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gif2herc.c

/*****************************************************************************
*   "Gif-Lib" - Yet another gif library.                         *
*                                                          *
* Written by:  Gershon Elber                    Ver 0.1, Jul. 1989   *
******************************************************************************
* Program to display GIF file on hercules device                       *
* Options:                                                 *
* -q : quiet printing mode.                                      *
* -z factor : zoom the pixels by the given factor.                     *
* -t level : set the threshold level of white in the result (0..100).        *
* -m mapping : methods for mapping the 24bits colors into 1 BW bit.          *
* -i : invert the image.                                         *
* -b : beeps disabled.                                           *
* -h : on-line help.                                             *
*                                                          *
*   This program uses TC2.0 hercules graphic driver.                   *
*   In this file Screen refers to GIF file screen, while Device to Hercules. *
******************************************************************************
* History:                                                 *
* 1 Jul 89 - Version 1.0 by Gershon Elber.                             *
*****************************************************************************/

#include <graphics.h>
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <ctype.h>
#include <alloc.h>
#include <string.h>
#include <io.h>
#include <dos.h>
#include <bios.h>
#include <fcntl.h>
#include "gif_lib.h"
#include "getarg.h"

#define PROGRAM_NAME    "Gif2Herc"

#define KEY_LEFT  256     /* Key Codes returned for operational keys */
#define KEY_RIGHT 257     /* as return by the GetKey routine.          */
#define KEY_UP          258
#define KEY_DOWN  259
#define KEY_RETURN      260
#define KEY_DELETE      261
#define KEY_INSERT      262
#define KEY_BSPACE      263
#define KEY_ESC         264
#define KEY_HOME  265
#define KEY_END         266
#define KEY_PGUP  267
#define KEY_PGDN  268

#define     C2BW_BACK_GROUND  0 /*Methods to map 24bits Colors to 1 BW bit.*/
#define     C2BW_GREY_LEVELS  1
#define C2BW_DITHER           2
#define C2BW_NUM_METHODS      3             /* Always hold # of methods. */

#define DEFAULT_THRESHOLD     5000       /* Color->BW threshold level. */
#define INCREMENT_THRESHOLD   1000

#define DITHER_MIN_MATRIX     2
#define DITHER_MAX_MATRIX     4

#define NORMAL_ATTR     0x07                     /* Text attributes. */
#define INVERSE_ATTR    0x70
#define BLINK_ATTR      0x90

#define SET_POSITION_RESET    0         /* Situations need positionings: */
#define SET_POSITION_ZOOM_U   1
#define SET_POSITION_ZOOM_D   2
#define SET_POSITION_PAN      3

#define DEVICE_BASE     0xb000                  /* Hercules frame buffer base. */
#define DEVICE_PAGE0    0xb000
#define DEVICE_PAGE1    0xb800
#define HERC_MAX_X      719
#define HERC_MAX_Y      347

#define CURSOR_TEXT_X   120

extern unsigned int
    _stklen = 16384;                     /* Increase default stack size. */

static char
    *VersionStr =
      PROGRAM_NAME
      GIF_LIB_VERSION
      "     Gershon Elber,    "
      __DATE__ ",   " __TIME__ "\n"
      "(C) Copyright 1989 Gershon Elber.\n";
static char
    *CtrlStr =
      PROGRAM_NAME
      " q%- d%-DitherSize!d z%-ZoomFactor!d t%-BWThreshold!d m%-Mapping!d i%- b%- h%- GifFile!*s";
static char
    *GifFileName;
/* Make some variables global, so we could access them faster: */
static int
    ImageNum = 0,
    BackGround = 0,
    BeepsDisabled = FALSE,
    DitherSize = 2, DitherFlag = FALSE,
    ZoomFactor = 1, ZoomFlag = FALSE,
    BWThresholdFlag = FALSE, Threshold,
    BWThreshold = DEFAULT_THRESHOLD,         /* Color->BW mapping threshold. */
    Mapping, MappingFlag = FALSE,
    InvertFlag = FALSE,
    HelpFlag = FALSE,
    ColorToBWMapping = C2BW_BACK_GROUND,
    InterlacedOffset[] = { 0, 4, 2, 1 }, /* The way Interlaced image should  */
    InterlacedJumps[] = { 8, 8, 4, 2 };    /* be read - offsets and jumps... */
static GifColorType
    *ColorMap;


static void DisplayScreen(GifRowType *ScreenBuffer, GifFileType *GifFile);
static void PrintSettingStatus(GifFileType *GifFile, GifRowType *DitherBuffer);
static void CPrintStr(char *Str, int y, int attr);
static void SetPositon(int Why,
                   int ScreenWidth, int ScreenHeight,
                   int DeviceMaxX,  int DeviceMaxY,
                   int *ScreenLeft, int *ScreenTop,
                   int *DeviceLeft, int *DeviceTop,
                   int MoveX,       int MoveY);
static void ClearGraphDevice(void);
static void OpenGraphDevice(void);
static void CloseGraphDevice(void);
static void EvalDitheredScanline(GifRowType *ScreenBuffer, int Row,
                              int RowSize, GifRowType *DitherBuffer);
static void DrawScreen(GifRowType *ScreenBuffer, GifRowType *DitherBuffer,
      int DeviceTop, int DeviceLeft, int DeviceMaxX, int DeviceMaxY,
      int ScreenTop, int ScreenLeft, int ScreenWidth, int ScreenHeight);
static void DoCursorMode(GifRowType *ScreenBuffer,
      int ScreenLeft, int ScreenTop, int ScreenWidth, int ScreenHeight,
      int DeviceLeft, int DeviceTop);
static int MyKbHit(void);
static int MyGetCh(void);
static int GetKey(void);
static void Tone(int Frequency, int Time);

