[libadwaita/wip/exalm/fixes: 10/10] clamp-layout: Fix measure()

[Alexander Mikhaylenko <alexm src gnome org>]

commit 87c68e4b6aa38b85656615f5f9b9592683af409f
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Tue Dec 7 21:47:59 2021 +0500

    clamp-layout: Fix measure()
    
    So turns out after all the fixes this was still wrong:
    
    - When get_child_size() gets for_size == -1, it returns the natural size
    of the child. That's all good and well, but in reality we need the natural
    size of the clamp itself - which would be larger because of the padding at
    that size. So we need to calculate it - reverse the lerp and ease out cubic
    we do on the clamp size to get the child size.
    
    Refactor everything, extract inverse clamp function since we use it in two
    places now.
    
    Fixes https://gitlab.gnome.org/GNOME/libadwaita/-/issues/347

 src/adw-clamp-layout.c | 102 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 66 insertions(+), 36 deletions(-)
---
diff --git a/src/adw-clamp-layout.c b/src/adw-clamp-layout.c
index 90621166..0907349f 100644
--- a/src/adw-clamp-layout.c
+++ b/src/adw-clamp-layout.c
@@ -9,6 +9,7 @@
 
 #include <math.h>
 
+#include "adw-animation-util.h"
 #include "adw-easing.h"
 #include "adw-macros-private.h"
 
@@ -120,37 +121,62 @@ adw_clamp_layout_set_property (GObject      *object,
   }
 }
 
+static inline double
+inverse_lerp (double a,
+              double b,
+              double t)
+{
+  return (t - a) / (b - a);
+}
+
 static int
-get_child_size (AdwClampLayout *self,
-                GtkWidget      *child,
-                int             for_size,
-                int            *child_minimum,
-                int            *child_maximum,
-                int            *lower_threshold,
-                int            *upper_threshold)
+clamp_size_from_child (AdwClampLayout *self,
+                       int             min,
+                       int             nat)
 {
-  int min = 0, nat = 0, max = 0, lower = 0, upper = 0;
-  double amplitude, progress;
+  int max = 0, lower = 0, upper = 0;
+  double progress;
+
+  lower = MAX (MIN (self->tightening_threshold, self->maximum_size), min);
+  max = MAX (lower, self->maximum_size);
+  upper = lower + ADW_EASE_OUT_TAN_CUBIC * (max - lower);
 
-  if (gtk_widget_get_visible (child))
-    gtk_widget_measure (child, self->orientation, -1, &min, &nat, NULL, NULL);
+  if (nat <= lower)
+    progress = 0;
+  else if (nat >= max)
+    progress = 1;
+  else {
+    double ease = inverse_lerp (lower, max, nat);
 
-  if (for_size < 0)
-    return nat;
+    progress = 1 + cbrt (ease - 1); // inverse ease out cubic
+  }
+
+  return ceil (adw_lerp (lower, upper, progress));
+}
+
+static int
+child_size_from_clamp (AdwClampLayout *self,
+                       GtkWidget      *child,
+                       int             for_size,
+                       int            *child_maximum,
+                       int            *lower_threshold)
+{
+  int min = 0, nat = 0, max = 0, lower = 0, upper = 0;
+  double progress;
+
+  gtk_widget_measure (child, self->orientation, -1, &min, &nat, NULL, NULL);
 
   lower = MAX (MIN (self->tightening_threshold, self->maximum_size), min);
   max = MAX (lower, self->maximum_size);
-  amplitude = max - lower;
-  upper = ADW_EASE_OUT_TAN_CUBIC * amplitude + lower;
+  upper = lower + ADW_EASE_OUT_TAN_CUBIC * (max - lower);
 
-  if (child_minimum)
-    *child_minimum = min;
   if (child_maximum)
     *child_maximum = max;
   if (lower_threshold)
     *lower_threshold = lower;
-  if (upper_threshold)
-    *upper_threshold = upper;
+
+  if (for_size < 0)
+    return MIN (nat, max);
 
   if (for_size <= lower)
     return for_size;
@@ -158,9 +184,9 @@ get_child_size (AdwClampLayout *self,
   if (for_size >= upper)
     return max;
 
-  progress = (double) (for_size - lower) / (double) (upper - lower);
+  progress = inverse_lerp (lower, upper, for_size);
 
-  return adw_easing_ease (ADW_EASE_OUT_CUBIC, progress) * amplitude + lower;
+  return adw_lerp (lower, max, adw_easing_ease (ADW_EASE_OUT_CUBIC, progress));
 }
 
 static GtkSizeRequestMode
@@ -190,7 +216,6 @@ adw_clamp_layout_measure (GtkLayoutManager *manager,
   for (child = gtk_widget_get_first_child (widget);
        child != NULL;
        child = gtk_widget_get_next_sibling (child)) {
-    int child_size = -1;
     int child_min = 0;
     int child_nat = 0;
     int child_min_baseline = -1;
@@ -199,13 +224,19 @@ adw_clamp_layout_measure (GtkLayoutManager *manager,
     if (!gtk_widget_should_layout (child))
       continue;
 
-    if (self->orientation != orientation)
-      child_size = get_child_size (self, child, for_size,
-                                   NULL, NULL, NULL, NULL);
+    if (self->orientation == orientation) {
+      gtk_widget_measure (child, orientation, -1,
+                          &child_min, &child_nat,
+                          &child_min_baseline, &child_nat_baseline);
 
-    gtk_widget_measure (child, orientation, child_size,
-                        &child_min, &child_nat,
-                        &child_min_baseline, &child_nat_baseline);
+      child_nat = clamp_size_from_child (self, child_min, child_nat);
+    } else {
+      int child_size = child_size_from_clamp (self, child, for_size, NULL, NULL);
+
+      gtk_widget_measure (child, orientation, child_size,
+                          &child_min, &child_nat,
+                          &child_min_baseline, &child_nat_baseline);
+    }
 
     *minimum = MAX (*minimum, child_min);
     *natural = MAX (*natural, child_nat);
@@ -243,18 +274,17 @@ adw_clamp_layout_allocate (GtkLayoutManager *manager,
     }
 
     if (self->orientation == GTK_ORIENTATION_HORIZONTAL) {
-      child_allocation.width = get_child_size (self, child, width,
-                                               NULL, &child_maximum,
-                                               &lower_threshold, NULL);
+      child_allocation.width = child_size_from_clamp (self, child, width,
+                                                      &child_maximum,
+                                                      &lower_threshold);
       child_allocation.height = height;
 
       child_clamped_size = child_allocation.width;
-    }
-    else {
+    } else {
       child_allocation.width = width;
-      child_allocation.height = get_child_size (self, child, height,
-                                                NULL, &child_maximum,
-                                                &lower_threshold, NULL);
+      child_allocation.height = child_size_from_clamp (self, child, height,
+                                                       &child_maximum,
+                                                       &lower_threshold);
 
       child_clamped_size = child_allocation.height;
     }