Thread: C programming on a legacy console system.

I own an Atari Jaguar legacy console system. I'm trying to wrap my head around how its C setup displays graphics at a basic level. I have no experience with graphics so am trying to start at the beginning with this system, the simplest HELLO C program it has. I figured that would be a good place to start. I'm going to post the full source code for it in this thread and I'd like to thank everyone for their patience with me as I post questions while trying to decipher the source code.

Code:

#include"font.h"

extern void *vidmem;
unsigned char *jagscreen;

void DrawCharLine (int charloc, int screenloc)
{
  static unsigned char shift[] = { 7, 6, 5, 4, 3, 2, 1, 0 };
  int xcnt;

  for (xcnt = 0; xcnt < F_WIDTH; xcnt++) 
  {
    if (((textfont[charloc] >> shift[xcnt]) & 0x1)) 
      jagscreen[screenloc++] = 1;
    else
      jagscreen[screenloc++] = 0;
  }
}

void DrawChar (int x, int y, char ch)
{
  int ycnt, charloc, screenloc;

  charloc = ch * F_CHARSIZE;

  screenloc = (y * T_XREZ) + x ;

  for (ycnt = 0; ycnt < F_HEIGHT; ycnt++) 
  {
    DrawCharLine (charloc, screenloc);
    screenloc += T_XREZ;
    charloc++;
  }
}

void DrawString (int x, int y, char *str)
{
  int cnt;

  for (cnt = 0; str[cnt] != 0; cnt++) 
  {
    DrawChar (x, y, str[cnt]);
    x += F_WIDTH;
  }
}


void __main(void) 
{
  int w,x=5,y=130;

  jagscreen = (unsigned char *)&vidmem;

  *(unsigned short int *) 0xf00400 = 0x0000; /* Color reg 0 = black */
  *(unsigned short int *) 0xf00402 = 0xffff; /* Color reg 1 = white */

  for(w=0; w<64000; w++) jagscreen[w]=0;
  

	DrawString(x,y,"Hello Jag Users");



  for(;;);  /* Infinite Loop.  Alpine users can delete this.  */
}

FONT.H

Code:

#define F_WIDTH          0x08
#define F_HEIGHT         0x08
#define F_CHARSIZE       0x08

