Text baseline & oblique option (#585)

docs/text.coffee.md

@@ -91,6 +91,8 @@ below.
 * `link` - a URL to link this text to (shortcut to create an annotation)
 * `underline` - whether to underline the text
 * `strike` - whether to strike out the text
+* `oblique` - whether to slant the text (angle in degrees or `true`)
+* `baseline` - the vertical alignment of the text with respect to its insertion point (values as [canvas textBaseline](https://www.w3schools.com/tags/canvas_textbaseline.asp))
 * `continued` - whether the text segment will be followed immediately by another segment. Useful for changing styling in the middle of a paragraph.
 * `features` - an array of [OpenType feature tags](https://www.microsoft.com/typography/otspec/featuretags.htm) to apply. If not provided, a set of defaults is used.
 

lib/font/afm.coffee

@@ -16,6 +16,8 @@ class AFMFont
     @bbox = (+e for e in @attributes['FontBBox'].split /\s+/)
     @ascender = +(@attributes['Ascender'] or 0)
     @descender = +(@attributes['Descender'] or 0)
+    @xHeight = +(@attributes['XHeight'] or 0)
+    @capHeight = +(@attributes['CapHeight'] or 0)
     @lineGap = (@bbox[3] - @bbox[1]) - (@ascender - @descender)
   
   parse: ->
@@ -192,4 +194,4 @@ class AFMFont
       udieresis     yacute         thorn          ydieresis
   '''.split(/\s+/)
     
-module.exports = AFMFont
+module.exports = AFMFont

lib/font/embedded.coffee

@@ -11,6 +11,8 @@ class EmbeddedFont extends PDFFont
     @scale = 1000 / @font.unitsPerEm
     @ascender = @font.ascent * @scale
     @descender = @font.descent * @scale
+    @xHeight = @font.xHeight * @scale
+    @capHeight = @font.capHeight * @scale
     @lineGap = @font.lineGap * @scale
     @bbox = @font.bbox
 

lib/font/standard.coffee

@@ -5,7 +5,7 @@ fs = require 'fs'
 class StandardFont extends PDFFont
   constructor: (@document, @name, @id) ->
     @font = new AFMFont STANDARD_FONTS[@name]()
-    {@ascender,@descender,@bbox,@lineGap} = @font
+    {@ascender,@descender,@bbox,@lineGap,@xHeight,@capHeight} = @font
     
   embed: ->
     @dictionary.data =

lib/mixins/text.coffee

@@ -207,6 +207,29 @@ module.exports =
           spaceWidth = @widthOfString(' ') + characterSpacing
           wordSpacing = Math.max 0, (options.lineWidth - textWidth) / Math.max(1, words.length - 1) - spaceWidth
 
+    # text baseline alignments based on http://wiki.apache.org/xmlgraphics-fop/LineLayout/AlignmentHandling
+    if typeof options.baseline is 'number'
+      dy = -options.baseline
+    else
+      switch options.baseline
+        when 'svg-middle'
+          dy = 0.5 * @_font.xHeight
+        when 'middle', 'svg-central'
+          dy = 0.5 * (@_font.descender + @_font.ascender)
+        when 'bottom', 'ideographic'
+          dy = @_font.descender
+        when 'alphabetic'
+          dy = 0;
+        when 'mathematical'
+          dy = 0.5 * @_font.ascender
+        when 'hanging'
+          dy = 0.8 * @_font.ascender
+        when 'top'
+          dy = @_font.ascender
+        else
+          dy = @_font.ascender
+      dy = dy / 1000 * @_fontSize
+
     # calculate the actual rendered width of the string after word and character spacing
     renderedWidth = options.textWidth + (wordSpacing * (options.wordCount - 1)) + (characterSpacing * (text.length - 1))
 
@@ -231,10 +254,21 @@ module.exports =
       @stroke()
       @restore()
 
-    # flip coordinate system
     @save()
+
+    # oblique (angle in degrees or boolean)
+    if options.oblique
+      if typeof options.oblique is 'number'
+        skew = -Math.tan(options.oblique * Math.PI / 180)
+      else
+        skew = -0.25
+      @transform 1, 0, 0, 1, x, y
+      @transform 1, 0, skew, 1, -skew * dy, 0
+      @transform 1, 0, 0, 1, -x, -y
+
+    # flip coordinate system
     @transform 1, 0, 0, -1, 0, @page.height
-    y = @page.height - y - (@_font.ascender / 1000 * @_fontSize)
+    y = @page.height - y - dy
 
     # add current font to page if necessary
     @page.fonts[@_font.id] ?= @_font.ref()