[gtksourceview] map: improve slider positioning

[Christian Hergert <chergert src gnome org>]

commit 0ae71303a46c8d67354c0367020ef1b76493a07d
Author: Christian Hergert <chergert redhat com>
Date:   Mon Jun 21 13:30:49 2021 -0700

    map: improve slider positioning
    
    Previously, we could end up with jagged scrolling because how positioning
    worked using whole iter location boundaries. Instead, we can calculate
    relative offsets so that we don't jump around.

 gtksourceview/gtksourcemap.c | 100 ++++++++++++++++++-------------------------
 1 file changed, 41 insertions(+), 59 deletions(-)
---
diff --git a/gtksourceview/gtksourcemap.c b/gtksourceview/gtksourcemap.c
index 1730e6d6..cbd893ff 100644
--- a/gtksourceview/gtksourcemap.c
+++ b/gtksourceview/gtksourcemap.c
@@ -96,9 +96,9 @@
  * pixel cache when cairo_scale is not 1-to-1. This results in layout
  * invalidation and worst case render paths.
  *
- * I also tried rendering the scrubber (overlay box) during the
+ * I also tried rendering the slider (overlay box) during the
  * GtkTextView::draw_layer() vfunc. The problem with this approach is that
- * the scrubber contents are actually pixel cached. So every time the scrubber
+ * the slider contents are actually pixel cached. So every time the slider
  * moves we have to invalidate the GtkTextLayout and redraw cached contents.
  * Where as drawing in the GtkTextView::draw() vfunc, after the pixel cache
  * contents have been drawn results in only a composite blend, not
@@ -162,7 +162,7 @@ typedef struct
        PangoFontDescription *font_desc;
 
        /*
-        * The easiest way to style the scrubber and the sourceview is
+        * The easiest way to style the slider and the sourceview is
         * by using CSS. This is necessary since we can't mess with the
         * fonts used in the textbuffer (as one might using GtkTextTag).
         */
@@ -177,8 +177,8 @@ typedef struct
        /* The slider widget */
        GtkSourceMapSlider *slider;
 
-       /* The location of the scrubber in widget coordinate space. */
-       GdkRectangle scrubber_area;
+       /* The location of the slider in widget coordinate space. */
+       GdkRectangle slider_area;
 
        /* Weak pointer view to child view bindings */
        GBinding *buffer_binding;
@@ -196,7 +196,7 @@ typedef struct
        /* Denotes if we are in a grab from button press */
        guint in_press : 1;
 
-       /* If we failed to locate a color for the scrubber, then this will
+       /* If we failed to locate a color for the slider, then this will
         * be set to 0 and that means we need to apply the "selection"
         * class when drawing so that we get an appropriate color.
         */
@@ -254,73 +254,55 @@ load_override_font (GtkSourceMap *map)
 #endif
 
 static void
-update_scrubber_position (GtkSourceMap *map)
+update_slider_position (GtkSourceMap *map)
 {
-       GtkSourceMapPrivate *priv;
+       GtkSourceMapPrivate *priv = gtk_source_map_get_instance_private (map);
+       GdkRectangle them_visible_rect;
+       GdkRectangle us_alloc;
+       GdkRectangle slider_area;
        GtkStyleContext *style_context;
-       GtkTextIter iter;
-       GdkRectangle visible_area;
-       GdkRectangle iter_area;
-       GdkRectangle scrubber_area;
-       GtkAllocation alloc;
-       GtkAllocation view_alloc;
+       GtkTextBuffer *buffer;
+       GtkTextIter end_iter;
+       GdkRectangle end_rect;
        GtkBorder border;
-       gint ignored;
-       gint child_height;
-       gint view_height;
-
-       priv = gtk_source_map_get_instance_private (map);
+       int us_height;
+       int them_height;
 
        if (priv->view == NULL)
        {
                return;
        }
 
-       gtk_widget_get_allocation (GTK_WIDGET (priv->view), &view_alloc);
-       gtk_widget_get_allocation (GTK_WIDGET (map), &alloc);
-
-       gtk_widget_measure (GTK_WIDGET (priv->view),
-                           GTK_ORIENTATION_VERTICAL,
-                           gtk_widget_get_width (GTK_WIDGET (priv->view)),
-                           NULL,
-                           &view_height,
-                           NULL, NULL);
-       GTK_WIDGET_CLASS (gtk_source_map_parent_class)->measure (GTK_WIDGET (map),
-                                                                GTK_ORIENTATION_VERTICAL,
-                                                                gtk_widget_get_width (GTK_WIDGET (map)),
-                                                                &ignored, &child_height, &ignored, &ignored);
-
-       gtk_text_view_get_visible_rect (GTK_TEXT_VIEW (priv->view), &visible_area);
-       gtk_text_view_get_iter_at_location (GTK_TEXT_VIEW (priv->view), &iter,
-                                           visible_area.x, visible_area.y);
-       gtk_text_view_get_iter_location (GTK_TEXT_VIEW (map), &iter, &iter_area);
+       gtk_widget_get_allocation (GTK_WIDGET (map), &us_alloc);
 
