abrash-black-book/38-03.md

title	author	date	isbn	publisher	category	chapter	pages
Michael Abrash's Graphics Programming Black Book, Special Edition	Michael Abrash	1997-07-01	1576101746	The Coriolis Group	Web and Software Development: Game Development,Web and Software Development: Graphics and Multimedia Development	38	717-720

LISTING 38.3 L38-3.C

/* Sample program to exercise the polygon-filling routines. This code
   and all polygon-filling code has been tested with Borland and
   Microsoft compilers. */

#include <conio.h>
#include <dos.h>
#include "polygon.h"

/* Draws the polygon described by the point list PointList in color
   Color with all vertices offset by (X,Y) */
#define DRAW_POLYGON(PointList,Color,X,Y)                   \
   Polygon.Length = sizeof(PointList)/sizeof(struct Point); \
   Polygon.PointPtr = PointList;                            \
   FillConvexPolygon(&Polygon, Color, X, Y);
  
void main(void);
extern int FillConvexPolygon(struct PointListHeader *, int, int, int);

void main() {
  int i, j;
  struct PointListHeader Polygon;
  static struct Point ScreenRectangle[] =
        {{0,0},{320,0},{320,200},{0,200}};
  static struct Point ConvexShape[] =
        {{0,0},{121,0},{320,0},{200,51},{301,51},{250,51},{319,143},
        {320,200},{22,200},{0,200},{50,180},{20,160},{50,140},
        {20,120},{50,100},{20,80},{50,60},{20,40},{50,20}};
  static struct Point Hexagon[] =
        {{90,-50},{0,-90},{-90,-50},{-90,50},{0,90},{90,50}};
  static struct Point Triangle1[] = {{30,0},{15,20},{0,0}};
  static struct Point Triangle2[] = {{30,20},{15,0},{0,20}};
  static struct Point Triangle3[] = {{0,20},{20,10},{0,0}};
  static struct Point Triangle4[] = {{20,20},{20,0},{0,10}};
  union REGS regset;

  /* Set the display to VGA mode 13h, 320x200 256-color mode */
  regset.x.ax = 0x0013;   /* AH = 0 selects mode set function,
                             AL = 0x13 selects mode 0x13
                             when set as parameters for INT 0x10 */
  int86(0x10, &regset, &regset);

  /* Clear the screen to cyan */
  DRAW_POLYGON(ScreenRectangle, 3, 0, 0);

  /* Draw an irregular shape that meets our definition of convex but
     is not convex by any normal description */
  DRAW_POLYGON(ConvexShape, 6, 0, 0);
  getch();    /* wait for a keypress */

  /* Draw adjacent triangles across the top half of the screen */
  for (j=0; j<=80; j+=20) {
     for (i=0; i<290; i += 30) {
        DRAW_POLYGON(Triangle1, 2, i, j);
        DRAW_POLYGON(Triangle2, 4, i+15, j);
     }
  }

  /* Draw adjacent triangles across the bottom half of the screen */
  for (j=100; j<=170; j+=20) {
     /* Do a row of pointing-right triangles */
     for (i=0; i<290; i += 20) {
        DRAW_POLYGON(Triangle3, 40, i, j);
     }
     /* Do a row of pointing-left triangles halfway between one row
        of pointing-right triangles and the next, to fit between */
     for (i=0; i<290; i += 20) {
        DRAW_POLYGON(Triangle4, 1, i, j+10);
     }
  }
  getch();    /* wait for a keypress */

  /* Finally, draw a series of concentric hexagons of approximately
     the same proportions in the center of the screen */
  for (i=0; i<16; i++) {
     DRAW_POLYGON(Hexagon, i, 160, 100);
     for (j=0; j<sizeof(Hexagon)/sizeof(struct Point); j++) {
        /* Advance each vertex toward the center */
        if (Hexagon[j].X != 0) {
           Hexagon[j].X -= Hexagon[j].X >= 0 ? 3 : -3;
           Hexagon[j].Y -= Hexagon[j].Y >= 0 ? 2 : -2;
        } else {
           Hexagon[j].Y -= Hexagon[j].Y >= 0 ? 3 : -3;
        }
     }
  }
  getch();    /* wait for a keypress */

  /* Return to text mode and exit */
  regset.x.ax = 0x0003;   /* AL = 3 selects 80x25 text mode */
  int86(0x10, &regset, &regset);
}

LISTING 38.4 POLYGON.H

/* POLYGON.H: Header file for polygon-filling code */

/* Describes a single point (used for a single vertex) */
struct Point {
  int X;   /* X coordinate */
  int Y;   /* Y coordinate */
};

/* Describes a series of points (used to store a list of vertices that
   describe a polygon; each vertex is assumed to connect to the two
   adjacent vertices, and the last vertex is assumed to connect to the
   first) */
struct PointListHeader {
  int Length;                /* # of points */
  struct Point * PointPtr;   /* pointer to list of points */
};

/* Describes the beginning and ending X coordinates of a single
   horizontal line */
struct HLine {
  int XStart; /* X coordinate of leftmost pixel in line */
  int XEnd;   /* X coordinate of rightmost pixel in line */
};

/* Describes a Length-long series of horizontal lines, all assumed to
   be on contiguous scan lines starting at YStart and proceeding
   downward (used to describe a scan-converted polygon to the
   low-level hardware-dependent drawing code) */
struct HLineList {
  int Length;                /* # of horizontal lines */
  int YStart;                /* Y coordinate of topmost line */
  struct HLine * HLinePtr;   /* pointer to list of horz lines */
};