Uniform: The TileBrush content is scaled to fit the tile dimensions. However, the aspect ratio of the content is preserved.
UniformToFill: The TileBrush content is scaled so that it completely fills the output area but preserves its original aspect ratio.
Fill: The TileBrush content is scaled to fit the tile. Because the content's height and width are scaled independently, the original aspect ratio of the content might not be preserved. That is, the TileBrush content might be distorted in order to completely fill the output tile.
The following image illustrates the different Stretch settings.
Different stretch settings
Note that you specify the dimensions of TileBrush content by using the Viewbox property; you specify the position and size of the TileBrush base tile by using the Viewport property.
The following illustration shows the effect of different Stretch settings on a TileBrush that has a Viewbox that is smaller than its Viewport. The parts of the image that are outside the Viewbox are tinted gray.