gsk: Use scaled font for glyph rendering

This changes the approach we take to rendering glyphs in the
presence of a scale transform: Instead of scaling the extents
and rendering to an image surface with device scale, simply
create a scaled font and use it for extents and rendering.

gsk/gpu/gskgpudevice.c

@@ -11,6 +11,7 @@
 #include "gdk/gdkprofilerprivate.h"
 
 #include "gsk/gskdebugprivate.h"
+#include "gsk/gskprivate.h"
 
 #define MAX_SLICES_PER_ATLAS 64
 
@@ -905,6 +906,7 @@ gsk_gpu_device_lookup_glyph_image (GskGpuDevice           *self,
   GskGpuImage *image;
   gsize atlas_x, atlas_y, padding;
   float subpixel_x, subpixel_y;
+  PangoFont *scaled_font;
 
   cache = g_hash_table_lookup (priv->glyph_cache, &lookup);
   if (cache)
@@ -916,13 +918,14 @@ gsk_gpu_device_lookup_glyph_image (GskGpuDevice           *self,
       return cache->image;
     }
 
+  scaled_font = gsk_get_scaled_font (font, scale);
   subpixel_x = (flags & 3) / 4.f;
   subpixel_y = ((flags >> 2) & 3) / 4.f;
-  pango_font_get_glyph_extents (font, glyph, &ink_rect, NULL);
-  origin.x = floor (ink_rect.x * scale / PANGO_SCALE + subpixel_x);
-  origin.y = floor (ink_rect.y * scale / PANGO_SCALE + subpixel_y);
-  rect.size.width = ceil ((ink_rect.x + ink_rect.width) * scale / PANGO_SCALE + subpixel_x) - origin.x;
-  rect.size.height = ceil ((ink_rect.y + ink_rect.height) * scale / PANGO_SCALE + subpixel_y) - origin.y;
+  pango_font_get_glyph_extents (scaled_font, glyph, &ink_rect, NULL);
+  origin.x = floor (ink_rect.x * 1.0 / PANGO_SCALE + subpixel_x);
+  origin.y = floor (ink_rect.y * 1.0 / PANGO_SCALE + subpixel_y);
+  rect.size.width = ceil ((ink_rect.x + ink_rect.width) * 1.0 / PANGO_SCALE + subpixel_x) - origin.x;
+  rect.size.height = ceil ((ink_rect.y + ink_rect.height) * 1.0 / PANGO_SCALE + subpixel_y) - origin.y;
   padding = 1;
 
   image = gsk_gpu_device_add_atlas_image (self,
@@ -956,7 +959,7 @@ gsk_gpu_device_lookup_glyph_image (GskGpuDevice           *self,
 
   gsk_gpu_upload_glyph_op (frame,
                            cache->image,
-                           font,
+                           scaled_font,
                            glyph,
                            &(cairo_rectangle_int_t) {
                                .x = rect.origin.x - padding,
@@ -964,7 +967,7 @@ gsk_gpu_device_lookup_glyph_image (GskGpuDevice           *self,
                                .width = rect.size.width + 2 * padding,
                                .height = rect.size.height + 2 * padding,
                            },
-                           scale,
+                           1.0,
                            &GRAPHENE_POINT_INIT (cache->origin.x + padding,
                                                  cache->origin.y + padding));
 

gsk/gskprivate.c

@@ -1,6 +1,10 @@
 #include "gskresources.h"
 #include "gskprivate.h"
 
+#include <cairo.h>
+#include <pango/pangocairo.h>
+#include <math.h>
+
 static gpointer
 register_resources (gpointer data)
 {
@@ -15,3 +19,106 @@ gsk_ensure_resources (void)
 
