/**************************************************************************
* bitmap.c *
* written by David Brackeen *
* http://www.brackeen.com/home/vga/ *
* *
* This is a 16-bit program. *
* Tab stops are set to 2. *
* Remember to compile in the LARGE memory model! *
* To compile in Borland C: bcc -ml bitmap.c *
* *
* This program will only work on DOS- or Windows-based systems with a *
* VGA, SuperVGA or compatible video adapter. *
* *
* Please feel free to copy this source code. *
* *
* DESCRIPTION: This program demostrates drawing bitmaps, including *
* transparent bitmaps. *
**************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <dos.h>
#include <mem.h>
#define VIDEO_INT 0x10 /* the BIOS video interrupt. */
#define SET_MODE 0x00 /* BIOS func to set the video mode. */
#define VGA_256_COLOR_MODE 0x13 /* use to set 256-color mode. */
#define TEXT_MODE 0x03 /* use to set 80x25 text mode. */
#define SCREEN_WIDTH 320 /* width in pixels of mode 0x13 */
#define SCREEN_HEIGHT 200 /* height in pixels of mode 0x13 */
#define NUM_COLORS 256 /* number of colors in mode 0x13 */
typedef unsigned char byte;
typedef unsigned short word;
typedef unsigned long dword;
byte *VGA=(byte *)0xA0000000L; /* this points to video memory. */
word *my_clock=(word *)0x0000046C; /* this points to the 18.2hz system
clock. */
typedef struct tagBITMAP /* the structure for a bitmap. */
{
word width;
word height;
byte *data;
} BITMAP;
/**************************************************************************
* fskip *
* Skips bytes in a file. *
**************************************************************************/
void fskip(FILE *fp, int num_bytes)
{
int i;
for (i=0; i<num_bytes; i++)
fgetc(fp);
}
/**************************************************************************
* set_mode *
* Sets the video mode. *
**************************************************************************/
void set_mode(byte mode)
{
union REGS regs;
regs.h.ah = SET_MODE;
regs.h.al = mode;
int86(VIDEO_INT, ®s, ®s);
}
/**************************************************************************
* load_bmp *
* Loads a bitmap file into memory. *
**************************************************************************/
void load_bmp(char *file,BITMAP *b)
{
FILE *fp;
long index;
word num_colors;
int x;
/* open the file */
if ((fp = fopen(file,"rb")) == NULL)
{
printf("Error opening file %s.\n",file);
exit(1);
}
/* check to see if it is a valid bitmap file */
if (fgetc(fp)!='B' || fgetc(fp)!='M')
{
fclose(fp);
printf("%s is not a bitmap file.\n",file);
exit(1);
}
/* read in the width and height of the image, and the
number of colors used; ignore the rest */
fskip(fp,16);
fread(&b->width, sizeof(word), 1, fp);
fskip(fp,2);
fread(&b->height,sizeof(word), 1, fp);
fskip(fp,22);
fread(&num_colors,sizeof(word), 1, fp);
fskip(fp,6);
/* assume we are working with an 8-bit file */
if (num_colors==0) num_colors=256;
/* try to allocate memory */
if ((b->data = (byte *) malloc((word)(b->width*b->height))) == NULL)
{
fclose(fp);
printf("Error allocating memory for file %s.\n",file);
exit(1);
}
/* Ignore the palette information for now.
See palette.c for code to read the palette info. */
fskip(fp,num_colors*4);
/* read the bitmap */
for(index=(b->height-1)*b->width;index>=0;index-=b->width)
for(x=0;x<b->width;x++)
b->data[(word)index+x]=(byte)fgetc(fp);
fclose(fp);
}
/**************************************************************************
* draw_bitmap *
* Draws a bitmap. *
**************************************************************************/
void draw_bitmap(BITMAP *bmp,int x,int y)
{
int j;
word screen_offset = (y<<8)+(y<<6)+x;
word bitmap_offset = 0;
for(j=0;j<bmp->height;j++)
{
memcpy(&VGA[screen_offset],&bmp->data[bitmap_offset],bmp->width);
bitmap_offset+=bmp->width;
screen_offset+=SCREEN_WIDTH;
}
}
/**************************************************************************
* draw_transparent_bitmap *
* Draws a transparent bitmap. *
**************************************************************************/
void draw_transparent_bitmap(BITMAP *bmp,int x,int y)
{
int i,j;
word screen_offset = (y<<8)+(y<<6);
word bitmap_offset = 0;
byte data;
for(j=0;j<bmp->height;j++)
{
for(i=0;i<bmp->width;i++,bitmap_offset++)
{
data = bmp->data[bitmap_offset];
if (data) VGA[screen_offset+x+i] = data;
}
screen_offset+=SCREEN_WIDTH;
}
}
/**************************************************************************
* wait *
* Wait for a specified number of clock ticks (18hz). *
**************************************************************************/
void wait(int ticks)
{
word start;
start=*my_clock;
while (*my_clock-start<ticks)
{
*my_clock=*my_clock; /* this line is for some compilers
that would otherwise ignore this
loop */
}
}
/**************************************************************************
* Main *
* Draws opaque and transparent bitmaps *
**************************************************************************/
void main()
{
int i,x,y;
BITMAP bmp;
load_bmp("rocket.bmp",&bmp); /* open the file */
set_mode(VGA_256_COLOR_MODE); /* set the video mode. */
/* draw the background */
for(i=0;i<200;i++)
memset(&VGA[320*i],i,SCREEN_WIDTH);
wait(25);
/* draw a tiled bitmap pattern on the left */
for(y=0;y<=SCREEN_HEIGHT-bmp.height;y+=bmp.height)
for(x=0;x<=(SCREEN_WIDTH)/2-bmp.width;x+=bmp.width)
draw_bitmap(&bmp,x,y);
wait(25);
/* draw a tiled transparent bitmap pattern on the right */
for(y=0;y<=SCREEN_HEIGHT-bmp.height;y+=bmp.height)
for(x=SCREEN_WIDTH-bmp.width;x>=SCREEN_WIDTH/2;x-=bmp.width)
draw_transparent_bitmap(&bmp,x,y);
wait(100);
free(bmp.data); /* free up memory used */
set_mode(TEXT_MODE); /* set the video mode back to
text mode. */
return;
}
