[gtk/gtk-3-24: 1/3] Quantization for corner mask cache

[Matthias Clasen <matthiasc src gnome org>]

commit 8d21c1459212c5a0664b667614b9e80ed09b6bf6
Author: Luca Bacci <luca bacci982 gmail com>
Date:   Wed Jun 17 14:28:25 2020 +0200

    Quantization for corner mask cache
    
    Fixes issue #2853

 gtk/gtkcssshadowvalue.c | 49 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 10 deletions(-)
---
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 4cc2cc3d47..8e3b52d3c0 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -30,6 +30,7 @@
 #include "gtkpango.h"
 
 #include <math.h>
+#include <float.h>
 
 struct _GtkCssValue {
   GTK_CSS_VALUE_BASE
@@ -663,16 +664,18 @@ draw_shadow (const GtkCssValue   *shadow,
 }
 
 typedef struct {
-  double radius;
-  GtkRoundedBoxCorner corner;
+  gint radius;
+  /* rounded box corner */
+  gint corner_horizontal;
+  gint corner_vertical;
 } CornerMask;
 
 static guint
 corner_mask_hash (CornerMask *mask)
 {
-  return ((guint)mask->radius << 24) ^
-    ((guint)(mask->corner.horizontal*4)) << 12 ^
-    ((guint)(mask->corner.vertical*4)) << 0;
+  return ((guint)mask->radius) << 24 ^
+    ((guint)mask->corner_horizontal) << 12 ^
+    ((guint)mask->corner_vertical) << 0;
 }
 
 static gboolean
@@ -681,8 +684,33 @@ corner_mask_equal (CornerMask *mask1,
 {
   return
     mask1->radius == mask2->radius &&
-    mask1->corner.horizontal == mask2->corner.horizontal &&
-    mask1->corner.vertical == mask2->corner.vertical;
+    mask1->corner_horizontal == mask2->corner_horizontal &&
+    mask1->corner_vertical == mask2->corner_vertical;
+}
+
+static gint
+truncate_to_int (double val)
+{
+  if (isnan (val))
+    return 0;
+  if (val >= G_MAXINT)
+    return G_MAXINT;
+  if (val <= G_MININT)
+    return G_MININT;
+  return (gint) val;
+}
+
+static inline gint
+round_to_int (double val)
+{
+  return truncate_to_int (val + (val > 0 ? 0.5 : -0.5));
+}
+
+static inline gint
+quantize_to_int (double val)
+{
+  const double precision_factor = 10.0;
+  return round_to_int (val * precision_factor);
 }
 
 static void
@@ -784,7 +812,7 @@ draw_shadow_corner (const GtkCssValue   *shadow,
    *
    * The blur radius (which also defines the clip_radius)
    *
-   * The the horizontal and vertical corner radius
+   * The horizontal and vertical corner radius
    *
    * We apply the first position and orientation when drawing the
    * mask, so we cache rendered masks based on the blur radius and the
@@ -795,8 +823,9 @@ draw_shadow_corner (const GtkCssValue   *shadow,
                                                (GEqualFunc)corner_mask_equal,
                                                g_free, (GDestroyNotify)cairo_surface_destroy);
 
-  key.radius = radius;
-  key.corner = box->corner[corner];
+  key.radius = quantize_to_int (radius);
+  key.corner_horizontal = quantize_to_int (box->corner[corner].horizontal);
+  key.corner_vertical = quantize_to_int (box->corner[corner].vertical);
 
   mask = g_hash_table_lookup (corner_mask_cache, &key);
   if (mask == NULL)