dos-vga-arena-shooter-game/bmp_loader.c

#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <dos.h>

#include "bmp_loader.h"
#include "pc_stuff.h"
#include "vga.h"

int readBMPHeader(FILE *fh, struct BMPImage *info) {
  int sizeOfHeader;
  unsigned int numberOfUsedColors;

  if ((fgetc(fh) != 'B') || (fgetc(fh) != 'M')) {
    printf("Not a BMP file\n");
    return 1;
  }

  fseek(fh, 12, SEEK_CUR);

  fread(&sizeOfHeader, sizeof(int), 1, fh);
  fread(&info->width, sizeof(int), 1, fh);
  fread(&info->height, sizeof(int), 1, fh);
  fseek(fh, 2, SEEK_CUR);
  fread(&info->bpp, sizeof(word), 1, fh);

  // for gimp, you need to add colors to the color map until it hits
  // 16 colors, then the image will be a 256 color, 8 bpp image
  //
  // https://www.gimp-forum.net/Thread-indexing-into-8-bit?pid=13233#pid13233
  if (info->bpp != 8) return 1;

  fseek(fh, 16, SEEK_CUR);
  fread(&numberOfUsedColors, sizeof(unsigned int), 1, fh);
  if (numberOfUsedColors > 256) return 1;

  // get down to color data
  fseek(fh, 14 + sizeOfHeader, SEEK_SET);

  fread(info->colors, sizeof(struct BMPColor), numberOfUsedColors, fh);

  return 0;
}

int readBMPIntoMemory(FILE *fh, struct BMPImage *info) {
  int x, y, plane;
  int result;
  byte *currentPointer;

  result = readBMPHeader(fh, info);
  if (result) return result;

  currentPointer = info->memoryStart;

  for (y = 0; y < info->height; ++y) {
    for (x = 0; x < info->width; ++x) {
      currentPointer[(info->height - 1 - y) * info->width + x] = fgetc(fh);
    }
  }

  return 0;
}

int readBMPIntoUnchainedMemory(FILE *fh, struct BMPImage* info) {
  int x, y, plane;
  int writeX, writeY, offset;
  int unchainedLineWidth;
  int result;
  byte *rowHolder;

  result = readBMPHeader(fh, info);
  if (result) return result;

  unchainedLineWidth = info->width / 4;

  // reserve a row's worth of data
  // read the bitmap data into the row, interleaving for planes
  // for each plane, memcpy the data to the plane
  for (y = 0; y < info->height; ++y) {
    writeY = ((info->height - 1) - y) * unchainedLineWidth;

    for (x = 0; x < info->width; ++x) {
      plane = x & 0x03;
      writeX = (x >> 2);

      offset = plane * (unchainedLineWidth * info->height);

      info->memoryStart[offset + writeY + writeX] = fgetc(fh);
    }
  }

  return 0;
}

int readBMPIntoUnchainedVGAMemory(FILE *fh, struct BMPImage* info) {
  int x, y, plane;
  int unchainedLineWidth;
  int result;
  byte *rowHolder;

  result = readBMPHeader(fh, info);
  if (result) return result;

  rowHolder = malloc(info->width);
  unchainedLineWidth = info->width / 4;

  // reserve a row's worth of data
  // read the bitmap data into the row, interleaving for planes
  // for each plane, memcpy the data to the plane
  for (y = 0; y < info->height; ++y) {
    for (x = 0; x < info->width; ++x) {
      rowHolder[((x & 3) * 80) + (x >> 2)] = fgetc(fh);
    }

    for (plane = 0; plane < 4; ++plane) {
      setActiveVGAMemoryPlanes(1 << plane);

      memcpy(info->memoryStart + ((info->height - 1) - y) * info->width / 4, rowHolder + unchainedLineWidth * plane, unchainedLineWidth);
    }
  }

  free(rowHolder);

  return 0;
}

void bmp256ColorPaletteToVGAColorPalette(struct BMPImage* bmpImage, struct VGAColor colors[]) {
  int i;

  for (i = 0; i < 256; ++i) {
    colors[i].red = bmpImage->colors[i].red >> 2;
    colors[i].green = bmpImage->colors[i].green >> 2;
    colors[i].blue = bmpImage->colors[i].blue >> 2;
  }
}