/******************************************************************************
* Interpret the command line and scan the given GIF file.               *
******************************************************************************/
void main(int argc, char **argv)
{
    int     i, j, Error, NumFiles, Size, Row, Col, Width, Height, ExtCode, Count;
    GifRecordType RecordType;
    GifByteType *Extension;
    char **FileName = NULL;
    GifRowType *ScreenBuffer;
    GifFileType *GifFile;

    if ((Error = GAGetArgs(argc, argv, CtrlStr,
            &GifQuietPrint, &DitherFlag, &DitherSize,
            &ZoomFlag, &ZoomFactor, &BWThresholdFlag,
            &Threshold, &MappingFlag, &Mapping, &InvertFlag,
            &BeepsDisabled, &HelpFlag, &NumFiles, &FileName)) != FALSE ||
            (NumFiles > 1 && !HelpFlag)) {
      if (Error)
          GAPrintErrMsg(Error);
      else if (NumFiles > 1)
          GIF_MESSAGE("Error in command line parsing - one GIF file please.");
      GAPrintHowTo(CtrlStr);
      exit(1);
    }

    if (HelpFlag) {
      fprintf(stderr, VersionStr);
      GAPrintHowTo(CtrlStr);
      exit(0);
    }

    if (DitherFlag) {
      /* Make sure we are o.k.: */
      if (DitherSize > DITHER_MAX_MATRIX) DitherSize = DITHER_MAX_MATRIX;
      if (DitherSize < DITHER_MIN_MATRIX) DitherSize = DITHER_MAX_MATRIX;
    }

    /* As Threshold is in [0..100] range and BWThreshold is [0..25500]: */
    if (BWThresholdFlag) {
      if (Threshold > 100 || Threshold < 0)
          GIF_EXIT("Threshold not in 0..100 percent.");
      BWThreshold = Threshold * 255;
      if (BWThreshold == 0) BWThreshold = 1;   /* Overcome divide by zero! */
    }

    /* No message is emitted, but mapping method is clipped to exists method.*/
    if (MappingFlag) ColorToBWMapping = Mapping % C2BW_NUM_METHODS;

    if (NumFiles == 1) {
      GifFileName = *FileName;
      if ((GifFile = DGifOpenFileName(*FileName)) == NULL) {
          PrintGifError();
          exit(-1);
      }
    }
    else {
      /* Use the stdin instead: */
      GifFileName = "Stdin";
      setmode(0, O_BINARY);
      if ((GifFile = DGifOpenFileHandle(0)) == NULL) {
          PrintGifError();
          exit(-1);
      }
    }

    /* Allocate the screen as vector of column of rows. We cannt allocate    */
    /* the all screen at once, as this broken minded CPU can allocate up to  */
    /* 64k at a time and our image can be bigger than that:            */
    /* Note this screen is device independent - its the screen as defined by */
    /* the GIF file parameters itself.                                 */
    if ((ScreenBuffer = (GifRowType *)
      malloc(GifFile->SHeight * sizeof(GifRowType *))) == NULL)
          GIF_EXIT("Failed to allocate memory required, aborted.");

    Size = GifFile->SWidth * sizeof(GifPixelType);/* Size in bytes one row.*/
    if ((ScreenBuffer[0] = (GifRowType) malloc(Size)) == NULL) /* First row. */
      GIF_EXIT("Failed to allocate memory required, aborted.");

    for (i = 0; i < GifFile->SWidth; i++)  /* Set its color to BackGround. */
      ScreenBuffer[0][i] = GifFile->SBackGroundColor;
    for (i = 1; i < GifFile->SHeight; i++) {
      /* Allocate the other rows, andset their color to background too: */
      if ((ScreenBuffer[i] = (GifRowType) malloc(Size)) == NULL)
          GIF_EXIT("Failed to allocate memory required, aborted.");

