gtk font rendering using native windows handle

Question

I made a small gui app for rendering text using gtk+2. To tackle horrible fonts on win32. I am creating a cairo surface using native windows handle (HDC). Now font look beautiful in windows but it appears that canvas do not update correctly after drawing operations unless i resize the window. this happens only on win32.

Below code compiles on linux and win32 both

#include <iostream>
#include <gtk/gtk.h>
#include <unistd.h>

#ifdef WIN32
#include <cairo-win32.h>
#include <gdk/gdkwin32.h>
#include <pango/pangowin32.h>
#include <windows.h>
#endif

using namespace std;

GtkWidget* drgArea;
GtkWidget* window;

int x = 0;
int y = 0;
string text = "click on this window";

void on_mouse_down(GtkWidget *widget, GdkEventButton *event, gpointer data) {
    x = event->x;
    y = event->y;
    gtk_widget_queue_draw(drgArea);
}

gboolean on_draw(GtkWidget *widget, GdkEventExpose *event, gpointer data) {
    cout << "on_draw=" << widget << endl;

    cairo_t* cr;
    PangoLayout* layout;
    PangoContext* pangoContext;
    GdkGC* gc;

#ifdef CAIRO_HAS_WIN32_SURFACE
    gc = gdk_gc_new(widget->window);
    HDC hdc = gdk_win32_hdc_get(widget->window, gc, GDK_GC_SUBWINDOW);
    cairo_surface_t* cairo_win_surf;
    cairo_win_surf = cairo_win32_surface_create (hdc);
    cr = cairo_create(cairo_win_surf);

#else
    cr = gdk_cairo_create(widget->window);
#endif

    pangoContext = pango_cairo_create_context(cr);
    layout = pango_layout_new(pangoContext);
    pango_layout_set_text(layout, (const char*) text.c_str(), text.size());
    cairo_set_source_rgb(cr, 0, 0, 0);
    cairo_move_to(cr, x, y);
    pango_cairo_show_layout(cr, layout);
    cairo_destroy(cr);

#ifdef CAIRO_HAS_WIN32_SURFACE
    gdk_win32_hdc_release(widget->window, gc, GDK_GC_SUBWINDOW);
#endif

    return TRUE;
}

int main(int argc, char** argv) {
    cout << "**** main ****" << endl;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    drgArea = gtk_drawing_area_new();
    gtk_widget_set_events(drgArea,
            GDK_POINTER_MOTION_MASK | GDK_BUTTON_PRESS_MASK
                    | GDK_BUTTON_RELEASE_MASK);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
    gtk_widget_set_size_request(window, 400, 300);
    gtk_container_add(GTK_CONTAINER(window), drgArea);
    gtk_widget_show_all(window);

    g_signal_connect(drgArea, "button-press-event", G_CALLBACK(on_mouse_down),
            NULL);
    g_signal_connect(drgArea, "expose-event", G_CALLBACK(on_draw), NULL);

    gtk_main();
    return 0;
}

I am also looking for any other suggestions that you might think appropriate.

Answer 1

I found the solution window double buffering must be set off

https://people.gnome.org/~federico/misc/gtk-drawing-model/