How to Set CSS Radial-Gradient (Drawing) on Cairo Surface in GTK4: A Comprehensive Guide

Are you tired of using plain old colors in your GTK4 application? Do you want to add some visual flair with a radial gradient? Look no further! In this article, we’ll show you how to set a CSS radial gradient on a Cairo surface in GTK4. Buckle up and let’s dive in!

What is a Radial Gradient?

A radial gradient is a visual effect where the color gradually changes from one color to another, radiating from a central point. It’s commonly used in UI design to add depth and visual interest to elements like buttons, backgrounds, and more.

Why Use a Radial Gradient in GTK4?

GTK4 is a powerful and flexible toolkit for building GUI applications. By using a radial gradient, you can:

• Enhance the visual appeal of your application
• Create a sense of depth and dimensionality
• Differentiate your application from others
• Provide a more engaging user experience

Step 1: Setting Up Your GTK4 Project

Before we dive into the nitty-gritty of setting up a radial gradient, make sure you have a GTK4 project set up and running. If you’re new to GTK4, start by creating a new project using the GTK4 template in your preferred IDE.

gtk4_new_project my_radial_gradient_app

This will create a basic GTK4 project structure for you to work with.

Step 2: Creating a Cairo Surface

To draw a radial gradient, we need a Cairo surface to render on. In GTK4, we can create a Cairo surface using the GdkDrawingContext class.

GtkWidget *drawing_area = gtk_drawing_area_new();
GdkDrawingContext *drawing_context = gtk_drawing_area_get_context(drawing_area);
cairo_surface_t *surface = gdk_drawing_context_get_surface(drawing_context);

In this code, we create a GtkDrawingArea widget, get its drawing context, and then retrieve the Cairo surface from the drawing context.

Step 3: Defining the Radial Gradient

Now that we have our Cairo surface, let’s define our radial gradient. We’ll use the cairo_pattern_create_radial function to create a radial gradient pattern.

cairo_pattern_t *pattern = cairo_pattern_create_radial(
  100, 100, 0,  // center of the gradient
  100, 100, 50  // focal point of the gradient
);

cairo_pattern_add_color_stop_rgb(pattern, 0, 1, 0, 0);  // red
cairo_pattern_add_color_stop_rgb(pattern, 1, 0, 0, 1);  // blue

In this code, we create a radial gradient pattern with a center at (100, 100) and a focal point at (100, 100) with a radius of 50. We then add two color stops: red at the center (0) and blue at the edge (1).

Step 4: Setting the Radial Gradient as the Source

To draw the radial gradient, we need to set it as the source for our Cairo context.

cairo_set_source(pattern, cairo_context);

This tells Cairo to use our radial gradient pattern as the source for drawing.

Step 5: Painting the Radial Gradient

Now that we have our radial gradient set as the source, we can paint it onto our Cairo surface.

cairo_paint(cairo_context);

This will render the radial gradient onto our Cairo surface.

Step 6: Displaying the Result

Finally, we need to display our radial gradient in our GTK4 application. We can do this by adding the GtkDrawingArea widget to our application’s UI.

gtk_box_append(GTK_BOX(box), drawing_area);
gtk_widget_show(drawing_area);

In this code, we add the GtkDrawingArea widget to a box layout and show it.

Putting it All Together

Here’s the complete code for setting a CSS radial gradient on a Cairo surface in GTK4:

gtk_widget_setup(
  GtkWidget *window,
  gpointer   data
) {
  GtkWidget *box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
  GtkWidget *drawing_area = gtk_drawing_area_new();
  GdkDrawingContext *drawing_context = gtk_drawing_area_get_context(drawing_area);
  cairo_surface_t *surface = gdk_drawing_context_get_surface(drawing_context);
  cairo_t *cairo_context = cairo_create(surface);

  cairo_pattern_t *pattern = cairo_pattern_create_radial(
    100, 100, 0,
    100, 100, 50
  );

  cairo_pattern_add_color_stop_rgb(pattern, 0, 1, 0, 0);
  cairo_pattern_add_color_stop_rgb(pattern, 1, 0, 0, 1);

  cairo_set_source(pattern, cairo_context);
  cairo_paint(cairo_context);

  gtk_box_append(GTK_BOX(box), drawing_area);
  gtk_widget_show(drawing_area);
  gtk_window_set_child(GTK_WINDOW(window), box);
}

This code sets up a GTK4 window with a GtkDrawingArea widget, creates a radial gradient pattern, sets it as the source, and paints it onto the Cairo surface. Finally, it adds the drawing area to the window and shows it.

Conclusion

In this article, we’ve shown you how to set a CSS radial gradient on a Cairo surface in GTK4. With these steps, you can add a touch of visual flair to your GUI application and make it stand out from the crowd.

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We hope this article has been informative and helpful. Happy coding!

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Get ready to unleash your creativity and bring your Cairo surface to life with stunning radial gradients in GTK4!