Changing image on mouse click

Question

I have been able to do the following:

  for (int i = 0; i < NUM_LEDS; ++i) {
    ledoff = gtk_image_new_from_file("./ledoff.png");
      leds[i].pos=ledpos[i];
      gtk_layout_put(GTK_LAYOUT(layout), ledoff, leds[i].pos.x, leds[i].pos.y);
      leds[i].status=OFF;
  }

Basically, this loads a bunch of "ledoff" images onto some window.

What I need is to change the image ledoff to ledon every time I click on leds[i].pos.x, leds[i].pos.y. At the beginning I thought it was just a matter of loading a new image and replacing the previous one, but then since this will be done thousands of times, I thought I was "malloc'ing" one new file everytime I do gtk_image_new_from_file! Is this true? Or am I just replacing the file and not adding a new one?

Answer 1

One solution is to create one GtkImage for each position where there will be a led. Don't use gtk_image_new_from_file, as it will load each time the image file. Instead:

• call gdk_pixbuf_new_from_file for each of your 2 image files
• call gtk_image_new to create each image widget, and immediately initialize them with the right pixel buffer using gtk_image_set_from_pixbuf
• when you need to change the image displayed, just get the corresponding previously created GtkImage, and change the image displayed with gtk_image_set_from_pixbuf

This ensures low memory consumption: you only have 2 pixel buffers that are allocated (and reference counted from the GtkImage instances), and you only create one GtkImage per led (instead of destroying/creating one each time you change the image displayed).

EDIT: here's an improved of Sean Bright's submission, in which I fixed a few mistakes.

#include <gtk/gtk.h>

#define MAX_LEDS_PER_LINE 50
#define NUM_LEDS 2500

static GdkPixbuf * led_on;
static GdkPixbuf * led_off;

static gboolean click_handler(GtkWidget *widget,
        GdkEvent *event,
        gpointer user_data)
{
    gboolean *is_led_on = user_data;
    GList * children = gtk_container_get_children (GTK_CONTAINER (widget));

    *is_led_on = ! *is_led_on; /* invert led state */
    gtk_image_set_from_pixbuf (GTK_IMAGE(children->data), (*is_led_on) ? led_on : led_off);
    g_list_free (children);
    return TRUE; /* stop event propagation */
}

int main(int argc, char** argv)
{
    GtkWidget *window, *table;
    gboolean leds[NUM_LEDS];
    int i = 0;

    gtk_init(&argc, &argv);

    /* Create a window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "LEDs");
    gtk_signal_connect(GTK_OBJECT(window),
            "destroy",
            G_CALLBACK(gtk_main_quit),
            NULL);

    /* Load leds on/off images */
    led_on = gdk_pixbuf_new_from_file ("on.png", NULL);
    led_off = gdk_pixbuf_new_from_file ("off.png", NULL);

    /* Create the container */
    int n_rows = (NUM_LEDS / MAX_LEDS_PER_LINE) + 1;
    int n_cols = (NUM_LEDS / MAX_LEDS_PER_LINE) + 1;
    table = gtk_table_new (n_rows, n_cols, FALSE);

    /* Create the leds */
    for (i = 0; i < NUM_LEDS; i++)
    {
        leds[i] = FALSE; /* FALSE means OFF, TRUE means ON */

        /*
         * A GtkImage doesn't have a window, so we need to put it inside
         * a GtkEventBox so we can capture events.
         */
        GtkWidget *image = gtk_image_new ();
        gtk_image_set_from_pixbuf (GTK_IMAGE(image), led_off);
        GtkWidget *eb = gtk_event_box_new();
        g_signal_connect(G_OBJECT(eb),
                "button-press-event",
                G_CALLBACK(click_handler),
                &leds[i]);
        gtk_container_add(GTK_CONTAINER(eb), image);
        int row = i / MAX_LEDS_PER_LINE;
        int col = i % MAX_LEDS_PER_LINE;
        gtk_table_attach (GTK_TABLE(table),
                eb,
                row, row + 1,
                col, col + 1,
                0,
                0,
                0,
                0);
    }

    gtk_container_add(GTK_CONTAINER(window), table);
    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

