/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */

#include <config.h>

#define _ISOC99_SOURCE /* for roundf */
#include <math.h>

#include <gdk/gdk.h> /* for gdk_rectangle_intersect() */

#include "compositor-private.h"
#include "meta-window-actor-private.h"
#include "meta-window-group.h"
#include "meta-background-actor-private.h"

struct _MetaWindowGroupClass
{
  ClutterGroupClass parent_class;
};

struct _MetaWindowGroup
{
  ClutterGroup parent;

  MetaScreen *screen;
};

G_DEFINE_TYPE (MetaWindowGroup, meta_window_group, CLUTTER_TYPE_GROUP);

/* This file uses pixel-aligned region computation to determine what
 * can be clipped out. This only really works if everything is aligned
 * to the pixel grid - not scaled or rotated and at integer offsets.
 *
 * (This could be relaxed - if we turned off filtering for unscaled
 * windows then windows would be, by definition aligned to the pixel
 * grid. And for rectangular windows without a shape, the outline that
 * we draw for an unrotated window is always a rectangle because we
 * don't use antialasing for the window boundary - with or without
 * filtering, with or without a scale. But figuring out exactly
 * what pixels will be drawn by the graphics system in these cases
 * gets tricky, so we just go for the easiest part - no scale,
 * and at integer offsets.)
 *
 * The way we check for pixel-aligned is by looking at the
 * transformation into screen space of the allocation box of an actor
 * and and checking if the corners are "close enough" to integral
 * pixel values.
 */

/* The definition of "close enough" to integral pixel values is
 * equality when we convert to 24.8 fixed-point.
 */
static inline int
round_to_fixed (float x)
{
  return roundf (x * 256);
}

/* This helper function checks if (according to our fixed point precision)
 * the vertices @verts form a box of width @widthf and height @heightf
 * located at integral coordinates. These coordinates are returned
 * in @x_origin and @y_origin.
 */
static gboolean
vertices_are_untransformed (ClutterVertex *verts,
                            float          widthf,
                            float          heightf,
                            int           *x_origin,
                            int           *y_origin)
{
  int width, height;
  int v0x, v0y, v1x, v1y, v2x, v2y, v3x, v3y;
  int x, y;

  width = round_to_fixed (widthf); height = round_to_fixed (heightf);

  v0x = round_to_fixed (verts[0].x); v0y = round_to_fixed (verts[0].y);
  v1x = round_to_fixed (verts[1].x); v1y = round_to_fixed (verts[1].y);
  v2x = round_to_fixed (verts[2].x); v2y = round_to_fixed (verts[2].y);
  v3x = round_to_fixed (verts[3].x); v3y = round_to_fixed (verts[3].y);

  /* Using shifting for converting fixed => int, gets things right for
   * negative values. / 256. wouldn't do the same
   */
  x = v0x >> 8;
  y = v0y >> 8;

  /* At integral coordinates? */
  if (x * 256 != v0x || y * 256 != v0y)
    return FALSE;

  /* Not scaled? */
  if (v1x - v0x != width || v2y - v0y != height)
    return FALSE;

  /* Not rotated/skewed? */
  if (v0x != v2x || v0y != v1y ||
      v3x != v1x || v3y != v2y)
    return FALSE;

  *x_origin = x;
  *y_origin = y;

  return TRUE;
}

/* Check if an actor is "untransformed" - which actually means transformed by
 * at most a integer-translation. The integer translation, if any, is returned.
 */
static gboolean
actor_is_untransformed (ClutterActor *actor,
                        int          *x_origin,
                        int          *y_origin)
{
  gfloat widthf, heightf;
  ClutterVertex verts[4];

  clutter_actor_get_size (actor, &widthf, &heightf);
  clutter_actor_get_abs_allocation_vertices (actor, verts);

  return vertices_are_untransformed (verts, widthf, heightf, x_origin, y_origin);
}

/* Help macros to scale from OpenGL <-1,1> coordinates system to
 * window coordinates ranging [0,window-size]. Borrowed from clutter-utils.c
 */
#define MTX_GL_SCALE_X(x,w,v1,v2) ((((((x) / (w)) + 1.0f) / 2.0f) * (v1)) + (v2))
#define MTX_GL_SCALE_Y(y,w,v1,v2) ((v1) - (((((y) / (w)) + 1.0f) / 2.0f) * (v1)) + (v2))