   g_once (&register_resources_once, register_resources, NULL);
 }
+
+/*< private >
+ * gsk_get_unhinted_font:
+ * @font: (transfer full): a `PangoFont`
+ *
+ * Returns a font that is just like @font, but does not apply
+ * hinting to its glyphs or metrics.
+ *
+ * Returns: (transfer full): an unhinted `PangoFont`
+ */
+PangoFont *
+gsk_get_unhinted_font (PangoFont *font)
+{
+  PangoFont *font2 = font;
+  cairo_scaled_font_t *sc;
+  cairo_font_options_t *options;
+
+  sc = pango_cairo_font_get_scaled_font (PANGO_CAIRO_FONT (font));
+  options = cairo_font_options_create ();
+  cairo_scaled_font_get_font_options (sc, options);
+  if (cairo_font_options_get_hint_metrics (options) != CAIRO_HINT_METRICS_OFF ||
+      cairo_font_options_get_hint_style (options) != CAIRO_HINT_STYLE_NONE)
+    {
+      font2 = PANGO_FONT (g_object_get_data (G_OBJECT (font), "gsk-unhinted-font"));
+      if (!font2)
+        {
+          PangoFontMap *fontmap = pango_font_get_font_map (font);
+          PangoContext *context;
+          PangoFontDescription *desc;
+
+          cairo_font_options_set_hint_metrics (options, CAIRO_HINT_METRICS_OFF);
+          cairo_font_options_set_hint_style (options, CAIRO_HINT_STYLE_NONE);
+
+          context = pango_font_map_create_context (fontmap);
+          pango_cairo_context_set_font_options (context, options);
+
+          desc = pango_font_describe (font);
+          font2 = pango_font_map_load_font (fontmap, context, desc);
+
+          pango_font_description_free (desc);
+          g_object_unref (context);
+
+          g_object_set_data_full (G_OBJECT (font), "gsk-unhinted-font",
+                                  font2, g_object_unref);
+        }
+    }
+
+  cairo_font_options_destroy (options);
+
+  return font2;
+}
+
+PangoFont *
+gsk_get_scaled_font (PangoFont *font,
+                     float      scale)
+{
+  GHashTable *fonts;
+  int key;
+  PangoFont *font2;
+  PangoFontDescription *desc;
+  int size;
+  PangoFontMap *fontmap;
+  PangoContext *context;
+
+  key = (int) CLAMP (roundf (scale * PANGO_SCALE), G_MININT, G_MAXINT);
+
+  if (key == PANGO_SCALE)
+    return font;
+
+  fonts = (GHashTable *) g_object_get_data (G_OBJECT (font), "gsk-scaled-fonts");
+
+  if (fonts)
+    {
+      font2 = g_hash_table_lookup (fonts, GINT_TO_POINTER (key));
+      if (font2)
+        return font2;
+    }
+  else
+    {
+      fonts = g_hash_table_new_full (g_direct_hash, g_direct_equal, NULL, g_object_unref);
+      g_object_set_data_full (G_OBJECT (font), "gsk-scaled-fonts",
+                              fonts, (GDestroyNotify) g_hash_table_unref);
+    }
+
+ desc = pango_font_describe (font);
+ size = pango_font_description_get_size (desc);
+
+ if (pango_font_description_get_size_is_absolute (desc))
+   pango_font_description_set_absolute_size (desc, size * scale);
+ else
+   pango_font_description_set_size (desc, (int) roundf (size * scale));
+
+ fontmap = pango_font_get_font_map (font);
+ context = pango_font_map_create_context (fontmap);
+ font2 = pango_font_map_load_font (fontmap, context, desc);
+
+ pango_font_description_free (desc);
+ g_object_unref (context);
+
+ g_hash_table_insert (fonts, GINT_TO_POINTER (key), font2);
+
+ return font2;
+}

gsk/gskprivate.h

@@ -5,7 +5,11 @@
 
 G_BEGIN_DECLS
 
-void gsk_ensure_resources (void);
+void       gsk_ensure_resources  (void);
+
+PangoFont *gsk_get_unhinted_font (PangoFont *font);
+PangoFont *gsk_get_scaled_font   (PangoFont *font,
+                                  float      scale);
 
 G_END_DECLS
 

gsk/gskrendernodeimpl.c

@@ -31,6 +31,7 @@
 #include "gskroundedrectprivate.h"
 #include "gskstrokeprivate.h"
 #include "gsktransformprivate.h"
+#include "gskprivate.h"
 
 #include "gdk/gdkmemoryformatprivate.h"
 #include "gdk/gdkprivate.h"
@@ -5791,6 +5792,12 @@ gsk_text_node_class_init (gpointer g_class,
   node_class->diff = gsk_text_node_diff;
 }
 
+static inline float
+pango_units_to_float (int i)
+{
+  return (float) i / PANGO_SCALE;
+}
+
 /**
  * gsk_text_node_new:
  * @font: the `PangoFont` containing the glyphs
@@ -5817,8 +5824,7 @@ gsk_text_node_new (PangoFont              *font,
   PangoGlyphInfo *glyph_infos;
   int n;
 
-  pango_glyph_string_extents (glyphs, font, &ink_rect, NULL);
-  pango_extents_to_pixels (&ink_rect, NULL);
+  pango_glyph_string_extents (glyphs, gsk_get_unhinted_font (font), &ink_rect, NULL);
 
   /* Don't create nodes with empty bounds */
   if (ink_rect.width == 0 || ink_rect.height == 0)
@@ -5855,10 +5861,10 @@ gsk_text_node_new (PangoFont              *font,
   self->num_glyphs = n;
 
   gsk_rect_init (&node->bounds,
-                 offset->x + ink_rect.x,
-                 offset->y + ink_rect.y,
-                 ink_rect.width,
-                 ink_rect.height);
+                 offset->x + pango_units_to_float (ink_rect.x),
+                 offset->y + pango_units_to_float (ink_rect.y),
+                 pango_units_to_float (ink_rect.width),
+                 pango_units_to_float (ink_rect.height));
 
   return node;
 }

testsuite/gsk/compare/o-from-hell.node

@@ -0,0 +1,16 @@
+blend {
+  mode: difference;
+  bottom: text {
+    color: rgb(255,0,0);
+    font: "Noto Sans Mono 300";
+    glyphs: "o";
+  }
+  top: transform {
+    transform: scale(100);
+    child: text {
+      color: rgb(255,0,0);
+      font: "Noto Sans Mono 3";
+      glyphs: "o";
+    }
+  }
+}

testsuite/gsk/compare/o-from-hell2.node

@@ -0,0 +1,16 @@
+blend {
+  mode: difference;
+  bottom: text {
+    color: rgb(255,0,0);
+    font: "Noto Sans Mono 300";
+    glyphs: "o";
+  }
+  top: transform {
+    transform: scale(0.01);
+    child: text {
+      color: rgb(255,0,0);
+      font: "Noto Sans Mono 30000";
+      glyphs: "o";
+    }
+  }
+}

testsuite/gsk/meson.build

@@ -98,6 +98,8 @@ compare_render_tests = [
   'mask-texture-color-alpha',
   'mipmap-generation-later',
   'nested-rounded-clips',
+  'o-from-hell',
+  'o-from-hell2',
   'offscreen-fractional-translate-nogl',
   'offscreen-pixel-alignment-nogl-nocairo',
   'offscreen-pixel-alignment2',