Problem solved.
To prevent flashes of the black screen during configure-event we need to
implicitly call actual drawing procedure right after the off-screen
buffer is recreated.
static gboolean configureCanvas(GtkWidget *widget, GdkEventConfigure
*event ) {
if (pixmap) g_object_unref(pixmap);
pixmap = gdk_pixmap_new(widget->window, widget->allocation.width,
widget->allocation.height, -1);
drawAll(); // just add this!
return TRUE;
}
Full source of my test application is in the attachment - may be it
would be useful for other cairo-newbies :)
On 12/13/2011 1:30 PM, George Brink wrote:
I am trying to make an animated image:
----------------------------------------------
static gboolean exposeCanvas(GtkWidget *widget, GdkEventExpose *event,
gpointer data) {
cairo_t *cr = gdk_cairo_create (event->window);
gdk_cairo_set_source_pixmap (cr, pixmap, 0, 0);
gdk_cairo_rectangle (cr, &event->area);
cairo_fill (cr);
cairo_destroy (cr);
return FALSE;
}
static gboolean configureCanvas(GtkWidget *widget, GdkEventConfigure
*event ) {
if (pixmap) g_object_unref(pixmap);
pixmap = gdk_pixmap_new(widget->window, widget->allocation.width,
widget->allocation.height, -1);
return TRUE;
}
GtkWidget *canvas = gtk_drawing_area_new();
gtk_container_add(GTK_CONTAINER(mainWindow), canvas);
g_signal_connect(G_OBJECT(canvas), "expose_event",
G_CALLBACK(exposeCanvas), NULL);
g_signal_connect(G_OBJECT(canvas), "configure_event",
G_CALLBACK(configureCanvas), NULL);
----------------------------------------------
It works fine on a static window, but when I actually change the size of
the window the whole drawing area goes black for a moment.
What am I doing wrong?
#include <glib.h>
#include <gtk/gtk.h>
#include <math.h>
static GdkPixmap *pixmap = NULL;
void drawAll() {
static gdouble angle=0;
// actual drawing - moving line over the grid
#define WIDTH 20
#define HEIGHT 20
#define LINE_LENGTH 5
guint width, height;
gdk_drawable_get_size(pixmap, &width, &height);
cairo_t *cr = gdk_cairo_create(pixmap);
cairo_set_source_rgb (cr, 0.8, 0.8, 0.8);
cairo_paint(cr);
guint x = (width -2)/WIDTH;
guint y = (height -2)/HEIGHT;
guint8 cellSize = x<y ? x : y;
guint leftPadding = (width - WIDTH*cellSize) / 2;
guint topPadding = (height - HEIGHT*cellSize) / 2;
cairo_set_line_width (cr, 1.0);
cairo_set_line_cap (cr, CAIRO_LINE_CAP_SQUARE);
cairo_set_source_rgb (cr, 0.3, 0.3, 0.3);
for(x=0; x<=WIDTH; x++) {
cairo_move_to (cr, leftPadding+x*cellSize, topPadding);
cairo_line_to (cr, leftPadding+x*cellSize, topPadding+HEIGHT*cellSize);
}
for(y=0; y<=HEIGHT; y++) {
cairo_move_to (cr, leftPadding, topPadding+y*cellSize);
cairo_line_to (cr, leftPadding+WIDTH*cellSize, topPadding+y*cellSize);
}
cairo_stroke(cr);
cairo_set_line_width (cr, 3.0);
cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
cairo_move_to (cr, width/2, height/2);
cairo_line_to (cr, width/2 + cos(angle)*LINE_LENGTH*cellSize, height/2 + sin(angle)*LINE_LENGTH*cellSize);
angle += M_PI/180.0;
if(angle> 2*M_PI) angle=0;
cairo_stroke(cr);
cairo_destroy(cr);
}
static gboolean exposeCanvas(GtkWidget *widget, GdkEventExpose *event, gpointer data) {
cairo_t *cr = gdk_cairo_create (event->window);
gdk_cairo_set_source_pixmap (cr, pixmap, 0, 0);
gdk_cairo_rectangle (cr, &event->area);
cairo_fill (cr);
cairo_destroy (cr);
return FALSE;
}
static gboolean configureCanvas(GtkWidget *widget, GdkEventConfigure *event ) {
if (pixmap) g_object_unref(pixmap);
pixmap = gdk_pixmap_new(widget->window, widget->allocation.width, widget->allocation.height, -1);
drawAll();
return TRUE;
}
static gboolean timerTick(gpointer data) {
drawAll();
GDK_THREADS_ENTER ();
gtk_widget_queue_draw (GTK_WIDGET(data));
GDK_THREADS_LEAVE ();
return TRUE;
}
int main(int argc, char **argv) {
gtk_init(&argc, &argv);
GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
gtk_window_set_title(GTK_WINDOW(window), "test");
GtkWidget *canvas = gtk_drawing_area_new();
gtk_container_add(GTK_CONTAINER(window), canvas);
g_signal_connect(G_OBJECT(canvas), "expose_event", G_CALLBACK(exposeCanvas), NULL);
g_signal_connect(G_OBJECT(canvas), "configure_event", G_CALLBACK(configureCanvas), NULL);
guint timerID = g_timeout_add(100, timerTick, canvas);
gtk_widget_show_all(window);
gtk_main();
return 0;
}
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