m2-GTK4/lib/m2gtkshim.c

/*
 * m2gtkshim.c - small C support library for the m2-GTK4 Modula-2 bindings.
 *
 * GNU Modula-2 cannot register GObject subclasses (no class_init /
 * vfunc overrides), which blocks widgets and paintables that need a
 * custom snapshot.  This shim provides two such types whose snapshot
 * vfuncs hand a Cairo context to a Modula-2 callback, so the drawing
 * itself reuses the existing Cairo binding:
 *
 *   M2GtkWidget  - a GtkWidget subclass; the M2 callback is
 *                  void draw(GtkWidget *w, cairo_t *cr,
 *                            int width, int height, gpointer user);
 *   M2Paintable  - a GdkPaintable implementation; the M2 callback is
 *                  void draw(cairo_t *cr, int width, int height,
 *                            gpointer user);
 *
 * The M2 callback addresses and user data are supplied at construction;
 * an optional destroy notify frees the user data.
 */

#include <gtk/gtk.h>

/* ------------------------------------------------------------------ */
/* M2GtkWidget                                                         */
/* ------------------------------------------------------------------ */

typedef void (*M2WidgetDrawFunc) (GtkWidget *widget, cairo_t *cr,
                                  int width, int height, gpointer user_data);

typedef struct _M2GtkWidget M2GtkWidget;
typedef struct _M2GtkWidgetClass M2GtkWidgetClass;

struct _M2GtkWidget
{
  GtkWidget parent_instance;
  M2WidgetDrawFunc draw;
  gpointer user_data;
  GDestroyNotify destroy;
};

struct _M2GtkWidgetClass
{
  GtkWidgetClass parent_class;
};

G_DEFINE_TYPE (M2GtkWidget, m2_gtk_widget, GTK_TYPE_WIDGET)

static void
m2_gtk_widget_snapshot (GtkWidget *widget, GtkSnapshot *snapshot)
{
  M2GtkWidget *self = (M2GtkWidget *) widget;
  int width = gtk_widget_get_width (widget);
  int height = gtk_widget_get_height (widget);

  if (self->draw == NULL || width <= 0 || height <= 0)
    return;

  graphene_rect_t bounds = GRAPHENE_RECT_INIT (0.f, 0.f, width, height);
  cairo_t *cr = gtk_snapshot_append_cairo (snapshot, &bounds);
  self->draw (widget, cr, width, height, self->user_data);
  cairo_destroy (cr);
}

static void
m2_gtk_widget_finalize (GObject *object)
{
  M2GtkWidget *self = (M2GtkWidget *) object;

  if (self->destroy != NULL)
    self->destroy (self->user_data);

  G_OBJECT_CLASS (m2_gtk_widget_parent_class)->finalize (object);
}

static void
m2_gtk_widget_class_init (M2GtkWidgetClass *klass)
{
  GObjectClass *object_class = G_OBJECT_CLASS (klass);
  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);

  object_class->finalize = m2_gtk_widget_finalize;
  widget_class->snapshot = m2_gtk_widget_snapshot;
}

static void
m2_gtk_widget_init (M2GtkWidget *self)
{
  self->draw = NULL;
  self->user_data = NULL;
  self->destroy = NULL;
}

GtkWidget *
m2_gtk_widget_new (M2WidgetDrawFunc draw, gpointer user_data,
                   GDestroyNotify destroy)
{
  M2GtkWidget *self = g_object_new (m2_gtk_widget_get_type (), NULL);

  self->draw = draw;
  self->user_data = user_data;
  self->destroy = destroy;
  return GTK_WIDGET (self);
}

/* ------------------------------------------------------------------ */
/* M2Paintable (implements GdkPaintable)                               */
/* ------------------------------------------------------------------ */

typedef void (*M2PaintableDrawFunc) (cairo_t *cr, int width, int height,
                                     gpointer user_data);

typedef struct _M2Paintable M2Paintable;
typedef struct _M2PaintableClass M2PaintableClass;

struct _M2Paintable
{
  GObject parent_instance;
  M2PaintableDrawFunc draw;
  gpointer user_data;
  GDestroyNotify destroy;
  int width;
  int height;
};

struct _M2PaintableClass
{
  GObjectClass parent_class;
};

static void
m2_paintable_snapshot (GdkPaintable *paintable, GtkSnapshot *snapshot,
                       double width, double height)
{
  M2Paintable *self = (M2Paintable *) paintable;
  graphene_rect_t bounds = GRAPHENE_RECT_INIT (0.f, 0.f, (float) width,
                                               (float) height);
  cairo_t *cr = gtk_snapshot_append_cairo (snapshot, &bounds);

  if (self->draw != NULL)
    self->draw (cr, (int) width, (int) height, self->user_data);

  cairo_destroy (cr);
}

static int
m2_paintable_get_intrinsic_width (GdkPaintable *paintable)
{
  return ((M2Paintable *) paintable)->width;
}

static int
m2_paintable_get_intrinsic_height (GdkPaintable *paintable)
{
  return ((M2Paintable *) paintable)->height;
}

static double
m2_paintable_get_intrinsic_aspect_ratio (GdkPaintable *paintable)
{
  M2Paintable *self = (M2Paintable *) paintable;

  return self->height > 0 ? (double) self->width / (double) self->height : 0.0;
}

static void
m2_paintable_paintable_init (GdkPaintableInterface *iface)
{
  iface->snapshot = m2_paintable_snapshot;
  iface->get_intrinsic_width = m2_paintable_get_intrinsic_width;
  iface->get_intrinsic_height = m2_paintable_get_intrinsic_height;
  iface->get_intrinsic_aspect_ratio = m2_paintable_get_intrinsic_aspect_ratio;
}

G_DEFINE_TYPE_WITH_CODE (M2Paintable, m2_paintable, G_TYPE_OBJECT,
                         G_IMPLEMENT_INTERFACE (GDK_TYPE_PAINTABLE,
                                                m2_paintable_paintable_init))

static void
m2_paintable_finalize (GObject *object)
{
  M2Paintable *self = (M2Paintable *) object;

  if (self->destroy != NULL)
    self->destroy (self->user_data);

  G_OBJECT_CLASS (m2_paintable_parent_class)->finalize (object);
}

static void
m2_paintable_class_init (M2PaintableClass *klass)
{
  G_OBJECT_CLASS (klass)->finalize = m2_paintable_finalize;
}

static void
m2_paintable_init (M2Paintable *self)
{
  self->draw = NULL;
  self->user_data = NULL;
  self->destroy = NULL;
  self->width = 0;
  self->height = 0;
}

GdkPaintable *
m2_paintable_new (M2PaintableDrawFunc draw, int width, int height,
                  gpointer user_data, GDestroyNotify destroy)
{
  M2Paintable *self = g_object_new (m2_paintable_get_type (), NULL);

  self->draw = draw;
  self->width = width;
  self->height = height;
  self->user_data = user_data;
  self->destroy = destroy;
  return GDK_PAINTABLE (self);
}