#define T_XREZ           320
#define T_YREZ           200



unsigned char textfont[] =
  { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x7E, 0x81, 0xA5, 0x81,
    0xBD, 0x99, 0x81, 0x7E, 0x7E, 0xFF, 0xDB, 0xFF, 0xC3, 0xE7, 0xFF, 0x7E,
    0x6C, 0xFE, 0xFE, 0xFE, 0x7C, 0x38, 0x10, 0x00, 0x10, 0x38, 0x7C, 0xFE,
    0x7C, 0x38, 0x10, 0x00, 0x38, 0x7C, 0x38, 0xFE, 0xFE, 0x7C, 0x38, 0x7C,
    0x10, 0x10, 0x38, 0x7C, 0xFE, 0x7C, 0x38, 0x7C, 0x00, 0x00, 0x18, 0x3C,
    0x3C, 0x18, 0x00, 0x00, 0xFF, 0xFF, 0xE7, 0xC3, 0xC3, 0xE7, 0xFF, 0xFF,
    0x00, 0x3C, 0x66, 0x42, 0x42, 0x66, 0x3C, 0x00, 0xFF, 0xC3, 0x99, 0xBD,
    0xBD, 0x99, 0xC3, 0xFF, 0x0F, 0x07, 0x0F, 0x7D, 0xCC, 0xCC, 0xCC, 0x78,
    0x3C, 0x66, 0x66, 0x66, 0x3C, 0x18, 0x7E, 0x18, 0x3F, 0x33, 0x3F, 0x30,
    0x30, 0x70, 0xF0, 0xE0, 0x7F, 0x63, 0x7F, 0x63, 0x63, 0x67, 0xE6, 0xC0,
    0x99, 0x5A, 0x3C, 0xE7, 0xE7, 0x3C, 0x5A, 0x99, 0x80, 0xE0, 0xF8, 0xFE,
    0xF8, 0xE0, 0x80, 0x00, 0x02, 0x0E, 0x3E, 0xFE, 0x3E, 0x0E, 0x02, 0x00,
    0x18, 0x3C, 0x7E, 0x18, 0x18, 0x7E, 0x3C, 0x18, 0x66, 0x66, 0x66, 0x66,
    0x66, 0x00, 0x66, 0x00, 0x7F, 0xDB, 0xDB, 0x7B, 0x1B, 0x1B, 0x1B, 0x00,
    0x3E, 0x63, 0x38, 0x6C, 0x6C, 0x38, 0xCC, 0x78, 0x00, 0x00, 0x00, 0x00,
    0x7E, 0x7E, 0x7E, 0x00, 0x18, 0x3C, 0x7E, 0x18, 0x7E, 0x3C, 0x18, 0xFF,
    0x18, 0x3C, 0x7E, 0x18, 0x18, 0x18, 0x18, 0x00, 0x18, 0x18, 0x18, 0x18,
    0x7E, 0x3C, 0x18, 0x00, 0x00, 0x18, 0x0C, 0xFE, 0x0C, 0x18, 0x00, 0x00,
    0x00, 0x30, 0x60, 0xFE, 0x60, 0x30, 0x00, 0x00, 0x00, 0x00, 0xC0, 0xC0,
    0xC0, 0xFE, 0x00, 0x00, 0x00, 0x24, 0x66, 0xFF, 0x66, 0x24, 0x00, 0x00,
    0x00, 0x18, 0x3C, 0x7E, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x7E,
    0x3C, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x30, 0x78, 0x78, 0x78, 0x30, 0x00, 0x30, 0x00, 0x6C, 0x6C, 0x6C, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x6C, 0x6C, 0xFE, 0x6C, 0xFE, 0x6C, 0x6C, 0x00,
    0x30, 0x7C, 0xC0, 0x78, 0x0C, 0xF8, 0x30, 0x00, 0x00, 0xC6, 0xCC, 0x18,
    0x30, 0x66, 0xC6, 0x00, 0x38, 0x6C, 0x38, 0x76, 0xDC, 0xCC, 0x76, 0x00,
    0x60, 0x60, 0xC0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x18, 0x30, 0x60, 0x60,
    0x60, 0x30, 0x18, 0x00, 0x60, 0x30, 0x18, 0x18, 0x18, 0x30, 0x60, 0x00,
    0x00, 0x66, 0x3C, 0xFF, 0x3C, 0x66, 0x00, 0x00, 0x00, 0x30, 0x30, 0xFC,
    0x30, 0x30, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x30, 0x60,
