EDIT: I solved it. See my fix in the answer below.
I'm working on an application that should open a small popup window on each screen connected to the computer it runs on. Simple enough to do on a single screen (using WindowStartupLocation = CenterScreen), but surprisingly difficult to do on multiple screens.
My current code is this:
foreach (var s in Screen.AllScreens) //System.Windows.Forms.Screen
{
var b = s.Bounds;
var w = new PopupWindow();
var oW = w.Width; //Keep track of original size ...
var oH = w.Height;
w.Width = 0; //then set the size to 0, to avoid that the
w.Height = 0;//popup shows before it is correctly positioned
w.Show(); //Now show it, so that we can place it (when I
//tried to place it before showing, the window
//was always repositioned when Show() was called)
double dpiX = 1, dpiY = 1;
var presentationsource = PresentationSource.FromVisual(w);
if (presentationsource != null)
{
dpiX = presentationsource.CompositionTarget.TransformToDevice.M11;
dpiY = presentationsource.CompositionTarget.TransformToDevice.M22;
}
var aW = oW*dpiX; //Calculate the actual size of the window
var aH = oH*dpiY;
//***** THIS IS WRONG, SEE ANSWER *****
w.Left = (b.X + (b.Width / dpiX - aW) / 2); //Place it
w.Top = (b.Y + (b.Height / dpiY - aH) / 2);
//*************************************
w.Width = oW; //And set the size back to the original size
w.Height = oH;
}
This seems to work only on the primary screen. On the other screens, the windows are not properly centered.
I guess this is because my knowledge of WPF and DPI is very limited, and I'm probably doing something wrong. Could somebody point me in the right direction?
Of course, I managed to solve it after posting it here. Looks like I did something else wrong when I tried to divide the entire location with the DPI, which led me onto the wrong path I posted above.
The correct lines for placing the form should be this (all the other code works):
w.Left = (b.X + (b.Width - aW) / 2) / dpiX;
w.Top = (b.Y + (b.Height - aH) / 2) / dpiX;
But, I still think this is a lot of code for a simple task, so if somebody has better ideas, please let me know!
So this is the (working) code I'm using now:
foreach (var s in Screen.AllScreens) //System.Windows.Forms.Screen
{
var b = s.Bounds;
var w = new PopupWindow();
var oW = w.Width; //Keep track of original size ...
var oH = w.Height;
w.Width = 0; //then set the size to 0, to avoid that the
w.Height = 0;//popup shows before it is correctly positioned
w.Show(); //Now show it, so that we can place it (when I
//tried to place it before showing, the window
//was always repositioned when Show() was called)
double dpiX = 1, dpiY = 1;
var ps = PresentationSource.FromVisual(w);
if (ps != null)
{
dpiX = ps.CompositionTarget.TransformToDevice.M11;
dpiY = ps.CompositionTarget.TransformToDevice.M22;
}
var aW = oW*dpiX; //Calculate the actual size of the window
var aH = oH*dpiY;
w.Left = (b.X + (b.Width - aW) / 2) / dpiX;
w.Top = (b.Y + (b.Height - aH) / 2) / dpiX;
w.Width = oW; //And set the size back to the original size
w.Height = oH;
}