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James Gregory 2013-12-31 11:38:48 +11:00
commit f658bfbb40
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142
45-05.md
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@ -23,77 +23,79 @@ flipping.
**LISTING 45.3 L45-3.C**
/* Sample program to exercise VGA 640x400 16-color mode page flipping, by
drawing a horizontal line at the top of page 0 and another at bottom of page 1,
then flipping between them once every 30 frames. Tested with Borland C++,
in C compilation mode. */
```c
/* Sample program to exercise VGA 640x400 16-color mode page flipping, by
drawing a horizontal line at the top of page 0 and another at bottom of page 1,
then flipping between them once every 30 frames. Tested with Borland C++,
in C compilation mode. */
#include <dos.h>
#include <conio.h>
#include <dos.h>
#include <conio.h>
#define SCREEN_SEGMENT 0xA000
#define SCREEN_HEIGHT 400
#define SCREEN_WIDTH_IN_BYTES 80
#define INPUT_STATUS_1 0x3DA /* color-mode address of Input Status 1
register */
/* The page start addresses must be even multiples of 256, because page
flipping is performed by changing only the upper start address byte */
#define PAGE_0_START 0
#define PAGE_1_START (400*SCREEN_WIDTH_IN_BYTES)
#define SCREEN_SEGMENT 0xA000
#define SCREEN_HEIGHT 400
#define SCREEN_WIDTH_IN_BYTES 80
#define INPUT_STATUS_1 0x3DA /* color-mode address of Input Status 1
register */
/* The page start addresses must be even multiples of 256, because page
flipping is performed by changing only the upper start address byte */
#define PAGE_0_START 0
#define PAGE_1_START (400*SCREEN_WIDTH_IN_BYTES)
void main(void);
void Wait30Frames(void);
extern void Set640x400(void);
void main(void);
void Wait30Frames(void);
extern void Set640x400(void);
void main()
{
int i;
unsigned int far *ScreenPtr;
union REGS regset;
void main()
{
int i;
unsigned int far *ScreenPtr;
union REGS regset;
Set640x400(); /* set to 640x400 16-color mode */
Set640x400(); /* set to 640x400 16-color mode */
/* Point to first line of page 0 and draw a horizontal line across screen */
FP_SEG(ScreenPtr) = SCREEN_SEGMENT;
FP_OFF(ScreenPtr) = PAGE_0_START;
for (i=0; i<(SCREEN_WIDTH_IN_BYTES/2); i++) *ScreenPtr++ = 0xFFFF;
/* Point to first line of page 0 and draw a horizontal line across screen */
FP_SEG(ScreenPtr) = SCREEN_SEGMENT;
FP_OFF(ScreenPtr) = PAGE_0_START;
for (i=0; i<(SCREEN_WIDTH_IN_BYTES/2); i++) *ScreenPtr++ = 0xFFFF;
/* Point to last line of page 1 and draw a horizontal line across screen */
FP_OFF(ScreenPtr) =
PAGE_1_START + ((SCREEN_HEIGHT-1)*SCREEN_WIDTH_IN_BYTES);
for (i=0; i<(SCREEN_WIDTH_IN_BYTES/2); i++) *ScreenPtr++ = 0xFFFF;
/* Point to last line of page 1 and draw a horizontal line across screen */
FP_OFF(ScreenPtr) =
PAGE_1_START + ((SCREEN_HEIGHT-1)*SCREEN_WIDTH_IN_BYTES);
for (i=0; i<(SCREEN_WIDTH_IN_BYTES/2); i++) *ScreenPtr++ = 0xFFFF;
/* Now flip pages once every 30 frames until a key is pressed */
do {
Wait30Frames();
/* Now flip pages once every 30 frames until a key is pressed */
do {
Wait30Frames();
/* Flip to page 1 */
outpw(0x3D4, 0x0C | ((PAGE_1_START >> 8) << 8));
/* Flip to page 1 */
outpw(0x3D4, 0x0C | ((PAGE_1_START >> 8) << 8));
Wait30Frames();
Wait30Frames();
/* Flip to page 0 */
outpw(0x3D4, 0x0C | ((PAGE_0_START >> 8) << 8));
} while (kbhit() == 0);
/* Flip to page 0 */
outpw(0x3D4, 0x0C | ((PAGE_0_START >> 8) << 8));
} while (kbhit() == 0);
getch(); /* clear the key press */
getch(); /* clear the key press */
/* Return to text mode and exit */
regset.x.ax = 0x0003; /* AL = 3 selects 80x25 text mode */
int86(0x10, &regset, &regset);
}
/* Return to text mode and exit */
regset.x.ax = 0x0003; /* AL = 3 selects 80x25 text mode */
int86(0x10, &regset, &regset);
}
void Wait30Frames()
{
int i;
void Wait30Frames()
{
int i;
for (i=0; i<30; i++) {
/* Wait until we're not in vertical sync, so we can catch leading edge */
while ((inp(INPUT_STATUS_1) & 0x08) != 0) ;
/* Wait until we are in vertical sync */
while ((inp(INPUT_STATUS_1) & 0x08) == 0) ;
}
}
for (i=0; i<30; i++) {
/* Wait until we're not in vertical sync, so we can catch leading edge */
while ((inp(INPUT_STATUS_1) & 0x08) != 0) ;
/* Wait until we are in vertical sync */
while ((inp(INPUT_STATUS_1) & 0x08) == 0) ;
}
}
```
After I described 640x400 mode in a magazine article, Bill Lindley, of
Mesa, Arizona, wrote me to suggest that when programming the VGA to a
@ -117,19 +119,21 @@ calls down the road.
**LISTING 45.4 L45-4.C**
/* Function to tell the BIOS to set up properly sized characters for 25 rows of
16 pixel high text in 640x400 graphics mode. Call immediately after mode set.
Based on a contribution by Bill Lindley. */
```c
/* Function to tell the BIOS to set up properly sized characters for 25 rows of
16 pixel high text in 640x400 graphics mode. Call immediately after mode set.
Based on a contribution by Bill Lindley. */
#include <dos.h>
#include <dos.h>
void Set640x400()
{
union REGS regs;
void Set640x400()
{
union REGS regs;
regs.h.ah = 0x11; /* character generator function */
regs.h.al = 0x24; /* use ROM 8x6 character set for graphics */
regs.h.bl = 2; /* 25 rows */
int86(0x10, &regs, &regs); /* invoke the BIOS video interrupt
to set up the text */
}
regs.h.ah = 0x11; /* character generator function */
regs.h.al = 0x24; /* use ROM 8x6 character set for graphics */
regs.h.bl = 2; /* 25 rows */
int86(0x10, &regs, &regs); /* invoke the BIOS video interrupt
to set up the text */
}
```