Virtually all distances, coordinates and sizes in D-Type Unicode Text Module are expressed in logical units called document units. Document units are device and resolution independent and have no particular physical meaning — their interpretation is entirely up to the application.
When rendering text, D-Type Unicode Text Module uses a zoom factor and/or transformation matrices to convert document units to the output pixel coordinates. When the zoom factor multiplied by the product of all the transformation matrices applied to the current textflow area is an identity matrix, the pixel coordinates and document units are the same.
Note that the following text styling/formatting attributes have a non-zero default value (in document units):
Font Width (TX_ATTR_FONT_WIDTH) and Font Height (TX_ATTR_FONT_HEIGHT): If the font width and/or font height is not specified when creating a new text document, the default value is 36 document units. This default applies even to empty textflow areas.
Row Spacing (TX_ATTR_SPACING_ROW): If row spacing is not specified when creating a new text document, the default value is 10 document units. This default applies even to empty textflow areas.
If necessary, these default values can be changed by calling the txTextSetNumericValue function, an a per-document basis. Just remember to call txTextSetNumericValue before building the text using the txTextMakeViaStream or txTextMakeViaBuffer function.