Implement TextStyle.letterSpacing

@@ -4,6 +4,7 @@
 
 - Allow MultiPage to relayout individual pages with support for flex
 - Implement BoxShadow for rect and circle BoxDecorations
+- Implement TextStyle.letterSpacing
 
 ## 1.8.1
 

@@ -140,7 +140,7 @@ See https://github.com/DavBfr/dart_pdf/wiki/Fonts-Management
   @Deprecated('Use `glyphMetrics` instead')
   PdfRect glyphBounds(int charCode) => glyphMetrics(charCode).toPdfRect();
 
-  PdfFontMetrics stringMetrics(String s) {
+  PdfFontMetrics stringMetrics(String s, {double letterSpacing = 0}) {
     if (s.isEmpty) {
       return PdfFontMetrics.zero;
     }
@@ -148,7 +148,7 @@ See https://github.com/DavBfr/dart_pdf/wiki/Fonts-Management
     try {
       final Uint8List chars = latin1.encode(s);
       final Iterable<PdfFontMetrics> metrics = chars.map(glyphMetrics);
-      return PdfFontMetrics.append(metrics);
+      return PdfFontMetrics.append(metrics, letterSpacing: letterSpacing);
     } catch (_) {
       assert(() {
         print(_cannotDecodeMessage);

@@ -39,7 +39,10 @@ class PdfFontMetrics {
         assert(top <= bottom),
         assert((descent ?? top) <= (ascent ?? bottom));
 
-  factory PdfFontMetrics.append(Iterable<PdfFontMetrics> metrics) {
+  factory PdfFontMetrics.append(
+    Iterable<PdfFontMetrics> metrics, {
+    double letterSpacing = 0,
+  }) {
     if (metrics.isEmpty) {
       return PdfFontMetrics.zero;
     }
@@ -51,10 +54,12 @@ class PdfFontMetrics {
     double ascent;
     double descent;
     double lastBearing;
+    double spacing;
 
     for (PdfFontMetrics metric in metrics) {
       left ??= metric.left;
-      right += metric.advanceWidth;
+      spacing = metric.advanceWidth > 0 ? letterSpacing : 0;
+      right += metric.advanceWidth + spacing;
       lastBearing = metric.rightBearing;
 
       top = math.min(top ?? metric.top, metric.top);
@@ -66,11 +71,11 @@ class PdfFontMetrics {
     return PdfFontMetrics(
         left: left,
         top: top,
-        right: right - lastBearing,
+        right: right - lastBearing - spacing,
         bottom: bottom,
         ascent: ascent,
         descent: descent,
-        advanceWidth: right);
+        advanceWidth: right - spacing);
   }
 
   static const PdfFontMetrics zero =

@@ -156,9 +156,9 @@ class PdfTtfFont extends PdfFont {
   }
 
   @override
-  PdfFontMetrics stringMetrics(String s) {
+  PdfFontMetrics stringMetrics(String s, {double letterSpacing = 0}) {
     if (s.isEmpty || !font.unicode) {
-      return super.stringMetrics(s);
+      return super.stringMetrics(s, letterSpacing: letterSpacing);
     }
 
     final Runes runes = s.runes;
@@ -166,6 +166,6 @@ class PdfTtfFont extends PdfFont {
     runes.forEach(bytes.add);
 
     final Iterable<PdfFontMetrics> metrics = bytes.map(glyphMetrics);
-    return PdfFontMetrics.append(metrics);
+    return PdfFontMetrics.append(metrics, letterSpacing: letterSpacing);
   }
 }

@@ -262,6 +262,7 @@ class _Word extends _Span {
       point.x + offset.x,
       point.y + offset.y,
       mode: style.renderingMode,
+      charSpace: style.letterSpacing,
     );
   }
 
@@ -569,12 +570,15 @@ class RichText extends Widget {
         for (int line = 0; line < spanLines.length; line++) {
           for (String word in spanLines[line].split(RegExp(r'\s'))) {
             if (word.isEmpty) {
-              offsetX += space.advanceWidth * style.wordSpacing;
+              offsetX +=
+                  space.advanceWidth * style.wordSpacing + style.letterSpacing;
               continue;
             }
 
-            final PdfFontMetrics metrics =
-                font.stringMetrics(word) * (style.fontSize * textScaleFactor);
+            final PdfFontMetrics metrics = font.stringMetrics(word,
+                    letterSpacing: style.letterSpacing /
+                        (style.fontSize * textScaleFactor)) *
+                (style.fontSize * textScaleFactor);
 
             if (offsetX + metrics.width > constraintWidth && spanCount > 0) {
               width = math.max(
@@ -583,7 +587,9 @@ class RichText extends Widget {
                     _spans.sublist(spanStart),
                     _decorations.sublist(decorationStart),
                     constraintWidth,
-                    offsetX - space.advanceWidth * style.wordSpacing,
+                    offsetX -
+                        space.advanceWidth * style.wordSpacing -
+                        style.letterSpacing,
                     false,
                     bottom,
                   ));
@@ -632,8 +638,9 @@ class RichText extends Widget {
               ),
             );
 
-            offsetX +=
-                metrics.advanceWidth + space.advanceWidth * style.wordSpacing;
+            offsetX += metrics.advanceWidth +
+                space.advanceWidth * style.wordSpacing +
+                style.letterSpacing;
           }
 
           if (softWrap && line < spanLines.length - 1) {
@@ -643,7 +650,9 @@ class RichText extends Widget {
                   _spans.sublist(spanStart),
                   _decorations.sublist(decorationStart),
                   constraintWidth,
-                  offsetX - space.advanceWidth * style.wordSpacing,
+                  offsetX -
+                      space.advanceWidth * style.wordSpacing -
+                      style.letterSpacing,
                   true,
                   bottom,
                 ));
@@ -672,7 +681,7 @@ class RichText extends Widget {
           }
         }
 
-        offsetX -= space.advanceWidth * style.wordSpacing;
+        offsetX -= space.advanceWidth * style.wordSpacing - style.letterSpacing;
       } else if (span is WidgetSpan) {
         span.child.layout(
             context,

@@ -157,10 +157,10 @@ class TextStyle {
       fontSize: _defaultFontSize,
       fontWeight: FontWeight.normal,
       fontStyle: FontStyle.normal,
-      letterSpacing: 1.0,
-      wordSpacing: 1.0,
-      lineSpacing: 0.0,
-      height: 1.0,
+      letterSpacing: 0,
+      wordSpacing: 1,
+      lineSpacing: 0,
+      height: 1,
       decoration: TextDecoration.none,
       decorationColor: null,
       decorationStyle: TextDecorationStyle.solid,

@@ -131,9 +131,12 @@ void main() {
     final String para = LoremText().paragraph(40);
 
     final List<Widget> widgets = <Widget>[];
-    for (double spacing = 0.0; spacing < 10.0; spacing += 2.0) {
+    for (double spacing = -1.0; spacing < 8.0; spacing += 2.0) {
       widgets.add(
-        Text(para, style: TextStyle(font: ttf, letterSpacing: spacing)),
+        Text(
+          '[$spacing] $para',
+          style: TextStyle(font: ttf, letterSpacing: spacing),
+        ),
       );
       widgets.add(
         SizedBox(height: 30),