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Microsoft Windows NT Build 511 (DDK SDK) 11-01-1993

/*************************************************************************\
* Module Name: Lines.cxx
*
* C template for the ASM version of the line DDA calculator.
* contains the C code associated with the c++ code (c++ does not handle
* READ/WRITE_REGISTER to well
*
* Copyright (c) 1993 Microsoft Corporation
* Copyright (c) 1992 Digital Equipment Corporation
\**************************************************************************/

#include "driver.h"
#include "lines.h"

#define S3_MAX_INT_LINE 	0x800
#define DEFAULT_DRAW_CMD	DRAW_LINE | \
                                DRAW | \
                                DIR_TYPE_XY | \
                                MULTIPLE_PIXELS | \
                                WRITE | \
                                LAST_PIXEL_OFF


/******************************************************************************
 * bIntegerLine
 *
 *
 * This routine attempts to draw a line segment between two points. It
 * will only draw if both end points are whole integers: it does not support
 * fractional endpoints.
 *
 * Returns:
 *   TRUE     if the line segment is drawn
 *   FALSE    otherwise
 *****************************************************************************/

BOOL
bIntegerLine (
	      PPDEV     ppdev,
	      ULONG	X1,
	      ULONG	Y1,
	      ULONG	X2,
	      ULONG	Y2
)
    {
	LONG		Cmd;
	LONG		DeltaX, DeltaY;
	LONG		ErrorTerm;
	LONG		Major, Minor;
	
	
	
	X1 >>= 4;
	Y1 >>= 4;
	X2 >>= 4;
	Y2 >>= 4;
	
	Cmd = DEFAULT_DRAW_CMD | PLUS_Y | PLUS_X | MAJOR_Y;
	
	DeltaX = X2 - X1;
	if (DeltaX < 0) {
	    DeltaX = -DeltaX;
	    Cmd &= ~PLUS_X;
	}
	DeltaY = Y2 - Y1;
	if (DeltaY < 0) {
	    DeltaY = -DeltaY;
	    Cmd &= ~PLUS_Y;
	}
	
	// Compute the major drawing axis
	
	if (DeltaX > DeltaY) {
	    Cmd &= ~MAJOR_Y;
	    Major = DeltaX;
	    Minor = DeltaY;
	} else {
	    Major = DeltaY;
	    Minor = DeltaX;
	}
	
	
	// Tell the S3 to draw the line
	
	FIFOWAIT (FIFO_7_EMPTY);
	OUTPW (CUR_X, X1);
	OUTPW (CUR_Y, Y1);
	OUTPW (LINE_MAX, Major);
	OUTPW (AXSTP, Minor * 2);
	OUTPW (DIASTP, 2 * Minor - 2 * Major);
	
	
	// Adjust the error term so that 1/2 always rounds down, to
	// conform with GIQ.
	
	ErrorTerm = 2 * Minor - Major;
	if (Cmd & MAJOR_Y) {
	    if (Cmd & PLUS_X) {
		ErrorTerm--;
	    }
	} else {
	    if (Cmd & PLUS_Y) {
		ErrorTerm--;
	    }
	}
	
	OUTPW (ERR_TERM, ErrorTerm);
	OUTPW (CMD, Cmd);
	
	
	// Wait until the S3 has finished drawing, and return success
	// to the caller
	
	GPWAIT();
	return TRUE;
	
    }

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