Merge pull request #3338 from harfbuzz/slant

[font] Add public API for synthetic slant

docs/harfbuzz-sections.txt

@@ -329,6 +329,7 @@ hb_font_get_parent
 hb_font_get_ppem
 hb_font_get_ptem
 hb_font_get_scale
+hb_font_get_synthetic_slant
 hb_font_get_user_data
 hb_font_get_variation_glyph
 hb_font_get_variation_glyph_func_t
@@ -346,6 +347,7 @@ hb_font_set_parent
 hb_font_set_ppem
 hb_font_set_ptem
 hb_font_set_scale
+hb_font_set_synthetic_slant
 hb_font_set_user_data
 hb_font_set_variations
 hb_font_set_var_coords_design

src/hb-font.cc

@@ -1477,6 +1477,8 @@ DEFINE_NULL_INSTANCE (hb_font_t) =
 
   1000, /* x_scale */
   1000, /* y_scale */
+  0., /* slant */
+  0., /* slant_xy; */
   1<<16, /* x_mult */
   1<<16, /* y_mult */
 
@@ -1588,6 +1590,7 @@ hb_font_create_sub_font (hb_font_t *parent)
 
   font->x_scale = parent->x_scale;
   font->y_scale = parent->y_scale;
+  font->slant = parent->slant;
   font->mults_changed ();
   font->x_ppem = parent->x_ppem;
   font->y_ppem = parent->y_ppem;
@@ -2025,7 +2028,7 @@ hb_font_set_ptem (hb_font_t *font,
  *
  * Return value: Point size.  A value of zero means "not set."
  *
- * Since: 0.9.2
+ * Since: 1.6.0
  **/
 float
 hb_font_get_ptem (hb_font_t *font)
@@ -2033,6 +2036,49 @@ hb_font_get_ptem (hb_font_t *font)
   return font->ptem;
 }
 
+/**
+ * hb_font_set_synthetic_slant:
+ * @font: #hb_font_t to work upon
+ * @ptem: font size in points.
+ *
+ * Sets the "synthetic slant" of a font.  By default is zero.
+ * Synthetic slant is the graphical skew that the renderer
+ * applies to the font at rendering time.
+ *
+ * HarfBuzz needs to know this value to adjust shaping results,
+ * metrics, and style values to match the slanted rendering.
+ *
+ * <note>Note: The slant value is a ratio.  For example, a
+ * 20% slant would be represented as a 0.2 value.</note>
+ *
+ * Since: REPLACEME
+ **/
+HB_EXTERN void
+hb_font_set_synthetic_slant (hb_font_t *font, float slant)
+{
+  if (hb_object_is_immutable (font))
+    return;
+
+  font->slant = slant;
+  font->mults_changed ();
+}
+
+/**
+ * hb_font_get_synthetic_slant:
+ * @font: #hb_font_t to work upon
+ *
+ * Fetches the "synthetic slant" of a font.
+ *
+ * Return value: Synthetic slant.  By default is zero.
+ *
+ * Since: REPLACEME
+ **/
+HB_EXTERN float
+hb_font_get_synthetic_slant (hb_font_t *font)
+{
+  return font->slant;
+}
+
 #ifndef HB_NO_VAR
 /*
  * Variations

src/hb-font.h

@@ -1023,6 +1023,12 @@ hb_font_set_ptem (hb_font_t *font, float ptem);
 HB_EXTERN float
 hb_font_get_ptem (hb_font_t *font);
 
+HB_EXTERN void
+hb_font_set_synthetic_slant (hb_font_t *font, float slant);
+
+HB_EXTERN float
+hb_font_get_synthetic_slant (hb_font_t *font);
+
 HB_EXTERN void
 hb_font_set_variations (hb_font_t *font,
 			const hb_variation_t *variations,

src/hb-font.hh

@@ -109,6 +109,8 @@ struct hb_font_t
 
   int32_t x_scale;
   int32_t y_scale;
+  float slant;
+  float slant_xy;
   int64_t x_mult;
   int64_t y_mult;
 
@@ -617,6 +619,7 @@ struct hb_font_t
     signed upem = face->get_upem ();
     x_mult = ((int64_t) x_scale << 16) / upem;
     y_mult = ((int64_t) y_scale << 16) / upem;
+    slant_xy = y_scale ? slant * x_scale / y_scale : 0.f;
   }
 
   hb_position_t em_mult (int16_t v, int64_t mult)

src/hb-ot-layout-gpos-table.hh

@@ -2951,7 +2951,7 @@ GPOS::position_finish_advances (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer H
 }
 
 void
-GPOS::position_finish_offsets (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer)
+GPOS::position_finish_offsets (hb_font_t *font, hb_buffer_t *buffer)
 {
   _hb_buffer_assert_gsubgpos_vars (buffer);
 
