Scaling UI with DPI change of non MFC application - winapi

Question

My application is a plug-in developed in VC++ (win32). The solutions I could find didn't work for me.
I have two options :
To disable DPI changes for my DLL plugin. That means my plug-in will not be affected with DPI changes.
To scale all the controls according to the DPI change.
Please help.
Thanks.

Answer 1

1. Disable DPI affect on my application UI when some one re-configures the DPI. Help required : If possible, how to do that pro-grammatically.
This is not possible. Adrian already told you that. DPI is a user setting, not an application setting. If the user wants to change their DPI, they can do so. They can also apply backwards-compatibility hacks that turn off high DPI for a particular application, but that functionality is not available to applications. As the developer, you're expected to make sure that you support high DPI environments, not disable it.
The only thing you can do as an app developer is to fail to indicate that your application is DPI-aware. This is roughly equivalent to walking around with an "IDIOT" sign taped to your forehead. You might find that people are slightly more accommodating of your shortcomings, but they won't have much respect for you and probably won't care to hang out with you very often. Windows will do much the same thing: it will hide the truth from you about the user's actual DPI settings (you can't handle the truth) and instead it will scale up your interface automatically to match. The effect is an ugly one.
Of course, you also say that you're creating a plug-in DLL, which changes things. DLLs can't alter the DPI-awareness of the entire process because that is determined by the host application. If the host application indicates that it is high DPI aware, then your DLL must also be high DPI aware. This is an all or nothing setting, just like the "IDIOT" sign.
2. Scale the UI of my application according to the DPI change. Help required : How to determine the current DPI and how to scale the UI accordingly? Is it necessary to scale every component or any other way to scale them automatically.
In order to correctly determine the current DPI settings, you need to indicate to Windows that you're not an idiot your application is high DPI aware. As discussed above, if you do not do this, Windows will assume that you cannot handle the truth and lie to you. But as we also established above, this probably does not apply to you because you're creating a DLL that runs in the context of another process that is already establishing itself as high DPI aware.
So, what you need to do is determine the DPI scale factor. You need that to scale your user interface elements accordingly when running in high DPI environments. The baseline DPI setting is taken to be 96. The following code scales a SIZE structure (that defines a width and height) relative to that baseline:
void ScaleDpi(SIZE& size)
{
// Determine the current screen DPI.
const HDC hDC = GetDC(NULL);
const int dpiX = GetDeviceCaps(hDC, LOGPIXELSX);
const int dpiY = GetDeviceCaps(hDC, LOGPIXELSY);
ReleaseDC(NULL, hDC);
// Perform the scaling.
size.cx = MulDiv(size.cx, dpiX, 96);
size.cy = MulDiv(size.cy, dpiY, 96);
}
However, if you follow good design practices, you may not need to scale every control manually. When defining windows and dialogs in a resource file (e.g., using the Visual Studio Dialog Editor), you specify the layout in logical units (known as DLUs, or dialog units). These units are independent of any particular DPI setting and are therefore preferable to using something like pixels. A simple dialog with a few controls therefore requires no special scaling effort. You'll only need to perform manual scaling if you're creating and/or laying out controls at run-time.
You'll find more tips and techniques on how to write high DPI aware applications on MSDN, in the Writing High-DPI Win32 Applications article. And I don't link this just to say RTFM—it's actually extremely helpful, and I highly recommend reading it all.
The folks who make the RealWorld Icon and Cursor editors also maintain a helpful article on their site: DPI-aware applications in Windows Vista and Windows 7.