GetDC(NULL) gets primary monitor or virtual screen?

Question

Looking around the net I see that most people think that GetDC(NULL) will get a device context for the entire primary monitor (the one with 0,0 at its top left). Ho

Answer 1

It gets a DC that covers the entire virtual screen. I just tested with:

#include <windows.h>
#include <conio.h>

int main() {

    HDC screen = GetDC(NULL);

    RECT r = {-1200, 100, -200, 500};
    HBRUSH br = CreateSolidBrush(RGB(0, 255, 0));

    FillRect(screen, &r, br);

    getch();
    InvalidateRect(NULL, &r, true);

    return 0;
}

...and it successfully draws a green rectangle on my secondary screen (positioned to the left of the primary screen so it has negative X coordinates).

Answer 2

I'm currently trying to rewrite a gamma setter utility, because it is using GetDC(NULL) instead of EnumDisplayMonitors + GetDC, and as a result, changes the gamma of the entire desktop.

Your program is similar, it paints both displays black.