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
55-04.html
40
55-04.html
|
|
@ -36,18 +36,18 @@
|
|||
</TABLE>
|
||||
</CENTER>
|
||||
<P><BR></P>
|
||||
<P>This is where it gets a little complicated. In write mode 3 (which incidentally is not available on the EGA), each byte value that the CPU writes to the VGA does not get written to display memory. Instead, it turns into the bit mask. (Actually, it’s ANDed with the Bit Mask register, and the result becomes the bit mask, but we’ll leave the Bit Mask register set to 0xFF, so the CPU value will become the bit mask.) The bit mask selects, on a bit-by-bit basis, between the data in the latches for each plane (the previously loaded background color, in this case) and the foreground color. Where does the foreground color come from, if not from the CPU? From the Set/Reset register, as shown in Figure 55.3. Thus, each byte written by the CPU (font data, presumably) selects foreground or background color for each of eight pixels, all done with a single write to display memory.
|
||||
<P>This is where it gets a little complicated. In write mode 3 (which incidentally is not available on the EGA), each byte value that the CPU writes to the VGA does not get written to display memory. Instead, it turns into the bit mask. (Actually, it’s ANDed with the Bit Mask register, and the result becomes the bit mask, but we’ll leave the Bit Mask register set to 0xFF, so the CPU value will become the bit mask.) The bit mask selects, on a bit-by-bit basis, between the data in the latches for each plane (the previously loaded background color, in this case) and the foreground color. Where does the foreground color come from, if not from the CPU? From the Set/Reset register, as shown in Figure 55.3. Thus, each byte written by the CPU (font data, presumably) selects foreground or background color for each of eight pixels, all done with a single write to display memory.
|
||||
</P>
|
||||
<P><A NAME="Fig3"><!-- </A><A HREF="javascript:displayWindow('images/55-03.jpg',407,375 )"> --><IMG SRC="images/55-03.jpg"><BR><!-- </A>
|
||||
<BR><A HREF="javascript:displayWindow('images/55-03.jpg',407,375)"> --><FONT COLOR="#000077"><B>Figure 55.3</B></FONT></A> <I>The data path in write mode 3.</I>
|
||||
</P>
|
||||
<P>I know this sounds pretty esoteric, but think of it this way: The latches hold the background color in a form suitable for writing eight background pixels (one full byte) at a pop. Write mode 3 allows each CPU byte to punch holes in the background color provided by the latches, holes through which the foreground color from the Set/Reset register can flow. The result is that a single write draws exactly the combination of foreground and background pixels described by each font byte written by the CPU. It may help to look at Listing 55.4, which shows The BitMan’s technique in action. And yes, this technique is absolutely worth the trouble; it’s about three times faster than the fill-then-draw approach described above, and about twice as fast as transparent text. So far as I know, there is no faster way to draw text on a VGA.
|
||||
<P>I know this sounds pretty esoteric, but think of it this way: The latches hold the background color in a form suitable for writing eight background pixels (one full byte) at a pop. Write mode 3 allows each CPU byte to punch holes in the background color provided by the latches, holes through which the foreground color from the Set/Reset register can flow. The result is that a single write draws exactly the combination of foreground and background pixels described by each font byte written by the CPU. It may help to look at Listing 55.4, which shows The BitMan’s technique in action. And yes, this technique is absolutely worth the trouble; it’s about three times faster than the fill-then-draw approach described above, and about twice as fast as transparent text. So far as I know, there is no faster way to draw text on a VGA.
|
||||
</P>
|
||||
<P>It’s important to note that the BitMan’s technique only works on full bytes of display memory. There’s no way to clip to finer precision; the background color will inevitably flood all of the eight destination pixels that aren’t selected as foreground pixels. This makes The BitMan’s technique most suitable for monospaced fonts with characters that are multiples of eight pixels in width, and for drawing to byte-aligned addresses; the technique can be used in other situations, but is considerably more difficult to apply.</P>
|
||||
<P>It’s important to note that the BitMan’s technique only works on full bytes of display memory. There’s no way to clip to finer precision; the background color will inevitably flood all of the eight destination pixels that aren’t selected as foreground pixels. This makes The BitMan’s technique most suitable for monospaced fonts with characters that are multiples of eight pixels in width, and for drawing to byte-aligned addresses; the technique can be used in other situations, but is considerably more difficult to apply.</P>
|
||||
<P><B>LISTING 55.4 L55-4.ASM</B></P>
|
||||
<!-- CODE //-->
|
||||
<PRE>
|
||||
; Demonstrates drawing solid text on the VGA, using the BitMan’s write mode
|
||||
; Demonstrates drawing solid text on the VGA, using the BitMan’s write mode
|
||||
; 3-based, one-pass technique.