      memcpy(ScreenBuffer[i], ScreenBuffer[0], Size);
    }

    /* Scan the content of the GIF file and load the image(s) in: */
    do {
      if (DGifGetRecordType(GifFile, &RecordType) == GIF_ERROR) {
          PrintGifError();
          exit(-1);
      }
      switch (RecordType) {
          case IMAGE_DESC_RECORD_TYPE:
            if (DGifGetImageDesc(GifFile) == GIF_ERROR) {
                PrintGifError();
                exit(-1);
            }
            Row = GifFile->Image.Top; /* Image Position relative to Screen. */
            Col = GifFile->Image.Left;
            Width = GifFile->Image.Width;
            Height = GifFile->Image.Height;
            GifQprintf("\n%s: Image %d at (%d, %d) [%dx%d]:     ",
                PROGRAM_NAME, ++ImageNum, Col, Row, Width, Height);
            if (GifFile->Image.Left + GifFile->Image.Width > GifFile->SWidth ||
               GifFile->Image.Top + GifFile->Image.Height > GifFile->SHeight) {
                fprintf(stderr, "Image %d is not confined to screen dimension, aborted\n");
                exit(-2);
            }
            if (GifFile->Image.Interlace) {
                /* Need to perform 4 passes on the images: */
                for (Count = i = 0; i < 4; i++)
                  for (j = Row + InterlacedOffset[i]; j < Row + Height;
                                     j += InterlacedJumps[i]) {
                      GifQprintf("\b\b\b\b%-4d", Count++);
                      if (DGifGetLine(GifFile, &ScreenBuffer[j][Col],
                        Width) == GIF_ERROR) {
                        PrintGifError();
                        exit(-1);
                      }
                  }
            }
            else {
                for (i = 0; i < Height; i++) {
                  GifQprintf("\b\b\b\b%-4d", i);
                  if (DGifGetLine(GifFile, &ScreenBuffer[Row++][Col],
                        Width) == GIF_ERROR) {
                      PrintGifError();
                      exit(-1);
                  }
                }
            }
            break;
          case EXTENSION_RECORD_TYPE:
            /* Skip any extension blocks in file: */
            if (DGifGetExtension(GifFile, &ExtCode, &Extension) == GIF_ERROR) {
                PrintGifError();
                exit(-1);
            }
            while (Extension != NULL) {
                if (DGifGetExtensionNext(GifFile, &Extension) == GIF_ERROR) {
                  PrintGifError();
                  exit(-1);
                }
            }
            break;
          case TERMINATE_RECORD_TYPE:
            break;
          default:                /* Should be traps by DGifGetRecordType. */
            break;
      }
    }
    while (RecordType != TERMINATE_RECORD_TYPE);

    /* Lets display it - set the global variables required and do it: */
    BackGround = GifFile->SBackGroundColor;
    ColorMap = (GifFile->Image.ColorMap ? GifFile->Image.ColorMap :
                               GifFile->SColorMap);
    Tone(500, 10);
    DisplayScreen(ScreenBuffer, GifFile);

    if (DGifCloseFile(GifFile) == GIF_ERROR) {
      PrintGifError();
      exit(-1);
    }
}

/******************************************************************************
* Given the screen buffer, display it:                                  *
* The following commands are available (case insensitive).              *
* 1. Four arrow to move along the screen (only if ScreenBuffer > physical     *
*    screen in that direction.                                          *
* 2. C - goto cursor mode - print current color & position in GIF screen      *
*        of the current pixel cursor is on.                             *
* 3. D - zoom out by factor of 2.                                 *
* 4. H - halftoning dithering matrix resize.                            *
* 5. I - invert the image.                                        *
* 6. M - toggles method of Color->BW mapping.                           *
* 7. R - redraw current image.                                          *
* 8. S - Print Current status/options.                                  *
* 9. U - zoom in by factor of 2.                                  *
* 10. ' ' - stop drawing current image.                                 *
* 11. ESC - to quit.                                              *
******************************************************************************/
static void DisplayScreen(GifRowType *ScreenBuffer, GifFileType *GifFile)
{
    int i, j, Size,
      DeviceTop, DeviceLeft,   /* Where ScreenBuffer is to mapped to ours. */
      ScreenTop, ScreenLeft,  /* Porsion of ScreenBuffer to start display. */
      DeviceMaxX, DeviceMaxY,             /* Physical device dimensions. */
      XPanning, YPanning,            /* Amount to move using the arrows. */
      GetK, DrawIt = TRUE;
    GifRowType *DitherBuffer;      /* Used to save dithered pixel scanned. */

    OpenGraphDevice();
    DeviceMaxX = HERC_MAX_X;            /* Read size of physical screen. */
    DeviceMaxY = HERC_MAX_Y;

    XPanning = DeviceMaxX / 2;
    YPanning = DeviceMaxY / 2;

    SetPositon(SET_POSITION_RESET, GifFile->SWidth, GifFile->SHeight,
            DeviceMaxX, DeviceMaxY,
            &ScreenLeft, &ScreenTop,
            &DeviceLeft, &DeviceTop,
            0, 0);

