[gtksourceview] view: improve grid placement

[Christian Hergert <chergert src gnome org>]

commit af74dfc9f4ca66b0af4c02ed2acda25772dd8076
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jan 6 09:52:25 2022 -0800

    view: improve grid placement
    
    This improves the placement of grid lines a bit by repeating at the whole
    character size rather than the half-height. The previous form was more
    likely to drift from the desired size just from odd-integer height of
    a sized character.
    
    Additionally, if we are not line-wrapping, we can use the lines yrange
    to find a better half-grid-height so that we don't alias the grid boxes
    across lines of text.

 gtksourceview/gtksourceview.c | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)
---
diff --git a/gtksourceview/gtksourceview.c b/gtksourceview/gtksourceview.c
index 3141f20e..ed55e1ef 100644
--- a/gtksourceview/gtksourceview.c
+++ b/gtksourceview/gtksourceview.c
@@ -2612,11 +2612,14 @@ gtk_source_view_paint_background_pattern_grid (GtkSourceView *view,
 {
        GtkSourceViewPrivate *priv = gtk_source_view_get_instance_private (view);
        GdkRectangle visible_rect;
-       gint x, y, x2, y2;
+       int x, y, x2, y2;
        PangoContext *context;
        PangoLayout *layout;
-       gint grid_width = 16;
-       gint grid_height = 16;
+       GtkTextIter iter;
+       int grid_half_height = 8;
+       int grid_width = 16;
+       int grid_height = 16;
+       int line_y, line_height;
 
        gtk_text_view_get_visible_rect (GTK_TEXT_VIEW (view), &visible_rect);
 
@@ -2626,25 +2629,41 @@ gtk_source_view_paint_background_pattern_grid (GtkSourceView *view,
        pango_layout_get_pixel_size (layout, &grid_width, &grid_height);
        g_object_unref (layout);
 
+       /* Try to take CSS line-height into account */
+       if (gtk_text_view_get_wrap_mode (GTK_TEXT_VIEW (view)) == GTK_WRAP_NONE)
+       {
+               gtk_text_view_get_iter_at_location (GTK_TEXT_VIEW (view), &iter, visible_rect.x, 
visible_rect.y);
+               gtk_text_view_get_line_yrange (GTK_TEXT_VIEW (view), &iter, &line_y, &line_height);
+
+               if (line_height > grid_height)
+               {
+                       grid_height = line_height;
+               }
+       }
+
        /* each character becomes 2 stacked boxes. */
-       grid_height = MAX (1, grid_height / 2);
+       grid_height = MAX (1, grid_height);
+       grid_half_height = grid_height / 2;
        grid_width = MAX (1, grid_width);
 
        /* Align our drawing position with a multiple of the grid size. */
        x = realign (visible_rect.x - grid_width, grid_width);
-       y = realign (visible_rect.y - grid_height, grid_height);
+       y = realign (visible_rect.y - grid_half_height, grid_half_height);
        x2 = realign (x + visible_rect.width + grid_width * 2, grid_width);
-       y2 = realign (y + visible_rect.height + grid_height * 2, grid_height);
+       y2 = realign (y + visible_rect.height + grid_height, grid_height);
 
        gtk_snapshot_push_repeat (snapshot,
                                  &GRAPHENE_RECT_INIT (x, y, x2 - x, y2 - y),
                                  &GRAPHENE_RECT_INIT (x, y, grid_width, grid_height));
        gtk_snapshot_append_color (snapshot,
                                   &priv->background_pattern_color,
-                                  &GRAPHENE_RECT_INIT (x, y, 1, grid_height));
+                                  &GRAPHENE_RECT_INIT (x+1, y, 1, grid_height));
        gtk_snapshot_append_color (snapshot,
                                   &priv->background_pattern_color,
                                   &GRAPHENE_RECT_INIT (x, y, grid_width, 1));
+       gtk_snapshot_append_color (snapshot,
+                                  &priv->background_pattern_color,
+                                  &GRAPHENE_RECT_INIT (x, y + grid_half_height, grid_width, 1));
        gtk_snapshot_pop (snapshot);
 }