How to refresh a GTK image? - c

Question

Hi people from Stackoverflow, I have some knowledge of programming, but not very much. My idea is to program something like a video-game or visualizer in c, to do so I make and process somehow an array that represents an image and it has to be visualized and always being refreshed, like a video-game. I have the algorithm already done, I need to optimize it, I mean I know how to create the array representing an image at anytime, what I need now is to visualize it like an animation and later optimize with opencl.
The program that I want to make has to do something like this:
"create the image"
"render it",
"create the image"
"render it",
...
For that reason I know that I could start easily from a very simple example and I don't have to learn everything of GTK. I have been intensively searching for simple examples and trying to understand how it works but it didn't help, I need just to do that simple action, refresh it. A command somewhere should be enough.
#include <gtk/gtk.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <glib.h>
const int Width = 1200, Height = 800;
char *buffer;
int i = 0;
GdkPixbuf *pixbuf;
GtkWidget *window;
GtkWidget* image;
void delay(int number_of_seconds){
int milli_seconds = 1000 * number_of_seconds;
clock_t start_time = clock();
while (clock() < start_time + milli_seconds);
}
int main (int argc, char *argv[]){
buffer = (char*)malloc(3 * Width * Height);
// CREATE AN IMAGE IN BUFFER SOMEHOW
// buffer = something;
//
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
pixbuf = gdk_pixbuf_new_from_data (buffer, GDK_COLORSPACE_RGB, FALSE, 8, Width, Height, (Width)*3, NULL, NULL);
image = gtk_image_new_from_pixbuf (pixbuf);
gtk_container_add(GTK_CONTAINER (window), image);
gtk_window_set_title (GTK_WINDOW (window), "Visualizador");
gtk_widget_show_all (window);
delay(0.04);
gtk_main ();
free (buffer);
return 0;
}
The program is really simple, when I create/load the image there it shows a picture, but I would like to put the function already programmed there, to return a "buffer" and then refresh the displayed image.
I read that gtk_widget_queue_draw has something to do, or gdk_pixbuf_simple_anim_add_frame or g_timeout_add but I have no idea how they work and what to put in this program.
Thank you in advance!

Answer 1

If you want a moving image or something that needs to get refreshed a lot then I would suggest using a GtkDrawingArea and implement it's draw signal, for that you'll need to use cairo. It should look something like this:
static gboolean
your_draw_cb(GtkWidget *widget, cairo_t *context, gpointer data)
{
// Do your drawing
return FALSE;
}
int main()
{
// Some code before ...
GtkWidget *area = gtk_drawing_area_new();
g_signal_connect(G_OBJECT(area), "draw", G_CALLBACK(your_draw_cb), your_data);
gtk_container_add(GTK_CONTAINER(your_container), area);
// More code ...
}
Each time you want to refresh it you should call
gtk_widget_queue_draw(area);
to get the draw signal called.
You won't need to store a buffer as that comes inside the cairo context.
But you may want to use other libraries for this purpose, like SDL2 or OpenGL as they are designed for videogames.
I hope this helps.