<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div> Hi Simon, Thanks for the very useful advice... I can make the GdkPixbufLoader work if the program does not prepare eventhandlers for area-prepared and area-updated. However, if I connect these they will not trigger and call the handlers. The test program is small so I can add it inline. Hope someone can see what is wrong... Ken P.S. The test program: static cairo_surface_t * imgpng ; static unsigned char bigbuf [ 200000 ] ; static GdkPixbuf * pixbuf; static GdkPixbufLoader * loader ; static GdkPixbuf * makepixbuf ( bool byfilename , const char * filename ) { GError * err = NULL ; if ( byfilename ) { return gdk_pixbuf_new_from_file(filename,&err); } // read file content into buffer FILE * f = fopen ( filename, "r"); int length = fread (bigbuf, 1, sizeof(bigbuf), f); fclose (f); loader = gdk_pixbuf_loader_new (); gdk_pixbuf_loader_write (loader, bigbuf, length, NULL); gdk_pixbuf_loader_close (loader , &err ) ; //printf ( "pixbuf may not yet be ready...\n" ) ; //return NULL ; // actually it is ready here!!!!! return pixbuf = gdk_pixbuf_loader_get_pixbuf (loader); } static void do_drawing(cairo_t *cr) { cairo_set_source_surface(cr, imgpng , 0,40); cairo_paint(cr); if ( pixbuf != NULL ) { gdk_cairo_set_source_pixbuf(cr, pixbuf, 0, 150); cairo_paint (cr); } } static gboolean on_draw_event(GtkWidget *widget, cairo_t *cr, gpointer user_data) { cr = gdk_cairo_create(gtk_widget_get_window(widget)); do_drawing(cr); cairo_destroy(cr); return FALSE; } static void on_area_prep( GdkPixbufLoader *loader, gpointer user_data) { // this is not called printf ( "area-prepared: pixbuf ready\n" ) ; pixbuf = gdk_pixbuf_loader_get_pixbuf (loader); } static void on_area_update( GdkPixbufLoader *loader, gint x , gint y , gint width , gint height , gpointer user_data) { // same here - not called printf ( "area-updated: pixbuf ready\n" ) ; pixbuf = gdk_pixbuf_loader_get_pixbuf (loader); } int main(int argc, char *argv[]) { GtkWidget *window; GtkWidget *darea; gtk_init(&argc, &argv); imgpng = cairo_image_surface_create_from_png("sample_7.png"); pixbuf = makepixbuf ( false , "parrots.jpg" ); window = gtk_window_new(GTK_WINDOW_TOPLEVEL); darea = gtk_drawing_area_new(); gtk_container_add(GTK_CONTAINER(window), darea); g_signal_connect(G_OBJECT(darea), "draw", G_CALLBACK(on_draw_event), NULL); g_signal_connect(G_OBJECT(loader), "area-prepared", G_CALLBACK(on_area_prep), NULL); g_signal_connect(G_OBJECT(loader), "area-updated", G_CALLBACK(on_area_update), NULL); g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL); gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER); gtk_window_set_default_size(GTK_WINDOW(window), 400, 90); gtk_window_set_title(GTK_WINDOW(window), "GTK window"); gtk_widget_show_all(window); gtk_main(); cairo_surface_destroy(imgpng); return 0; } </div><div> </div> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <hr size="1"> From: Simon Sapin <simon.sapin@exyr.org> To: cairo@cairographics.org Sent: Friday, 5 April 2013, 15:13 Subject: Re: [cairo] How to output images from data originating from files? </div> Le 05/04/2013 16:03, Ken Resander a écrit : > I am new to Cairo and have fairly limited knowlege of graphics (Windows > GDI,GDI+ years ago). > I am now on Ubuntu 12.04 and need to render images in png and jpg from > GTK in C/C++. > > I know how to do this when specifying .png and .jpg file names: > > cairo_surface_t * imgpng = > cairo_image_surface_create_from_png("sample_7.png"); > cairo_set_source_surface(cr, imgpng, 0,40); > cairo_paint(cr); > > GError * err = NULL; > GdkPixbuf * imgpxb = gdk_pixbuf_new_from_file("parrots.jpg",&err); > gdk_cairo_set_source_pixbuf(cr, imgpxb, 0, 150); > cairo_paint (cr); > > My program will receive image data from another computer via standard > protocols. There might be hundreds of small to small-medium images > coming, so it would more efficient to batch the file content of these > into a huge buffer and pass that across (from the other computer) along > with the image format, buffer offset and length of each chunk. > > Of course I could copy a chunk into a tmp file and use the png surface > and gdkpixbuf filename api calls above, but it seems such a shame having > to put the data back into a file for cairo/gdk to read and convert it to > the format needed. > > Is there a better way? Hi, If you have images (not all PNG) in memory, the easiest way to load them without going through temporary files is to use GdkPixbufLoader: <a href="https://developer.gnome.org/gdk-pixbuf/stable/GdkPixbufLoader.html" target="_blank">https://developer.gnome.org/gdk-pixbuf/stable/GdkPixbufLoader.html</a> This will give you GdkPixbuf objects that you can convert to cairo patterns with gdk_cairo_set_source_pixbuf, as you do above. Cheers, -- Simon Sapin -- cairo mailing list <a ymailto="mailto:cairo@cairographics.org" href="mailto:cairo@cairographics.org">cairo@cairographics.org</a> <a href="http://lists.cairographics.org/mailman/listinfo/cairo" target="_blank">http://lists.cairographics.org/mailman/listinfo/cairo</a> </div> </div> </div></body></html>