|
||||
|
||||
CHAR_HEIGHT equ 8 ;# of scan lines per character (must be <256)
|
||||
|
|
@ -69,9 +69,9 @@
|
|||
LineWidthBytes dw ? ;offset from one scan line to the next
|
||||
FontPtr dd ? ;pointer to font with which to draw
|
||||
SampleString label byte
|
||||
db ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ’
|
||||
db ‘abcdefghijklmnopqrstuvwxyz’
|
||||
db ‘0123456789!@#$%^&*(),<.>/?;:’,0
|
||||
db ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ’
|
||||
db ‘abcdefghijklmnopqrstuvwxyz’
|
||||
db ‘0123456789!@#$%^&*(),<.>/?;:’,0
|
||||
|
||||
.code
|
||||
start:
|
||||
|
|
@ -86,7 +86,7 @@
|
|||
mov bh,3 ;get 8x8 ROM font subsubfunction
|
||||
int 10h ;get the pointer to the BIOS 8x8 font
|
||||
mov word ptr [FontPtr],bp
|
||||
mov word ptr [FontPtr+2],es
|
||||
mov word ptr [FontPtr+2],es
|
||||
|
||||
mov bx,CHAR_HEIGHT
|
||||
mov [CharHeight],bx ;# of scan lines per character
|
||||
|
|
@ -134,7 +134,7 @@ LineLoop:
|
|||
; CharHeight must be set to the height of each character
|
||||
; FontPtr must be set to the font with which to draw
|
||||
; LineWidthBytes must be set to the scan line width in bytes
|
||||
; Don’t count on any registers other than DS, SS, and SP being preserved.
|
||||
; Don’t count on any registers other than DS, SS, and SP being preserved.
|
||||
; The X coordinate is truncated to a multiple of 8. Characters are
|
||||
; assumed to be 8 pixels wide.
|
||||
align 2
|
||||
|
|
@ -148,17 +148,17 @@ LineLoop:
|
|||
mul bx ; start offset of initial scan line
|
||||
add di,ax ;start offset of initial byte
|
||||
mov ax,SCREEN_SEGMENT
|
||||
mov es,ax ;ES:DI = offset of initial character’s
|
||||
mov es,ax ;ES:DI = offset of initial character’s
|
||||
; first scan line
|
||||
;set up the VGA’s hardware so that we can
|
||||
;set up the VGA’s hardware so that we can
|
||||
; fill the latches with the background color
|
||||
mov dx,GC_INDEX
|
||||
mov ax,(0ffh SHL 8) + BIT_MASK
|
||||
out dx,ax ;set Bit Mask register to 0xFF (that’s the
|
||||
; default, but I’m doing this just to make sure
|
||||
mov ax,(0ffh SHL 8) + BIT_MASK
|
||||
out dx,ax ;set Bit Mask register to 0xFF (that’s the
|
||||
; default, but I’m doing this just to make sure
|
||||
; you understand that Bit Mask register and
|
||||
; CPU data are ANDed in write mode 3)
|
||||
mov ax,(003h SHL 8) + G_MODE
|
||||
mov ax,(003h SHL 8) + G_MODE
|
||||
out dx,ax ;select write mode 3
|
||||
mov ah,cl ;background color
|
||||
mov al,SET_RESET
|
||||
|
|
@ -169,17 +169,17 @@ LineLoop:
|
|||
mov cl,es:[0ffffh] ;read the background color back into the
|
||||
; latches; the latches are now filled with
|
||||
; the background color. The value in CL
|
||||
; doesn’t matter, we just needed a target
|
||||
; doesn’t matter, we just needed a target
|
||||
; for the read, so we could load the latches
|
||||
mov ah,ch ;foreground color
|
||||
out dx,ax ;set the Set/Reset (drawing) color to the
|
||||
; foreground color
|
||||
;we’re ready to draw!
|
||||
;we’re ready to draw!
|
||||
DrawTextLoop:
|
||||
lodsb ;next character to draw
|
||||
and al,al ;end of string?
|
||||
jz DrawTextDone ;yes
|
||||
push ds ;remember string’s segment
|
||||
push ds ;remember string’s segment
|
||||
push si ;remember offset of next character in string
|
||||
push di ;remember drawing offset
|
||||
;load these variables before we wipe out DS
|
||||
|
|
@ -204,14 +204,14 @@ DrawCharLoop: ;draw all lines of the character
|
|||
pop di ;retrieve initial drawing offset
|
||||
inc di ;drawing offset for next char
|
||||
pop si ;retrieve offset of next character in string
|
||||
pop ds ;retrieve string’s segment
|
||||
pop ds ;retrieve string’s segment
|
||||
jmp DrawTextLoop ;draw next character, if any
|
||||
|
||||
align2
|
||||
DrawTextDone: ;restore the Graphics Mode register to its
|
||||
; default state of write mode 0
|
||||
mov dx,GC_INDEX
|
||||
mov ax,(000h SHL 8) + G_MODE
|
||||
mov ax,(000h SHL 8) + G_MODE
|
||||
out dx,ax ;select write mode 0
|
||||
ret
|
||||
DrawTextString endp
|
||||
|
|
|
|||
Loading…
Reference in a new issue