High DPI
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Definition
DPI (dot per inch) is the relation between size in pixels and the actual display size. Here dot is an equivalent for pixel in printing terminology. Applications can either use pixel sizes, or take into account that actual display size. In this second cases, sizes are given in points.
On Windows Vista and further, it is possible to change the DPI ratio to make elements bigger. High DPI means any custom DPI setting with more than 96 DPI (the default setting) *.
High DPI awareness means that an application takes this DPI setting into account.
Pixels and points
For example 300 DPI means that there are 300 pixels (or dot) per inch. There are 72 points per inch, so :
300 pixels ↔ 1 inch
300/72 pixels ↔ 1 point
4.16 pixels ↔ 1 point
Now with 96 DPI :
72 pixels ↔ 1 inch
1.33 pixel ↔ 1 point
Now with 144 DPI :
144 pixels ↔ 1 inch
2 pixels ↔ 1 point
Setting High DPI in Windows
In Windows 7 go to Control Panel > Appareance and Personalization > Display. Select Smaller 100% (default), Medium 125% or Larger 150%. If you select 100% (96 DPI) is the default Windows DPI setting, not High DPI. If you select 125% (120 DPI) the option "Use Windows XP style DPI scaling" is enabled, applications you run under this setting are scaled like at Windows XP. If you select 150% (144 DPI) the option "Use Windows XP style DPI scaling" is disabled (DPI Virtualization enabled), applications you run under this setting must be High DPI Awareness else they will be scaled by the system like a blurred image. Also you can set your custom DPI setting in the option "Set custom text size (DPI)" and enable/disable the DPI Virtualization. The best way to get it is changing the settings and running applications under the different settings.
High DPI in Lazarus
With Lazarus we have to follow those steps in order to make an High DPI Awareness application for Windows 7. I'm not using ScaleBy & ScaleControls because those have a lot of bugs for this purpose.
STEP 1 - Declare High DPI Awareness
To do this we need a manifest file that includes the declaration, with the newest Lazarus subversion we can do this going to Options > Project Options > then select the options "Use Manifest to Enable Themes (Windows)" and "Dpi Aware application (for Vista +)".
Else you can copy the below code and save to a text file "manifest.xml":
<xml><?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0"> <description>Lazarus Application</description> <dependency> <dependentAssembly> <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="6.0.0.0" processorArchitecture="*" publicKeyToken="6595b64144ccf1df" language="*" /> </dependentAssembly> </dependency> <trustInfo xmlns="urn:schemas-microsoft-com:asm.v3"> <security> <requestedPrivileges> <requestedExecutionLevel level="asInvoker" uiAccess="false"/> </requestedPrivileges> </security> </trustInfo> <application xmlns="urn:schemas-microsoft-com:asm.v3"> <windowsSettings> <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true</dpiAware> </windowsSettings> </application>
</assembly></xml>
And save the below code to a text file "manifest.rc":
1 24 "manifest.xml"
Then copy those files to the main folder of your project:
MyProject\manifest.xml MyProject\manifest.rc
And include in your project:
<delphi>implementation
{$R *.lfm} {$R manifest.rc} // This includes Windows Manifest to enable Themes and High DPI</delphi>
STEP 2 - Scale Forms and Controls
To do this we can call ScaleDPI procedure OnCreate event of each form in your project.
First copy the below code and save to a text file "uscaledpi.pas":
<delphi>unit uscaledpi;
{$mode objfpc}{$H+}
interface
uses
Graphics, Controls;
procedure ScaleDPI(Control: TControl; FromDPI: Integer);
implementation
procedure ScaleDPI(Control: TControl; FromDPI: Integer); var
n: Integer; WinControl: TWinControl;
begin
with Control do begin Left:=ScaleX(Left,FromDPI); Top:=ScaleY(Top,FromDPI); Width:=ScaleX(Width,FromDPI); Height:=ScaleY(Height,FromDPI); end; if Control is TWinControl then begin WinControl:=TWinControl(Control); if WinControl.ControlCount > 0 then begin for n:=0 to WinControl.ControlCount-1 do begin if WinControl.Controls[n] is TControl then begin ScaleDPI(WinControl.Controls[n],FromDPI); end; end; end; end;
end;
end.</delphi>
Copy the "uscaledpi.pas" file to the main folder of your project:
MyProject\uscaledpi.pas
In the "uses" section of your project you need to add "uScaleDPI":
<delphi>unit form1;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, uScaleDPI; // This includes ScaleDPI procedure </delphi>
OnCreate event of each form call the procedure in this way:
<delphi>procedure TForm1.FormCreate(Sender: TObject); begin
if Screen.PixelsPerInch <> 96 then begin ScaleDPI(Self,96); // 96 is the DPI you designed the Form1 end;
end;</delphi>
External Links
- High DPI (Windows) MSDN article about High DPI