Execution time of GetDC on Windows 8

Question

Im trying to check if there pixel with white (#FFFFFF) or green (#00FF00) color of the screen's region. Usualy its 500x500 (250'000 pixels). Im checking every 5th pixel:

x := iMRXDef; // starting region coordinates
y := iMRYDef;
while DoMR do // global boolean variable
  begin
    inc(x, 4);
    if x >= iMRXMax then  // ending region coordinates
      if y < iMRYMax then
        begin
          inc(y, 4);
          x := iMRXDef;
        end
      else
        begin
          x := iMRXDef;
          y := iMRYDef;
        end;
    DC := GetDC(0);
    ColorValue := GetPixel(DC, X, Y);
    ReleaseDC(0, DC);
    if (ColorValue = iMRColorV) or (ColorValue = iMRColorV2) then
      begin
        performClick(X, Y); // clicking by SendInput.
        x := x + 30; // skip some area
        y := y + 20;
        sleep(500);
      end;
  end;

For some reason, on win8 running my programm takes a lot of time (couple of minutes) whilst on win7 its about couple of seconds. What causes this difference?

Answer 1

Take a screenshot of the area you're interested in and read the pixels from that bitmap. Then access the pixels from the scanlines property of the bitmap if possible. Should be a lot faster.

GetPixel is generally not a fast function. And some Windows 8 screen dpi changes can also slow down graphics quite a lot. So it is hard to tell what is slowing down your code. You'd have to profile your code if you want to know which part is so much slower on this Win8 PC.