Merge branch 'synthetic-slant' into 'main'

Pass synthetic slant to harfbuzz

See merge request GNOME/pango!474

4 files changed, 72 insertions, 2 deletions

diff --git a/pango/pango-matrix.c b/pango/pango-matrix.c
index a066eb57..3bc0ff16 100644
--- a/pango/pango-matrix.c
+++ b/pango/pango-matrix.c
@@ -263,6 +263,40 @@ pango_matrix_get_font_scale_factors (const PangoMatrix *matrix,
 }
 
 /**
+ * pango_matrix_get_slant_ratio:
+ * @matrix: a `PangoMatrix`
+ *
+ * Gets the slant ratio of a matrix.
+ *
+ * For a simple shear matrix in the form:
+ *
+ *     1 λ
+ *     0 1
+ *
+ * this is simply λ.
+ *
+ * Returns: the slant ratio of @matrix
+ *
+ * Since: 1.50
+ */
+double
+pango_matrix_get_slant_ratio (const PangoMatrix *matrix)
+{
+  double x0, y0;
+  double x1, y1;
+
+  x0 = 0;
+  y0 = 1;
+  pango_matrix_transform_distance (matrix, &x0, &y0);
+
+  x1 = 1;
+  y1 = 0;
+  pango_matrix_transform_distance (matrix, &x1, &y1);
+
+  return (x0 * x1 + y0 * y1) / (x0 * x0 + y0 * y0);
+}
+
+/**
  * pango_matrix_transform_distance:
  * @matrix: (nullable): a `PangoMatrix`
  * @dx: (inout): in/out X component of a distance vector
diff --git a/pango/pango-matrix.h b/pango/pango-matrix.h
index d4277401..cb53a422 100644
--- a/pango/pango-matrix.h
+++ b/pango/pango-matrix.h
@@ -121,6 +121,8 @@ double pango_matrix_get_font_scale_factor (const PangoMatrix *matrix) G_GNUC_PUR
 PANGO_AVAILABLE_IN_1_38
 void pango_matrix_get_font_scale_factors (const PangoMatrix *matrix,
 					  double *xscale, double *yscale);
+PANGO_AVAILABLE_IN_1_50
+double pango_matrix_get_slant_ratio (const PangoMatrix *matrix) G_GNUC_PURE;
 
 
 G_END_DECLS
diff --git a/pango/pangofc-font.c b/pango/pangofc-font.c
index 03f15efa..9d555a37 100644
--- a/pango/pangofc-font.c
+++ b/pango/pangofc-font.c
@@ -964,10 +964,12 @@ pango_fc_font_create_hb_font (PangoFont *font)
   double x_scale, y_scale;
   double pixel_size;
   double point_size;
+  double slant G_GNUC_UNUSED;
 
   x_scale_inv = y_scale_inv = 1.0;
   pixel_size = 1.0;
   point_size = 1.0;
+  slant = 0.0;
 
   key = _pango_fc_font_get_font_key (fc_font);
   if (key)
@@ -988,11 +990,12 @@ pango_fc_font_create_hb_font (PangoFont *font)
         FcMatrixMultiply (&fc_matrix, &fc_matrix, fc_matrix_val);
 
       font_matrix.xx = fc_matrix.xx;
-      font_matrix.yx = fc_matrix.yx;
+      font_matrix.yx = - fc_matrix.yx;
       font_matrix.xy = fc_matrix.xy;
-      font_matrix.yy = fc_matrix.yy;
+      font_matrix.yy = - fc_matrix.yy;
 
       pango_matrix_get_font_scale_factors (&font_matrix, &x, &y);
+      slant = pango_matrix_get_slant_ratio (&font_matrix);
 
       x_scale_inv /= x;
       y_scale_inv /= y;
@@ -1003,6 +1006,7 @@ pango_fc_font_create_hb_font (PangoFont *font)
           x_scale_inv = -x_scale_inv;
           y_scale_inv = -y_scale_inv;
         }
+
       get_font_size (key, &pixel_size, &point_size);
     }
 
@@ -1017,6 +1021,10 @@ pango_fc_font_create_hb_font (PangoFont *font)
                      pixel_size * PANGO_SCALE * y_scale);
   hb_font_set_ptem (hb_font, point_size);
 
+#if HB_VERSION_ATLEAST (3, 3, 0)
+  hb_font_set_synthetic_slant (hb_font, slant);
+#endif
+
   if (key)
     {
       const FcPattern *pattern = pango_fc_font_key_get_pattern (key);
diff --git a/tests/testmatrix.c b/tests/testmatrix.c
index 607f2b5f..1ba79839 100644
--- a/tests/testmatrix.c
+++ b/tests/testmatrix.c
@@ -21,6 +21,7 @@
 
 #include <glib.h>
 #include <pango/pango.h>
+#include <math.h>
 
 #define matrix_equal(m1, m2) \
   (G_APPROX_VALUE ((m1)->xx, (m2)->xx, 0.0001) && \
@@ -185,6 +186,30 @@ test_matrix_transform_pixel_rect (void)
   g_assert_cmpfloat_with_epsilon (rect.height, 2, 0.1);
 }
 
+static void
+test_matrix_slant_ratio (void)
+{
+  PangoMatrix m = (PangoMatrix) { 1, 0, 0.2, 1, 0, 0 };
+  PangoMatrix m2 = (PangoMatrix) { 1, 0.4, 0, 1, 0, 0 };
+  double r;
+
+  r = pango_matrix_get_slant_ratio (&m);
+  g_assert_cmphex (r, ==, 0.2);
+
+  pango_matrix_rotate (&m, 45);
+
+  r = pango_matrix_get_slant_ratio (&m);
+  g_assert_cmphex (r, ==, 0.2);
+
+  pango_matrix_scale (&m, 2, 3);
+
+  r = pango_matrix_get_slant_ratio (&m);
+  g_assert_cmphex (r, ==, 0.2);
+
+  r = pango_matrix_get_slant_ratio (&m2);
+  g_assert_cmphex (r, ==, 0.4);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -199,6 +224,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/matrix/transform-distance", test_matrix_transform_distance);
   g_test_add_func ("/matrix/transform-rect", test_matrix_transform_rect);
   g_test_add_func ("/matrix/transform-pixel-rect", test_matrix_transform_pixel_rect);
+  g_test_add_func ("/matrix/slant-ratio", test_matrix_slant_ratio);
 
   return g_test_run ();
 }