[vte/vte-0-62] widget: Define text_view_bg in fallback CSS if the theme doesn't

[Simon McVittie <smcv src gnome org>]

commit ed887c2e3768083cfc59e93470eb74f2485812d4
Author: Simon McVittie <smcv debian org>
Date:   Wed Sep 23 09:52:13 2020 +0100

    widget: Define text_view_bg in fallback CSS if the theme doesn't
    
    Adwaita defines text_view_bg since GTK 3.24.22, but non-Adwaita themes
    such as the built-in HighContrast[Inverse] and the third-party Numix
    don't necessarily. Unfortunately, if it isn't defined, GTK treats that
    as equivalent to it being fully transparent, leading to misrendering
    that often makes terminal text unreadable.
    
    Use a fallback style provider to make sure text_view_bg is always
    defined, using the theme base colour if necessary. This is done at a
    low priority, so that themes like Adwaita have the opportunity to
    override it.
    
    Resolves: https://gitlab.gnome.org/GNOME/vte/-/issues/284
    Signed-off-by: Simon McVittie <smcv debian org>

 src/vtegtk.cc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)
---
diff --git a/src/vtegtk.cc b/src/vtegtk.cc
index 39f1c0ba..66456cec 100644
--- a/src/vtegtk.cc
+++ b/src/vtegtk.cc
@@ -75,6 +75,7 @@
 #define VTE_TERMINAL_CSS_NAME "vte-terminal"
 
 struct _VteTerminalClassPrivate {
+        GtkStyleProvider *fallback_style_provider;
         GtkStyleProvider *style_provider;
 };
 
@@ -555,6 +556,9 @@ try
        _vte_debug_print(VTE_DEBUG_LIFECYCLE, "vte_terminal_init()\n");
 
         context = gtk_widget_get_style_context(&terminal->widget);
+        gtk_style_context_add_provider (context,
+                                        VTE_TERMINAL_GET_CLASS (terminal)->priv->fallback_style_provider,
+                                        GTK_STYLE_PROVIDER_PRIORITY_FALLBACK);
         gtk_style_context_add_provider (context,
                                         VTE_TERMINAL_GET_CLASS (terminal)->priv->style_provider,
                                         GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
@@ -2015,15 +2019,16 @@ vte_terminal_class_init(VteTerminalClass *klass)
 
         klass->priv = G_TYPE_CLASS_GET_PRIVATE (klass, VTE_TYPE_TERMINAL, VteTerminalClassPrivate);
 
+        klass->priv->fallback_style_provider = GTK_STYLE_PROVIDER (gtk_css_provider_new ());
+        /* Some themes don't define text_view_bg */
+        gtk_css_provider_load_from_data (GTK_CSS_PROVIDER (klass->priv->fallback_style_provider),
+                                         "@define-color text_view_bg @theme_base_color;",
+                                         -1, NULL);
         klass->priv->style_provider = GTK_STYLE_PROVIDER (gtk_css_provider_new ());
         gtk_css_provider_load_from_data (GTK_CSS_PROVIDER (klass->priv->style_provider),
                                          "VteTerminal, " VTE_TERMINAL_CSS_NAME " {\n"
                                          "padding: 1px 1px 1px 1px;\n"
-#if GTK_CHECK_VERSION (3, 24, 22)
                                          "background-color: @text_view_bg;\n"
-#else
-                                         "background-color: @theme_base_color;\n"
-#endif
                                          "color: @theme_text_color;\n"
                                          "}\n",
                                          -1, NULL);