How to draw something in DrawingVisual with millimeter unit instead of pixels?

Question

I'm trying to draw something in a System.Windows.Media.DrawingVisual but I need to draw thins in millimeter unit. How can I do that?

Answer 1

In WPF, you can't even draw something in pixel units without at least some extra effort. WPF uses "device independent units" where each unit is 1/96th of an inch. Even that is only a theoretical relationship, as it depends on the display device correctly reporting its resolution, which in turn is dependent on the display, its configuration, and what the user has set e.g. in the "large fonts" setting (i.e. in the screen resolution settings, clicking the link that reads "Make text and other items larger or smaller").

All of these affect WPF's interpretation of the available display resolution information, which in turn affect how WPF chooses to render its "device independent" 1/96th of a inch units.

The bottom line is that the link commenter Sheridan offered really is the closest you can come to displaying in millimeters, barring a lot of extra work and help from the user. By scaling your input units, intended as millimeters, by the factor value provided (i.e. 96/ 25.4…in the expression, you can see the 25.4 to convert from millimeters to inches, then the 96 that converts inches to 1/96ths of an inch), you can convert your millimeters into the 96 dpi units that WPF uses natively.

Assuming the display is configured correctly (an optimistic assumption, but it does happen :) ), this will result in reasonably accurate presentation on the screen according to your desired millimeter-based dimensions.

Note that you can accomplish this scaling through the use of a transform on your rendered UI elements. The easiest thing to do would be to set the LayoutTransform property of the outer-most container object where you want the millimeter-based rendering. Then you can just lay out your objects in that container using the millimeters values for their location and size, and WPF will use the transform to present the container and the rendered objects within at the scale you want.