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

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

#include "bmpload.h"
#include "system/pc_stuff.h"
#include "system/vga.h"

int readBMPHeader(FILE *fh, struct BMPImage *info) {
  int sizeOfHeader;
  char value;
  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 readBMPIntoNewMemory(FILE *fh, struct BMPImage *info) {
  int result;

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

  info->memoryStart = malloc(info->width * info->height);

  return readBMPIntoMemory(fh, info);
}

void freeBMP(struct BMPImage *info) {
  free(info->memoryStart);
}

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

  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;
}

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;
  }
}