Programatically take screen shots and save as PNG - winapi

Question

I've been using the following code for quite a while:
#include <fstream>
#include <gdiplus.h>
#include <windows.h>
#include <iostream>
using namespace std;
void CaptureScreen(const char* filename)
{
HDC hScreenDC = GetDC(0);
HDC hMemoryDC = CreateCompatibleDC(hScreenDC);
int upper_left_x = GetSystemMetrics(SM_XVIRTUALSCREEN);
int upper_left_y = GetSystemMetrics(SM_YVIRTUALSCREEN);
int bitmap_dx = GetSystemMetrics(SM_CXVIRTUALSCREEN ) * 1.25f;
int bitmap_dy = GetSystemMetrics(SM_CYVIRTUALSCREEN ) * 1.25f;
// create file
ofstream file(filename, ios::binary);
if(!file) return;
// save bitmap file headers
BITMAPFILEHEADER fileHeader;
BITMAPINFOHEADER infoHeader;
fileHeader.bfType = 0x4d42;
fileHeader.bfSize = 0;
fileHeader.bfReserved1 = 0;
fileHeader.bfReserved2 = 0;
fileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
infoHeader.biSize = sizeof(infoHeader);
infoHeader.biWidth = bitmap_dx;
infoHeader.biHeight = -bitmap_dy;
infoHeader.biPlanes = 1;
infoHeader.biBitCount = 16;
infoHeader.biCompression = BI_RGB;
infoHeader.biSizeImage = 0;
infoHeader.biXPelsPerMeter = 0;
infoHeader.biYPelsPerMeter = 0;
infoHeader.biClrUsed = 0;
infoHeader.biClrImportant = 0;
file.write((char*)&fileHeader, sizeof(fileHeader));
file.write((char*)&infoHeader, sizeof(infoHeader));
// dibsection information
BITMAPINFO info;
info.bmiHeader = infoHeader;
// ------------------
// THE IMPORTANT CODE
// ------------------
// create a dibsection and blit the window contents to the bitmap
BYTE* memory = 0;
HBITMAP bitmap = CreateDIBSection(hScreenDC, &info, DIB_RGB_COLORS, (void**)&memory, 0, 0);
SelectObject(hMemoryDC, bitmap);
BitBlt(hMemoryDC, 0, 0, bitmap_dx, bitmap_dy, hScreenDC, upper_left_x, upper_left_y, SRCCOPY);
DeleteDC(hMemoryDC);
ReleaseDC(NULL, hScreenDC);
// save dibsection data
int bytes = (((16*bitmap_dx + 31) & (~31))/8)*bitmap_dy;
file.write((const char *)memory, bytes);
DeleteObject(bitmap);
}
int main()
{
CaptureScreen("ok.jpg");
return 0;
}
But it seems to generate a too large BMP file because the bitmaps are saved uncompressed.
I'm looking for a way to capture a screen shot and save it to a buffer in PNG format, send it over a TCP connection and save it as a PNG file there.
I believe it has something to do with assigning BI_PNG to infoHeader.biCompression and a different calculation of bytes but I can't figure exactly what.

Answer 1

http://lodev.org/lodepng/
#include <fstream>
#include <gdiplus.h>
#include <windows.h>
#include <iostream>
#include "lodepng.h"
const int bits_per_pixel = 24;
using namespace std;
void CaptureScreen(const char* filename)
{
HDC hScreenDC = GetDC(0);
HDC hMemoryDC = CreateCompatibleDC(hScreenDC);
int upper_left_x = GetSystemMetrics(SM_XVIRTUALSCREEN);
int upper_left_y = GetSystemMetrics(SM_YVIRTUALSCREEN);
int bitmap_dx = GetSystemMetrics(SM_CXVIRTUALSCREEN ) * 1.25f;
int bitmap_dy = GetSystemMetrics(SM_CYVIRTUALSCREEN ) * 1.25f;
// create file
ofstream file(filename, ios::binary);
if(!file) return;
// save bitmap file headers
BITMAPFILEHEADER fileHeader;
BITMAPINFOHEADER infoHeader;
fileHeader.bfType = 0x4d42;
fileHeader.bfSize = 0;
fileHeader.bfReserved1 = 0;
fileHeader.bfReserved2 = 0;
fileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
infoHeader.biSize = sizeof(infoHeader);
infoHeader.biWidth = bitmap_dx;
infoHeader.biHeight = -bitmap_dy;
infoHeader.biPlanes = 1;
infoHeader.biBitCount = bits_per_pixel;
infoHeader.biCompression = BI_RGB;
infoHeader.biSizeImage = 0;
infoHeader.biXPelsPerMeter = 0;
infoHeader.biYPelsPerMeter = 0;
infoHeader.biClrUsed = 0;
infoHeader.biClrImportant = 0;
file.write((char*)&fileHeader, sizeof(fileHeader));
file.write((char*)&infoHeader, sizeof(infoHeader));
// dibsection information
BITMAPINFO info;
info.bmiHeader = infoHeader;
// ------------------
// THE IMPORTANT CODE
// ------------------
// create a dibsection and blit the window contents to the bitmap
BYTE* memory = 0;
HBITMAP bitmap = CreateDIBSection(hScreenDC, &info, DIB_RGB_COLORS, (void**)&memory, 0, 0);
SelectObject(hMemoryDC, bitmap);
BitBlt(hMemoryDC, 0, 0, bitmap_dx, bitmap_dy, hScreenDC, upper_left_x, upper_left_y, SRCCOPY);
DeleteDC(hMemoryDC);
ReleaseDC(NULL, hScreenDC);
// save dibsection data
int bytes = (((bits_per_pixel*bitmap_dx + 31) & (~31))/8)*bitmap_dy;
file.write((const char *)memory, bytes);
unsigned char *out_buffer;
size_t out_buffer_len;
unsigned error;
if ( bits_per_pixel == 24 )
{
// convert memory from bgr format to rgb
for ( unsigned i = 0; i< bytes-2; i+=3)
{
int tmp = memory[i+2];
memory[i+2] = memory[i];
memory[i] = tmp;
}
error = lodepng_encode24(&out_buffer,
&out_buffer_len,
memory,
bitmap_dx,
bitmap_dy);
}
if ( bits_per_pixel == 32 )
{
// convert memory from bgr format to rgb
for ( unsigned i = 0; i< bytes-3; i+=4)
{
int tmp = memory[i+2];
memory[i+2] = memory[i];
memory[i] = tmp;
}
error = lodepng_encode32(&out_buffer,
&out_buffer_len,
memory,
bitmap_dx,
bitmap_dy);
}
if ( error )
{
std::cout << "error: " << error << '\n';
return;
}
lodepng_save_file(out_buffer, out_buffer_len, "stam.png");
// free(out);
DeleteObject(bitmap);
}
int main()
{
CaptureScreen("ok.jpg");
return 0;
}