gistfile1.txt

// custom-cell-renderer-text.h
#ifndef CUSTOM_CELL_RENDERER_H
#define CUSTOM_CELL_RENDERER_H

#include <gtk/gtk.h>

G_DECLARE_FINAL_TYPE (CustomCellRendererText,
                      custom_cell_renderer_text,
                      CUSTOM, CELL_RENDERER_TEXT,
                      GtkCellRendererText)

#define CUSTOM_TYPE_CELL_RENDERER_TEXT custom_cell_renderer_text_get_type()

GtkCellRenderer *custom_cell_renderer_text_new(void);

#endif //CUSTOM_CELL_RENDERER_H


// custom-cell-renderer-text.c
#include "custom-cell-renderer.h"

struct _CustomCellRendererText {
    GtkCellRendererText  renderer;
};

G_DEFINE_TYPE(CustomCellRendererText,
              custom_cell_renderer_text,
              GTK_TYPE_CELL_RENDERER_TEXT);

static void custom_cell_renderer_text_render(GtkCellRenderer *cell,
                                      cairo_t *cr,
                                      GtkWidget *widget,
                                      const GdkRectangle *backarea,
                                      const GdkRectangle *cellarea,
                                      GtkCellRendererState state)
{
    if (state & GTK_CELL_RENDERER_PRELIT) {
        const PangoUnderline prelit = PANGO_UNDERLINE_SINGLE;
        PangoUnderline curr;
        g_object_get(cell, "underline", &curr, NULL);
        g_object_set(cell, "underline", prelit, NULL);
        ((GtkCellRendererClass *)custom_cell_renderer_text_parent_class)->render(cell, cr, widget, backarea, cellarea, state);
        g_object_set(cell, "underline", curr, NULL);
    } else
        ((GtkCellRendererClass *)custom_cell_renderer_text_parent_class)->render(cell, cr, widget, backarea, cellarea, state);
}

static void custom_cell_renderer_text_class_init(CustomCellRendererTextClass *cls)
{
    ((GtkCellRendererClass *)cls)->render = custom_cell_renderer_text_render;
    return;
}

static void custom_cell_renderer_text_init(CustomCellRendererText *renderer)
{
    return;
}

GtkCellRenderer *custom_cell_renderer_text_new(void)
{
    return g_object_new(CUSTOM_TYPE_CELL_RENDERER_TEXT, NULL);
}