Here’s a basic example of how to use Cairo with GTK 4 in C:

#include <gtk/gtk.h> #include

static cairo_surface_t *surface = NULL;

static void clear_surface (void) { cairo_t *cr;

cr = cairo_create(surface);
cairo_set_source_rgb(cr, 1, 1, 1); // White
cairo_paint(cr);
cairo_destroy(cr); }

static void resize_cb (GtkWidget *widget, int width, int height, gpointer data) { if (surface) cairo_surface_destroy(surface);

surface = gdk_surface_create_similar_surface(gtk_widget_get_native(widget)->surface,
                                            CAIRO_CONTENT_COLOR,
                                            width, height);

clear_surface(); }

static gboolean draw_callback (GtkDrawingArea *area, cairo_t *cr, int width, int height, gpointer user_data) { cairo_set_source_surface(cr, surface, 0, 0); cairo_paint(cr); return FALSE; }

static void draw_brush (GtkWidget *widget, double x, double y) { cairo_t *cr;

cr = cairo_create(surface);
cairo_rectangle(cr, x - 3, y - 3, 6, 6);
cairo_fill(cr);
cairo_destroy(cr);

gtk_widget_queue_draw(widget); }

static void drag_begin (GtkGestureDrag *gesture, double x, double y, GtkWidget *area) { draw_brush(area, x, y); }

static void drag_update (GtkGestureDrag *gesture, double x, double y, GtkWidget *area) { draw_brush(area, x, y); }

int main(int argc, char *argv[]) { GtkApplication *app; GtkWidget *window, *drawing_area;

app = gtk_application_new("org.example.DrawingApp", G_APPLICATION_DEFAULT_FLAGS);
g_signal_connect(app, "activate", G_CALLBACK(lambda_main), NULL);

window = gtk_application_window_new(app);
gtk_window_set_title(GTK_WINDOW(window), "Cairo Drawing");

drawing_area = gtk_drawing_area_new();

g_signal_connect(drawing_area, "draw", G_CALLBACK(draw_callback), NULL);
g_signal_connect(drawing_area, "resize", G_CALLBACK(resize_cb), NULL);

gtk_container_add(GTK_CONTAINER(window), drawing_area);

gtk_widget_show_all(window);

g_application_run(G_APPLICATION(app), argc, argv); }

void lambda_main(GtkApplication *app, gpointer user_data) { // Implementation of lambda_main… }

Summary and best practices:

This example demonstrates how to use Cairo with GTK 4 in C. Here’s a summary of the key components and best practices:

We create a surface to store our drawings.
The clear_surface function initializes the surface to white.
The resize_cb function recreates the surface when the widget is resized.
The draw_callback function is called when the drawing area needs to be redrawn. It paints the surface onto the widget.
The draw_brush function allows us to draw on the surface.
We handle drag events to allow freehand drawing.
We use GTK Application and connect signals properly.

Best practices followed:

Properly managing Cairo surfaces
Handling resize events
Using appropriate event handlers
Separating drawing logic from UI construction

This example provides a foundation for using Cairo with GTK 4. You can expand upon this to create more complex drawings or add additional features as needed.