Fix text spacing with vertical fonts (#6387)

According to the PDF spec 5.3.2, a positive value means in horizontal,
that the next glyph is further to the left (so narrower), and in
vertical that it is further down (so wider).
This change fixes the way PDF.js has interpreted the value.

src/core/evaluator.js

@@ -731,11 +731,12 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
               var arr = args[0];
               var combinedGlyphs = [];
               var arrLength = arr.length;
+              var state = stateManager.state;
               for (i = 0; i < arrLength; ++i) {
                 var arrItem = arr[i];
                 if (isString(arrItem)) {
                   Array.prototype.push.apply(combinedGlyphs,
-                    self.handleText(arrItem, stateManager.state));
+                    self.handleText(arrItem, state));
                 } else if (isNum(arrItem)) {
                   combinedGlyphs.push(arrItem);
                 }
@@ -1131,17 +1132,26 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
                 if (typeof items[j] === 'string') {
                   buildTextGeometry(items[j], textChunk);
                 } else {
-                  var val = items[j] / 1000;
-                  if (!textState.font.vertical) {
-                    offset = -val * textState.fontSize * textState.textHScale *
-                      textState.textMatrix[0];
-                    textState.translateTextMatrix(offset, 0);
-                    textChunk.width += offset;
-                  } else {
-                    offset = -val * textState.fontSize *
-                      textState.textMatrix[3];
+                  // PDF Specification 5.3.2 states:
+                  // The number is expressed in thousandths of a unit of text
+                  // space.
+                  // This amount is subtracted from the current horizontal or
+                  // vertical coordinate, depending on the writing mode.
+                  // In the default coordinate system, a positive adjustment
+                  // has the effect of moving the next glyph painted either to
+                  // the left or down by the given amount.
+                  var val = items[j] * textState.fontSize / 1000;
+                  if (textState.font.vertical) {
+                    offset = val * textState.textMatrix[3];
                     textState.translateTextMatrix(0, offset);
+                    // Value needs to be added to height to paint down.
                     textChunk.height += offset;
+                  } else {
+                    offset = val * textState.textHScale *
+                                   textState.textMatrix[0];
+                    textState.translateTextMatrix(offset, 0);
+                    // Value needs to be subtracted from width to paint left.
+                    textChunk.width -= offset;
                   }
                   if (items[j] < 0 && textState.font.spaceWidth > 0) {
                     var fakeSpaces = -items[j] / textState.font.spaceWidth;

src/display/canvas.js

@@ -1360,6 +1360,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       var textHScale = current.textHScale * fontDirection;
       var glyphsLength = glyphs.length;
       var vertical = font.vertical;
+      var spacingDir = vertical ? 1 : -1;
       var defaultVMetrics = font.defaultVMetrics;
       var widthAdvanceScale = fontSize * current.fontMatrix[0];
 
@@ -1406,7 +1407,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
           x += fontDirection * wordSpacing;
           continue;
         } else if (isNum(glyph)) {
-          x += -glyph * fontSize * 0.001;
+          x += spacingDir * glyph * fontSize / 1000;
           continue;
         }
 
@@ -1476,6 +1477,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       var font = current.font;
       var fontSize = current.fontSize;
       var fontDirection = current.fontDirection;
+      var spacingDir = font.vertical ? 1 : -1;
       var charSpacing = current.charSpacing;
       var wordSpacing = current.wordSpacing;
       var textHScale = current.textHScale * fontDirection;
@@ -1483,7 +1485,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       var glyphsLength = glyphs.length;
       var isTextInvisible =
         current.textRenderingMode === TextRenderingMode.INVISIBLE;
-      var i, glyph, width;
+      var i, glyph, width, spacingLength;
 
       if (isTextInvisible || fontSize === 0) {
         return;
@@ -1504,7 +1506,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
           current.x += wordSpacing * textHScale;
           continue;
         } else if (isNum(glyph)) {
-          var spacingLength = -glyph * 0.001 * fontSize;
+          spacingLength = spacingDir * glyph * fontSize / 1000;
           this.ctx.translate(spacingLength, 0);
           current.x += spacingLength * textHScale;
           continue;

test/pdfs/.gitignore

@@ -100,6 +100,7 @@
 !issue5747.pdf
 !issue6099.pdf
 !issue6336.pdf
+!issue6387.pdf
 !issue6410.pdf
 !gradientfill.pdf
 !bug903856.pdf

test/test_manifest.json

@@ -1574,6 +1574,19 @@
        "lastPage": 1,
        "type": "eq"
     },
+    {  "id": "issue6387-canvas",
+       "file": "pdfs/issue6387.pdf",
+       "md5": "08c39ac6d0aab1596e6e59793eaf3ee4",
+       "rounds": 1,
+       "type": "eq"
+    },
+    {  "id": "issue6387-text",
+       "file": "pdfs/issue6387.pdf",
+       "md5": "08c39ac6d0aab1596e6e59793eaf3ee4",
+       "rounds": 1,
+       "type": "text",
+       "about": "Note that the text layer seems to be off to the right."
+    },
     {  "id": "issue4890",
        "file": "pdfs/issue4890.pdf",
        "md5": "1666feb4cd26318c2bdbea6a175dce87",