[cairo] Call to cairo_paint triggers an assertion

Tim Corio tcorio at rochester.rr.com
Wed Jan 6 11:31:53 PST 2010


I chanced upon a function called gdk_cairo_set_source_pixbuf(...).  This
let me get rid of the Cairo Surface.  Now, this code works.

For review:  This demo program loads an image file called orig.jpg,
rotates it, then draws it to a GtkImage that had previously been created
by loading an image called blank.jpg.

Both these test images are 200x200 pixels.  I'm assuming the handling of
images of arbitrary size is a solved problem in GTK.

I appreciate the help I've gotten on this list.  You've been patient and
helpful with my newbie questions.

Thank You,
Tim Corio

#include <gtk/gtk.h>

#define WIDTH  200
#define HEIGHT 200

static void destroy( GtkWidget *widget,
                     gpointer   data )
  gtk_main_quit ();

int main( int   argc,
          char *argv[] )
  GtkWidget *window;
  GtkWidget *box_image;

  GdkPixbuf *pxb_orig;
  GdkPixmap *pxm_dest;

  GtkImage  *img_orig;
  GtkImage  *img_dest;

  GError *gerror = NULL;

  cairo_t   *cr = NULL;

  GdkColor blue;
  GdkColor black;
  GdkColor white;

  gtk_init (&argc, &argv);

  blue.red   =0x0000; blue.green   =0x0000; blue.blue   =0xffff;
  black.red  =0x0000; black.green  =0x0000; black.blue  =0x0000;
  white.red  =0xffff; white.green  =0xffff; white.blue  =0xffff;

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (G_OBJECT (window),
                    G_CALLBACK (destroy),
  gtk_window_set_title (GTK_WINDOW (window), "GtkScrolledWindow
  gtk_container_set_border_width (GTK_CONTAINER (window), 5);
  gtk_widget_set_size_request (window, 700, 300);

  box_image = gtk_hbox_new (TRUE, 5);

  pxb_orig = gdk_pixbuf_new_from_file("orig.jpg", &gerror);
  img_orig = (GtkImage *)gtk_image_new_from_pixbuf (pxb_orig);

  gtk_container_add (GTK_CONTAINER (window), box_image);

  gtk_box_pack_start (GTK_BOX (box_image), GTK_WIDGET(img_orig), FALSE,
FALSE, 0);

  img_dest    = (GtkImage *)gtk_image_new_from_file ("blank.jpg");

  gtk_box_pack_start (GTK_BOX (box_image), GTK_WIDGET(img_dest), FALSE,
FALSE, 0);

  gtk_widget_show ((GtkWidget *)img_dest);
  gtk_widget_show ((GtkWidget *)img_orig);
  gtk_widget_show (box_image);
  gtk_widget_show (window);

  /* ************************************************** */
  /* Draw to the output image. */

  guchar          *data;
  int              datasize;

  datasize   = WIDTH * HEIGHT * 4;
  data       = g_malloc0 (datasize);

  pxm_dest = gdk_pixmap_create_from_data (window->window,    /* drawable
                                          data,              /* data */
                                          WIDTH,   /* width */
                                          HEIGHT,  /* height */
                                          24,                /* depth */
                                          &black,            /*
forground */
                                          &white);           /*
background */

  gdk_drawable_set_colormap (pxm_dest, gdk_colormap_get_system());

  cr = gdk_cairo_create (pxm_dest);
  cairo_rotate (cr, 0.5);
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  gdk_cairo_set_source_pixbuf (cr, pxb_orig, 0, 0);

  gtk_image_set_from_pixmap (GTK_IMAGE(img_dest), pxm_dest, NULL);

  /* ************************************************** */


  return 0;

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