Replace invalid characters with HTML entities
— with — ’ with ’ + with + × with x ç with ç “ with “ ” with ” ‘ with ‘ • with • – with - µ with µ † with † Fix C++ θ with θ Yen symbol instead of times Fix broken apos Bullet again E-circumflex
This commit is contained in:
James Gregory
parent
9e52de9586
commit
500e7f5654
353 changed files with 5091 additions and 5091 deletions
40
47-04.html
40
47-04.html
|
|
@ -37,7 +37,7 @@
|
|||
</CENTER>
|
||||
<P><BR></P>
|
||||
<H3><A NAME="Heading5"></A><FONT COLOR="#000077">Designing from a Mode X Perspective</FONT></H3>
|
||||
<P>Listing 47.4 shows Mode X rectangle fill code. The plane is selected for each pixel in turn, with drawing cycling from plane 0 to plane 3, then wrapping back to plane 0. This is the sort of code that stems from a write-pixel line of thinking; it reflects not a whit of the unique perspective that Mode X demands, and although it looks reasonably efficient, it is in fact some of the slowest graphics code you will ever see. I’ve provided Listing 47.4 partly for illustrative purposes, but mostly so we’ll have a point of reference for the substantial speed-up that’s possible with code that’s designed from a Mode X perspective.
|
||||
<P>Listing 47.4 shows Mode X rectangle fill code. The plane is selected for each pixel in turn, with drawing cycling from plane 0 to plane 3, then wrapping back to plane 0. This is the sort of code that stems from a write-pixel line of thinking; it reflects not a whit of the unique perspective that Mode X demands, and although it looks reasonably efficient, it is in fact some of the slowest graphics code you will ever see. I’ve provided Listing 47.4 partly for illustrative purposes, but mostly so we’ll have a point of reference for the substantial speed-up that’s possible with code that’s designed from a Mode X perspective.
|
||||
</P>
|
||||
<P><B>LISTING 47.4 L47-4.ASM</B></P>
|
||||
<!-- CODE //-->
|
||||
|
|
@ -73,37 +73,37 @@ parms ends
|
|||
.code
|
||||
public _FillRectangleX
|
||||
_FillRectangleX proc near
|
||||
push bp ;preserve caller’s stack frame
|
||||
push bp ;preserve caller’s stack frame
|
||||
mov bp,sp ;point to local stack frame
|
||||
push si ;preserve caller’s register variables
|
||||
push si ;preserve caller’s register variables
|
||||
push di
|
||||
|
||||
mov ax,SCREEN_WIDTH
|
||||
mul [bp+StartY] ;offset in page of top rectangle scan line
|
||||
mov di,[bp+StartX]
|
||||
mul [bp+StartY] ;offset in page of top rectangle scan line
|
||||
mov di,[bp+StartX]
|
||||
shr di,1
|
||||
shr di,1 ;X/4 = offset of first rectangle pixel in scan
|
||||
; line
|
||||
add di,ax ;offset of first rectangle pixel in page
|
||||
add di,[bp+PageBase] ;offset of first rectangle pixel in
|
||||
add di,[bp+PageBase] ;offset of first rectangle pixel in
|
||||
; display memory
|
||||
mov ax,SCREEN_SEG
|
||||
mov es,ax ;point ES:DI to the first rectangle pixel’s
|
||||
mov es,ax ;point ES:DI to the first rectangle pixel’s
|
||||
; address
|
||||
mov dx,SC_INDEX ;set the Sequence Controller Index to
|
||||
mov al,MAP_MASK ; point to the Map Mask register
|
||||
out dx,al
|
||||
inc dx ;point DX to the SC Data register
|
||||
mov cl,byte ptr [bp+StartX]
|
||||
and cl,011b ;CL = first rectangle pixel’s plane
|
||||
mov cl,byte ptr [bp+StartX]
|
||||
and cl,011b ;CL = first rectangle pixel’s plane
|
||||
mov al,01h
|
||||
shl al,cl ;set only the bit for the pixel’s plane to 1
|
||||
mov ah,byte ptr [bp+Color] ;color with which to fill
|
||||
mov bx,[bp+EndY]
|
||||
sub bx,[bp+StartY] ;BX = height of rectangle
|
||||
shl al,cl ;set only the bit for the pixel’s plane to 1
|
||||
mov ah,byte ptr [bp+Color] ;color with which to fill
|
||||
mov bx,[bp+EndY]
|
||||
sub bx,[bp+StartY] ;BX = height of rectangle
|
||||
jle FillDone ;skip if 0 or negative height
|
||||
mov si,[bp+EndX]
|
||||
sub si,[bp+StartX] ;CX = width of rectangle
|
||||
mov si,[bp+EndX]
|
||||
