#pragma regalloc- 

//NOTE that v1 to v8 and i must be in registers!  
register char v1 @4; 
register char v2 @5;
register char v3 @6;
register char v4 @7;
register char v5 @8;
register char v6 @9;
register char v7 @10;
register char v8 @11; 
register int i @12;

#pragma regalloc+ 

//==================================
//plot one point 
//at x,y with color 1=white 0=black 2=invert 
#pragma warn-
void video_pt(char x, char y, char c)
begin   
	
	#asm
	;  i=(x>>3) + ((int)y<<4) ;   the byte with the pixel in it

	push r16
	ldd r30,y+2 		;get x
	lsr r30
	lsr r30
	lsr r30     		;divide x by 8
	ldd r12,y+1 		;get y
       	lsl r12     		;mult y by 16
       	clr r13
	lsl r12
	rol r13
	lsl r12
	rol r13
	lsl r12
	rol r13
	add r12, r30     	;add in x/8
	
	;v2 = screen[i];   r5
        ;v3 = pos[x & 7];  r6
	;v4 = c            r7
	ldi r30,low(_screen)
	ldi r31,high(_screen)
	add r30, r12
	adc r31, r13
	ld r5,Z  		;get screen byte
	ldd r26,y+2 		;get x
	ldi r27,0
	andi r26,0x07           ;form x & 7 
	ldi r30,low(_pos*2)  
	ldi r31,high(_pos*2)
	add r30,r26
	adc r31,r27
	lpm r6,Z
	ld r16,y 		;get c 
       
       ;if (v4==1) screen[i] = v2 | v3 ; 
       ;if (v4==0) screen[i] = v2 & ~v3; 
       ;if (v4==2) screen[i] = v2 ^ v3 ; 
       
       cpi r16,1
       brne tst0
       or  r5,r6
       tst0:
       cpi r16,0
       brne tst2 
       com r6
       and r5,r6
       tst2:
       cpi r16,2
       brne writescrn
       eor r5,r6
       writescrn:
       	ldi r30,low(_screen)
	ldi r31,high(_screen)
	add r30, r12
	adc r31, r13
	st Z, r5        	;write the byte back to the screen
	
	pop r16
	#endasm
       
end
#pragma warn+

//==================================
void video_putarrow(char x, char y, int c)//draw 7x7 arrows
begin
	v7 = x;
	for (v6=0;v6<7;v6++)
	begin
	     v1 = arrowmap[c][v6];
	     v8 = y+v6;
	      video_pt(v7,   v8, (v1 & 0x80)==0x80);  
       	video_pt(v7+1, v8, (v1 & 0x40)==0x40); 
       	video_pt(v7+2, v8, (v1 & 0x20)==0x20);
       	video_pt(v7+3, v8, (v1 & 0x10)==0x10);
       	video_pt(v7+4, v8, (v1 & 0x08)==0x08);
	      video_pt(v7+5, v8, (v1 & 0x04)==0x04);  
       	video_pt(v7+6, v8, (v1 & 0x02)==0x02);
	end
end
void video_inv_putarrow(char x, char y, int c)//draw inverse 7x7 arrows
begin
	v7 = x;
	for (v6=0;v6<7;v6++)
	begin
	     v1 = arrowmap[c][v6];
	     v8 = y+v6;
	      video_pt(v7,   v8, (~v1 & 0x80)==0x80);  
       	video_pt(v7+1, v8, (~v1 & 0x40)==0x40); 
       	video_pt(v7+2, v8, (~v1 & 0x20)==0x20);
       	video_pt(v7+3, v8, (~v1 & 0x10)==0x10);
       	video_pt(v7+4, v8, (~v1 & 0x08)==0x08);
	      video_pt(v7+5, v8, (~v1 & 0x04)==0x04);  
       	video_pt(v7+6, v8, (~v1 & 0x02)==0x02);
	end
end
//==================================
// put a big character on the screen
// c is index into bitmap
void video_putchar(char x, char y, char c)  
begin 
    v7 = x;
    for (v6=0;v6<7;v6++) 
    begin
        v1 = bitmap[c][v6]; 
        v8 = y+v6;
        video_pt(v7,   v8, (v1 & 0x80)==0x80);  
        video_pt(v7+1, v8, (v1 & 0x40)==0x40); 
        video_pt(v7+2, v8, (v1 & 0x20)==0x20);
        video_pt(v7+3, v8, (v1 & 0x10)==0x10);
        video_pt(v7+4, v8, (v1 & 0x08)==0x08);
    end
end
//==================================
// put a string of big characters on the screen
void video_puts(char x, char y, char *str)
begin
	char i ;
	for (i=0; str[i]!=0; i++)
	begin  
		if (str[i]>=0x30 && str[i]<=0x3a) 
			video_putchar(x,y,str[i]-0x30);
		else if (str[i]==0x20) video_putchar(x,y,39);  //put space here
		else if (str[i]==0x25) video_putchar(x,y,41);  //%
		else video_putchar(x,y,str[i]-0x40+10);
		x = x+6;	
	end
end
      