/* Check if we're painting the MetaWindowGroup "untransformed". This can
 * differ from the result of actor_is_untransformed(window_group) if we're
 * inside a clone paint. The integer translation, if any, is returned.
 */
static gboolean
painting_untransformed (MetaWindowGroup *window_group,
                        int             *x_origin,
                        int             *y_origin)
{
  CoglMatrix modelview, projection, modelview_projection;
  ClutterVertex vertices[4];
  int width, height;
  float viewport[4];
  int i;

  cogl_get_modelview_matrix (&modelview);
  cogl_get_projection_matrix (&projection);

  cogl_matrix_multiply (&modelview_projection,
                        &projection,
                        &modelview);

  meta_screen_get_size (window_group->screen, &width, &height);

  vertices[0].x = 0;
  vertices[0].y = 0;
  vertices[0].z = 0;
  vertices[1].x = width;
  vertices[1].y = 0;
  vertices[1].z = 0;
  vertices[2].x = 0;
  vertices[2].y = height;
  vertices[2].z = 0;
  vertices[3].x = width;
  vertices[3].y = height;
  vertices[3].z = 0;

  cogl_get_viewport (viewport);

  for (i = 0; i < 4; i++)
    {
      float w = 1;
      cogl_matrix_transform_point (&modelview_projection, &vertices[i].x, &vertices[i].y, &vertices[i].z, &w);
      vertices[i].x = MTX_GL_SCALE_X (vertices[i].x, w,
                                      viewport[2], viewport[0]);
      vertices[i].y = MTX_GL_SCALE_Y (vertices[i].y, w,
                                      viewport[3], viewport[1]);
    }

  return vertices_are_untransformed (vertices, width, height, x_origin, y_origin);
}

static void
meta_window_group_paint (ClutterActor *actor)
{
  cairo_region_t *visible_region;
  ClutterActor *stage;
  cairo_rectangle_int_t visible_rect;
  GList *children, *l;
  int paint_x_origin, paint_y_origin;
  int actor_x_origin, actor_y_origin;
  int paint_x_offset, paint_y_offset;

  MetaWindowGroup *window_group = META_WINDOW_GROUP (actor);
  MetaCompScreen *info = meta_screen_get_compositor_data (window_group->screen);

  /* Normally we expect an actor to be drawn at it's position on the screen.
   * However, if we're inside the paint of a ClutterClone, that won't be the
   * case and we need to compensate. We look at the position of the window
   * group under the current model-view matrix and the position of the actor.
   * If they are both simply integer translations, then we can compensate
   * easily, otherwise we give up.
   *
   * Possible cleanup: work entirely in paint space - we can compute the
   * combination of the model-view matrix with the local matrix for each child
   * actor and get a total transformation for that actor for how we are
   * painting currently, and never worry about how actors are positioned
   * on the stage.
   */
  if (!painting_untransformed (window_group, &paint_x_origin, &paint_y_origin) ||
      !actor_is_untransformed (actor, &actor_x_origin, &actor_y_origin))
    {
      CLUTTER_ACTOR_CLASS (meta_window_group_parent_class)->paint (actor);
      return;
    }

  paint_x_offset = paint_x_origin - actor_x_origin;
  paint_y_offset = paint_y_origin - actor_y_origin;

  /* We walk the list from top to bottom (opposite of painting order),
   * and subtract the opaque area of each window out of the visible
   * region that we pass to the windows below.
   */
  children = clutter_container_get_children (CLUTTER_CONTAINER (actor));
  children = g_list_reverse (children);

