Magick::TypeMetric Class

Magick::TypeMetric

The TypeMetric class provides the means to pass data from the Image class's TypeMetric method to the user. It provides information regarding font metrics such as ascent, descent, text width, text height, and maximum horizontal advance. The units of these font metrics are in pixels, and that the metrics are dependent on the current Image font (default Ghostscript's "Helvetica"), pointsize (default 12 points), and x/y resolution (default 72 DPI) settings.

The pixel units may be converted to points (the standard resolution-independent measure used by the typesetting industry) via the following equation:

size_points = (size_pixels * 72)/resolution

where resolution is in dots-per-inch (DPI). This means that at the default image resolution, there is one pixel per point.

Note that a font's pointsize is only a first-order approximation of the font height (ascender + descender) in points. The relationship between the specified pointsize and the rendered font height is determined by the font designer.

See FreeType Glyph Conventions for a detailed description of font metrics related issues.

The methods available in the TypeMetric class are shown in the following table:

TypeMetric Methods
Method Returns Units Signature Description

ascent double Pixels void Returns the distance in pixels from the text baseline to the highest/upper grid coordinate used to place an outline point. Always a positive value.

descent double Pixels void Returns the the distance in pixels from the baseline to the lowest grid coordinate used to place an outline point. Always a negative value.

textWidth double Pixels void Returns text width in pixels.

textHeight double Pixels void Returns text height in pixels.

maxHorizontalAdvance double Pixels void Returns the maximum horizontal advance (advance from the beginning of a character to the beginning of the next character) in pixels.

Method	Returns	Units	Signature	Description
ascent	double	Pixels	void	Returns the distance in pixels from the text baseline to the highest/upper grid coordinate used to place an outline point. Always a positive value.
descent	double	Pixels	void	Returns the the distance in pixels from the baseline to the lowest grid coordinate used to place an outline point. Always a negative value.
textWidth	double	Pixels	void	Returns text width in pixels.
textHeight	double	Pixels	void	Returns text height in pixels.
maxHorizontalAdvance	double	Pixels	void	Returns the maximum horizontal advance (advance from the beginning of a character to the beginning of the next character) in pixels.