+       buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (map));
        style_context = gtk_widget_get_style_context (GTK_WIDGET (map));
        gtk_style_context_get_border (style_context, &border);
 
-       scrubber_area.x = 0;
-       scrubber_area.width = alloc.width - border.left - border.right;
-       scrubber_area.y = iter_area.y;
-       scrubber_area.height = ((gdouble)view_alloc.height /
-                               (gdouble)view_height *
-                               (gdouble)child_height) +
-                              iter_area.height;
+       gtk_text_buffer_get_end_iter (buffer, &end_iter);
+       gtk_text_view_get_iter_location (GTK_TEXT_VIEW (map), &end_iter, &end_rect);
+       us_height = end_rect.y + end_rect.height;
+       gtk_text_view_get_iter_location (GTK_TEXT_VIEW (priv->view), &end_iter, &end_rect);
+       them_height = end_rect.y + end_rect.height;
+
+       gtk_text_view_get_visible_rect (GTK_TEXT_VIEW (priv->view), &them_visible_rect);
 
-       if (scrubber_area.height > alloc.height)
-               scrubber_area.height = alloc.height;
-       else if (scrubber_area.height < 0)
-               scrubber_area.height = 1;
+       slider_area.x = 0;
+       slider_area.width = us_alloc.width - border.left - border.right;
+       slider_area.height = 100;
+       slider_area.y = (double)them_visible_rect.y / (double)them_height * (double)us_height;
+       slider_area.height = ((double)(them_visible_rect.y + them_visible_rect.height) / (double)them_height 
* (double)us_height) - slider_area.y;
 
-       if (memcmp (&scrubber_area, &priv->scrubber_area, sizeof scrubber_area) != 0)
+       if (memcmp (&slider_area, &priv->slider_area, sizeof slider_area) != 0)
        {
-               priv->scrubber_area = scrubber_area;
+               priv->slider_area = slider_area;
                gtk_widget_set_size_request (GTK_WIDGET (priv->slider),
-                                            scrubber_area.width,
-                                            scrubber_area.height);
+                                            MAX (0, slider_area.width),
+                                            MAX (0, slider_area.height));
                gtk_text_view_move_overlay (GTK_TEXT_VIEW (map),
                                            GTK_WIDGET (priv->slider),
-                                           scrubber_area.x,
-                                           scrubber_area.y);
+                                           slider_area.x,
+                                           slider_area.y);
                gtk_widget_queue_allocate (GTK_WIDGET (map));
        }
 }
@@ -344,17 +326,17 @@ gtk_source_map_rebuild_css (GtkSourceMap *map)
 
        /*
         * This is where we calculate the CSS that maps the font for the
-        * minimap as well as the styling for the scrubber.
+        * minimap as well as the styling for the slider.
         *
         * The font is calculated from #GtkSourceMap:font-desc. We convert this
         * to CSS using _gtk_source_utils_pango_font_description_to_css(). It
         * gets applied to the minimap widget via the CSS style provider which
         * we attach to the view in gtk_source_map_init().
         *
-        * The rules for calculating the style for the scrubber are as follows.
+        * The rules for calculating the style for the slider are as follows.
         *
         * If the current style scheme provides a background color for the
-        * scrubber using the "map-overlay" style name, we use that without
+        * slider using the "map-overlay" style name, we use that without
         * any transformations.
         *
         * If the style scheme contains a "selection" style scheme, used for
@@ -471,7 +453,7 @@ view_vadj_value_changed (GtkSourceMap  *map,
                          GtkAdjustment *vadj)
 {
        update_child_vadjustment (map);
-       update_scrubber_position (map);
+       update_slider_position (map);
 }
 
 static void
@@ -479,7 +461,7 @@ view_vadj_notify_upper (GtkSourceMap  *map,
                         GParamSpec    *pspec,
                         GtkAdjustment *vadj)
 {
-       update_scrubber_position (map);
+       update_slider_position (map);
 }
 
 static void