Misc/abrash-black-book
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Replace invalid characters with HTML entities

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+ with +
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Fix C++
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Yen symbol instead of times
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Bullet again
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James Gregory 2013-12-30 12:50:32 +11:00
commit 500e7f5654
353 changed files with 5091 additions and 5091 deletions
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26
25-02.html
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@ -40,12 +40,12 @@
<!-- CODE //-->
<PRE>
; Program to illustrate operation of data rotate and bit mask
; features of Graphics Controller. Draws 8&#215;8 character at
; specified location, using VGA&#146;s 8&#215;8 ROM font. Designed
; features of Graphics Controller. Draws 8x8 character at
; specified location, using VGA&rsquo;s 8x8 ROM font. Designed
; for use with modes 0Dh, 0Eh, 0Fh, 10h, and 12h.
; By Michael Abrash.
;
stack segment para stack &#145;STACK&#146;
stack segment para stack &lsquo;STACK&rsquo;
db 512 dup(?)
stack ends
;
@ -60,13 +60,13 @@ GC_ROTATE equ 3 ;GC data rotate/logical function
; register index
GC_BIT_MASK equ 8 ;GC bit mask register index
;
dseg segment para common &#145;DATA&#146;
dseg segment para common &lsquo;DATA&rsquo;
TEST_TEXT_ROW equ 69 ;row to display test text at
TEST_TEXT_COL equ 17 ;column to display test text at
TEST_TEXT_WIDTH equ 8 ;width of a character in pixels
TestString label byte
db &#145;Hello, world!&#146;,0 ;test string to print.
db &lsquo;Hello, world!&rsquo;,0 ;test string to print.
FontPointer dd ? ;font offset
dseg ends
;
@ -78,22 +78,22 @@ SETGC macro INDEX, SETTING
out dx,ax
endm
;
cseg segment para public &#145;CODE&#146;
cseg segment para public &lsquo;CODE&rsquo;
assume cs:cseg, ds:dseg
start proc near
mov ax,dseg
mov ds,ax
;
; Select 640&#215;480 graphics mode.
; Select 640x480 graphics mode.
;
mov ax,012h
int 10h
;
; Set driver to use the 8&#215;8 font.
; Set driver to use the 8x8 font.
;
mov ah,11h ;VGA BIOS character generator function,
mov al,30h ; return info subfunction
mov bh,3;get 8&#215;8 font pointer
mov bh,3;get 8x8 font pointer
int 10h
call SelectFont
;
@ -141,7 +141,7 @@ Start endp
; BX = row to draw text character at
; CX = column to draw text character at
;
; Forces ALU function to &#147;move&#148;.
; Forces ALU function to &ldquo;move&rdquo;.
;
DrawChar proc near
push ax
@ -263,7 +263,7 @@ DrawChar endp
;
SelectFont proc near
mov word ptr [FontPointer],bp ;save pointer
mov word ptr [FontPointer&#43;2],es
mov word ptr [FontPointer+2],es
ret
SelectFont endp
;
@ -271,9 +271,9 @@ cseg ends
end start
</PRE>
<!-- END CODE //-->
<P>The bit mask can be used for much more than bit-aligned fonts. For example, the bit mask is useful for fast pixel drawing, such as that performed when drawing lines, as we&#146;ll see in Chapter 35. It&#146;s also useful for drawing the edges of primitives, such as filled polygons, that potentially involve modifying some but not all of the pixels controlled by a single byte of display memory.
<P>The bit mask can be used for much more than bit-aligned fonts. For example, the bit mask is useful for fast pixel drawing, such as that performed when drawing lines, as we&rsquo;ll see in Chapter 35. It&rsquo;s also useful for drawing the edges of primitives, such as filled polygons, that potentially involve modifying some but not all of the pixels controlled by a single byte of display memory.
</P>
<P>Basically, the bit mask is handy whenever only <I>some</I> of the eight pixels in a byte of display memory need to be changed, because it allows full use of the VGA&#146;s four-way parallel processing capabilities for the pixels that are to be drawn, without interfering with the pixels that are to be left unchanged. The alternative would be plane-by-plane processing, which from a performance perspective would be undesirable indeed.</P><P><BR></P>
<P>Basically, the bit mask is handy whenever only <I>some</I> of the eight pixels in a byte of display memory need to be changed, because it allows full use of the VGA&rsquo;s four-way parallel processing capabilities for the pixels that are to be drawn, without interfering with the pixels that are to be left unchanged. The alternative would be plane-by-plane processing, which from a performance perspective would be undesirable indeed.</P><P><BR></P>
<CENTER>
<TABLE BORDER>
<TR>