  /* Get the clipped redraw bounds from Clutter so that we can avoid
   * painting shadows on windows that don't need to be painted in this
   * frame. In the case of a multihead setup with mismatched monitor
   * sizes, we could intersect this with an accurate union of the
   * monitors to avoid painting shadows that are visible only in the
   * holes. */
  stage = clutter_actor_get_stage (actor);
  clutter_stage_get_redraw_clip_bounds (CLUTTER_STAGE (stage),
                                        &visible_rect);

  visible_region = cairo_region_create_rectangle (&visible_rect);

  if (info->unredirected_window != NULL)
    {
      cairo_rectangle_int_t unredirected_rect;
      meta_window_actor_get_shape_bounds (META_WINDOW_ACTOR (info->unredirected_window), &unredirected_rect);
      cairo_region_subtract_rectangle (visible_region, &unredirected_rect);
    }

  for (l = children; l; l = l->next)
    {
      if (!CLUTTER_ACTOR_IS_VISIBLE (l->data))
        continue;

      if (l->data == info->unredirected_window)
        continue;

      /* If an actor has effects applied, then that can change the area
       * it paints and the opacity, so we no longer can figure out what
       * portion of the actor is obscured and what portion of the screen
       * it obscures, so we skip the actor.
       *
       * This has a secondary beneficial effect: if a ClutterOffscreenEffect
       * is applied to an actor, then our clipped redraws interfere with the
       * caching of the FBO - even if we only need to draw a small portion
       * of the window right now, ClutterOffscreenEffect may use other portions
       * of the FBO later. So, skipping actors with effects applied also
       * prevents these bugs.
       *
       * Theoretically, we should check clutter_actor_get_offscreen_redirect()
       * as well for the same reason, but omitted for simplicity in the
       * hopes that no-one will do that.
       */
      if (clutter_actor_has_effects (l->data))
        continue;

      if (META_IS_WINDOW_ACTOR (l->data))
        {
          MetaWindowActor *window_actor = l->data;
          int x, y;

          if (!actor_is_untransformed (CLUTTER_ACTOR (window_actor), &x, &y))
            continue;

          x += paint_x_offset;
          y += paint_y_offset;

          /* Temporarily move to the coordinate system of the actor */
          cairo_region_translate (visible_region, - x, - y);

          meta_window_actor_set_visible_region (window_actor, visible_region);

          if (clutter_actor_get_paint_opacity (CLUTTER_ACTOR (window_actor)) == 0xff)
            {
              cairo_region_t *obscured_region = meta_window_actor_get_obscured_region (window_actor);
              if (obscured_region)
                cairo_region_subtract (visible_region, obscured_region);
            }

          meta_window_actor_set_visible_region_beneath (window_actor, visible_region);
          cairo_region_translate (visible_region, x, y);
        }
      else if (META_IS_BACKGROUND_ACTOR (l->data))
        {
          MetaBackgroundActor *background_actor = l->data;
          int x, y;

          if (!actor_is_untransformed (CLUTTER_ACTOR (background_actor), &x, &y))
            continue;

          x += paint_x_offset;
          y += paint_y_offset;

          cairo_region_translate (visible_region, - x, - y);
          meta_background_actor_set_visible_region (background_actor, visible_region);
          cairo_region_translate (visible_region, x, y);
        }
    }

  cairo_region_destroy (visible_region);

  CLUTTER_ACTOR_CLASS (meta_window_group_parent_class)->paint (actor);

  /* Now that we are done painting, unset the visible regions (they will
   * mess up painting clones of our actors)
   */
  for (l = children; l; l = l->next)
    {
      if (META_IS_WINDOW_ACTOR (l->data))
        {
          MetaWindowActor *window_actor = l->data;
          meta_window_actor_reset_visible_regions (window_actor);
        }
      else if (META_IS_BACKGROUND_ACTOR (l->data))
        {
          MetaBackgroundActor *background_actor = l->data;
          meta_background_actor_set_visible_region (background_actor, NULL);
        }
    }

  g_list_free (children);
}

static void
meta_window_group_class_init (MetaWindowGroupClass *klass)
{
  ClutterActorClass *actor_class = CLUTTER_ACTOR_CLASS (klass);

  actor_class->paint = meta_window_group_paint;
}

static void
meta_window_group_init (MetaWindowGroup *window_group)
{
}

ClutterActor *
meta_window_group_new (MetaScreen *screen)
{
  MetaWindowGroup *window_group;

  window_group = g_object_new (META_TYPE_WINDOW_GROUP, NULL);

  window_group->screen = screen;

  return CLUTTER_ACTOR (window_group);
}