GTK+ Drawing_Area Image Redraw with Expose Event - c

Question

I have a program in C that basically reads an image into a char buffer, performs some manipulation to its pixels before displaying the image back to the screen.
So far, the image displays fine; but I encountered the two issues below:
When I minimize the GTK window and bring it back up again, the image just disappears, leaving the Drawing_Area empty.
How do I redraw/update the image in the Drawing_Area with a button push?
Here's the function that does the drawing:
void Draw_Img(GtkWidget *widget, unsigned char **buffer,int x_offset,int y_offset,int x1, int y1,int x2, int y2)
{
int i,j;
int width,height;
width=x2-x1+1;
height=y2-y1+1;
for(j=0;j<width*height;j++)
tmp_buf[j]=0;
for(j=y1;j<=y2;j++)
for(i=x1;i<=x2;i++)
tmp_buf[j*width+i-x1]=buffer[j][i];
gdk_draw_gray_image(widget->window,
widget->style->fg_gc[GTK_STATE_NORMAL], x_offset, y_offset,
width, height, GDK_RGB_DITHER_NONE, tmp_buf, width);
}
The main function:
int main(int argc,char **argv)
{
gtk_init (&argc, &argv);
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_title(GTK_WINDOW (window), "RESET DEMO");
gtk_window_set_resizable(GTK_WINDOW(window), FALSE);
g_signal_connect (G_OBJECT (window), "destroy",
G_CALLBACK (gtk_main_quit), NULL);
button = gtk_button_new_from_stock (GTK_STOCK_CLOSE);
g_signal_connect_swapped (button, "clicked", G_CALLBACK (display), drawing_area);
vbox = gtk_vbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (window), vbox);
gtk_widget_show (vbox);
gtk_widget_set_size_request(drawing_area, Test_Size*3, Test_Size);
gtk_box_pack_start (GTK_BOX (vbox), drawing_area, TRUE, TRUE, 0);
gtk_widget_show(drawing_area);
gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
gtk_widget_set_can_default (button, TRUE);
gtk_widget_grab_default (button);
gtk_widget_show (button);
gtk_widget_show(window);
/*
reads image into buffer before calling the "display" function in which
calls the Draw_Img function
*/
myinit();
g_signal_connect (G_OBJECT (drawing_area), "expose_event",
G_CALLBACK (display), NULL);
gtk_main();
}
Thanks in advance for any help/input.

Answer 1

gtk_widget_queue_draw will requeue the widget to be redrawn.
Minimiziing and un-minimizing should not cause a blank window, smells like a bug in code you did not provide.

Answer 2

I found the solution here : http://blog.csdn.net/zhongguomin/article/details/7088575
After debug two days , I know the way.
Attention： un-minimize will cause expose-event.
Draw (pix,line,arc,rect,pixbuf) on pixmap , and then queue_draw (will emit expose_event), put a gdk_draw_drawable(pixmap) in expose_event.
g_signal_connect (G_OBJECT (drawarea), "expose_event", G_CALLBACK (expose_event_callback), NULL);
gboolean expose_event_callback (GtkWidget * widget, GdkEventExpose * event, gpointer data)
{
g_message ("expose_event");
gdk_draw_drawable (widget->window, gc, pixmap, 0, 0, 0, 0, widget->allocation.width, widget->allocation.height);
return TRUE;
}
......
gdk_draw_line (pixmap, gc, xa, ya, xb, yb);
gtk_widget_queue_draw (drawarea);
gdk_draw_rectangle (pixmap, gc, FALSE, x, y, w, h);
gtk_widget_queue_draw (drawarea);
gdk_draw_arc (pixmap, gc, FALSE, xb, ya, w, h, 0, 360 * 64);
gtk_widget_queue_draw (drawarea);
//image from file !!!
filename = gtk_file_chooser_get_filename (GTK_FILE_CHOOSER (FCD));
GdkPixbuf *pixbuf = gdk_pixbuf_new_from_file (filename, &error);
gdk_draw_pixbuf (pixmap, gc, pixbuf, 0, 0, 0, 0, -1, -1, GDK_RGB_DITHER_NORMAL, 0, 0);
gtk_widget_queue_draw (drawarea);
But I still have a problem , when I try to resize the drawarea , the pixmap will crash.
Then I del if(pixmap)g_object_unref(pixmap); , the crash disappeared , it is really a big hole !
Then I make a new pixmap of new size , the size can change !
And allocation.width , allocation.height do not take effect before queue_draw , you can not use pixmap = gdk_pixmap_new (GDK_DRAWABLE (drawarea->window), widget->allocation.width, widget->allocation.height, -1); right now !
int wpb = gdk_pixbuf_get_width (pixbuf);
int hpb = gdk_pixbuf_get_height (pixbuf);
g_message ("%d X %d", wpb, hpb);
gtk_widget_set_size_request(drawarea,wpb,hpb);
pixmap = gdk_pixmap_new (GDK_DRAWABLE (drawarea->window),wpb,hpb, -1);
......