Question

in Windows XP, C programming language

I want to read a pixel of the screen(i.e. 1024*768 which you can see now) in fast way

I think the framebuffer is the solution.

so

I tried

#include "SDL.h"
#include <stdio.h>
#include <time.h>

SDL_Surface *screen;

int main(int argc, char *argv[])
{
  if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) 
  {
    fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
    exit(1);
  }
  screen = SDL_GetVideoSurface();
  if ( screen == NULL ) 
  {
    exit(1);
  }

  return 0;
}

but the screen seems NULL

sorry for newb question

but could somebody let me know how to access framebuffer for reading a pixel?

any possible ways are welcome

Answer 1

SDL doesn’t let you read the pixels of the desktop. It abstracts away those features since they are non-portable (for example, what would it mean on a console or embedded device to read a desktop pixel?) As a result, you will need to use the Windows API directly. It has been a while since I’ve used windows, but at least a couple of years ago the process worked something like this:

1. Get the desktop device context.

2. Read the pixel from that.

For example, the code might look something like this (again roughly speaking, I don’t use windows any more so I am not 100% here):

 HDC desktopDC = CreateDCAsNull("DISPLAY", NULL, NULL, NULL);
 int pixel=GetPixel(desktopDC, x, y);