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| - | In this part of the Cairo graphics programming tutorial, we will define compositing operations.
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| - | <b>Compositing</b> is the combining of visual elements from separate sources into single images.
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| - | They are used to create the illusion that all those elements are parts of the same scene.
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| - | Compositing is videly used in film industry to create crowds, entire new worlds which would be expensive or impossible to create otherwise. (wikipedia.org)
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| - | == Operations ==
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| - | There are several compositing operations. The Cairo graphics library has 14 different compositing operations.
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| - | <source lang="cpp">
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| - | #include <cairo.h>
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| - | #include <gtk/gtk.h>
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| - | static void draw(cairo_t *cr, gint x, gint w,
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| - | gint h, cairo_operator_t op)
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| - | {
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| - | cairo_t *first_cr, *second_cr;
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| - | cairo_surface_t *first, *second;
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| - | first = cairo_surface_create_similar(cairo_get_target(cr),
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| - | CAIRO_CONTENT_COLOR_ALPHA, w, h);
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| - | second = cairo_surface_create_similar(cairo_get_target(cr),
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| - | CAIRO_CONTENT_COLOR_ALPHA, w, h);
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| - | first_cr = cairo_create(first);
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| - | cairo_set_source_rgb(first_cr, 0, 0, 0.4);
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| - | cairo_rectangle(first_cr, x, 20, 50, 50);
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| - | cairo_fill(first_cr);
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| - | second_cr = cairo_create(second);
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| - | cairo_set_source_rgb(second_cr, 0.5, 0.5, 0);
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| - | cairo_rectangle(second_cr, x+10, 40, 50, 50);
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| - | cairo_fill(second_cr);
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| - | cairo_set_operator(first_cr, op);
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| - | cairo_set_source_surface(first_cr, second, 0, 0);
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| - | cairo_paint(first_cr);
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| - | cairo_set_source_surface(cr, first, 0, 0);
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| - | cairo_paint(cr);
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| - | cairo_surface_destroy(first);
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| - | cairo_surface_destroy(second);
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| - | cairo_destroy(first_cr);
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| - | cairo_destroy(second_cr);
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| - | }
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| - | static gboolean
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| - | on_expose_event(GtkWidget *widget,
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| - | GdkEventExpose *event,
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| - | gpointer data)
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| - | {
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| - | cairo_t *cr;
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| - | gint w, h;
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| - | gint x, y;
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| - | cairo_operator_t oper[] = {
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| - | CAIRO_OPERATOR_DEST_OVER,
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| - | CAIRO_OPERATOR_DEST_IN,
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| - | CAIRO_OPERATOR_OUT,
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| - | CAIRO_OPERATOR_ADD,
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| - | CAIRO_OPERATOR_ATOP,
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| - | CAIRO_OPERATOR_DEST_ATOP,
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| - | };
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| - | gtk_window_get_size(GTK_WINDOW(widget), &w, &h);
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| - | cr = gdk_cairo_create(widget->window);
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| - | gint i;
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| - | for(x=20, y=20, i=0; i < 6; x+=80, i++) {
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| - | draw(cr, x, w, h, oper[i] );
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| - | }
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| - | cairo_destroy(cr);
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| - | return FALSE;
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| - | }
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| - | int main (int argc, char *argv[])
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| - | {
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| - | GtkWidget *window;
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| - |
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| - | gtk_init(&argc, &argv);
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| - | window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
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| - | g_signal_connect(window, "expose-event",
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| - | G_CALLBACK(on_expose_event), NULL);
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| - | g_signal_connect(window, "destroy",
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| - | G_CALLBACK(gtk_main_quit), NULL);
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| - | gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
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| - | gtk_window_set_default_size(GTK_WINDOW(window), 510, 120);
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| - | gtk_widget_set_app_paintable(window, TRUE);
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| - | gtk_widget_show_all(window);
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| - | gtk_main();
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| - | return 0;
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| - | }
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| - | </source>
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| - | In our example, we will show 6 different compositing operations on two squares.
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| - |
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| - | <source lang="cpp">
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| - | first = cairo_surface_create_similar(cairo_get_target(cr),
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| - | CAIRO_CONTENT_COLOR_ALPHA, w, h);
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| - | second = cairo_surface_create_similar(cairo_get_target(cr),
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| - | CAIRO_CONTENT_COLOR_ALPHA, w, h);
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| - | </source>
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| - | We create two surfaces.
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| - | <source lang="cpp">
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| - | first_cr = cairo_create(first);
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| - | cairo_set_source_rgb(first_cr, 0, 0, 0.4);
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| - | cairo_rectangle(first_cr, x, 20, 50, 50);
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| - | cairo_fill(first_cr);
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| - | </source>
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| - | We draw a rectangle into the surface.
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| - | <source lang="cpp">
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| - | cairo_set_operator(first_cr, op);
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| - | cairo_set_source_surface(first_cr, second, 0, 0);
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| - | cairo_paint(first_cr);
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| - | </source>
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| - | We apply the compositing operation on the surfaces.
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| - | <source lang="cpp">
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| - | cairo_set_source_surface(cr, first, 0, 0);
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| - | cairo_paint(cr);
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| - | </source>
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| - | Finally we draw the outcome onto the GTK+ window.
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| - | <source lang="cpp">
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| - | cairo_operator_t oper[] = {
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| - | CAIRO_OPERATOR_DEST_OVER,
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| - | CAIRO_OPERATOR_DEST_IN,
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| - | CAIRO_OPERATOR_OUT,
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| - | CAIRO_OPERATOR_ADD,
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| - | CAIRO_OPERATOR_ATOP,
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| - | CAIRO_OPERATOR_DEST_ATOP,
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| - | };
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| - | </source>
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| - | In our example, we use these six compositing operations.
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| - | [[image: cairo_faq_compositing.png | center]]
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| - | [[Категория:GTK+]]
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| - | [[Категория:Cairo]]
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