The density value for specifying the compactness of various UI components.
Density, in the context of a UI, is the vertical and horizontal "compactness" of the elements in the UI. It is unitless, since it means different things to different UI elements. For buttons, it affects the spacing around the centered label of the button. For lists, it affects the distance between baselines of entries in the list.
Typically, density values are integral, but any value in range may be used. The range includes values from VisualDensity.minimumDensity (which is -4), to VisualDensity.maximumDensity (which is 4), inclusive, where negative values indicate a denser, more compact, UI, and positive values indicate a less dense, more expanded, UI. If a component doesn't support the value given, it will clamp to the nearest supported value.
The default for visual densities is zero for both vertical and horizontal densities, which corresponds to the default visual density of components in the Material Design specification.
As a rule of thumb, a change of 1 or -1 in density corresponds to 4 logical pixels. However, this is not a strict relationship since components interpret the density values appropriately for their needs.
A larger value translates to a spacing increase (less dense), and a smaller value translates to a spacing decrease (more dense).
In Material Design 3, the visualDensity does not override the value of
IconButton.visualDensity which defaults to VisualDensity.standard
for all platforms. To override the default value of IconButton.visualDensity,
final VisualDensity visualDensity;