    /*   Allocate the buffer to save the dithered information. If fails to   */
    /* allocate, set it to NULL, and no dithering will take place.           */
    if ((DitherBuffer = (GifRowType *)
      malloc(DITHER_MAX_MATRIX * sizeof(GifRowType *))) != NULL) {
      Size = GifFile->SWidth * sizeof(GifPixelType); /* Size of one row. */
      for (i = 0; i < DITHER_MAX_MATRIX; i++) {
          if ((DitherBuffer[i] = (GifRowType) malloc(Size)) == NULL) {
            for (j = 0; j < i; j++) free((char *) DitherBuffer[i]);
            free((char *) DitherBuffer);
            DitherBuffer = NULL;
            break;
          }
      }
    }
    if (DitherBuffer == NULL) {
      Tone(300, 100);
      Tone(100, 300);
    }

    do {
      if (DrawIt && !MyKbHit()) {
          DrawScreen(ScreenBuffer, DitherBuffer,
            DeviceTop, DeviceLeft, DeviceMaxX, DeviceMaxY,
            ScreenTop, ScreenLeft, GifFile->SWidth, GifFile->SHeight);
          Tone(2000, 200);
      }
      DrawIt = TRUE;
      switch (GetK = GetKey()) {
          case 'C':
            DoCursorMode(ScreenBuffer, ScreenLeft, ScreenTop,
                       GifFile->SWidth, GifFile->SHeight,
                       DeviceLeft, DeviceTop);
            DrawIt = FALSE;
            break;
          case 'D':
            if (ZoomFactor > 1) {
                ZoomFactor >>= 1;
                SetPositon(SET_POSITION_ZOOM_D,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  0, 0);
            }
            else {
                Tone(1000, 100);
                DrawIt = FALSE;
            }
            break;
          case 'H':
            if (++DitherSize > DITHER_MAX_MATRIX)
                DitherSize = DITHER_MIN_MATRIX;
            break;
          case 'I':
            InvertFlag = !InvertFlag;
            break;
          case 'M':
            ColorToBWMapping = (ColorToBWMapping + 1) % C2BW_NUM_METHODS;

            break;
          case 'R':
            break;
          case 'S':
            PrintSettingStatus(GifFile, DitherBuffer);
            break;
          case 'U':
            if (ZoomFactor < 256) {
                ZoomFactor <<= 1;
                SetPositon(SET_POSITION_ZOOM_U,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  0, 0);
            }
            else {
                Tone(1000, 100);
                DrawIt = FALSE;
            }
            break;
          case KEY_ESC:
            break;
          case KEY_LEFT:
            SetPositon(SET_POSITION_PAN,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  -XPanning, 0);
            break;
          case KEY_RIGHT:
            SetPositon(SET_POSITION_PAN,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  XPanning, 0);
            break;
          case KEY_UP:
            SetPositon(SET_POSITION_PAN,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  0, -YPanning);
            break;
          case KEY_DOWN:
            SetPositon(SET_POSITION_PAN,
                  GifFile->SWidth, GifFile->SHeight,
                  DeviceMaxX, DeviceMaxY,
                  &ScreenLeft, &ScreenTop,
                  &DeviceLeft, &DeviceTop,
                  0, YPanning);
            break;
          case KEY_DELETE:
            BWThreshold += INCREMENT_THRESHOLD;
            if (BWThreshold == 0) BWThreshold = 1;
            break;
          case KEY_INSERT:
            BWThreshold -= INCREMENT_THRESHOLD;
            if (BWThreshold == 0) BWThreshold = 1;
            break;
          default:
            DrawIt = FALSE;
            Tone(800, 100);
            Tone(300, 200);
            break;
      }
    }
    while (GetK != KEY_ESC);

    CloseGraphDevice();
}

/******************************************************************************
* Routine to print (in text mode), current program status.              *
******************************************************************************/
static void PrintSettingStatus(GifFileType *GifFile, GifRowType *DitherBuffer)
{
    char s[80];

    CloseGraphDevice();

    CPrintStr(PROGRAM_NAME, 1, INVERSE_ATTR);

    sprintf(s, "GIF File - %s", GifFileName);
    CPrintStr(s, 3, NORMAL_ATTR);

    sprintf(s, "Gif Screen Size = [%d, %d]. Contains %d image(s).",
      GifFile->SWidth, GifFile->SHeight, ImageNum);
    CPrintStr(s, 5, NORMAL_ATTR);

    if (GifFile->SColorMap)
      sprintf(s,
          "Has Screen Color map of %d bits. BackGround = [%d, %d, %d]",
          GifFile->SBitsPerPixel,
          GifFile->SColorMap[GifFile->SBackGroundColor].Red,
          GifFile->SColorMap[GifFile->SBackGroundColor].Green,
          GifFile->SColorMap[GifFile->SBackGroundColor].Blue);
    else
      sprintf(s, "No Screen color map.");
    CPrintStr(s, 7, NORMAL_ATTR);

    if (GifFile->Image.ColorMap)
      sprintf(s, "Has Image map of %d bits (last image). Image is %s.",
          GifFile->Image.BitsPerPixel,
          (GifFile->Image.Interlace ? "interlaced" : "non interlaced"));
    else
      sprintf(s, "No Image color map.");
    CPrintStr(s, 9, NORMAL_ATTR);

    sprintf(s, "Color to BW threshold level - %d%%.\n", BWThreshold / 255);
    CPrintStr(s, 11, NORMAL_ATTR);

