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864e5562df
Argument names and @$arg suffered from various little mismatches, fix them in a batch commit. (cherry picked from commit d2ac3c5a88d980e7519c98bd261111b93cf73a6e)
252 lines
8.1 KiB
C
252 lines
8.1 KiB
C
/*
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* Cogl
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*
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* An object oriented GL/GLES Abstraction/Utility Layer
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*
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* Copyright (C) 2010 Intel Corporation.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*
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* Authors:
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* Robert Bragg <robert@linux.intel.com>
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*/
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#if !defined(__COGL_H_INSIDE__) && !defined(COGL_COMPILATION)
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#error "Only <cogl/cogl.h> can be included directly."
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#endif
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#ifndef __COGL_EULER_H
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#define __COGL_EULER_H
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#include <cogl/cogl-types.h>
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COGL_BEGIN_DECLS
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/**
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* SECTION:cogl-euler
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* @short_description: Functions for initializing and manipulating
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* euler angles.
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*
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* Euler angles are a simple representation of a 3 dimensional
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* rotation; comprised of 3 ordered heading, pitch and roll rotations.
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* An important thing to understand is that the axis of rotation
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* belong to the object being rotated and so they also rotate as each
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* of the heading, pitch and roll rotations are applied.
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*
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* One way to consider euler angles is to imagine controlling an
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* aeroplane, where you first choose a heading (Such as flying south
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* east), then you set the pitch (such as 30 degrees to take off) and
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* then you might set a roll, by dipping the left, wing as you prepare
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* to turn.
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*
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* They have some advantages and limitations that it helps to be
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* aware of:
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*
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* Advantages:
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* <itemizedlist>
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* <listitem>
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* Easy to understand and use, compared to quaternions and matrices,
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* so may be a good choice for a user interface.
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* </listitem>
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* <listitem>
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* Efficient storage, needing only 3 components any rotation can be
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* represented.
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* <note>Actually the #CoglEuler type isn't optimized for size because
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* we may cache the equivalent #CoglQuaternion along with a euler
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* rotation, but it would be trivial for an application to track the
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* components of euler rotations in a packed float array if optimizing
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* for size was important. The values could be passed to Cogl only when
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* manipulation is necessary.</note>
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* </listitem>
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* </itemizedlist>
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*
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* Disadvantages:
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* <itemizedlist>
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* <listitem>
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* Aliasing: it's possible to represent some rotations with multiple
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* different heading, pitch and roll rotations.
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* </listitem>
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* <listitem>
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* They can suffer from a problem called Gimbal Lock. A good
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* explanation of this can be seen on wikipedia here:
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* http://en.wikipedia.org/wiki/Gimbal_lock but basically two
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* of the axis of rotation may become aligned and so you loose a
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* degree of freedom. For example a pitch of +-90° would mean that
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* heading and bank rotate around the same axis.
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* </listitem>
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* <listitem>
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* If you use euler angles to orient something in 3D space and try to
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* transition between orientations by interpolating the component
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* angles you probably wont get the transitions you expect as they may
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* not follow the shortest path between the two orientations.
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* </listitem>
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* <listitem>
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* There's no standard to what order the component axis rotations are
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* applied. The most common convention seems to be what we do in Cogl
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* with heading (y-axis), pitch (x-axis) and then roll (z-axis), but
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* other software might apply x-axis, y-axis then z-axis or any other
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* order so you need to consider this if you are accepting euler
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* rotations from some other software. Other software may also use
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* slightly different aeronautical terms, such as "yaw" instead of
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* "heading" or "bank" instead of "roll".
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* </listitem>
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* </itemizedlist>
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*
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* To minimize the aliasing issue we may refer to "Canonical Euler"
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* angles where heading and roll are restricted to +- 180° and pitch is
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* restricted to +- 90°. If pitch is +- 90° bank is set to 0°.
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*
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* Quaternions don't suffer from Gimbal Lock and they can be nicely
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* interpolated between, their disadvantage is that they don't have an
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* intuitive representation.
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*
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* A common practice is to accept angles in the intuitive Euler form
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* and convert them to quaternions internally to avoid Gimbal Lock and
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* handle interpolations. See cogl_quaternion_init_from_euler().
