mutter/src/compositor/clutter-utils.c
Ray Strode 842bc4421c compositor: export actor_is_untransformed function
actor_is_untransformed is a function meta-window-group uses to determine
if an actor is relatively pixel aligned and not contorted. It then
returns the coordinates of the actor.

In a subsequent commit will need the function in a different file, so
this commit separates it out.

https://bugzilla.gnome.org/show_bug.cgi?id=682427
2013-02-19 18:18:29 -05:00

121 lines
4.1 KiB
C

/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
/*
* Utilities for use with Cogl
*
* Copyright 2010 Red Hat, Inc.
* Copyright 2010 Intel Corporation
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
* 02111-1307, USA.
*/
#include "clutter-utils.h"
#include <math.h>
/* 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.
*/
gboolean
meta_actor_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.
*/
gboolean
meta_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 meta_actor_vertices_are_untransformed (verts, widthf, heightf, x_origin, y_origin);
}