alphademo

from http://plan99.net/~mike/files/alphademo.c

1 files changed, 127 insertions, 0 deletions

diff --git a/alphademo.c b/alphademo.c
new file mode 100644
index 0000000..5e19429
--- /dev/null
+++ b/alphademo.c
@@ -0,0 +1,127 @@
+// gcc -o alphademo alphademo.c `pkg-config --cflags --libs gtk+-2.0`
+
+#include <gtk/gtk.h>
+#include <gdk/gdk.h>
+#include <cairo.h>
+
+/*
+ * This program shows you how to create semi-transparent windows,
+ * without any of the historical screenshot hacks. It requires
+ * a modern system, with a compositing manager. I use xcompmgr
+ * and the nvidia drivers with RenderAccel, and it works well.
+ *
+ * I'll take you through each step as we go. Minimal GTK+ knowledge is
+ * assumed.
+ */
+
+static void screen_changed(GtkWidget *widget, GdkScreen *old_screen, gpointer user_data);
+static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer user_data);
+static void clicked(GtkWindow *win, GdkEventButton *event, gpointer user_data);
+
+int main(int argc, char **argv)
+{
+    /* boilerplate initialization code */
+    gtk_init(&argc, &argv);
+    
+    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
+    gtk_window_set_title(GTK_WINDOW(window), "Alpha Demo");
+    g_signal_connect(G_OBJECT(window), "delete-event", gtk_main_quit, NULL);
+
+
+    /* Tell GTK+ that we want to draw the windows background ourself.
+     * If we don't do this then GTK+ will clear the window to the
+     * opaque theme default color, which isn't what we want.
+     */
+    gtk_widget_set_app_paintable(window, TRUE);
+
+    /* We need to handle two events ourself: "expose-event" and "screen-changed".
+     *
+     * The X server sends us an expose event when the window becomes
+     * visible on screen. It means we need to draw the contents.  On a
+     * composited desktop expose is normally only sent when the window
+     * is put on the screen. On a non-composited desktop it can be
+     * sent whenever the window is uncovered by another.
+     *
+     * The screen-changed event means the display to which we are
+     * drawing changed. GTK+ supports migration of running
+     * applications between X servers, which might not support the
+     * same features, so we need to check each time.
+     */
+
+    g_signal_connect(G_OBJECT(window), "expose-event", G_CALLBACK(expose), NULL);
+    g_signal_connect(G_OBJECT(window), "screen-changed", G_CALLBACK(screen_changed), NULL);
+
+    /* toggle title bar on click - we add the mask to tell X we are interested in this event */
+    gtk_window_set_decorated(GTK_WINDOW(window), FALSE);
+    gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);
+    g_signal_connect(G_OBJECT(window), "button-press-event", G_CALLBACK(clicked), NULL);
+
+    /* initialize for the current display */
+    screen_changed(window, NULL, NULL);
+
+    /* Run the program */
+    gtk_widget_show_all(window);
+    gtk_main();
+
+    return 0;
+}
+
+
+/* Only some X servers support alpha channels. Always have a fallback */
+gboolean supports_alpha = FALSE;
+
+static void screen_changed(GtkWidget *widget, GdkScreen *old_screen, gpointer userdata)
+{
+    /* To check if the display supports alpha channels, get the colormap */
+    GdkScreen *screen = gtk_widget_get_screen(widget);
+    GdkColormap *colormap = gdk_screen_get_rgba_colormap(screen);
+
+    if (!colormap)
+    {
+        printf("Your screen does not support alpha channels!\n");
+        colormap = gdk_screen_get_rgb_colormap(screen);
+        supports_alpha = FALSE;
+    }
+    else
+    {
+        printf("Your screen supports alpha channels!\n");
+        supports_alpha = TRUE;
+    }
+
+    /* Now we have a colormap appropriate for the screen, use it */
+    gtk_widget_set_colormap(widget, colormap);
+}
+
+/* This is called when we need to draw the windows contents */
+static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer userdata)
+{
+    cairo_t *cr = gdk_cairo_create(widget->window);
+
+    if (supports_alpha)
+        cairo_set_source_rgba (cr, 1.0, 1.0, 1.0, 0.0); /* transparent */
+    else
+        cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* opaque white */
+
+    /* draw the background */
+    cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
+    cairo_paint (cr);
+
+    /* draw a circle */
+    int width, height;
+    gtk_window_get_size(GTK_WINDOW(widget), &width, &height);
+
+    cairo_set_source_rgba(cr, 1, 0.2, 0.2, 0.6);
+    cairo_arc(cr, width / 2, height / 2, (width < height ? width : height) / 2 - 8 , 0, 2 * 3.14);
+    cairo_fill(cr);
+    cairo_stroke(cr);
+    
+    cairo_destroy(cr);
+    return FALSE;
+}
+
+static void clicked(GtkWindow *win, GdkEventButton *event, gpointer user_data)
+{
+    /* toggle window manager frames */
+    gtk_window_set_decorated(win, !gtk_window_get_decorated(win));
+}
+