    CPrintStr("Color To BW mapping:", 15, NORMAL_ATTR);
    switch(ColorToBWMapping) {
      case C2BW_BACK_GROUND:
          CPrintStr("Color != BackGround", 16, NORMAL_ATTR);
          break;
      case C2BW_GREY_LEVELS:
          CPrintStr(".3 * R + .59 * G + .11 * B > threshold", 16,
                                                NORMAL_ATTR);
          break;
      case C2BW_DITHER:
          sprintf(s, ".3 * R + .59 * G + .11 * B dithered (Size = %d).",
            DitherSize);
          CPrintStr(s, 16, NORMAL_ATTR);
          break;
    }

    sprintf(s, "Dither Buffer %s (Size = %d), Zoom = %d.",
      DitherBuffer ? "allocated succesfully" : "not allocated (failed)",
      DitherSize, ZoomFactor);

    CPrintStr(s, 18, NORMAL_ATTR);

    CPrintStr("Press anything to continue:", 23, BLINK_ATTR);
    MyGetCh();

    OpenGraphDevice();
}

/******************************************************************************
* Routine to cprintf given string centered at given Y level, and attr:        *
******************************************************************************/
static void CPrintStr(char *Str, int y, int attr)
{
    gotoxy(40 - (strlen(Str) + 1) / 2, y);
    textattr(attr);
    cputs(Str);
}

/******************************************************************************
* Routine to set the position of Screen in Device, and what porsion of the    *
* screen should be visible:                                       *
* MoveX, MoveY are the panning factors (if both zero - initialize).           *
******************************************************************************/
static void SetPositon(int Why,
                   int ScreenWidth, int ScreenHeight,
                   int DeviceMaxX,  int DeviceMaxY,
                   int *ScreenLeft, int *ScreenTop,
                   int *DeviceLeft, int *DeviceTop,
                   int MoveX,       int MoveY)
{

    MoveX /= ZoomFactor;         /* Make sure move same amount independent */
    MoveY /= ZoomFactor;                     /* of what ZoomFactor is. */

    /* Figure out position of GIF file in real device X axis: */
    if (ScreenWidth * ZoomFactor <= DeviceMaxX + 1) {
      /* Device is big enough to hold all the image X axis: */
      *ScreenLeft = 0;
      *DeviceLeft = (DeviceMaxX - ScreenWidth * ZoomFactor) / 2;
    }
    else {
      /* Device is too small to hold all the image X axis: */
      switch (Why) {
          case SET_POSITION_RESET:
            *ScreenLeft = 0;
            break;
          case SET_POSITION_ZOOM_U:
            *ScreenLeft += DeviceMaxX / (2 * ZoomFactor);
            break;
          case SET_POSITION_ZOOM_D:
            *ScreenLeft -= DeviceMaxX / (4 * ZoomFactor);
            break;
          case SET_POSITION_PAN:
            if (MoveX != 0) *ScreenLeft += MoveX;
            break;
      }
      if (*ScreenLeft < 0) *ScreenLeft = 0;
      if ((ScreenWidth - *ScreenLeft) * ZoomFactor < DeviceMaxX + 1)
          *ScreenLeft = (ScreenWidth * ZoomFactor -
                                    DeviceMaxX + 1) / ZoomFactor;
      *DeviceLeft = 0;
    }

    /* Figure out position of GIF file in real device Y axis: */
    if (ScreenHeight * ZoomFactor <= DeviceMaxY + 1) {
      /* Device is big enough to hold all the image Y axis: */
      *ScreenTop = 0;
      *DeviceTop = (DeviceMaxY - ScreenHeight * ZoomFactor) / 2;
    }
    else {
      /* Device is too small to hold all the image Y axis: */
      switch (Why) {
          case SET_POSITION_RESET:
            *ScreenTop = 0;
            break;
          case SET_POSITION_ZOOM_U:
            *ScreenTop += DeviceMaxY / (2 * ZoomFactor);
            break;
          case SET_POSITION_ZOOM_D:
            *ScreenTop -= DeviceMaxY / (4 * ZoomFactor);
            break;
          case SET_POSITION_PAN:
            if (MoveY != 0) *ScreenTop += MoveY;
            break;
      }
      if (*ScreenTop < 0) *ScreenTop = 0;
      if ((ScreenHeight - *ScreenTop) * ZoomFactor < DeviceMaxY + 1)
          *ScreenTop = (ScreenHeight * ZoomFactor -
                                     DeviceMaxY - 1) / ZoomFactor;
      *DeviceTop = 0;
    }

    /* Make sure the position is on Byte boundary (8 pixels per byte): */
    *DeviceLeft &= 0xfff8;
}

/******************************************************************************
* Routine to clear graphic device:                                *
******************************************************************************/
static void ClearGraphDevice(void)
{
    cleardevice();
}

/******************************************************************************
* Routine to open graphic device:                                 *
******************************************************************************/
static void OpenGraphDevice(void)
{
    int GraphDriver = HERCMONO, GraphMode = HERCMONOHI;

    if (registerbgidriver(Herc_driver) < 0)
      GIF_EXIT("Cannt register graphic device.");

    initgraph(&GraphDriver, &GraphMode, "");
    if (graphresult() != grOk)
      GIF_EXIT("Graphics System Error (No Hercules!?).");
}

/*****************************************************************************
* Routine to close and shutdown     graphic     mode :                             *
*****************************************************************************/
static void CloseGraphDevice(void)
{
    closegraph();               /* Return the system to text mode. */
}