//==================================
// put a small character on the screen
// x-cood must be on divisible by 4 
// c is index into bitmap
void video_smallchar(char x, char y, char c)  
begin 
	  char mask;
	  i=((int)x>>3) + ((int)y<<4) ;
	  if (x == (x & 0xf8)) mask = 0x0f;     //f8
	  else mask = 0xf0;
	
	  screen[i] =    (screen[i] & mask) | (smallbitmap[c][0] & ~mask); 
   	screen[i+16] = (screen[i+16] & mask) | (smallbitmap[c][1] & ~mask);
    screen[i+32] = (screen[i+32] & mask) | (smallbitmap[c][2] & ~mask);
    screen[i+48] = (screen[i+48] & mask) | (smallbitmap[c][3] & ~mask);
   	screen[i+64] = (screen[i+64] & mask) | (smallbitmap[c][4] & ~mask); 
end  
//==================================
// put a string of small characters on the screen
// x-cood must be on divisible by 4 
void video_putsmalls(char x, char y, char *str)
begin
	char i ;
	for (i=0; str[i]!=0; i++)
	begin  
		if (str[i]>=0x30 && str[i]<=0x3a) //3a=58
			 video_smallchar(x,y,str[i]-0x30);
		else if (str[i]==0x20) video_smallchar(x,y,12);  //put space here
		else if (str[i]==0x21) video_smallchar(x,y,39);  //put ":"
		else video_smallchar(x,y,str[i]-0x40+12);
		x = x+4;	
	end
end
       
//==================================
//plot a line 
//at x1,y1 to x2,y2 with color 1=white 0=black 2=invert 
//NOTE: this function requires signed chars   
//Code is from David Rodgers,
//"Procedural Elements of Computer Graphics",1985
void video_line(char x1, char y1, char x2, char y2, char c)
begin   
	int e;
	signed char dx,dy,j, temp;
	signed char s1,s2, xchange;
  signed char x,y;
        
	x = x1;
	y = y1;
	dx = cabs(x2-x1);
	dy = cabs(y2-y1);
	s1 = csign(x2-x1);
	s2 = csign(y2-y1);
	xchange = 0;   
	if (dy>dx)
	begin
		temp = dx;
		dx = dy;
		dy = temp;
		xchange = 1;
	end 
	e = ((int)dy<<1) - dx;   
	for (j=0; j<=dx; j++)
	begin
		video_pt(x,y,c) ; 
		if (e>=0)
		begin
			if (xchange==1) x = x + s1;
			else y = y + s2;
			e = e - ((int)dx<<1);
		end
		if (xchange==1) y = y + s2;
		else x = x + s1;
		e = e + ((int)dy<<1);
	end
end

//==================================
//return the value of one point 
//at x,y with color nonzero=white 0=black 
char video_set(char x, char y)
begin
	//The following construction 
  	//detects exactly one bit at the x,y location
	i=((int)x>>3) + ((int)y<<4) ;  
    return ( screen[i] & 1<<(7-(x & 0x7)));   	
end
//highlight a region form (x0,y0) to (x1,y1)
void video_highlight(unsigned char x0,unsigned char y0,unsigned char x1, unsigned char y1)
{  
  int i,j;
  for (i=x0;i<=x1;i++){
      for (j=y0;j<=y1;j++) video_pt(i,j,2);   
  } 
}
//clear a region form (x0,y0) to (x1,y1)
void video_clear(unsigned char x0,unsigned char y0,unsigned char x1, unsigned char y1)
{
  int i,j;
  for (i=x0;i<=x1;i++){
  for (j=y0;j<=y1;j++) video_pt(i,j,0);  
  }
}
//a chain to clean screen
void cleanscreen(void){

  //left hafe of screem
  if (k==0)     {video_clear(1,1,63,8);k++;}
  else if (k==1){video_clear(1,9,63,16);k++;}
  else if (k==2){video_clear(1,17,63,24);k++;}
  else if (k==3){video_clear(1,25,63,32);k++;}
  else if (k==4){video_clear(1,33,63,40);k++;}
  else if (k==5){video_clear(1,41,63,48);k++;}
  else if (k==6){video_clear(1,49,63,56);k++;}
  else if (k==7){video_clear(1,57,63,64);k++;}
  else if (k==8){video_clear(1,65,63,72);k++;}
  else if (k==9){video_clear(1,73,63,80);k++;}
  else if (k==10){video_clear(1,81,63,88);k++;}
  //right hafe of screem
  else if (k==11){video_clear(64,9,126,16);k++;}
  else if (k==12){video_clear(64,17,126,24);k++;}
  else if (k==13){video_clear(64,25,126,32);k++;}
  else if (k==14){video_clear(64,33,126,40);k++;}
  else if (k==15){video_clear(64,41,126,48);k++;}
  else if (k==16){video_clear(64,49,126,56);k++;}
  else if (k==17){video_clear(64,57,126,64);k++;}
  else if (k==18){video_clear(64,65,126,72);k++;}
  else if (k==19){video_clear(64,73,126,80);k++;}
  else if (k==20){video_clear(64,81,126,88);k++;}
  else if (k==21){video_clear(64,1,126,8);k++;}
  //botton line; can be dismissed if use small screen
  else if (k==22){video_clear(1,89,63,96);k++;}
  else if (k==23){video_clear(1,97,63,98);k++;}
  else if (k==24){video_clear(64,89,126,96);k++;}
  else if (k==25){video_clear(64,97,126,98);k=0;clean=0;}
}