    0x00, 0x00, 0x00, 0xFC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x30, 0x30, 0x00, 0x06, 0x0C, 0x18, 0x30, 0x60, 0xC0, 0x80, 0x00,
    0x7C, 0xC6, 0xCE, 0xDE, 0xF6, 0xE6, 0x7C, 0x00, 0x30, 0x70, 0x30, 0x30,
    0x30, 0x30, 0xFC, 0x00, 0x78, 0xCC, 0x0C, 0x38, 0x60, 0xCC, 0xFC, 0x00,
    0x78, 0xCC, 0x0C, 0x38, 0x0C, 0xCC, 0x78, 0x00, 0x1C, 0x3C, 0x6C, 0xCC,
    0xFE, 0x0C, 0x1E, 0x00, 0xFC, 0xC0, 0xF8, 0x0C, 0x0C, 0xCC, 0x78, 0x00,
    0x38, 0x60, 0xC0, 0xF8, 0xCC, 0xCC, 0x78, 0x00, 0xFC, 0xCC, 0x0C, 0x18,
    0x30, 0x30, 0x30, 0x00, 0x78, 0xCC, 0xCC, 0x78, 0xCC, 0xCC, 0x78, 0x00,
    0x78, 0xCC, 0xCC, 0x7C, 0x0C, 0x18, 0x70, 0x00, 0x00, 0x30, 0x30, 0x00,
    0x00, 0x30, 0x30, 0x00, 0x00, 0x30, 0x30, 0x00, 0x00, 0x30, 0x30, 0x60,
    0x18, 0x30, 0x60, 0xC0, 0x60, 0x30, 0x18, 0x00, 0x00, 0x00, 0xFC, 0x00,
    0x00, 0xFC, 0x00, 0x00, 0x60, 0x30, 0x18, 0x0C, 0x18, 0x30, 0x60, 0x00,
    0x78, 0xCC, 0x0C, 0x18, 0x30, 0x00, 0x30, 0x00, 0x7C, 0xC6, 0xDE, 0xDE,
    0xDE, 0xC0, 0x78, 0x00, 0x30, 0x78, 0xCC, 0xCC, 0xFC, 0xCC, 0xCC, 0x00,
    0xFC, 0x66, 0x66, 0x7C, 0x66, 0x66, 0xFC, 0x00, 0x3C, 0x66, 0xC0, 0xC0,
    0xC0, 0x66, 0x3C, 0x00, 0xF8, 0x6C, 0x66, 0x66, 0x66, 0x6C, 0xF8, 0x00,
    0x7E, 0x60, 0x60, 0x78, 0x60, 0x60, 0x7E, 0x00, 0x7E, 0x60, 0x60, 0x78,
    0x60, 0x60, 0x60, 0x00, 0x3C, 0x66, 0xC0, 0xC0, 0xCE, 0x66, 0x3E, 0x00,
    0xCC, 0xCC, 0xCC, 0xFC, 0xCC, 0xCC, 0xCC, 0x00, 0x78, 0x30, 0x30, 0x30,
    0x30, 0x30, 0x78, 0x00, 0x1E, 0x0C, 0x0C, 0x0C, 0xCC, 0xCC, 0x78, 0x00,
    0xE6, 0x66, 0x6C, 0x78, 0x6C, 0x66, 0xE6, 0x00, 0x60, 0x60, 0x60, 0x60,
    0x60, 0x60, 0x7E, 0x00, 0xC6, 0xEE, 0xFE, 0xFE, 0xD6, 0xC6, 0xC6, 0x00,
    0xC6, 0xE6, 0xF6, 0xDE, 0xCE, 0xC6, 0xC6, 0x00, 0x38, 0x6C, 0xC6, 0xC6,
    0xC6, 0x6C, 0x38, 0x00, 0xFC, 0x66, 0x66, 0x7C, 0x60, 0x60, 0xF0, 0x00,
    0x78, 0xCC, 0xCC, 0xCC, 0xDC, 0x78, 0x1C, 0x00, 0xFC, 0x66, 0x66, 0x7C,
    0x6C, 0x66, 0xE6, 0x00, 0x78, 0xCC, 0xE0, 0x70, 0x1C, 0xCC, 0x78, 0x00,
    0xFC, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x00, 0xCC, 0xCC, 0xCC, 0xCC,
    0xCC, 0xCC, 0xFC, 0x00, 0xCC, 0xCC, 0xCC, 0xCC, 0xCC, 0x78, 0x30, 0x00,
    0xC6, 0xC6, 0xC6, 0xD6, 0xFE, 0xEE, 0xC6, 0x00, 0xC6, 0xC6, 0x6C, 0x38,
    0x38, 0x6C, 0xC6, 0x00, 0xCC, 0xCC, 0xCC, 0x78, 0x30, 0x30, 0x78, 0x00,
    0xFE, 0x06, 0x0C, 0x18, 0x30, 0x60, 0xFE, 0x00, 0x78, 0x60, 0x60, 0x60,