/*****************************************************************************
* Routine to evaluate dithered scanlines out of given ones, using Size       *
* dithering matrix, starting from Row. The given scanlines are NOT modified. *
*****************************************************************************/
static void EvalDitheredScanline(GifRowType *ScreenBuffer, int Row,
                               int RowSize, GifRowType *DitherBuffer)
{
    static char Dither2[2][2] = {    /* See Foley & Van Dam pp. 597-601. */
      { 1, 3 },
      { 4, 2 }
    };
    static char Dither3[3][3] = {
      { 7, 9, 5 },
      { 2, 1, 4 },
      { 6, 3, 8 }
    };
    static char Dither4[4][4] = {
      { 1,  9,  3,  11 },
      { 13, 5,  15, 7 },
      { 4,  12, 2,  10 },
      { 16, 8,  14, 6 }
    };
    int i, j, k, Level;
    long Intensity;
    GifColorType *ColorMapEntry;

    /* Scan the Rows (Size rows) evaluate intensity every Size pixel and use */
    /* the dither matrix to set the dithered result;                   */
    for (i = 0; i <= RowSize - DitherSize; i += DitherSize) {
      Intensity = 0;
      for (j = Row; j < Row + DitherSize; j++)
          for (k = 0; k < DitherSize; k++) {
            ColorMapEntry = &ColorMap[ScreenBuffer[j][i+k]];
            Intensity += 30 * ((int) ColorMapEntry->Red) +
                       59 * ((int) ColorMapEntry->Green) +
                       11 * ((int) ColorMapEntry->Blue);
          }

      /* Find the intensity level (between 0 and Size^2) of our matrix: */
      /* Expression is "Intensity * BWThreshold / (25500 * DefThresh)"  */
      /* but to prevent from overflow in the long evaluation we do this:*/
      Level = ((Intensity / 2550) * ((long) DEFAULT_THRESHOLD) /
                                    (((long) BWThreshold) * 10));
      switch (DitherSize) {
          case 2:
            for (j = 0; j < DitherSize; j++)
                for (k = 0; k < DitherSize; k++)
                  DitherBuffer[j][i+k] = Dither2[j][k] <= Level;
            break;
          case 3:
            for (j = 0; j < DitherSize; j++)
                for (k = 0; k < DitherSize; k++)
                  DitherBuffer[j][i+k] = Dither3[j][k] <= Level;
            break;
          case 4:
            for (j = 0; j < DitherSize; j++)
                for (k = 0; k < DitherSize; k++)
                  DitherBuffer[j][i+k] = Dither4[j][k] <= Level;
            break;
      }
    }
}

/******************************************************************************
* The real drawing of the image is performed here. Few things are taken into  *
* account:                                                  *
* 1. The zoom factor. If > 1 each pixel is multiplied this amount vertically  *
*    and horizontally.                                            *
* 2. The Invert flag. If TRUE each pixel before drawn is inverted.            *
* 3. The rendering mode and dither matrix flag if dithering is selected.      *
*   The image is drawn from ScreenBuffer ScreenTop/Left in the bottom/right   *
* directions, onto the Device DeviceTop/Left in the bottom/right direction    *
*     This routine was optimized for the hercules graphic card and should be  *
* handled carfully as it is device dependent.                           *
*   Pressing space during drawing will abort this routine.              *
******************************************************************************/
static void DrawScreen(GifRowType *ScreenBuffer, GifRowType *DitherBuffer,
      int DeviceTop, int DeviceLeft, int DeviceMaxX, int DeviceMaxY,
      int ScreenTop, int ScreenLeft, int ScreenWidth, int ScreenHeight)
{
    unsigned int Offset;
    int i, j, k, l, m, CountZoomJ, CountZoomI,
      DitheredLinesLeft = 0, DitheredLinesCount, MapInvert[2];
    GifByteType DeviceByte;
    GifPixelType *Line;
    GifColorType *ColorMapEntry;

    ClearGraphDevice();              /* Make sure we start from scratch. */

    if (InvertFlag) {            /* Make the inversion as fast a possible. */
      MapInvert[0] = 1;
      MapInvert[1] = 0;
    }
    else {
      MapInvert[0] = 0;
      MapInvert[1] = 1;
    }

    for (CountZoomJ = ZoomFactor, j = ScreenTop, l = DeviceTop, DeviceByte = 0;
       j < ScreenHeight && l <= DeviceMaxY; l++) {
      Line = ScreenBuffer[j];

      /* We are going to access the hercules frame buffer directly: */
      Offset = 0x2000 * (l & 0x03) + (l >> 2) * 90 + (DeviceLeft >> 3);

      /* Abort drawing if space bar was pressed: */
      if (MyKbHit() && GetKey() == ' ') return;

