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This commit is contained in:
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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54
35-03.html
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@ -37,15 +37,15 @@
</CENTER>
<P><BR></P>
<H3><A NAME="Heading6"></A><FONT COLOR="#000077">An Implementation in C</FONT></H3>
<P>It&#146;s time to get down and look at some actual working code. Listing 35.1 is a C implementation of Bresenham&#146;s line-drawing algorithm for modes 0EH, 0FH, 10H, and 12H of the VGA, called as function <B>EVGALine</B>. Listing 35.2 is a sample program to demonstrate the use of <B>EVGALine</B>.</P>
<P>It&rsquo;s time to get down and look at some actual working code. Listing 35.1 is a C implementation of Bresenham&rsquo;s line-drawing algorithm for modes 0EH, 0FH, 10H, and 12H of the VGA, called as function <B>EVGALine</B>. Listing 35.2 is a sample program to demonstrate the use of <B>EVGALine</B>.</P>
<P><B>LISTING 35.1 L35-1.C</B></P>
<!-- CODE //-->
<PRE>
/*
* C implementation of Bresenham&#146;s line drawing algorithm
* for the EGA and VGA. Works in modes 0&#215;E, 0&#215;F, 0&#215;10, and 0&#215;12.
* C implementation of Bresenham&rsquo;s line drawing algorithm
* for the EGA and VGA. Works in modes 0xE, 0xF, 0x10, and 0x12.
*
* Compiled with Borland C&#43&#43;
* Compiled with Borland C++
*
* By Michael Abrash
*/
@ -55,12 +55,12 @@
#define EVGA_SCREEN_WIDTH_IN_BYTES 80
/* memory offset from start of
one row to start of next */
#define EVGA_SCREEN_SEGMENT 0&#215;A000
#define EVGA_SCREEN_SEGMENT 0xA000
/* display memory segment */
#define GC_INDEX 0&#215;3CE
#define GC_INDEX 0x3CE
/* Graphics Controller
Index register port */
#define GC_DATA 0&#215;3CF
#define GC_DATA 0x3CF
/* Graphics Controller
Data register port */
#define SET_RESET_INDEX 0 /* indexes of needed */
@ -82,23 +82,23 @@ unsigned int Y0; /* (0,0) at the upper left of the screen */
/* Calculate the offset in the screen segment of the byte in
which the pixel lies */
PixelBytePtr = MK_FP(EVGA_SCREEN_SEGMENT,
( Y0 * EVGA_SCREEN_WIDTH_IN_BYTES ) &#43; ( X0 / 8 ));
( Y0 * EVGA_SCREEN_WIDTH_IN_BYTES ) + ( X0 / 8 ));
/* Generate a mask with a 1 bit in the pixel&#146;s position within the
/* Generate a mask with a 1 bit in the pixel&rsquo;s position within the
screen byte */
PixelMask = 0&#215;80 &gt;&gt; ( X0 &amp 0&#215;07 );
PixelMask = 0x80 &gt;&gt; ( X0 &amp 0x07 );
/* Set up the Graphics Controller&#146;s Bit Mask register to allow
/* Set up the Graphics Controller&rsquo;s Bit Mask register to allow
only the bit corresponding to the pixel being drawn to
be modified */
outportb(GC_INDEX, BIT_MASK_INDEX);
outportb(GC_DATA, PixelMask);
/* Draw the pixel. Because of the operation of the set/reset
feature of the EGA/VGA, the value written doesn&#146;t matter.
feature of the EGA/VGA, the value written doesn&rsquo;t matter.
The screen byte is ORed in order to perform a read to latch the
display memory, then perform a write in order to modify it. */
*PixelBytePtr |= 0&#215;FE;
*PixelBytePtr |= 0xFE;
}
/*
@ -121,18 +121,18 @@ int XDirection; /* 1 if line is drawn left to right,
/* Draw the line */
EVGADot(X0, Y0); /* draw the first pixel */
while ( DeltaX&#151; ) {
/* See if it&#146;s time to advance the Y coordinate */
while ( DeltaX&mdash; ) {
/* See if it&rsquo;s time to advance the Y coordinate */
if ( ErrorTerm &gt;= 0 ) {
/* Advance the Y coordinate &amp adjust the error term
back down */
Y0&#43;&#43;;
ErrorTerm &#43;= DeltaYx2MinusDeltaXx2;
Y0++;
ErrorTerm += DeltaYx2MinusDeltaXx2;
} else {
/* Add to the error term */
ErrorTerm &#43;= DeltaYx2;
ErrorTerm += DeltaYx2;
}
X0 &#43;= XDirection; /* advance the X coordinate */
X0 += XDirection; /* advance the X coordinate */
EVGADot(X0, Y0); /* draw a pixel */
}
}
@ -156,18 +156,18 @@ int XDirection; /* 1 if line is drawn left to right,
ErrorTerm = DeltaXx2 - (int) DeltaY;
EVGADot(X0, Y0); /* draw the first pixel */
while ( DeltaY&#151; ) {
/* See if it&#146;s time to advance the X coordinate */
while ( DeltaY&mdash; ) {
/* See if it&rsquo;s time to advance the X coordinate */
if ( ErrorTerm &gt;= 0 ) {
/* Advance the X coordinate &amp adjust the error term
back down */
X0 &#43;= XDirection;
ErrorTerm &#43;= DeltaXx2MinusDeltaYx2;
X0 += XDirection;
ErrorTerm += DeltaXx2MinusDeltaYx2;
} else {
/* Add to the error term */
ErrorTerm &#43;= DeltaXx2;
ErrorTerm += DeltaXx2;
}
Y0&#43;&#43;; /* advance the Y coordinate */
Y0++; /* advance the Y coordinate */
EVGADot(X0, Y0); /* draw a pixel */
}
}
@ -190,7 +190,7 @@ char Color; /* color to draw line in */
outportb(GC_DATA, Color);
/* Cause all planes to be forced to the Set/Reset color */
outportb(GC_INDEX, ENABLE_SET_RESET_INDEX);
outportb(GC_DATA, 0&#215;F);
outportb(GC_DATA, 0xF);
/* Save half the line-drawing cases by swapping Y0 with Y1
and X0 with X1 if Y0 is greater than Y1. As a result, DeltaY
@ -229,7 +229,7 @@ char Color; /* color to draw line in */
outportb(GC_INDEX, ENABLE_SET_RESET_INDEX);
outportb(GC_DATA, 0);
outportb(GC_INDEX, BIT_MASK_INDEX);
outportb(GC_DATA, 0&#215;FF);
outportb(GC_DATA, 0xFF);
}
</PRE>
<!-- END CODE //-->