Get Pixel color fastest way?

Question

I'm trying to make an auto-cliker for an windows app. It works well, but it's incredibly slow! I'm currently using the method "getPixel" which reloads an array everytime it's called.

Here is my current code:

hdc = GetDC(HWND_DESKTOP);
bx = GetSystemMetrics(SM_CXSCREEN);
by = GetSystemMetrics(SM_CYSCREEN);
start_bx = (bx/2) - (MAX_WIDTH/2);
start_by = (by/2) - (MAX_HEIGHT/2);
end_bx = (bx/2) + (MAX_WIDTH/2);
end_by = (by/2) + (MAX_HEIGHT/2);

for(y=start_by; y<end_by; y+=10)
{   
    for(x=start_bx; x<end_bx; x+=10)
    {
        pixel = GetPixel(*hdc, x, y);
        if(pixel==RGB(255, 0, 0))
        {
            SetCursorPos(x,y);
            mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
            Sleep(50);
            mouse_event(MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
            Sleep(25);
        }
    }
}

So basically, it just scan a range of pixel in the screen and starts a mouse event if it detects a red button.

I know there are other ways to get the pixel color, such as bitblt. But I've made some researches, and I don't understand how I'm supposed to do, in order to scan a color array. I need something which scans screen very fast in order to catch the button.

Could you please help me?

Thanks.

Answer 1

The simple answer is that if this is the method you insist on using then there isn't much to optimize. As others have pointed out in comments, you should probably use a different method for locating the area to click. Have a look at using FindWindow, for example.

If you don't want to change your method, then at least sleep your thread for a bit after each complete screen scan.

Answer 2

I found a perfect way which is clearly faster than the GetPixel one:

HDC hdc, hdcTemp;
RECT rect;
BYTE* bitPointer;
int x, y;
int red, green, blue, alpha;

while(true)
{
    hdc = GetDC(HWND_DESKTOP);
    GetWindowRect(hWND_Desktop, &rect);
            int MAX_WIDTH = rect.right;
        int MAX_HEIGHT = rect.bottom;

    hdcTemp = CreateCompatibleDC(hdc);
    BITMAPINFO bitmap;
    bitmap.bmiHeader.biSize = sizeof(bitmap.bmiHeader);
    bitmap.bmiHeader.biWidth = MAX_WIDTH;
    bitmap.bmiHeader.biHeight = MAX_HEIGHT;
    bitmap.bmiHeader.biPlanes = 1;
    bitmap.bmiHeader.biBitCount = 32;
    bitmap.bmiHeader.biCompression = BI_RGB;
    bitmap.bmiHeader.biSizeImage = MAX_WIDTH * 4 * MAX_HEIGHT;
    bitmap.bmiHeader.biClrUsed = 0;
    bitmap.bmiHeader.biClrImportant = 0;
    HBITMAP hBitmap2 = CreateDIBSection(hdcTemp, &bitmap, DIB_RGB_COLORS, (void**)(&bitPointer), NULL, NULL);
    SelectObject(hdcTemp, hBitmap2);
    BitBlt(hdcTemp, 0, 0, MAX_WIDTH, MAX_HEIGHT, hdc, 0, 0, SRCCOPY);

    for (int i=0; i<(MAX_WIDTH * 4 * MAX_HEIGHT); i+=4)
    {
        red = (int)bitPointer[i];
        green = (int)bitPointer[i+1];
        blue = (int)bitPointer[i+2];
        alpha = (int)bitPointer[i+3];

        x = i / (4 * MAX_HEIGHT);
        y = i / (4 * MAX_WIDTH);

        if (red == 255 && green == 0 && blue == 0)
        {
            SetCursorPos(x,y);
            mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
            Sleep(50);
            mouse_event(MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
            Sleep(25);
        }
    }
}

I hope this could help someone else.