bitmap.h

一个OpenGL的地形算法

#include <stdlib.h>
#include <windows.h>

#define BITMAP_ID   0x4D42    // the universal bitmap ID


/*****************************************************************************
 LoadBitmapFile()

 Returns a pointer to the bitmap image of the bitmap specified by filename.
 Also returns the bitmap header information. No support for 8-bit bitmaps.
*****************************************************************************/
unsigned char *LoadBitmapFile(char *filename, BITMAPINFOHEADER *bitmapInfoHeader)
{
  FILE *filePtr;                        // the file pointer
  BITMAPFILEHEADER  bitmapFileHeader;   // bitmap file header
  unsigned char    *bitmapImage;        // bitmap image data
  unsigned int      imageIdx = 0;       // image index counter
  unsigned char     tempRGB;            // swap variable

  // open filename in "read binary" mode
  filePtr = fopen(filename, "rb");
  if (filePtr == NULL)
    return NULL;

  // read the bitmap file header
  fread(&bitmapFileHeader, sizeof(BITMAPFILEHEADER), 1, filePtr);

  // verify that this is a bitmap by checking for the universal bitmap id
  if (bitmapFileHeader.bfType != BITMAP_ID)
  {
    fclose(filePtr);
    return NULL;
  }

  // read the bitmap information header
  fread(bitmapInfoHeader, sizeof(BITMAPINFOHEADER), 1, filePtr);

  // move file pointer to beginning of bitmap data
  fseek(filePtr, bitmapFileHeader.bfOffBits, SEEK_SET);

  // allocate enough memory for the bitmap image data
  bitmapImage = (unsigned char*)malloc(bitmapInfoHeader->biSizeImage);

  // verify memory allocation
  if (!bitmapImage)
  {
    free(bitmapImage);
    fclose(filePtr);
    return NULL;
  }

  // read in the bitmap image data
  fread(bitmapImage, 1, bitmapInfoHeader->biSizeImage, filePtr);

  // make sure bitmap image data was read
  if (bitmapImage == NULL)
  {
    fclose(filePtr);
    return NULL;
  }

  // swap the R and B values to get RGB since the bitmap color format is in BGR
  for (imageIdx = 0; imageIdx < bitmapInfoHeader->biSizeImage; imageIdx+=3)
  {
    tempRGB = bitmapImage[imageIdx];
    bitmapImage[imageIdx] = bitmapImage[imageIdx + 2];
    bitmapImage[imageIdx + 2] = tempRGB;
  }

  // close the file and return the bitmap image data
  fclose(filePtr);
  return bitmapImage;
} // end LoadBitmapFile()