@@ -2961,8 +2961,15 @@ GPOS::position_finish_offsets (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer)
 
   /* Handle attachments */
   if (buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT)
-    for (unsigned int i = 0; i < len; i++)
+    for (unsigned i = 0; i < len; i++)
       propagate_attachment_offsets (pos, len, i, direction);
+
+  if (unlikely (font->slant))
+  {
+    for (unsigned i = 0; i < len; i++)
+      if (unlikely (pos[i].y_offset))
+        pos[i].x_offset += _hb_roundf (font->slant_xy * pos[i].y_offset);
+  }
 }
 
 

src/hb-ot-metrics.cc

@@ -160,9 +160,50 @@ hb_ot_metrics_get_position (hb_font_t           *font,
     (position && (*position = font->em_scalef_y (face->table.TABLE->ATTR + GET_VAR)), true))
   case HB_OT_METRICS_TAG_HORIZONTAL_CLIPPING_ASCENT:  return GET_METRIC_Y (OS2, usWinAscent);
   case HB_OT_METRICS_TAG_HORIZONTAL_CLIPPING_DESCENT: return GET_METRIC_Y (OS2, usWinDescent);
-  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE:       return GET_METRIC_Y (hhea, caretSlopeRise);
-  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RUN:        return GET_METRIC_X (hhea, caretSlopeRun);
+
+  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE:
+  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RUN:
+  {
+    unsigned mult = 1u;
+
+    if (font->slant)
+    {
+      unsigned rise = face->table.hhea->caretSlopeRise;
+      unsigned upem = face->get_upem ();
+      mult = (rise && rise < upem) ? hb_min (upem / rise, 256u) : 1u;
+    }
+
+    if (metrics_tag == HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE)
+    {
+      bool ret = GET_METRIC_Y (hhea, caretSlopeRise);
+
+      if (position)
+	*position *= mult;
+
+      return ret;
+    }
+    else
+    {
+      hb_position_t rise = 0;
+
+      if (font->slant && position && GET_METRIC_Y (hhea, caretSlopeRise))
+	rise = *position;
+
+      bool ret = GET_METRIC_X (hhea, caretSlopeRun);
+
+      if (position)
+      {
+	*position *= mult;
+
+	if (font->slant)
+	  *position += _hb_roundf (mult * font->slant_xy * rise);
+      }
+
+      return ret;
+    }
+  }
   case HB_OT_METRICS_TAG_HORIZONTAL_CARET_OFFSET:     return GET_METRIC_X (hhea, caretOffset);
+
 #ifndef HB_NO_VERTICAL
   case HB_OT_METRICS_TAG_VERTICAL_CARET_RISE:         return GET_METRIC_X (vhea, caretSlopeRise);
   case HB_OT_METRICS_TAG_VERTICAL_CARET_RUN:          return GET_METRIC_Y (vhea, caretSlopeRun);

src/hb-style.cc

@@ -48,13 +48,12 @@ _hb_angle_to_ratio (float a)
 {
   return tanf (a * float (M_PI / 180.));
 }
-#if 0
+
 static inline float
 _hb_ratio_to_angle (float r)
 {
   return atanf (r) * float (180. / M_PI);
 }
-#endif
 
 /**
  * hb_style_get_value:
@@ -73,7 +72,8 @@ float
 hb_style_get_value (hb_font_t *font, hb_style_tag_t style_tag)
 {
   if (unlikely (style_tag == HB_STYLE_TAG_SLANT_RATIO))
-    return _hb_angle_to_ratio (hb_style_get_value (font, HB_STYLE_TAG_SLANT_ANGLE));
+    return _hb_angle_to_ratio (hb_style_get_value (font, HB_STYLE_TAG_SLANT_ANGLE))
+	 + font->slant;
 
   hb_face_t *face = font->face;
 
@@ -109,7 +109,14 @@ hb_style_get_value (hb_font_t *font, hb_style_tag_t style_tag)
 	   : 12.f;
   }
   case HB_STYLE_TAG_SLANT_ANGLE:
-    return face->table.post->table->italicAngle.to_float ();
+  {
+    float angle = face->table.post->table->italicAngle.to_float ();
+
+    if (font->slant)
+      angle = _hb_ratio_to_angle (font->slant + _hb_angle_to_ratio (angle));
+
+    return angle;
+  }
   case HB_STYLE_TAG_WIDTH:
     return face->table.OS2->has_data ()
 	   ? face->table.OS2->get_width ()