mi/miscanfill.h

   1 /*
   2
   3 Copyright 1987, 1998  The Open Group
   4
   5 Permission to use, copy, modify, distribute, and sell this software and its
   6 documentation for any purpose is hereby granted without fee, provided that
   7 the above copyright notice appear in all copies and that both that
   8 copyright notice and this permission notice appear in supporting
   9 documentation.
  10
  11 The above copyright notice and this permission notice shall be included
  12 in all copies or substantial portions of the Software.
  13
  14 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  15 OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  16 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  17 IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
  18 OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  19 ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  20 OTHER DEALINGS IN THE SOFTWARE.
  21
  22 Except as contained in this notice, the name of The Open Group shall
  23 not be used in advertising or otherwise to promote the sale, use or
  24 other dealings in this Software without prior written authorization
  25 from The Open Group.
  26
  27 */
  28
  29 #ifdef HAVE_DIX_CONFIG_H
  30 #include <dix-config.h>
  31 #endif
  32
  33 #ifndef SCANFILLINCLUDED
  34 #define SCANFILLINCLUDED
  35 /*
  36  *     scanfill.h
  37  *
  38  *     Written by Brian Kelleher; Jan 1985
  39  *
  40  *     This file contains a few macros to help track
  41  *     the edge of a filled object.  The object is assumed
  42  *     to be filled in scanline order, and thus the
  43  *     algorithm used is an extension of Bresenham's line
  44  *     drawing algorithm which assumes that y is always the
  45  *     major axis.
  46  *     Since these pieces of code are the same for any filled shape,
  47  *     it is more convenient to gather the library in one
  48  *     place, but since these pieces of code are also in
  49  *     the inner loops of output primitives, procedure call
  50  *     overhead is out of the question.
  51  *     See the author for a derivation if needed.
  52  */
  53 \f
  54 /*
  55  *  In scan converting polygons, we want to choose those pixels
  56  *  which are inside the polygon.  Thus, we add .5 to the starting
  57  *  x coordinate for both left and right edges.  Now we choose the
  58  *  first pixel which is inside the pgon for the left edge and the
  59  *  first pixel which is outside the pgon for the right edge.
  60  *  Draw the left pixel, but not the right.
  61  *
  62  *  How to add .5 to the starting x coordinate:
  63  *      If the edge is moving to the right, then subtract dy from the
  64  *  error term from the general form of the algorithm.
  65  *      If the edge is moving to the left, then add dy to the error term.
  66  *
  67  *  The reason for the difference between edges moving to the left
  68  *  and edges moving to the right is simple:  If an edge is moving
  69  *  to the right, then we want the algorithm to flip immediately.
  70  *  If it is moving to the left, then we don't want it to flip until
  71  *  we traverse an entire pixel.
  72  */
  73 #define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
  74     int dx;      /* local storage */ \
  75 \
  76     /* \
  77      *  if the edge is horizontal, then it is ignored \
  78      *  and assumed not to be processed.  Otherwise, do this stuff. \
  79      */ \
  80     if ((dy) != 0) { \
  81         xStart = (x1); \
  82         dx = (x2) - xStart; \
  83         if (dx < 0) { \
  84             m = dx / (dy); \
  85             m1 = m - 1; \
  86             incr1 = -2 * dx + 2 * (dy) * m1; \
  87             incr2 = -2 * dx + 2 * (dy) * m; \
  88             d = 2 * m * (dy) - 2 * dx - 2 * (dy); \
  89         } else { \
  90             m = dx / (dy); \
  91             m1 = m + 1; \
  92             incr1 = 2 * dx - 2 * (dy) * m1; \
  93             incr2 = 2 * dx - 2 * (dy) * m; \
  94             d = -2 * m * (dy) + 2 * dx; \
  95         } \
  96     } \
  97 }
  98 \f
  99 #define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
 100     if (m1 > 0) { \
 101         if (d > 0) { \
 102             minval += m1; \
 103             d += incr1; \
 104         } \
 105         else { \
 106             minval += m; \
 107             d += incr2; \
 108         } \
 109     } else {\
 110         if (d >= 0) { \
 111             minval += m1; \
 112             d += incr1; \
 113         } \
 114         else { \
 115             minval += m; \
 116             d += incr2; \
 117         } \
 118     } \
 119 }
 120 \f
 121 /*
 122  *     This structure contains all of the information needed
 123  *     to run the bresenham algorithm.
 124  *     The variables may be hardcoded into the declarations
 125  *     instead of using this structure to make use of
 126  *     register declarations.
 127  */
 128 typedef struct {
 129     int minor;                  /* minor axis        */
 130     int d;                      /* decision variable */
 131     int m, m1;                  /* slope and slope+1 */
 132     int incr1, incr2;           /* error increments */
 133 } BRESINFO;
 134
 135 #define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
 136         BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \
 137                      bres.m, bres.m1, bres.incr1, bres.incr2)
 138
 139 #define BRESINCRPGONSTRUCT(bres) \
 140         BRESINCRPGON(bres.d, bres.minor, bres.m, bres.m1, bres.incr1, bres.incr2)
 141
 142 #endif