @@GetOut
sub bx, _BottomBound ; bottom margin = bottom edge - BottomBound
jle @@NoBottomBound
sub cx, bx ; clip bottom margin from height
@@NoBottomBound:
mov bx, _TopBound
sub bx, ax ; top margin = TopBound - Y
jle @@NoTopBound
add ax, bx ; top edge = Y + top margin
sub cx, bx ; clip top margin from height
jmp @@KeepMargin
@@NoTopBound:
xor bx, bx
@@KeepMargin:
mov clipped_height, cx

mul _ScrnLogicalByteWidth
mov di, ax
add di, ScreenOffs ; row of upper-left corner of blit

mov cl, byte ptr es:[si] ; width of bitmap (ch is still 0 from height)
mov ax, cx
mul bx
add si, ax
add si, 2 ; starting position in bitmap

; horizontal position
mov width_copy, cx
mov dx, X
cmp dx, _RightBound
jg @@GetOut
mov dx, 0 ; unclipped value for right delay

mov ax, cx
shl ax, 2 ; width in pixels
add ax, X
dec ax ; right edge = X + width in pixels - 1
cmp ax, _LeftBound
jl @@GetOut
sub ax, _RightBound ; right margin = right edge - RightBound
jle @@NoRightBound
mov bx, ax
and bx, 3
mov dl, RightDelay[bx]
shr ax, 2
sub cx, ax ; subtract clipped bytes from width
@@NoRightBound:
mov right_counter, dx
mov dx, 0 ; unclipped value for left delay
mov ax, _LeftBound
sub ax, X ; left margin = LeftBound - X
jle @@NoLeftBound
mov bx, ax
and bx, 3
mov dl, LeftDelay[bx]
add ax, 3
shr ax, 2 ; left margin/4, rounded up
sub cx, ax ; subtract clipped bytes from width
add si, ax ; move starting position in bitmap past margin
add di, ax ; move starting position on screen past margin
@@NoLeftBound:
mov left_counter, dx
mov ax, cx
imul ax, (-1 * MaskedPointSize)
add ax, offset @@LineDone + 2
mov cx, ax ; jump offset for plotting

mov ax, X ; add x coordinate to screen position
mov bx, ax
shr ax, 2
add di, ax

mov dx, SC_INDEX
mov al, MAP_MASK
out dx, al
inc dx

and bx, 3 ; initial mask
xor ax, ax
mov al, ColumnMask[bx]
mov VGA_mask, ax
out dx, al

mov column, 4
mov bitmap_pos, si
mov screen_pos, di
mov ax, _ScrnLogicalByteWidth
mov screen_width, ax ; since we move ds

; we've used all our tables, so we can change ds to point to the bitmap,
; and es to point to the screen
mov ds, word ptr [Bitmap + 2]
mov ax, SCREEN_SEG
mov es, ax

mov bx, width_copy

; let's actually draw something for a change
mov ax, clipped_height
mov height_temp, ax
mov dx, screen_width
jmp cx

; 90 bottles of beer on the wall...
PointLoop = 89
rept 89
MaskedPoint PointLoop
PointLoop = PointLoop - 1
endm
; one bottle of beer...

; final point needs a different branch offset, so we don't use MaskedPoint
mov al, [si]
or al, al
jz @@LineDone
mov es:[di], al

@@LineDone:
add si, bx ; advance one bitmap line
add di, dx ; advance one screen line
dec height_temp
jz @@PlaneDone
jmp cx

@@PlaneDone:
dec column
jz @@OuttaHere ; only four columns per customer, please
mov dx, SC_INDEX + 1
rol byte ptr VGA_mask, 1
adc screen_pos, 0 ; move to new column if we've wrapped to plane 0
mov al, byte ptr VGA_mask
out dx, al ; set VGA for next column

shr right_counter, 1
jnc @@NoRightCounter
add cx, MaskedPointSize ; cut off right edge for later planes
@@NoRightCounter:
shr left_counter, 1
jnc @@NoLeftCounter
sub cx, MaskedPointSize ; add to left edge for later planes
dec bitmap_pos
dec screen_pos
@@NoLeftCounter:
mov si, bitmap_pos
add si, bitmap_size
mov bitmap_pos, si
mov di, screen_pos

mov ax, clipped_height
mov height_temp, ax
mov dx, screen_width
jmp cx

@@OuttaHere: ; return a 0 -- something was inside the boundary
pop ds
pop di
pop si
mov ax, 0
mov sp, bp
pop bp
ret
_x_clip_masked_pbm endp

end