mkconvert

/*
 * mkconvert
 * =========
 *
 * Written 2012 by Magnus Kalkuhl
 *
 * [email protected]
 * http://twitter.com/magnuskalkuhl
 *
 * For "About", "Important to know", "Disclaimer" and
 * "Redistribution" rules please check the text in the main() section.
 *
 * COMPILATION (ON UBUNTU LINUX)
 * -----------------------------
 *
 * - Install required GD library: sudo apt-get install libgd2-xpm-dev
 * - Compile with: gcc -std=c99 mkconvert.c -o mkconvert -lgd
 *
 * USAGE
 * -----
 *
 * ./mkconvert <source directory> <target directory>
 *
 * USEFUL LINKS
 * ------------
 *
 * - Libre office extension to export slides as PNG files:
 *   http://extensions.libreoffice.org/extension-center/export-as-images
 *   Ensure you disable antialiasing in Libre Office
 *   (Tools -> Options -> LibreOffice -> View)
 *   or text edges will look fuzzy.
 *
 * - Original mkviewer and the presentation it was used for:
 *   http://t.co/csih7QtO
 *
 * - Editor for C64 disk images: http://www.d64editor.com
 *   Windows only :(
 *
*/

#include <stdio.h>
#include <gd.h>
#include <dirent.h>
#include <string.h>

#define WIDTH       320
#define HEIGHT      200
#define PATH_MAX    4096

int grayscaleImage[WIDTH*HEIGHT];
int c64bitmap[(WIDTH*HEIGHT)/8];

int importFileAsGrayscale(char *sourceName)
    {
    // Read PNG file and turn colors into gray scale luminance
    // (range from black to white: 0 - 255)

    gdImagePtr im;

    FILE *in;
    in = fopen(sourceName, "rb");
    if (in == NULL)
        {
        printf("Failed to open image '%s'!\n",sourceName);
        return -1;
        }
    im = gdImageCreateFromPng(in);
    fclose(in);

    if (gdImageSX(im) != WIDTH || gdImageSY(im) != HEIGHT)
        {
        printf("Wrong size of '%s' (should be %i x %i, but has %i x %i)\n",
        sourceName,WIDTH,HEIGHT, gdImageSX(im),gdImageSY(im));
        return -1;
        }

    // Import image
    for (int y = 0; y < HEIGHT; y++)
        {
        for (int x = 0; x < WIDTH; x++)
            {
            int c;
            c = gdImageGetPixel(im, x, y);
            grayscaleImage[y*WIDTH+x] = (gdImageRed(im, c)+gdImageGreen(im, c)+gdImageBlue(im, c))/3;
            }
        }
    gdImageDestroy(im);
    return 0;
    }

void ditherGrayScaleIntoBlackAndWhite()
    {
    // Dither grayscale image into black (0) and white (255) pixels

    for (int y = 0; y < HEIGHT; y++)
        {
        for (int x = 0; x < WIDTH; x++)
            {
            int cMix = grayscaleImage[y*WIDTH+x];
            int cNew;

            int level = 0;
            if (cMix > 100) level = 1;
            if (cMix > 120) level = 2;
            if (cMix > 140) level = 3;
            if (cMix > 160) level = 4;

            if (level == 0) cNew = 0;

            if (level == 1)
                {
                cNew = 0;
                if ((x & 1) == 0 && (y & 1) == 0) cNew = 255;
                }

            if (level == 2)
                {
                cNew = 0;
                if (((x+y) & 1) == 0) cNew = 255;
                }

            if (level == 3)
                {
                cNew = 255;
                if ((x & 1) == 1 && (y & 1) == 0) cNew = 0;
                }

            if (level == 4) cNew = 255;

            grayscaleImage[y*WIDTH+x] = cNew;
            }
        }

    }

void convertBlackWhiteImageIntoC64Bitmap()
    {
    // Convert black/white image into real C64 bitmap

