Lower the DPI of an application

[redman]

Is there a way to set the DPI of an application?

If I have a 7 inch device with the resolution 1280×800, I want the application to run at 800x480. Changing the canvas in Qt Creator to 800 by 480 makes the widget leaves a blank space for the rest of the pixels and the application just occupies the top-left corner. This is in landscape mode.