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How to ensure that your application displays properly on high-DPI displays

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Although DirectWrite addresses many high-DPI issues for you, there are two steps you should take to ensure that your application works properly on high-DPI displays.

Step 1: Use the window's own DPI after creating it

This can be done by using Direct2D or by using GDI.

Direct2D

The GetDpiForWindow function retrieves the dots per inch (dpi) value for a specified window. To use that value to set the width of a window, use the following formula:

<DPI> * <width, in pixels> / <default DPI>

...where DPI is the value retrived by GetDpiForWindow, and default DPI is 96. The formula is similar for the vertical axis:

<DPI> * <height, in pixels> / <default vertical DPI>

The code example in step 2.3 of Create a simple Direct2D application retrieves a window's DPI, and then sets its size to 640 × 480, scaled to the DPI.

Note

For a Universal Windows Platform (UWP) app, you can use the DisplayInformation::LogicalDpi property.

GDI

GDI provides the GetDeviceCaps function for retrieving device information. You can retrieve DPI information by passing the LOGPIXELSX and LOGPIXELSY index values. The formula for determining the horizontal and vertical size of a window is the same as with the Direct2D example above.

The following code uses the GetDeviceCaps function to create a 640 x 480 window, scaled to the system DPI.

FLOAT dpiX, dpiY;

HDC screen = GetDC(0);
dpiX = static_cast<FLOAT>(GetDeviceCaps(screen, LOGPIXELSX));
dpiY = static_cast<FLOAT>(GetDeviceCaps(screen, LOGPIXELSY));
ReleaseDC(0, screen);

hWnd = CreateWindow(
    TEXT("DirectWriteApp"),
    TEXT("DirectWrite Demo App"),
    WS_OVERLAPPEDWINDOW,
    CW_USEDEFAULT,
    CW_USEDEFAULT,
    static_cast<INT>(dpiX * 640.f / 96.f),
    static_cast<INT>(dpiY * 480.f / 96.f),
    NULL,
    NULL,
    hInstance,
    NULL);

Step 2: Declare that the application is DPI-aware

When an application declares itself to be DPI-aware, it is a statement specifying that the application behaves well at DPI settings up to 200 DPI. In Windows Vista and Windows 7, when DPI virtualization is enabled, applications that are not DPI-aware are scaled, and applications receive virtualized data from the system APIs, such as the GetSystemMetric function. To declare that your application is DPI-aware, complete the following steps.

  1. Create a file called DeclareDPIAware.manifest.

  2. Copy the following xml into the file and save it:

    <assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3" >
  <asmv3:application>
    <asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
      <dpiAware>true</dpiAware>
    </asmv3:windowsSettings>
  </asmv3:application>
</assembly>

  3. In the project's .vcproj file, add the following entry inside each Configuration element under VisualStudioProject/Configurations:

    <Tool
    Name="VCManifestTool"
    AdditionalManifestFiles="DeclareDPIAware.manifest"/>