Step by Step solution about How to resolve the algorithm Greyscale bars/Display step by step in the C programming language

This program draws a greyscale plot using the GTK+ library in C. Here's a detailed explanation of the code:

1. Header Files: The program includes the header file <gtk/gtk.h> for using the GTK+ library.

2. Function gsplot:

   • This function takes a Cairo context (cairo_t *cr), x coordinate (int x), y coordinate (int y), and a scaling factor (double s) as parameters.
   • Inside the function:
     • It sets the source color to grayscale using cairo_set_source_rgb(cr, s, s, s).
     • It moves the cursor to the given coordinates (x+0.5, y) using cairo_move_to(cr, x+0.5, y).
     • It draws a vertical line with a length of 1 using cairo_rel_line_to(cr, 0, 1) and then strokes it using cairo_stroke(cr).

3. Function expose_event:

   • This function handles the "expose" event, which occurs when the widget becomes visible or needs to be redrawn.
   • Inside the function:
     • It iterates through rows r and columns c to draw greyscale lines.
     • It sets the drawing parameters and initializes the Cairo context.
     • It iteratively calls gsplot to draw vertical lines at specific coordinates and with appropriate scaling.
     • Finally, it destroys the Cairo context using cairo_destroy(cr).

4. Function main:

   • This is the entry point of the program.
   • It initializes the GTK+ library by calling gtk_init(&argc, &argv).
   • It creates a new top-level window using gtk_window_new(GTK_WINDOW_TOPLEVEL).
   • It connects the "expose-event" signal to the expose_event function.
   • It sets the default size of the window to 320x200 pixels.
   • It sets the widget to be paintable using gtk_widget_set_app_paintable(window, TRUE).
   • It makes the window visible using gtk_widget_show_all(window).
   • Finally, it starts the GTK+ main loop using gtk_main(), which processes events and keeps the window open.

In summary, this program uses GTK+ and Cairo to create a widget that displays a greyscale plot. It handles the widget's expose event to draw the plot using a specific algorithm that iteratively draws vertical lines with varying grayscale shades.

#include <gtk/gtk.h>
/* do some greyscale plotting */
void gsplot (cairo_t *cr,int x,int y,double s) {
    cairo_set_source_rgb (cr,s,s,s);
    cairo_move_to (cr,x+0.5,y);
    cairo_rel_line_to (cr,0,1);
    cairo_stroke (cr);
}
/* make a shaded widget */
gboolean expose_event (GtkWidget *widget,GdkEventExpose *event,gpointer data) {
    int r,c,x=0;
    cairo_t *cr;
    cr = gdk_cairo_create (widget->window);
    cairo_scale (cr,5,50);
    cairo_set_line_width (cr,1);
    for (r=0;r<4;r++) {
        c = (r&1)*64-(r%2);
        do gsplot (cr,x++%64,r,c/(1<<(3-r))/(8*(1<<r)-1.0));
        while ((c+=2*!(r%2)-1)!=(!(r%2))*64-(r%2));
    } cairo_destroy (cr);
    return FALSE;
}
/* main */
int main (int argc, char *argv[]) {
    GtkWidget *window;
    gtk_init (&argc, &argv);
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    g_signal_connect (window, "expose-event",G_CALLBACK (expose_event), NULL);
    g_signal_connect (window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);
    gtk_window_set_default_size (GTK_WINDOW(window), 320, 200);
    gtk_widget_set_app_paintable (window, TRUE);
    gtk_widget_show_all (window);
    gtk_main ();
    return 0;
}