102 lines
2.3 KiB
C
102 lines
2.3 KiB
C
/*************************************************************************\
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* Module Name: intline.c
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*
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* Copyright (c) 1993-1994 Microsoft Corporation
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* Copyright (c) 1992 Digital Equipment Corporation
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\**************************************************************************/
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#include "precomp.h"
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#define DEFAULT_DRAW_CMD DRAW_LINE | \
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DRAW | \
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DIR_TYPE_XY | \
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MULTIPLE_PIXELS | \
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WRITE | \
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LAST_PIXEL_OFF
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/******************************************************************************
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* bIntegerLine
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*
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* This routine attempts to draw a line segment between two points. It
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* will only draw if both end points are whole integers: it does not support
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* fractional endpoints.
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*
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* Returns:
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* TRUE if the line segment is drawn
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* FALSE otherwise
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*****************************************************************************/
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BOOL
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bIntegerLine (
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PDEV* ppdev,
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ULONG X1,
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ULONG Y1,
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ULONG X2,
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ULONG Y2
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)
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{
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LONG Cmd;
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LONG DeltaX, DeltaY;
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LONG ErrorTerm;
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LONG Major, Minor;
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X1 >>= 4;
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Y1 >>= 4;
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X2 >>= 4;
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Y2 >>= 4;
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Cmd = DEFAULT_DRAW_CMD | PLUS_Y | PLUS_X | MAJOR_Y;
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DeltaX = X2 - X1;
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if (DeltaX < 0) {
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DeltaX = -DeltaX;
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Cmd &= ~PLUS_X;
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}
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DeltaY = Y2 - Y1;
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if (DeltaY < 0) {
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DeltaY = -DeltaY;
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Cmd &= ~PLUS_Y;
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}
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// Compute the major drawing axis
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if (DeltaX > DeltaY) {
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Cmd &= ~MAJOR_Y;
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Major = DeltaX;
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Minor = DeltaY;
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} else {
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Major = DeltaY;
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Minor = DeltaX;
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}
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// Tell the S3 to draw the line
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IO_FIFO_WAIT (ppdev, 7);
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IO_CUR_X (ppdev, X1);
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IO_CUR_Y (ppdev, Y1);
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IO_MAJ_AXIS_PCNT (ppdev, Major);
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IO_AXSTP (ppdev, Minor * 2);
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IO_DIASTP (ppdev, 2 * Minor - 2 * Major);
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// Adjust the error term so that 1/2 always rounds down, to
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// conform with GIQ.
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ErrorTerm = 2 * Minor - Major;
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if (Cmd & MAJOR_Y) {
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if (Cmd & PLUS_X) {
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ErrorTerm--;
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}
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} else {
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if (Cmd & PLUS_Y) {
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ErrorTerm--;
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}
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}
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IO_ERR_TERM (ppdev, ErrorTerm);
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IO_CMD (ppdev, Cmd);
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return TRUE;
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}
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