    /* Some words about C64 bitmaps:
     * Each byte contains 8 pixel (from left to right).
     * After each byte, line increases by one.
     * After eight bytes, line decreases by 8 and column increases by 8
     *
     * See below:
     *
     * BYTE  PIXELS ON SCREEN
     * 00    Line 0, Columns 0-7
     * 01    Line 1, Columns 0-7
     * 02    Line 2, Columns 0-7
     * 03    Line 3, Columns 0-7
     * 04    Line 4, Columns 0-7
     * 05    Line 5, Columns 0-7
     * 06    Line 6, Columns 0-7
     * 07    Line 7, Columns 0-7
     * 08    Line 0, Columns 8-15
     * 09    Line 1, Columns 8-15
     * 10    Line 2, Columns 8-15
     * 11    Line 3, Columns 8-15
     * ...
     */

    int xc = 0;
    int yc = 0;
    int subLine = 0;
    for (int i = 0; i < ((WIDTH*HEIGHT)/8); i++)
        {
        c64bitmap[i] =
                ((grayscaleImage[(yc+subLine)*WIDTH+xc+0] & 1) << 7)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+1] & 1) << 6)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+2] & 1) << 5)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+3] & 1) << 4)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+4] & 1) << 3)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+5] & 1) << 2)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+6] & 1) << 1)
              + ((grayscaleImage[(yc+subLine)*WIDTH+xc+7] & 1) << 0);

        subLine++;

        if (subLine == 8)
            {
            subLine = 0;
            xc = xc + 8;
            if (xc == WIDTH)
                {
                xc = 0;
                yc = yc + 8;
                }
            }
        }
    }

int compressC64Bitmap(char *targetName)
    {
    /*
     * Some words about the proprietary .pk image format:
     *
     * First two bytes: The start address ($00 $04 -> $4000) of the file
     *
     * All other bytes contain the image data:
     *
     * - Any value that is NOT 123 is taken as it is
     *   (1 Byte -> 8 Pixels, from left to right)
     * - magic byte "123" (0x7B) + n -> repeat the previous byte n times
     *                                  (n is never 0 or 1 here)
     * - magic byte 123 + 0 -> byte 123
     * - magic byte 123 + 1 -> end of file
     *
     */

    FILE *out;

    char compressedName[1000];
    sprintf(compressedName,"%s.pk",targetName);
    out = fopen(compressedName,"wb");
    if (out == NULL)
        {
        printf("Failed to create '%s'\n",compressedName);
        return -1;
        }

    // Ensure that the file is going to be loaded at $4000
    fputc(0x00,out); fputc(0x40,out);

    int lastCol = 0;

    int i = 0;

    while (i < (WIDTH*HEIGHT)/8)
        {

        // in case the color value matches the "magic byte" (123) accidentally
        if (c64bitmap[i] == 123)
            {
            fputc(123,out);
            fputc(0,out);
            lastCol = 123;
            i++;
            continue;
            }

        // find sequence of repeating bytes
        int sequenceCounter = 0;
        while (c64bitmap[i+sequenceCounter] == lastCol && sequenceCounter < 255) sequenceCounter++;

        if (sequenceCounter >= 3)
            {
            fputc(123,out);
            fputc(sequenceCounter-1,out);
            i = i + sequenceCounter;
            continue;
            }

        if (sequenceCounter > 0)
            {
            for (int p = 0; p < sequenceCounter; p++) fputc(lastCol,out);
            i = i + sequenceCounter;
            continue;
            }

        // Standard: normal byte
        fputc(c64bitmap[i],out);
        lastCol = c64bitmap[i];
        i++;
        }

    fputc(123,out); fputc(1,out); // write end-marker

    fclose(out);

    printf("Created %s\n",targetName);
    return 0;
    }

int createImageForValidation(char *targetName)
    {
    // Recreate PNG image from C64 bitmap
    gdImagePtr im;
    im = gdImageCreateTrueColor(WIDTH,HEIGHT);
    int xc = 0;
    int yc = 0;
    int subLine = 0;
    for (int i = 0; i < ((WIDTH*HEIGHT)/8); i++)
        {
        int v; int c;

        int byte = c64bitmap[i];

        v = ((byte >> 7) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+0, yc+subLine, c);
        v = ((byte >> 6) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+1, yc+subLine, c);
        v = ((byte >> 5) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+2, yc+subLine, c);
        v = ((byte >> 4) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+3, yc+subLine, c);
        v = ((byte >> 3) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+4, yc+subLine, c);
        v = ((byte >> 2) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+5, yc+subLine, c);
        v = ((byte >> 1) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+6, yc+subLine, c);
        v = ((byte >> 0) & 1)*255; c = gdTrueColor(v,v,v); gdImageSetPixel(im, xc+7, yc+subLine, c);

        subLine++;
        if (subLine == 8)
            {
            subLine = 0;
            xc = xc + 8;
            if (xc == WIDTH)
                {
                xc = 0;
                yc = yc + 8;
                }
            }

