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.

When your code is called? in idle time? when the user moves the mouse? There are different ways to detect a red button, using FindWindow() for example. — Adriano Repetti
Btw, my code is in an infinite loop. But I want to use a color catcher whereas a offset one. So, when I start my code, it just go into the loop and check for the red button. — Manitoba
If this code is in an infinite loop, then the problem is not GetPixel. It's the fact that your app is not letting other apps have any CPU time. — tenfour
Btw, all my stuff is in a Thread. And as I said, it works well with getPixel. i'm just looking for a better way to do that — Manitoba
It doesn't work well -- you said it's slow. Without profiling data, I gave the best reason it's slow. — tenfour

Manitoba Manitoba · Accepted Answer · 2012-05-09T12:59:11

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.

Get Pixel color fastest way?

2 Answers