sub si,[bp+StartX] ;CX = width of rectangle
|
||||
jle FillDone ;skip if 0 or negative width
|
||||
FillRowsLoop:
|
||||
push ax ;remember the plane mask for the left edge
|
||||
|
|
@ -112,7 +112,7 @@ FillRowsLoop:
|
|||
FillScanLineLoop:
|
||||
out dx,al ;set the plane for this pixel
|
||||
mov es:[di],ah ;draw the pixel
|
||||
shl al,1 ;adjust the plane mask for the next pixel’s
|
||||
shl al,1 ;adjust the plane mask for the next pixel’s
|
||||
and al,01111b ; bit, modulo 4
|
||||
jnz AddressSet ;advance address if we turned over from
|
||||
inc di ; plane 3 to plane 0
|
||||
|
|
@ -126,16 +126,16 @@ AddressSet:
|
|||
dec bx ;count down scan lines
|
||||
jnz FillRowsLoop
|
||||
FillDone:
|
||||
pop di ;restore caller’s register variables
|
||||
pop di ;restore caller’s register variables
|
||||
pop si
|
||||
pop bp ;restore caller’s stack frame
|
||||
pop bp ;restore caller’s stack frame
|
||||
ret
|
||||
_FillRectangleX endp
|
||||
end
|
||||
</PRE>
|
||||
<!-- END CODE //-->
|
||||
<P>The two major weaknesses of Listing 47.4 both result from selecting the plane on a pixel by pixel basis. First, endless <B>OUT</B>s (which are particularly slow on 386s, 486s, and Pentiums, much slower than accesses to display memory) must be performed, and, second, <B>REP STOS</B> can’t be used. Listing 47.5 overcomes both these problems by tailoring the fill technique to the organization of display memory. Each plane is filled in its entirety in one burst before the next plane is processed, so only five <B>OUT</B>s are required in all, and <B>REP STOS</B> can indeed be used; I’ve used <B>REP STOSB</B> in Listings 47.5 and 47.6. <B>REP STOSW</B> could be used and would improve performance on most VGAs; however, <B>REP STOSW</B> requires extra overhead to set up, so it can be slower for small rectangles, especially on 8-bit VGAs. Note that doing an entire plane at a time can produce a “fading-in” effect for large images, because all columns for one plane are drawn before any columns for the next. If this is a problem, the four planes can be cycled through once for each scan line, rather than once for the entire rectangle.</P>
|
||||
<P>Listing 47.5 is 2.5 times faster than Listing 47.4 at clearing the screen on a 20-MHz cached 386 with a Paradise VGA. Although Listing 47.5 is slightly slower than an equivalent mode 13H fill routine would be, it’s not grievously so.</P><P><BR></P>
|
||||
<P>The two major weaknesses of Listing 47.4 both result from selecting the plane on a pixel by pixel basis. First, endless <B>OUT</B>s (which are particularly slow on 386s, 486s, and Pentiums, much slower than accesses to display memory) must be performed, and, second, <B>REP STOS</B> can’t be used. Listing 47.5 overcomes both these problems by tailoring the fill technique to the organization of display memory. Each plane is filled in its entirety in one burst before the next plane is processed, so only five <B>OUT</B>s are required in all, and <B>REP STOS</B> can indeed be used; I’ve used <B>REP STOSB</B> in Listings 47.5 and 47.6. <B>REP STOSW</B> could be used and would improve performance on most VGAs; however, <B>REP STOSW</B> requires extra overhead to set up, so it can be slower for small rectangles, especially on 8-bit VGAs. Note that doing an entire plane at a time can produce a “fading-in” effect for large images, because all columns for one plane are drawn before any columns for the next. If this is a problem, the four planes can be cycled through once for each scan line, rather than once for the entire rectangle.</P>
|
||||
<P>Listing 47.5 is 2.5 times faster than Listing 47.4 at clearing the screen on a 20-MHz cached 386 with a Paradise VGA. Although Listing 47.5 is slightly slower than an equivalent mode 13H fill routine would be, it’s not grievously so.</P><P><BR></P>
|
||||
<CENTER>
|
||||
<TABLE BORDER>
|
||||
<TR>
|
||||
|
|
|
|||
Loading…
Reference in a new issue