/* hr_pixel.c - Set the color of the pixel at column x, row y according
 * to color c.  sop is the starting address of the display page. eop is the
 * ending address.  Note:  If the color is not possible at the
 * specified position, it is shifted left.  If the color is other than
 * BLACK or WHITE, the adjacent bits are both turned off.  If the color
 * is WHITE, the bit to the left is also turned on. This shifting is not
 * performed when the adjacent pixel is in a different row.  Returns void.
 *
 * Environment:	Apple II, Aztec c65 V1.05B
 * Programmer:	Don Strayer
 * Date:		15-Jun-88
 */

#include <math.h,d1>
#include <hr_apple2.h>

hr_pixel( x, y, c, sop , eop )
	int x;										/* column */
	int y;										/* row */
	int c;										/* color */
	int sop;									/* start of page */
	int eop;									/* end of page */

{	static char *pa;							/* pixel address */

	/* convert row number y to its equivalent blocking in display memory */

	y = ( ( y / 8 ) * 3 ) + ( ( y % 8 ) * 24 ) - ( ( y / 64 ) * 24 )
			+ ( y / 64 );

	/* adjust offset for the 8 byte padding every 3rd row */

	sop += ( y / 3 ) * 8;

	/* set the pixel to the specified color, adjusting as necessary */

	switch ( c )

	{	case HR_BLACK:
		{	pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );		/* pixel address */
			*pa = *pa & ( ( 1 << ( x % HR_PPB ) ) ^ 255 );	/* set pixel off */
			break;
		}

		case HR_PURPLE:
		{	if ( x & 1 )					/* decrement column if odd */
				--x;

			pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );	/* pixel address */
			*pa = *pa | ( 1 << ( x % HR_PPB ) );		/* set pixel on */
			*pa = *pa & 127;							/* high order off */

			break;
		}
		
		case HR_BLUE:
		{	if ( x & 1 )					/* decrement column if odd */
				--x;

			pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );	/* pixel address */
			*pa = *pa | ( 1 << ( x % HR_PPB ) );		/* set pixel on */
			*pa = *pa | 128;							/* high order on */

			break;
		}

		case HR_GREEN:
		{	if ( x == 0 )						/* exit if column zero */
				break;							/* (can't decrment) */

			if ( ! ( x & 1 ) )					/* decrement column if even */
				--x;

			pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );	/* pixel address */
			*pa = *pa | ( 1 << ( x % HR_PPB ) );		/* set pixel on */
			*pa = *pa & 127;							/* high order off */

			break;
		}

		case HR_ORANGE:
		{	if ( x == 0 )					/* exit if column zero */
			break;							/* (can't decrement) */

			if ( ! ( x & 1 ) )				/* decrement column if even */
				--x;

			pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );	/* pixel address */
			*pa = *pa | ( 1 << ( x % HR_PPB ) );		/* set pixel on */
			*pa = *pa | 128;							/* high order off */

			break;
		}

		case HR_WHITE:
		{	pa = sop + ( y * HR_BPR ) + ( x / HR_PPB );	/* pixel address */
			*pa = *pa | ( 1 << ( x % HR_PPB ) );		/* set pixel on */

			/* set pixel on left on if within current row */

			if ( x )
			{	pa = sop + ( y * HR_BPR ) + ( --x / HR_PPB );
				*pa = *pa | ( 1 << ( x % HR_PPB ) );
				++x;
			}

		break;
		}

		default:							/* invalid color */
			break;
	}

	/* if the pixel is colored, set the adjacent positions off,
	   provided within the current row */

	if ( ( c != HR_BLACK ) && ( c != HR_WHITE ) )
	{	if ( x )
		{	pa = sop + ( y * HR_BPR ) + ( --x / HR_PPB );
			*pa = *pa & ( ( 1 << ( x % HR_PPB ) ) ^ 255 );
			++x;
		}
		if ( x < 278 )
		{	pa = sop + ( y * HR_BPR ) + ( ++x / HR_PPB );
			*pa = *pa & ( ( 1 << ( x % HR_PPB ) ) ^ 255 );
			--x;
		}
	}

	return();
}