      /* We decide right here what method to map Colors to BW so the inner */
      /* loop will be independent of it (and therefore faster):        */
      switch(ColorToBWMapping) {
          case C2BW_BACK_GROUND:
            for (CountZoomI = ZoomFactor, i = ScreenLeft, k = DeviceLeft, m = 0;
                 i < ScreenWidth && k <= DeviceMaxX;) {
                /* The following lines are equivalent to the putpixel    */
                /* (and making it real machine dependent...) by almost   */
                /* factor of 3:                                  */
                /* putpixel(k++, l, MapInvert[ColorToBW(Line[i])]);          */
                DeviceByte = (DeviceByte << 1) +
                              MapInvert[Line[i] != BackGround];
                if (++m == 8) {
                  /* We have byte - place it on hercules frame buffer: */
                  k += 8;
                  pokeb(DEVICE_BASE, Offset++, DeviceByte);
                  m = 0;
                }

                if (!--CountZoomI) {
                  /* Go to next column: */
                  i++;
                  CountZoomI = ZoomFactor;
                }
            }
            if (k < DeviceMaxX) {
                /* Poke last byte also: */
                DeviceByte <<= 8 - m;
                pokeb(DEVICE_BASE, Offset++, DeviceByte);
            }
            break;
          case C2BW_GREY_LEVELS:
            for (CountZoomI = ZoomFactor, i = ScreenLeft, k = DeviceLeft, m = 0;
                 i < ScreenWidth && k <= DeviceMaxX;) {
                /* The following lines are equivalent to the putpixel    */
                /* (and making it real machine dependent...) by almost   */
                /* factor of 3:                                  */
                /* putpixel(k++, l, MapInvert[ColorToBW(Line[i])]);          */

                ColorMapEntry = &ColorMap[Line[i]];
                /* For the transformation from RGB to BW, see Folley &   */
                /* Van Dam pp 613: The Y channel is the BW we need:          */
                /* As colors are 255 maximum, the result can be up to    */
                /* 25500 which is still in range of our 16 bits integers.*/
                DeviceByte = (DeviceByte << 1) +
                  MapInvert[(30 * (int) ColorMapEntry->Red) +
                           59 * ((int) ColorMapEntry->Green) +
                           11 * ((int) ColorMapEntry->Blue) >
                              BWThreshold];
                if (++m == 8) {
                  /* We have byte - place it on hercules frame buffer: */
                  k += 8;
                  pokeb(DEVICE_BASE, Offset++, DeviceByte);
                  m = 0;
                }

                if (!--CountZoomI) {
                  /* Go to next column: */
                  i++;
                  CountZoomI = ZoomFactor;
                }
            }
            if (k < DeviceMaxX) {
                /* Poke last byte also: */
                DeviceByte <<= 8 - m;
                pokeb(DEVICE_BASE, Offset++, DeviceByte);
            }
            break;
          case C2BW_DITHER:
            if (DitheredLinesLeft-- == 0) {
                EvalDitheredScanline(ScreenBuffer,
                  (j < ScreenHeight - DitherSize ? j :
                                     ScreenHeight - DitherSize),
                  ScreenWidth, DitherBuffer);
                DitheredLinesLeft = DitherSize - 1;
                DitheredLinesCount = 0;
            }
            Line = DitherBuffer[DitheredLinesCount++];
            for (CountZoomI = ZoomFactor, i = ScreenLeft, k = DeviceLeft, m = 0;
                 i < ScreenWidth && k <= DeviceMaxX;) {
                /* The following lines are equivalent to the putpixel    */
                /* (and making it real machine dependent...) by almost   */
                /* factor of 3:                                  */
                /* putpixel(k++, l, MapInvert[Line[i]]);               */
                DeviceByte = (DeviceByte << 1) + MapInvert[Line[i]];
                if (++m == 8) {
                  /* We have byte - place it on hercules frame buffer: */
                  k += 8;
                  pokeb(DEVICE_BASE, Offset++, DeviceByte);
                  m = 0;
                }

                if (!--CountZoomI) {
                  /* Go to next column: */
                  i++;
                  CountZoomI = ZoomFactor;
                }
            }
            if (k < DeviceMaxX) {
                /* Poke last byte also: */
                DeviceByte <<= 8 - m;
                pokeb(DEVICE_BASE, Offset++, DeviceByte);
            }
            break;
      }

      if (!--CountZoomJ) {
          /* Go to next row: */
          j++;
          CountZoomJ = ZoomFactor;
      }
    }
}

/******************************************************************************
* Walks along the current image, while printing pixel value and position.     *
* 4 arrows may be used, and any other key will abort this operation           *
* As there is no XOR mode for text, we copy all Page 0 to Page 1 before we    *
* start this, and copy it back each time...                             *
******************************************************************************/
static void DoCursorMode(GifRowType *ScreenBuffer,
      int ScreenLeft, int ScreenTop, int ScreenWidth, int ScreenHeight,
      int DeviceLeft, int DeviceTop)
{
    int GetK, DeviceRight, DeviceBottom, x, y, CursorTextY, Step;
    GifPixelType Pixel;
    char s[80];
    char far *Page0, *Page1;

    Page0 = MK_FP(DEVICE_PAGE0, 0);
    Page1 = MK_FP(DEVICE_PAGE1, 0);

    memcpy(Page1, Page0, 0x8000);


    DeviceRight = DeviceLeft + (ScreenWidth - ScreenLeft) * ZoomFactor;
    if (DeviceRight > HERC_MAX_X) DeviceRight = HERC_MAX_X;

