[gtk/wip/exalm/textview-selection: 2/4] textlayout: Only special case selection rendering for opaque colors

[Alexander Mikhaylenko <alexm src gnome org>]

commit 960414b82e89cff2e803695c60d54127c5f038d5
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon May 3 19:03:47 2021 +0500

    textlayout: Only special case selection rendering for opaque colors
    
    If the selection is partially transparent, it may still be desirable to
    see the colors from tags underneath.

 gtk/gtktextlayout.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtktextlayout.c b/gtk/gtktextlayout.c
index 20ef614437..c746752be5 100644
--- a/gtk/gtktextlayout.c
+++ b/gtk/gtktextlayout.c
@@ -3873,8 +3873,11 @@ render_para (GskPangoRenderer   *crenderer,
       if (at_last_line)
         selection_height += line_display->bottom_margin;
 
+      /* Don't draw the text underneath if the whole line is selected. We can
+       * only do it if the selection is opaque. */
       if (selection_start_index < byte_offset &&
-          selection_end_index > line->length + byte_offset) /* All selected */
+          selection_end_index > line->length + byte_offset &&
+          selection->alpha >= 1)
         {
           gtk_snapshot_append_color (crenderer->snapshot,
                                      selection,