GtkSourceView/ GtkSourceBuffer - How to mark a line in red and show an icon

I would like to mark some text in a GtkSourceView in red and show an icon. Here my current attempt which seems to do nothing at all:

void plainTextEditor_textView_addLineMarker(int lineNumber, linemarker* marker, context_base* context)
{
    GtkWidget* plainTextEditor_textView = get_plainTextEditor_textView_from_notebook(context->notebook);
    GtkTextIter iter;
    GtkTextBuffer * buffer = gtk_text_view_get_buffer( GTK_TEXT_VIEW(plainTextEditor_textView) );
    gtk_text_buffer_get_iter_at_line( buffer, &iter, lineNumber );
    printf("extendedEditor_linebox_markError %i\n", lineNumber);
    gtk_source_buffer_create_source_mark( GTK_SOURCE_BUFFER(buffer), marker->message, "dialog-error", &iter );
}

The printf prints the correct linenumber.

If I call the method twice, gtk prints some gtk-critical: "Mark myMark already exists in the buffer".

However there is no visible change at all on the gtksourceview.

Probably I should do something with gtk_source_mark_attributes to change properties for a specific category ? But how ? I cannot find any good info on how to use it.

Solution

Ok, I figured it out myself. Here a version which marks the background red and displays a small error-dialog item. If the mouse if hovered over the item, an error-message will be displayed.

//data which is needed in different methods
typedef struct
{
    GtkSourceMarkAttributes* plainTextEditor_lineMarkers_warningAttributes;
    GtkSourceMarkAttributes* plainTextEditor_lineMarkers_errorAttributes;
    ...
} context_base;

// things to do only once
int main(int argc, char *argv[])
{
    ...
    GtkWidget * plainTextEditor_textView = gtk_source_view_new();
    gtk_source_view_set_highlight_current_line (GTK_SOURCE_VIEW(plainTextEditor_textView),TRUE);
    gtk_source_view_set_show_line_numbers (GTK_SOURCE_VIEW(plainTextEditor_textView),TRUE);
    gtk_source_view_set_show_line_marks (GTK_SOURCE_VIEW(plainTextEditor_textView), TRUE);

    context->plainTextEditor_lineMarkers_errorAttributes = gtk_source_mark_attributes_new();
    gtk_source_mark_attributes_set_background(context->plainTextEditor_lineMarkers_errorAttributes, &error_color);
    gtk_source_mark_attributes_set_icon_name(context->plainTextEditor_lineMarkers_errorAttributes,"dialog-error");
    gtk_source_view_set_mark_attributes( GTK_SOURCE_VIEW(plainTextEditor_textView), sourceMarkCategory_error, context->plainTextEditor_lineMarkers_errorAttributes, 10);
    ...
}

// callback to display message when hovering on the linemarker
gchar* on_lineMarkerTooltip_displayed(GtkSourceMarkAttributes *attributes, GtkSourceMark *mark, linemarker* marker)
{
    if( marker->message == NULL)
        return NULL;
    return strdup(marker->message);
}

// method to create new linemark
void plainTextEditor_textView_addLineMarker(int lineNumber, linemarker* marker, context_base* context)
{
    if( context->plainTextEditor_lineMarkers[lineNumber-1]->message != NULL ) // there is a message on this line
    {
        if( strcmp(context->plainTextEditor_lineMarkers[lineNumber-1]->message, marker->message ) == 0 ) // its the same message, nothing to do
        {
            return;
        }
    }
    GtkWidget* plainTextEditor_textView = get_plainTextEditor_textView_from_notebook(context->notebook);
    GtkTextIter iter;
    GtkTextBuffer * buffer = gtk_text_view_get_buffer( GTK_TEXT_VIEW(plainTextEditor_textView) );
    gtk_text_buffer_get_iter_at_line( buffer, &iter, lineNumber );

    context->plainTextEditor_lineMarkers[lineNumber-1]->message = strdup(marker->message);

    char sourceMarkName[sourceMarkNameMaxDigits];
    snprintf(sourceMarkName, sourceMarkNameMaxDigits, "%i", lineNumber);
    gtk_source_view_set_mark_attributes (GTK_SOURCE_VIEW(plainTextEditor_textView),sourceMarkCategory_error,context->plainTextEditor_lineMarkers_errorAttributes,10);
    gtk_source_buffer_create_source_mark( GTK_SOURCE_BUFFER(buffer), sourceMarkName, sourceMarkCategory_error, &iter );
    g_signal_connect(G_OBJECT(context->plainTextEditor_lineMarkers_errorAttributes), "query-tooltip-text", G_CALLBACK(on_lineMarkerTooltip_displayed), context->plainTextEditor_lineMarkers[lineNumber-1]);
}