scale

Example: Cartesian coordinate system (I):

public static int main (string[] args) {
	// Create a context:
	Cairo.ImageSurface surface = new Cairo.ImageSurface (Cairo.Format.ARGB32, 500, 500);
	Cairo.Context context = new Cairo.Context (surface);

	// Transformations:
	context.translate (250, 250);
	context.scale (1, -1);

	// Y-Axis:
	context.move_to (-250, 0);
	context.line_to (250, 0);
	context.stroke ();

	// X-Axis:
	context.move_to (0, -250);
	context.line_to (0, 250);
	context.stroke ();

	// P (20, 10)
	context.set_source_rgba (0, 0, 0, 1);
	context.arc (20, 10, 2, 0, 2*Math.PI);
	context.fill ();

	// Save the image:
	surface.write_to_png ("img.png");

	return 0;
}

valac --pkg cairo cartesian-coordinate-system.vala

Example: Scale and rotate:

public static int main (string[] args) {
	// Create a context:
	Cairo.ImageSurface surface = new Cairo.ImageSurface (Cairo.Format.ARGB32, 256, 256);
	Cairo.Context context = new Cairo.Context (surface);

	// The image:
	string image_path = Path.build_filename (Path.get_dirname (args[0]) , "romedalen.png");
	Cairo.ImageSurface image = new Cairo.ImageSurface.from_png (image_path);
	int w = image.get_width ();
	int h = image.get_height ();

	context.translate (128.0, 128.0);
	context.rotate (45*Math.PI/180);
	context.scale  (256.0/w, 256.0/h);
	context.translate (-0.5*w, -0.5*h);
	context.set_source_surface (image, 0, 0);
	context.paint ();

	// Save the image:
	surface.write_to_png ("img.png");

	return 0;
}

valac --pkg cairo image-rotate.vala