mutter/cogl/cogl-euler.h

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/*
* Cogl
*
* An object oriented GL/GLES Abstraction/Utility Layer
*
* Copyright (C) 2010 Intel Corporation.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*
* Authors:
* Robert Bragg <robert@linux.intel.com>
*/
#if !defined(__COGL_H_INSIDE__) && !defined(COGL_COMPILATION)
#error "Only <cogl/cogl.h> can be included directly."
#endif
#ifndef __COGL_EULER_H
#define __COGL_EULER_H
#include <cogl/cogl-types.h>
COGL_BEGIN_DECLS
/**
* SECTION:cogl-euler
* @short_description: Functions for initializing and manipulating
* euler angles.
*
* Euler angles are a simple representation of a 3 dimensional
* rotation; comprised of 3 ordered heading, pitch and roll rotations.
* An important thing to understand is that the axis of rotation
* belong to the object being rotated and so they also rotate as each
* of the heading, pitch and roll rotations are applied.
*
* One way to consider euler angles is to imagine controlling an
* aeroplane, where you first choose a heading (Such as flying south
* east), then you set the pitch (such as 30 degrees to take off) and
* then you might set a roll, by dipping the left, wing as you prepare
* to turn.
*
* They have some advantages and limitations that it helps to be
* aware of:
*
* Advantages:
* <itemizedlist>
* <listitem>
* Easy to understand and use, compared to quaternions and matrices,
* so may be a good choice for a user interface.
* </listitem>
* <listitem>
* Efficient storage, needing only 3 components any rotation can be
* represented.
* <note>Actually the #CoglEuler type isn't optimized for size because
* we may cache the equivalent #CoglQuaternion along with a euler
* rotation, but it would be trivial for an application to track the
* components of euler rotations in a packed float array if optimizing
* for size was important. The values could be passed to Cogl only when
* manipulation is necessary.</note>
* </listitem>
* </itemizedlist>
*
* Disadvantages:
* <itemizedlist>
* <listitem>
* Aliasing: it's possible to represent some rotations with multiple
* different heading, pitch and roll rotations.
* </listitem>
* <listitem>
* They can suffer from a problem called Gimbal Lock. A good
* explanation of this can be seen on wikipedia here:
* http://en.wikipedia.org/wiki/Gimbal_lock but basically two
* of the axis of rotation may become aligned and so you loose a
* degree of freedom. For example a pitch of +-90° would mean that
* heading and bank rotate around the same axis.
* </listitem>
* <listitem>
* If you use euler angles to orient something in 3D space and try to
* transition between orientations by interpolating the component
* angles you probably wont get the transitions you expect as they may
* not follow the shortest path between the two orientations.
* </listitem>
* <listitem>
* There's no standard to what order the component axis rotations are
* applied. The most common convention seems to be what we do in Cogl
* with heading (y-axis), pitch (x-axis) and then roll (z-axis), but
* other software might apply x-axis, y-axis then z-axis or any other
* order so you need to consider this if you are accepting euler
* rotations from some other software. Other software may also use
* slightly different aeronautical terms, such as "yaw" instead of
* "heading" or "bank" instead of "roll".
* </listitem>
* </itemizedlist>
*
* To minimize the aliasing issue we may refer to "Canonical Euler"
* angles where heading and roll are restricted to +- 180° and pitch is
* restricted to +- 90°. If pitch is +- 90° bank is set to 0°.
*
* Quaternions don't suffer from Gimbal Lock and they can be nicely
* interpolated between, their disadvantage is that they don't have an
* intuitive representation.
*
* A common practice is to accept angles in the intuitive Euler form
* and convert them to quaternions internally to avoid Gimbal Lock and
* handle interpolations. See cogl_quaternion_init_from_euler().
*/
/**
* CoglEuler:
* @heading: Angle to rotate around an object's y axis
* @pitch: Angle to rotate around an object's x axis
* @roll: Angle to rotate around an object's z axis
*
* Represents an ordered rotation first of @heading degrees around an
* object's y axis, then @pitch degrees around an object's x axis and
* finally @roll degrees around an object's z axis.
*
* <note>It's important to understand the that axis are associated
* with the object being rotated, so the axis also rotate in sequence
* with the rotations being applied.</note>
*
* The members of a #CoglEuler can be initialized, for example, with
* cogl_euler_init() and cogl_euler_init_from_quaternion ().
*
* You may also want to look at cogl_quaternion_init_from_euler() if
* you want to do interpolation between 3d rotations.
*
* Since: 2.0
*/
struct _CoglEuler
{
/*< public > */
float heading;
float pitch;
float roll;
/*< private > */
/* May cached a quaternion here in the future */
float padding0;
float padding1;
float padding2;
float padding3;
float padding4;
};
COGL_STRUCT_SIZE_ASSERT (CoglEuler, 32);
/**
* cogl_euler_init:
* @euler: The #CoglEuler angle to initialize
* @heading: Angle to rotate around an object's y axis
* @pitch: Angle to rotate around an object's x axis
* @roll: Angle to rotate around an object's z axis
*
* Initializes @euler to represent a rotation of @x_angle degrees
* around the x axis, then @y_angle degrees around the y_axis and
* @z_angle degrees around the z axis.
*
* Since: 2.0
*/
void
cogl_euler_init (CoglEuler *euler,
float heading,
float pitch,
float roll);
/**
* cogl_euler_init_from_matrix:
* @euler: The #CoglEuler angle to initialize
* @matrix: A #CoglMatrix containing a rotation, but no scaling,
* mirroring or skewing.
*
* Extracts a euler rotation from the given @matrix and
* initializses @euler with the component x, y and z rotation angles.
*/
void
cogl_euler_init_from_matrix (CoglEuler *euler,
const CoglMatrix *matrix);
/**
* cogl_euler_init_from_quaternion:
* @euler: The #CoglEuler angle to initialize
* @quaternion: A #CoglEuler with the rotation to initialize with
*
* Initializes a @euler rotation with the equivalent rotation
* represented by the given @quaternion.
*/
void
cogl_euler_init_from_quaternion (CoglEuler *euler,
const CoglQuaternion *quaternion);
/**
* cogl_euler_equal:
* @v1: The first euler angle to compare
* @v2: The second euler angle to compare
*
* Compares the two given euler angles @v1 and @v1 and it they are
* equal returns %TRUE else %FALSE.
*
* <note>This function only checks that all three components rotations
* are numerically equal, it does not consider that some rotations
* can be represented with different component rotations</note>
*
* Returns: %TRUE if @v1 and @v2 are equal else %FALSE.
* Since: 2.0
*/
CoglBool
cogl_euler_equal (const void *v1, const void *v2);
/**
* cogl_euler_copy:
* @src: A #CoglEuler to copy
*
* Allocates a new #CoglEuler and initilizes it with the component
* angles of @src. The newly allocated euler should be freed using
* cogl_euler_free().
*
* Returns: A newly allocated #CoglEuler
* Since: 2.0
*/
CoglEuler *
cogl_euler_copy (const CoglEuler *src);
/**
* cogl_euler_free:
* @euler: A #CoglEuler allocated via cogl_euler_copy()
*
* Frees a #CoglEuler that was previously allocated using
* cogl_euler_copy().
*
* Since: 2.0
*/
void
cogl_euler_free (CoglEuler *euler);
COGL_END_DECLS
#endif /* __COGL_EULER_H */