2da24ab863
To help catch accidental changes to the size of public structs that can be allocated on the stack this patch adds compile time checks that our struct sizes haven't changed.
254 lines
8.2 KiB
C
254 lines
8.2 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(CLUTTER_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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#include <glib.h>
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G_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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* </itemlist>
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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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* @v1: 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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gboolean
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cogl_euler_equal (gconstpointer v1, gconstpointer 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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G_END_DECLS
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#endif /* __COGL_EULER_H */
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