Can not save screen shot bitmap to file using xlib - c

Question

I am trying to copy the screen to a bitmap file, I found this write XImage to .bmp file in C thread. I tried the code provided myself, but I can not make the code work. It can save a img file, but won't be able to open it. Anything wrong I am doing here?
#include <iostream>
#include <X11/Xlib.h>
#include <cstring>
#include<stdio.h>
typedef unsigned short WORD; // 2bytes
typedef unsigned long DWORD; //4bytes
typedef long LONG;
using namespace std;
void saveXImageToBitmap(XImage *pImage);
int main()
{
Display *display;
int screen;
Window root;
display = XOpenDisplay(0);
screen = DefaultScreen(display);
root = RootWindow(display, screen);
XImage *img = XGetImage(display,root,0,0,400,400,XAllPlanes(),ZPixmap);
if (img != NULL)
{
saveXImageToBitmap(img);
//save image here
}
return 0;
}
#pragma pack(push, 1)
typedef struct BITMAPFILEHEADER {
WORD bfType;
DWORD bfSize;
WORD bfReserved1;
WORD bfReserved2;
DWORD bfOffBits;
};
#pragma pack(pop)
#pragma pack (push,1)
typedef struct BITMAPINFOHEADER{
DWORD biSize;
LONG biWidth;
LONG biHeight;
WORD biPlanes;
WORD biBitCount;
DWORD biCompression;
DWORD biSizeImage;
LONG biXPelsPerMeter;
LONG biYPelsPerMeter;
DWORD biClrUsed;
DWORD biClrImportant;
};
#pragma pack(pop)
void saveXImageToBitmap(XImage *pImage)
{
BITMAPFILEHEADER bmpFileHeader;
BITMAPINFOHEADER bmpInfoHeader;
FILE *fp;
static int cnt = 0;
int dummy;
char filePath[255];
memset(&bmpFileHeader, 0, sizeof(BITMAPFILEHEADER));
memset(&bmpInfoHeader, 0, sizeof(BITMAPINFOHEADER));
bmpFileHeader.bfType = 0x4D42;
bmpFileHeader.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + pImage->width*pImage->height*4;
bmpFileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bmpFileHeader.bfReserved1 = 0;
bmpFileHeader.bfReserved2 = 0;
bmpInfoHeader.biSize = sizeof(BITMAPINFOHEADER);
bmpInfoHeader.biWidth = pImage->width;
bmpInfoHeader.biHeight = pImage->height;
bmpInfoHeader.biPlanes = 1;
bmpInfoHeader.biBitCount = 32;
dummy = (pImage->width * 3) % 4;
if((4-dummy)==4)
dummy=0;
else
dummy=4-dummy;
bmpInfoHeader.biSizeImage = ((pImage->width*3)+dummy)*pImage->height;
bmpInfoHeader.biCompression = 0;
bmpInfoHeader.biXPelsPerMeter = 0;
bmpInfoHeader.biYPelsPerMeter = 0;
bmpInfoHeader.biClrUsed = 0;
bmpInfoHeader.biClrImportant = 0;
sprintf(filePath, "bitmap%d.bmp", cnt++);
fp = fopen(filePath,"wb");
if(fp == NULL)
return;
fwrite(&bmpFileHeader, sizeof(bmpFileHeader), 1, fp);
fwrite(&bmpInfoHeader, sizeof(bmpInfoHeader), 1, fp);
fwrite(pImage->data, 4*pImage->width*pImage->height, 1, fp);
fclose(fp);
}

Answer 1

I figured it out, the struct BITMAPFILEHEADER size should be 14 based on bitmap file format, the types I was using was wrong. please check the revised code for answer
#include <iostream>
#include <X11/Xlib.h>
#include <cstring>
#include<stdio.h>
using namespace std;
void saveXImageToBitmap(XImage *pImage);
int main()
{
Display *display;
int screen;
Window root;
display = XOpenDisplay(0);
screen = DefaultScreen(display);
root = RootWindow(display, screen);
XWindowAttributes gwa;
XGetWindowAttributes(display, root, &gwa);
int width = gwa.width;
int height = gwa.height;
XImage *img = XGetImage(display,root,0,0,width,height,XAllPlanes(),ZPixmap);
if (img != NULL)
{
saveXImageToBitmap(img);
//save image here
}
return 0;
}
#pragma pack (1)
typedef struct BITMAPFILEHEADER
{
short bfType;
int bfSize;
short bfReserved1;
short bfReserved2;
int bfOffBits;
};
typedef struct BITMAPINFOHEADER
{
int biSize;
int biWidth;
int biHeight;
short biPlanes;
short biBitCount;
int biCompression;
int biSizeImage;
int biXPelsPerMeter;
int biYPelsPerMeter;
int biClrUsed;
int biClrImportant;
};
void saveXImageToBitmap(XImage *pImage)
{
BITMAPFILEHEADER bmpFileHeader;
BITMAPINFOHEADER bmpInfoHeader;
FILE *fp;
static int cnt = 0;
int dummy;
char filePath[255];
memset(&bmpFileHeader, 0, sizeof(BITMAPFILEHEADER));
memset(&bmpInfoHeader, 0, sizeof(BITMAPINFOHEADER));
bmpFileHeader.bfType = 0x4D42;
bmpFileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bmpFileHeader.bfReserved1 = 0;
bmpFileHeader.bfReserved2 = 0;
int biBitCount =32;
int dwBmpSize = ((pImage->width * biBitCount + 31) / 32) * 4 * pImage->height;
printf("size of short:%d\r\n",(int)sizeof(short));
printf("size of int:%d\r\n",(int)sizeof(int));
printf("size of long:%d\r\n",(int)sizeof(long));
printf("dwBmpSize:%d\r\n",(int)dwBmpSize);
printf("BITMAPFILEHEADER:%d\r\n",(int)sizeof(BITMAPFILEHEADER));
printf("BITMAPINFOHEADER:%d\r\n",(int)sizeof(BITMAPINFOHEADER));
bmpFileHeader.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwBmpSize;
bmpInfoHeader.biSize = sizeof(BITMAPINFOHEADER);
bmpInfoHeader.biWidth = pImage->width;
bmpInfoHeader.biHeight = pImage->height;
bmpInfoHeader.biPlanes = 1;
bmpInfoHeader.biBitCount = biBitCount;
bmpInfoHeader.biSizeImage = 0;
bmpInfoHeader.biCompression = 0;
bmpInfoHeader.biXPelsPerMeter = 0;
bmpInfoHeader.biYPelsPerMeter = 0;
bmpInfoHeader.biClrUsed = 0;
bmpInfoHeader.biClrImportant = 0;
sprintf(filePath, "bitmap%d.bmp", cnt++);
fp = fopen(filePath,"wb");
if(fp == NULL)
return;
fwrite(&bmpFileHeader, sizeof(bmpFileHeader), 1, fp);
fwrite(&bmpInfoHeader, sizeof(bmpInfoHeader), 1, fp);
fwrite(pImage->data, dwBmpSize, 1, fp);
fclose(fp);
}