Save memory bitmap data into a .bmp file

save_bmp.cpp

//typedef's to adapter to struct BMP_FILEHDR & BMP_INFOHDR;
typedef unsigned char UINT8;
typedef signed char SINT8;
typedef unsigned short UINT16;
typedef signed short SINT16;
typedef unsigned int UINT32;
typedef signed int SINT32;

//struct BMP_FILEHDR & BMP_INFOHDR defines are copied from Win32 .h files;
struct BMP_FILEHDR // BMP file header
{
    UINT32  bfSize;      // size of file
    UINT16  bfReserved1;
    UINT16  bfReserved2;
    UINT32  bfOffBits;   // pointer to the pixmap bits
};

struct BMP_INFOHDR // BMP information header
{
    UINT32  biSize;            // size of this struct
    UINT32  biWidth;           // pixmap width
    UINT32  biHeight;          // pixmap height
    UINT16  biPlanes;          // should be 1
    UINT16  biBitCount;        // number of bits per pixel
    UINT32  biCompression;     // compression method
    UINT32  biSizeImage;       // size of image
    UINT32  biXPelsPerMeter;   // horizontal resolution
    UINT32  biYPelsPerMeter;   // vertical resolution
    UINT32  biClrUsed;         // number of colors used
    UINT32  biClrImportant;    // number of important colors
};
#define BitmapColorGetA(color)      (((color) >> 24) & 0xFF)
#define BitmapColorGetR(color)      (((color) >> 16) & 0xFF)
#define BitmapColorGetG(color)      (((color) >>  8) & 0xFF)
#define BitmapColorGetB(color)      (((color) >>  0) & 0xFF)

//当前以result.bmp输出，忽略img_path参数！！
int saveToBMPFile(char* img_data, int width, int height, int stride, const char* img_path){
    //Normally, width*4 == stride
    //virtual PixelFormat& GetPixelFormat() =0; //assume pf is ARGB;
    FILE* fp = fopen(img_path, "wb");
    if(!fp){
        printf("fopen error!\n");
        return -1;
    }
    SINT32 bpl=width*4;
    // BMP file header.
    BMP_FILEHDR fhdr;
    fputc('B', fp);
    fputc('M', fp);
    fhdr.bfReserved1=fhdr.bfReserved2=0;
    fhdr.bfOffBits=14+40; // File header size + header size.
    fhdr.bfSize=fhdr.bfOffBits+bpl*height;
    fwrite(&fhdr, 1, 12, fp);

    // BMP header.
    BMP_INFOHDR bhdr;
    bhdr.biSize=40;
    bhdr.biBitCount=32;
    bhdr.biCompression=0; // RGB Format.
    bhdr.biPlanes=1;
    bhdr.biWidth=bmpWidth;
    bhdr.biHeight=height;
    bhdr.biClrImportant=0;
    bhdr.biClrUsed=0;
    bhdr.biXPelsPerMeter=2384;
    bhdr.biYPelsPerMeter=2384;
    bhdr.biSizeImage=bpl*height;
    fwrite(&bhdr, 1, 40, fp);

    // BMP data.
    //for(UINT32 y=0; y<m_height; y++)
    for(SINT32 y=height-1; y>=0; y--) //I hate this, But BMP file stores data from image's bottom to up;
    {
        SINT32 base=data+stride;
        for(SINT32 x=0; x<(SINT32)width; x++)
        {
            UINT32 i=base+x*4;
            UINT32 pixelData = *(UINT32*)(data + i);
            UINT8 b=BitmapColorGetB(pixelData);
            UINT8 g=BitmapColorGetG(pixelData);
            UINT8 r=BitmapColorGetR(pixelData);
            UINT8 a=BitmapColorGetA(pixelData);
            r=r*a/255;
            g=g*a/255;
            b=b*a/255;//BMP does not supper alpha bits;
            UINT32 colorData=(a<<24)|(r<<16)|(g<<8)|b;//a bmp pixel in little endian is B、G、R、A
            fwrite(&colorData, 4, 1, fp);
        }
    }

    fflush(fp);
    fclose(fp);
    return 1;
}