bug 1343802 consider scrollbar trough min-width/min-height properties r=jhorak+328198

in determining breadth of trough and scrollbar.

MozReview-Commit-ID: 3orNXdv6uZh

widget/gtk/gtk3drawing.cpp

@@ -437,6 +437,18 @@ calculate_arrow_rect(GtkWidget* arrow, GdkRectangle* rect,
     return MOZ_GTK_SUCCESS;
 }
 
+static MozGtkSize
+GetMinContentBox(GtkStyleContext* style)
+{
+    GtkStateFlags state_flags = gtk_style_context_get_state(style);
+    gint width, height;
+    gtk_style_context_get(style, state_flags,
+                          "min-width", &width,
+                          "min-height", &height,
+                          nullptr);
+    return {width, height};
+}
+
 /**
  * Get minimum widget size as sum of margin, padding, border and
  * min-width/min-height.
@@ -2639,34 +2651,42 @@ GetScrollbarMetrics(GtkOrientation aOrientation)
     // track
     style = ClaimStyleContext(track);
     metrics->border.track = GetMarginBorderPadding(style);
+    MozGtkSize trackMinSize = GetMinContentBox(style) + metrics->border.track;
     ReleaseStyleContext(style);
     MozGtkSize trackSizeForThumb = metrics->size.thumb + metrics->border.track;
     // button
     if (hasButtons) {
         metrics->size.button = GetMinMarginBox(MOZ_GTK_SCROLLBAR_BUTTON);
-        if (aOrientation == GTK_ORIENTATION_HORIZONTAL) {
-            metrics->size.button.Rotate();
-            // If the buttons will cause Gecko to expand the track to fill
-            // available breadth, then add to the track border to prevent Gecko
-            // from expanding the thumb to fill available breadth.
-            gint extra = metrics->size.button.height - trackSizeForThumb.height;
-            if (extra > 0) {
-                // If extra is odd, then the thumb is 0.5 pixels above
-                // center as in gtk_range_compute_slider_position().
-                metrics->border.track.top += extra / 2;
-                metrics->border.track.bottom += extra - extra / 2;
-                // Update size for change in border.
-                trackSizeForThumb.height += extra;
-            }
-        } else {
-            gint extra = metrics->size.button.width - trackSizeForThumb.width;
-            if (extra > 0) {
-                // If extra is odd, then the thumb is 0.5 pixels to the left
-                // of center as in gtk_range_compute_slider_position().
-                metrics->border.track.left += extra / 2;
-                metrics->border.track.right += extra - extra / 2;
-                trackSizeForThumb.width += extra;
-            }
+    } else {
+        metrics->size.button = {0, 0};
+    }
+    if (aOrientation == GTK_ORIENTATION_HORIZONTAL) {
+        metrics->size.button.Rotate();
+        // If the track is wider than necessary for the thumb, including when
+        // the buttons will cause Gecko to expand the track to fill
+        // available breadth, then add to the track border to prevent Gecko
+        // from expanding the thumb to fill available breadth.
+        gint extra =
+            std::max(trackMinSize.height,
+                     metrics->size.button.height) - trackSizeForThumb.height;
+        if (extra > 0) {
+            // If extra is odd, then the thumb is 0.5 pixels above
+            // center as in gtk_range_compute_slider_position().
+            metrics->border.track.top += extra / 2;
+            metrics->border.track.bottom += extra - extra / 2;
+            // Update size for change in border.
+            trackSizeForThumb.height += extra;
+        }
+    } else {
+        gint extra =
+            std::max(trackMinSize.width,
+                     metrics->size.button.width) - trackSizeForThumb.width;
+        if (extra > 0) {
+            // If extra is odd, then the thumb is 0.5 pixels to the left
+            // of center as in gtk_range_compute_slider_position().
+            metrics->border.track.left += extra / 2;
+            metrics->border.track.right += extra - extra / 2;
+            trackSizeForThumb.width += extra;
         }
     }