public static int CalculateLineSpacing(this Typeface typeface, LineSpacingChoice choice)
{
switch (choice)
{
default:
case LineSpacingChoice.Windows:
return(Calculate_BTBD_Windows(typeface));
case LineSpacingChoice.Mac:
return(CalculateBTBD_Mac(typeface));
case LineSpacingChoice.TypoMetric:
return(Calculate_TypoMetricLineSpacing(typeface));
}
}
public static int CalculateRecommendLineSpacing(this Typeface typeface, out LineSpacingChoice choice)
{
if (RecommendToUseTypoMetricsForLineSpacing(typeface))
{
choice = LineSpacingChoice.TypoMetric;
return(Calculate_TypoMetricLineSpacing(typeface));
}
else
{
//check if we are on Windows or mac
if (CurrentEnv.CurrentOSName == CurrentOSName.Mac)
{
choice = LineSpacingChoice.Mac;
return(CalculateBTBD_Mac(typeface));
}
else
{
choice = LineSpacingChoice.Windows;
return(Calculate_BTBD_Windows(typeface));
}
}
}
public static int CalculateRecommendLineSpacing(this Typeface typeface, out LineSpacingChoice choice)
{
//from https://docs.microsoft.com/en-us/typography/opentype/spec/os2#wa
//usWinAscent
//Format: uint16
//Description:
//The “Windows ascender” metric.
//This should be used to specify the height above the baseline for a clipping region.
//This is similar to the sTypoAscender field,
//and also to the ascender field in the 'hhea' table.
//There are important differences between these, however.
//In the Windows GDI implementation,
//the usWinAscent and usWinDescent values have been used to determine
//the size of the bitmap surface in the TrueType rasterizer.
//Windows GDI will clip any portion of a TrueType glyph outline that appears above the usWinAscent value.
//If any clipping is unacceptable, then the value should be set greater than or equal to yMax.
//Note: This pertains to the default position of glyphs,
//not their final position in layout after data from the GPOS or 'kern' table has been applied.
//Also, this clipping behavior also interacts with the VDMX table:
//if a VDMX table is present and there is data for the current device aspect ratio and rasterization size,
//then the VDMX data will supersede the usWinAscent and usWinDescent values.
//****
//Some legacy applications use the usWinAscent and usWinDescent values to determine default line spacing.
//This is **strongly discouraged**. The sTypo* fields should be used for this purpose.
//Note that some applications use either the usWin* values or the sTypo* values to determine default line spacing,
//depending on whether the USE_TYPO_METRICS flag (bit 7) of the fsSelection field is set.
//This may be useful to provide **compatibility with legacy documents using older fonts**,
//while also providing better and more-portable layout using newer fonts.
//See fsSelection for additional details.
//Applications that use the sTypo* fields for default line spacing can use the usWin*
//values to determine the size of a clipping region.
//Some applications use a clipping region for editing scenarios to determine what portion of the display surface to re-draw when text is edited, or how large a selection rectangle to draw when text is selected. This is an appropriate use for the usWin* values.
//Early versions of this specification suggested that the usWinAscent value be computed as the yMax
//for all characters in the Windows “ANSI” character set.
//For new fonts, the value should be determined based on the primary languages the font is designed to support,
//and **should take into consideration additional height that may be required to accommodate tall glyphs or mark positioning.***
//-----------------------------------------------------------------------------------
//usWinDescent
//Format: uint16
//Description:
//The “Windows descender” metric.This should be used to specify the vertical extent
//below the baseline for a clipping region.
//This is similar to the sTypoDescender field,
//and also to the descender field in the 'hhea' table.
//***
//There are important differences between these, however.
//Some of these differences are described below.
//In addition, the usWinDescent value treats distances below the baseline as positive values;
//thus, usWinDescent is usually a positive value, while sTypoDescender and hhea.descender are usually negative.
//In the Windows GDI implementation,
//the usWinDescent and usWinAscent values have been used
//to determine the size of the bitmap surface in the TrueType rasterizer.
//Windows GDI will clip any portion of a TrueType glyph outline that appears below(-1 × usWinDescent).
//If any clipping is unacceptable, then the value should be set greater than or equal to(-yMin).
//Note: This pertains to the default position of glyphs,
//not their final position in layout after data from the GPOS or 'kern' table has been applied.
//Also, this clipping behavior also interacts with the VDMX table:
//if a VDMX table is present and there is data for the current device aspect ratio and rasterization size,
//***then the VDMX data will supersede the usWinAscent and usWinDescent values.****
//-----------------------------------------------------------------------------------
//so ...
choice = LineSpacingChoice.TypoMetric;
return(Calculate_TypoMetricLineSpacing(typeface));
//if (RecommendToUseTypoMetricsForLineSpacing(typeface))
//{
// choice = LineSpacingChoice.TypoMetric;
// return Calculate_TypoMetricLineSpacing(typeface);
//}
//else
//{
// //check if we are on Windows or mac
// if (CurrentEnv.CurrentOSName == CurrentOSName.Mac)
// {
// choice = LineSpacingChoice.Mac;
// return CalculateBTBD_Mac(typeface);
// }
// else
// {
// choice = LineSpacingChoice.Windows;
// return Calculate_BTBD_Windows(typeface);
// }
//}
}
