[gtk/glyphy2: 4/4] glyphy: Implement synthetic italic

[Matthias Clasen <matthiasc src gnome org>]

commit 8a193061f0a3a8afc5131dd317e7b54a2d67c44b
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Apr 4 21:52:04 2022 -0400

    glyphy: Implement synthetic italic
    
    Use the font matrix found in the FcPattern to transform
    the quads we use to render the glyphs. This makes
    Cantarell Italic come out just like it does with freetype.

 gsk/gl/gskglrenderjob.c | 40 ++++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)
---
diff --git a/gsk/gl/gskglrenderjob.c b/gsk/gl/gskglrenderjob.c
index 4fe13b2791..b1f58b0e89 100644
--- a/gsk/gl/gskglrenderjob.c
+++ b/gsk/gl/gskglrenderjob.c
@@ -3124,19 +3124,32 @@ add_encoded_glyph (GskGLDrawVertex    *vertices,
   *vertices = (GskGLDrawVertex) { .position = { eg->x, eg->y}, .uv = { eg->g16hi, eg->g16lo}, .color = { 
c[0], c[1], c[2], c[3] } };
 }
 
-static gboolean
-font_is_synthetic_bold (PangoFont *font)
+static void
+get_synthetic_font_params (PangoFont   *font,
+                           gboolean    *embolden,
+                           PangoMatrix *matrix)
 {
+  *embolden = FALSE;
+
   if (PANGO_IS_FC_FONT (font))
     {
       FcPattern *pattern = pango_fc_font_get_pattern (PANGO_FC_FONT (font));
-      gboolean ret;
+      FcBool b;
+      FcMatrix mat;
+      FcMatrix *m;
 
-      if (FcPatternGetBool (pattern, FC_EMBOLDEN, 0, &ret) == FcResultMatch)
-        return ret;
-    }
+      if (FcPatternGetBool (pattern, FC_EMBOLDEN, 0, &b) == FcResultMatch)
+        *embolden = b;
+
+      FcMatrixInit (&mat);
+      for (int i = 0; FcPatternGetMatrix (pattern, FC_MATRIX, i, &m) == FcResultMatch; i++)
+        FcMatrixMultiply (&mat, &mat, m);
 
-  return FALSE;
+      matrix->xx = mat.xx;
+      matrix->xy = mat.xy;
+      matrix->yx = mat.yx;
+      matrix->yy = mat.yy;
+    }
 }
 
 static inline void
@@ -3162,7 +3175,8 @@ gsk_gl_render_job_visit_text_node_glyphy (GskGLRenderJob      *job,
   guint i;
   int x_position = 0;
   float font_scale;
-  gboolean synthetic_bold;
+  gboolean embolden;
+  PangoMatrix matrix = PANGO_MATRIX_INIT;
 
 #define GRID_SIZE 20
 
@@ -3175,7 +3189,7 @@ gsk_gl_render_job_visit_text_node_glyphy (GskGLRenderJob      *job,
     return;
 
   font = (PangoFont *)gsk_text_node_get_font (node);
-  synthetic_bold = font_is_synthetic_bold (font);
+  get_synthetic_font_params (font, &embolden, &matrix);
 
   glyphs = gsk_text_node_get_glyphs (node, NULL);
   library = job->driver->glyphy_library;
@@ -3243,7 +3257,7 @@ gsk_gl_render_job_visit_text_node_glyphy (GskGLRenderJob      *job,
           /* 0.0208 is the value used by freetype for synthetic emboldening */
           gsk_gl_program_set_uniform1f (job->current_program,
                                         UNIFORM_GLYPHY_BOLDNESS, 0,
-                                        synthetic_bold ? 0.0208 * GRID_SIZE : 0.0);
+                                        embolden ? 0.0208 * GRID_SIZE : 0.0);
 
 #if 0
           gsk_gl_program_set_uniform1f (job->current_program,
@@ -3266,8 +3280,10 @@ gsk_gl_render_job_visit_text_node_glyphy (GskGLRenderJob      *job,
       EncodedGlyph encoded[4];
 #define ENCODE_CORNER(_cx, _cy) \
   G_STMT_START { \
-    float _vx = x + cx + font_scale * ((1-_cx) * glyph->extents.min_x + _cx * glyph->extents.max_x); \
-    float _vy = y + cy - font_scale * ((1-_cy) * glyph->extents.min_y + _cy * glyph->extents.max_y); \
+    float _dx = _cx * (glyph->extents.max_x - glyph->extents.min_x); \
+    float _dy = _cy * (glyph->extents.max_y - glyph->extents.min_y); \
+    float _vx = x + cx + font_scale * (glyph->extents.min_x + matrix.xx * _dx + matrix.xy * _dy); \
+    float _vy = y + cy - font_scale * (glyph->extents.min_y + matrix.yx * _dx + matrix.yy * _dy); \
     encoded_glyph_init (&encoded[_cx * 2 + _cy], _vx, _vy, _cx, _cy, glyph); \
   } G_STMT_END
       ENCODE_CORNER (0, 0);