    DeviceBottom = DeviceTop + (ScreenHeight - ScreenTop) * ZoomFactor;
    if (DeviceBottom > HERC_MAX_Y) DeviceBottom = HERC_MAX_Y;

    x = (DeviceLeft + DeviceRight) / 2;
    y = (DeviceTop + DeviceBottom) / 2;

    while (TRUE) {
      Pixel = ScreenBuffer[ScreenTop + (y - DeviceTop) / ZoomFactor]
                      [ScreenLeft + (x - DeviceLeft) / ZoomFactor];
      sprintf(s, "Color = %d [%d, %d, %d], X = %d, Y = %d.",
            Pixel,
            ColorMap[Pixel].Red,
            ColorMap[Pixel].Green,
            ColorMap[Pixel].Blue,
            (x - DeviceLeft) / ZoomFactor,
            (y - DeviceTop) / ZoomFactor);
      CursorTextY = (y > HERC_MAX_Y / 2 ? HERC_MAX_Y / 4 :
                                  3 * HERC_MAX_Y / 4);
      setviewport(CURSOR_TEXT_X, CursorTextY,
                CURSOR_TEXT_X + textwidth(s), CursorTextY + textheight(s),
                TRUE);
      clearviewport();
      setviewport(0, 0, HERC_MAX_X, HERC_MAX_Y, TRUE);
      setcolor(1);                       /* We only have one color here. */
      line(0, y, HERC_MAX_X, y);
      line(x, 0, x, HERC_MAX_Y);
      outtextxy(CURSOR_TEXT_X, CursorTextY, s);
      GetK = GetKey();

      memcpy(Page0, Page1, 0x8000);

      Step = 10;
      switch (GetK) {
          case '1':
            GetK = KEY_END;
            break;
          case '2':
            GetK = KEY_DOWN;
            break;
          case '3':
            GetK = KEY_PGDN;
            break;
          case '4':
            GetK = KEY_LEFT;
            break;
          case '6':
            GetK = KEY_RIGHT;
            break;
          case '7':
            GetK = KEY_HOME;
            break;
          case '8':
            GetK = KEY_UP;
            break;
          case '9':
            GetK = KEY_PGUP;
            break;
          default:
            Step = 1;
      }

      switch (GetK) {
          case KEY_LEFT:
            x -= Step;
            break;
          case KEY_RIGHT:
            x += Step;
            break;
          case KEY_UP:
            y -= Step;
            break;
          case KEY_DOWN:
            y += Step;
            break;
          case KEY_PGUP:
            y -= Step;
            x += Step;
            break;
          case KEY_PGDN:
            y += Step;
            x += Step;
            break;
          case KEY_HOME:
            y -= Step;
            x -= Step;
            break;
          case KEY_END:
            y += Step;
            x -= Step;
            break;
          default:
            return;
      }
      if (x < DeviceLeft) x = DeviceLeft;
      if (x >= DeviceRight) x = DeviceRight;
      if (y < DeviceTop) y = DeviceTop;
      if (y >= DeviceBottom) y = DeviceBottom;
    }
}

/******************************************************************************
* Return non zero value if at list one character exists in keyboard queue.    *
* This routine emulates kbhit() which do uses stdin and useless for us.       *
******************************************************************************/
static int MyKbHit(void)
{
    return bioskey(1);
}

/******************************************************************************
* Get a key from keyboard directly (bypass stdin as we might redirect it).    *
* This routine emulates getch() which do uses stdin and useless for us.       *
******************************************************************************/
static int MyGetCh(void)
{
    static int Extended = 0;
    int c;

    if (Extended) {
      c = Extended;
      Extended = 0;
      return c;
    }
    else {
      c = bioskey(0);
      if (c & 0x0ff)
          return c;
      else {
          Extended = c >> 8;
          return 0;
      }
    }
}

/******************************************************************************
* Get a key from keyboard, and translating operational keys into special      *
* codes (>255).   Lower case characters are upercased.                        *
******************************************************************************/
static int GetKey(void)
{
    char c;

    while (TRUE) switch (c = MyGetCh()) {
      case 0:                 /* Extended code - get the next extended char. */
          switch (MyGetCh()) {
            case 75: return KEY_LEFT;
            case 77: return KEY_RIGHT;
            case 72: return KEY_UP;
            case 80: return KEY_DOWN;
            case 71: return KEY_HOME;
            case 79: return KEY_END;
            case 73: return KEY_PGUP;
            case 81: return KEY_PGDN;
            case 83: return KEY_DELETE;
            case 82: return KEY_INSERT;
          }
          break;
      case 8:
          return KEY_BSPACE;
      case 10:
      case 13:
          return KEY_RETURN;
      case 27:
          return KEY_ESC;
      default:
          if (isprint(c)) {
            if (islower(c))
                return toupper(c);
            else
                return c;
          }
          else {
            Tone(800, 100);
            Tone(300, 200);
          }
    }

    return 0;                          /* Should never be here any case. */
}

/******************************************************************************
* Routine to make some sound with given Frequency, Time milliseconds:         *
******************************************************************************/
static void Tone(int Frequency, int Time)
{
    if (BeepsDisabled) return;

    sound(Frequency);
    delay(Time);
    nosound();
}

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