Here, I implemented my first remarks, and improved a few things:

• I fixed the signature of the click_handler callback
• I fixed the return value of the click_handler callback
• I removed the structs, as we just need a boolean to know the led states. It could even have been a property stored in the GtkImage, but it's often a good idea to separate the backend logic from the user interface.
• I used GtkTable instead of GtkLayout, because I saw no need for pixel-exact placement of the leds. In GTK 3, though, GtkTable is replaced by GtkGrid. GtkTable however had difficulties with gtk_table_add_defaults, because resizing the window caused recalculating the size of 2500 widgets, so I just used the most simple size calculation options.

Answer 2

Here is a working example that creates a 50x50 "LED" array in a window and allows you to toggle their status by clicking on them. It's not really that efficient, and as I pointed out in comments you're better of drawing the images yourself right onto the GtkLayout, but this will at least serve as a proof of concept.

Edit: I've updated the sample code to take into account liberforce's suggestions, which make things cleaner and more memory efficient.

#include <gtk/gtk.h>

#define ICON_WIDTH 16
#define ICON_HEIGHT 16
#define NUM_LEDS 2500

typedef enum {
    ON,
    OFF
} led_status;

typedef struct {
    GtkWidget *img;
    struct {
        gint x;
        gint y;
    } pos;
    led_status status;
} led;

static led leds[NUM_LEDS];
static GdkPixbuf *led_on;
static GdkPixbuf *led_off;

static gboolean click_handler(GtkWidget *widget,
                              GdkEvent *event,
                              gpointer user_data)
{
    led *info = user_data;

    if (info->status == ON) {
        gtk_image_set_from_pixbuf(GTK_IMAGE(info->img), led_off);
        info->status = OFF;
    } else {
        gtk_image_set_from_pixbuf(GTK_IMAGE(info->img), led_on);
        info->status = ON;
    }

    return TRUE;
}

int main(int argc, char** argv)
{
    GtkWidget *window, *layout;
    int i = 0, x, y;

    gtk_init(&argc, &argv);

    /* Load our images (ignoring errors - as any good sample code would) */
    led_on  = gdk_pixbuf_new_from_file("led-on.png", NULL);
    led_off = gdk_pixbuf_new_from_file("led-off.png", NULL);

    /* Initialize our array */
    for (x = 0; x < 50; x++) {
        for (y = 0; y < 50; y++) {
            leds[i].img = gtk_image_new();
            leds[i].pos.x = x * ICON_WIDTH;
            leds[i].pos.y = y * ICON_HEIGHT;
            leds[i].status = OFF;

            /* Initialize our image from the pixbuf we've already loaded */
            gtk_image_set_from_pixbuf(GTK_IMAGE(leds[i].img), led_off);
            i++;
        }
    }

    /* Create a window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "LEDs");
    gtk_signal_connect(GTK_OBJECT(window),
                       "destroy",
                       G_CALLBACK(gtk_main_quit),
                       NULL);

    /* Create the widget */
    layout = gtk_layout_new(NULL, NULL);

    for (i = 0; i < NUM_LEDS; i++) {
        /*
         * A GtkImage doesn't have a window, so we need to put it inside
         * a GtkEventBox so we can capture events.
         */
        GtkWidget *eb = gtk_event_box_new();
        g_signal_connect(G_OBJECT(eb),
                         "button_press_event",
                         G_CALLBACK(click_handler),
                         &leds[i]);
        gtk_container_add(GTK_CONTAINER(eb), leds[i].img);
        gtk_layout_put(GTK_LAYOUT(layout), eb, leds[i].pos.x, leds[i].pos.y);
    }

    gtk_container_add(GTK_CONTAINER(window), layout);
    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

Answer 3

I am not sure of this but you should place your 2 images in the same position on the screen and then show the one you need and hide the one you don't need. I don't know if it is a good way to do that but I am pretty sure that you are not allocing stuff using this way.

gtk_widget_hide(your_image2);
gtk_widget_show(your_image1);

Hope it helps.

Regards,