Win81+ GetWindowRect Not Including Complete Drag A

I am trying to get the width and height of all the windows. I did this easily with GetWindowRect however the styling in Win8.1+ seems such that there is a border on some windows and thats not being included. When I move/drag the window, this area moves with the window, so I expected it would be apart of its geometry. Is this known? Is there away to include the border width?

New Example

I created a second screenshot to explain after I see some confusion in the comments.

I have two windows side by side as seen in this image here:

Now if I take the GetWindowRect of the left and right windows, it should be a continuous rectangle around both of thse windows. However in the below we see this is not the case. I put a black fade over the whole desktop and cut out just the parts of the GetWindowRect for each window, we see the left window GetWindowRect is a bit smaller, this is my problem.

Old Example

For example this is a screenshot, using the cleared/non-black curtain area is what GetWindowRect identified as the width height, x and y:

We see there is some area of the window not included, I think this is the border? I used photoshop here to put a blue border around what all should have been:

And just for clarity I put an inner red border to show that the area between the red and blue borders was what should have been included, but was not:

Does anyone know how to include this "border" in the GetWindowRect?

Yes, GetWindowRect() lies to you. As you found out. It is a necessary lie. Goes back to Vista, the first Windows version that gave resizable windows their fat border. A pretty necessary feature, high screen resolutions were getting pretty common and the traditional 2-pixel border was getting too hard to hit with a mouse.

That created a massive compatibility problem however, many programs that create a window use CreateWindowEx(), you specify the outer window size. And don't use AdjustWindowRectEx(), the function that you must use to calculate the window size you need. Necessary because almost every window actually cares about the client size of the window. The part you fill with content. If they would have done nothing then legacy programs would end up creating windows with a client area that is too small, no longer fitting the content or aligning it out of whack. Very, very ugly.

So GetWindowRect() lies and pretends that the window has the traditional 2-pixel border. Pretty consistent lie, if you ask for the border size with GetSystemMetrics() then you get 2 back, even though it is 5. All works pretty well, until you start caring about positioning windows next to each other. Impossible to lie about that.

Turning off the lies requires letting Windows know that you are aware of the consequences of the fat borders. And know how to deal with Aero being turned off, possible on Vista and Win7. You must select the sub-system version number in the EXE file header and pick at least 6.00. The vast majority of programs use the legacy value, 4.00. Exactly how that's done depends on your tooling, for the Microsoft linker it is the /SUBSYSTEM option. It can be changed after the program was built with Editbin.exe, /SUBSYSTEM option. The program will no longer run on XP and earlier.

Windows 10 took an interesting new approach to this problem. The skinny borders are back. But now with a much bigger drop-shadow, the mouse is active beyond the border, even for windows that don't have a shadow. Works pretty well, hopefully we can all forget about this appcompat detail soon :)