        }

    char extendedTargetName[500];
    sprintf(extendedTargetName,"%s.png",targetName);

    FILE *out = fopen(extendedTargetName,"wb");
    if (out == NULL)
        {
        printf("Failed to create %s\n",extendedTargetName);
        gdImageDestroy(im);
        return -1;
        }
    gdImagePng(im, out);
    fclose(out);
    gdImageDestroy(im);
    return 0;
    }

int processPic(char *sourceName,char *targetName)
    {
    if (importFileAsGrayscale(sourceName) != 0) return -1;
    ditherGrayScaleIntoBlackAndWhite();
    convertBlackWhiteImageIntoC64Bitmap();
    if (compressC64Bitmap(targetName) != 0) return -1;
    if (createImageForValidation(targetName) != 0) return -1;
    return 0;
    }

int processDirectory(char *sourcePath, char *targetPath)
    {
    DIR *directoryPointer = opendir(sourcePath);
    struct dirent *files;
    if (directoryPointer == NULL)
        {
        printf("Failed opening dir %s\n",sourcePath);
        return -1;
        }

    char newp[PATH_MAX];

    while ((files=readdir(directoryPointer))!=NULL)
        {
        if (!strcmp(files->d_name,".") || !strcmp(files->d_name,"..")) continue;

        if ((strlen(sourcePath)+strlen(files->d_name)+1) >= PATH_MAX)
            {
            printf("Won't read '%s/%s' as it exceeds the max. path length (%i characters).\n",sourcePath,files->d_name,PATH_MAX-1);
            continue;
            }

        sprintf(newp,"%s/%s",sourcePath,files->d_name);

        int c1 = files->d_name[strlen(files->d_name)-6]-'0';
        int c2 = files->d_name[strlen(files->d_name)-5]-'0';
        int slideNumber = (c1*10+c2);
        if (slideNumber < 1) printf("Invalid slide name: %s (expected format: NN.png, e.g. 01.png)\n", files->d_name);
        else
            {
            if ((strlen(sourcePath)+strlen(files->d_name)+1) >= PATH_MAX)
                {
                printf("Won't write '%s/%s' as it exceeds the max. path length (%i characters).\n",sourcePath,files->d_name,PATH_MAX-1);
                continue;
                }

            char outPath[PATH_MAX];
            sprintf(outPath,"%s/%.2i",targetPath,slideNumber);
            processPic(newp,outPath);
            }
        }

    closedir(directoryPointer);
    return 0;
    }

int main(int argc, char *argv[])
    {
    if (argc == 3) return processDirectory(argv[1],argv[2]);

    printf("Usage: mkconvert <source directory> <target directory>\n");
    printf("       e.g. mkconvert src out\n");
    printf("         or mkconvert --help (for disclaimer, redistribution rules etc.)\n");
    printf("\n");

    if (argc == 2)
        {
        if (strcmp(argv[1],"--help") == 0 || strcmp(argv[1],"--about") == 0)
            {
            printf("About:\n");
            printf("\"mkconvert\" was written 2012 by Magnus Kalkuhl <[email protected]>.\n");
            printf("This program reads PNG images from \"src\" directory and converts them\n");
            printf("into the proprietary .pk format that can then be read by the mkviewer on the C64.\n");
            printf("\n");
            printf("Important to know:\n");
            printf("- All source files must be named 01.png, 02.png, 03.png etc.\n");
            printf("- All source files must have a resolution of 320x200 pixel.\n");
            printf("\n");
            printf("Disclaimer:\n");
            printf("I developed this program as a quick and dirty one-time-tool for a\n");
            printf("presentation I did (see https://twitter.com/magnuskalkuhl/status/251697621931028480).\n");
            printf("It is in no way an official software release and therefore comes without any guarantees.\n");
            printf("Use at your own risk.\n");
            printf("\n");
            printf("Redistribution:\n");
            printf("Feel free to redistribute this program or improve it\n");
            printf("as long as the information about author, disclaimer and redistribution remains.\n");
            printf("\n");
            }
        }

    return 0;
    }