use the PangoLayout to get baseline

Instead of getting it via the PangoContext, which seems to be buggy

Fixes Automattic#1037

src/CanvasRenderingContext2d.cc

@@ -1945,19 +1945,23 @@ NAN_METHOD(Context2d::StrokeText) {
 }
 
 /*
- * Gets the baseline adjustment in device pixels, taking into account the
- * transformation matrix. TODO This does not handle skew (which cannot easily
- * be extracted from the matrix separately from rotation).
+ * Gets the baseline adjustment in device pixels
  */
-inline double getBaselineAdjustment(PangoFontMetrics* metrics, cairo_matrix_t matrix, short baseline) {
-  double yScale = sqrt(matrix.yx * matrix.yx + matrix.yy * matrix.yy);
+inline double getBaselineAdjustment(PangoLayout* layout, short baseline) {
+  PangoRectangle logical_rect;
+  pango_layout_line_get_extents(pango_layout_get_line(layout, 0), NULL, &logical_rect);
+
+  double scale = 1.0 / PANGO_SCALE;
+  double ascent = scale * pango_layout_get_baseline(layout);
+  double descent = scale * logical_rect.height - ascent;
+
   switch (baseline) {
   case TEXT_BASELINE_ALPHABETIC:
-    return (pango_font_metrics_get_ascent(metrics) / PANGO_SCALE) * yScale;
+    return ascent;
   case TEXT_BASELINE_MIDDLE:
-    return ((pango_font_metrics_get_ascent(metrics) + pango_font_metrics_get_descent(metrics)) / (2.0 * PANGO_SCALE)) * yScale;
+    return (ascent + descent) / 2.0;
   case TEXT_BASELINE_BOTTOM:
-    return ((pango_font_metrics_get_ascent(metrics) + pango_font_metrics_get_descent(metrics)) / PANGO_SCALE) * yScale;
+    return ascent + descent;
   default:
     return 0;
   }
@@ -1970,13 +1974,10 @@ inline double getBaselineAdjustment(PangoFontMetrics* metrics, cairo_matrix_t ma
 void
 Context2d::setTextPath(const char *str, double x, double y) {
   PangoRectangle logical_rect;
-  cairo_matrix_t matrix;
 
   pango_layout_set_text(_layout, str, -1);
   pango_cairo_update_layout(_context, _layout);
 
-  cairo_get_matrix(_context, &matrix);
-
   switch (state->textAlignment) {
     // center
     case 0:
@@ -1990,9 +1991,7 @@ Context2d::setTextPath(const char *str, double x, double y) {
       break;
   }
 
-  PangoFontMetrics *metrics = PANGO_LAYOUT_GET_METRICS(_layout);
-  y -= getBaselineAdjustment(metrics, matrix, state->textBaseline);
-  pango_font_metrics_unref(metrics);
+  y -= getBaselineAdjustment(_layout, state->textBaseline);
 
   cairo_move_to(_context, x, y);
   if (state->textDrawingMode == TEXT_DRAW_PATHS) {
@@ -2132,7 +2131,7 @@ NAN_METHOD(Context2d::MeasureText) {
 
   cairo_matrix_t matrix;
   cairo_get_matrix(ctx, &matrix);
-  double y_offset = getBaselineAdjustment(metrics, matrix, context->state->textBaseline);
+  double y_offset = getBaselineAdjustment(layout, context->state->textBaseline);
 
   obj->Set(Nan::New<String>("width").ToLocalChecked(),
            Nan::New<Number>(logical_rect.width));