    0x60, 0x60, 0x78, 0x00, 0xC0, 0x60, 0x30, 0x18, 0x0C, 0x06, 0x02, 0x00,
    0x78, 0x18, 0x18, 0x18, 0x18, 0x18, 0x78, 0x00, 0x10, 0x38, 0x6C, 0xC6,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF,
    0x30, 0x30, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x78, 0x0C,
    0x7C, 0xCC, 0x76, 0x00, 0xE0, 0x60, 0x60, 0x7C, 0x66, 0x66, 0xDC, 0x00,
    0x00, 0x00, 0x78, 0xCC, 0xC0, 0xCC, 0x78, 0x00, 0x1C, 0x0C, 0x0C, 0x7C,
    0xCC, 0xCC, 0x76, 0x00, 0x00, 0x00, 0x78, 0xCC, 0xFC, 0xC0, 0x78, 0x00,
    0x38, 0x6C, 0x60, 0xF0, 0x60, 0x60, 0xF0, 0x00, 0x00, 0x00, 0x76, 0xCC,
    0xCC, 0x7C, 0x0C, 0xF8, 0xE0, 0x60, 0x6C, 0x76, 0x66, 0x66, 0xE6, 0x00,
    0x30, 0x00, 0x70, 0x30, 0x30, 0x30, 0x78, 0x00, 0x0C, 0x00, 0x0C, 0x0C,
    0x0C, 0xCC, 0xCC, 0x78, 0xE0, 0x60, 0x66, 0x6C, 0x78, 0x6C, 0xE6, 0x00,
    0x70, 0x30, 0x30, 0x30, 0x30, 0x30, 0x78, 0x00, 0x00, 0x00, 0xCC, 0xFE,
    0xFE, 0xD6, 0xC6, 0x00, 0x00, 0x00, 0xF8, 0xCC, 0xCC, 0xCC, 0xCC, 0x00,
    0x00, 0x00, 0x78, 0xCC, 0xCC, 0xCC, 0x78, 0x00, 0x00, 0x00, 0xDC, 0x66,
    0x66, 0x7C, 0x60, 0xF0, 0x00, 0x00, 0x76, 0xCC, 0xCC, 0x7C, 0x0C, 0x1E,
    0x00, 0x00, 0xDC, 0x76, 0x66, 0x60, 0xF0, 0x00, 0x00, 0x00, 0x7C, 0xC0,
    0x78, 0x0C, 0xF8, 0x00, 0x10, 0x30, 0x7C, 0x30, 0x30, 0x34, 0x18, 0x00,
    0x00, 0x00, 0xCC, 0xCC, 0xCC, 0xCC, 0x76, 0x00, 0x00, 0x00, 0xCC, 0xCC,
    0xCC, 0x78, 0x30, 0x00, 0x00, 0x00, 0xC6, 0xD6, 0xFE, 0xFE, 0x6C, 0x00,
    0x00, 0x00, 0xC6, 0x6C, 0x38, 0x6C, 0xC6, 0x00, 0x00, 0x00, 0xCC, 0xCC,
    0xCC, 0x7C, 0x0C, 0xF8, 0x00, 0x00, 0xFC, 0x98, 0x30, 0x64, 0xFC, 0x00,
    0x1C, 0x30, 0x30, 0xE0, 0x30, 0x30, 0x1C, 0x00, 0x18, 0x18, 0x18, 0x00,
    0x18, 0x18, 0x18, 0x00, 0xE0, 0x30, 0x30, 0x1C, 0x30, 0x30, 0xE0, 0x00,
    0x76, 0xDC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x38, 0x6C,
    0xC6, 0xC6, 0xFE, 0x00, 0xE9
};

Code:

void DrawChar (int x, int y, char ch)
{
  int ycnt, charloc, screenloc;

  charloc = ch * F_CHARSIZE;

  screenloc = (y * T_XREZ) + x;

  for (ycnt = 0; ycnt < F_HEIGHT; ycnt++) 
  {
	DrawCharLine (charloc, screenloc);
	screenloc += T_XREZ;
	charloc++;
  }
}

My first specific question from the above code. In the first pass it passes the character 'H' from 'Hello Jag users! '

So the line :

Code:

charloc = ch * F_CHARSIZE;

translates to 'charloc = 'H' * 0x08;

Is this multiplying the character H by 0x08 hexadecimal? I'm not following this line all that clearly.