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*/
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/**
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* CoglEuler:
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* @heading: Angle to rotate around an object's y axis
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* @pitch: Angle to rotate around an object's x axis
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* @roll: Angle to rotate around an object's z axis
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*
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* Represents an ordered rotation first of @heading degrees around an
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* object's y axis, then @pitch degrees around an object's x axis and
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* finally @roll degrees around an object's z axis.
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*
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* <note>It's important to understand the that axis are associated
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* with the object being rotated, so the axis also rotate in sequence
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* with the rotations being applied.</note>
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*
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* The members of a #CoglEuler can be initialized, for example, with
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* cogl_euler_init() and cogl_euler_init_from_quaternion ().
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*
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* You may also want to look at cogl_quaternion_init_from_euler() if
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* you want to do interpolation between 3d rotations.
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*
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* Since: 2.0
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*/
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struct _CoglEuler
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{
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/*< public > */
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float heading;
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float pitch;
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float roll;
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/*< private > */
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/* May cached a quaternion here in the future */
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float padding0;
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float padding1;
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float padding2;
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float padding3;
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float padding4;
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};
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COGL_STRUCT_SIZE_ASSERT (CoglEuler, 32);
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/**
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* cogl_euler_init:
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* @euler: The #CoglEuler angle to initialize
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* @heading: Angle to rotate around an object's y axis
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* @pitch: Angle to rotate around an object's x axis
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* @roll: Angle to rotate around an object's z axis
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*
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* Initializes @euler to represent a rotation of @x_angle degrees
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* around the x axis, then @y_angle degrees around the y_axis and
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* @z_angle degrees around the z axis.
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*
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* Since: 2.0
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*/
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void
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cogl_euler_init (CoglEuler *euler,
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float heading,
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float pitch,
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float roll);
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/**
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* cogl_euler_init_from_matrix:
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* @euler: The #CoglEuler angle to initialize
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* @matrix: A #CoglMatrix containing a rotation, but no scaling,
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* mirroring or skewing.
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*
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* Extracts a euler rotation from the given @matrix and
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* initializses @euler with the component x, y and z rotation angles.
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*/
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void
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cogl_euler_init_from_matrix (CoglEuler *euler,
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const CoglMatrix *matrix);
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/**
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* cogl_euler_init_from_quaternion:
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* @euler: The #CoglEuler angle to initialize
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* @quaternion: A #CoglEuler with the rotation to initialize with
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*
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* Initializes a @euler rotation with the equivalent rotation
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* represented by the given @quaternion.
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*/
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void
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cogl_euler_init_from_quaternion (CoglEuler *euler,
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const CoglQuaternion *quaternion);
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/**
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* cogl_euler_equal:
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* @v1: The first euler angle to compare
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* @v2: The second euler angle to compare
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*
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* Compares the two given euler angles @v1 and @v1 and it they are
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* equal returns %TRUE else %FALSE.
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*
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* <note>This function only checks that all three components rotations
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* are numerically equal, it does not consider that some rotations
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* can be represented with different component rotations</note>
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*
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* Returns: %TRUE if @v1 and @v2 are equal else %FALSE.
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* Since: 2.0
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*/
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CoglBool
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cogl_euler_equal (const void *v1, const void *v2);
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/**
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* cogl_euler_copy:
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* @src: A #CoglEuler to copy
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*
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* Allocates a new #CoglEuler and initilizes it with the component
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* angles of @src. The newly allocated euler should be freed using
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* cogl_euler_free().
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*
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* Returns: A newly allocated #CoglEuler
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* Since: 2.0
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*/
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CoglEuler *
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cogl_euler_copy (const CoglEuler *src);
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/**
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* cogl_euler_free:
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* @euler: A #CoglEuler allocated via cogl_euler_copy()
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*
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* Frees a #CoglEuler that was previously allocated using
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* cogl_euler_copy().
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*
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* Since: 2.0
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*/
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void
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cogl_euler_free (CoglEuler *euler);
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COGL_END_DECLS
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#endif /* __COGL_EULER_H */
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