libcamera/vivid.git - libcamera pipeline handler for VIVID

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2020, Raspberry Pi Ltd
 *
 * 2D plane transforms.
 */

#include <libcamera/transform.h>

#include <libcamera/orientation.h>

/**
 * \file transform.h
 * \brief Enum to represent and manipulate 2D plane transforms
 */

namespace libcamera {

/**
 * \enum Transform
 * \brief Enum to represent a 2D plane transform
 *
 * The Transform can take 8 distinct values, representing the usual 2D plane
 * transforms listed below. Each of these transforms can be constructed
 * out of 3 basic operations, namely a horizontal flip (mirror), a vertical
 * flip, and a transposition (about the main diagonal). The transforms are
 * encoded such that a single bit indicates the presence of each of the 3
 * basic operations:
 *
 * - bit 0 - presence of a horizontal flip
 * - bit 1 - presence of a vertical flip
 * - bit 2 - presence of a transposition.
 *
 * We regard these 3 basic operations as being applied in a specific order:
 * first the two flip operations (actually they commute, so the order between
 * them is unimportant) and finally any transpose operation.
 *
 * Functions are provided to manipulate directly the bits within the transform
 * encoding, but there are also higher-level functions to invert and compose
 * transforms. Transforms are composed according to the usual mathematical
 * convention such that the right transform is applied first, and the left
 * transform is applied second.
 *
 * Finally, we have a total of 8 distinct transformations, as follows (a
 * couple of them have additional synonyms for convenience). We illustrate each
 * with its nominal effect on a rectangle with vertices labelled A, B, C and D.
 *
 * \sa https://en.wikipedia.org/wiki/Examples_of_groups#dihedral_group_of_order_8
 *
 * The set of 2D plane transforms is also known as the symmetry group of a
 * square, described in the link. Note that the group can be generated by
 * only 2 elements (the horizontal flip and a 90 degree rotation, for
 * example), however, the encoding used here makes the presence of the vertical
 * flip explicit.
 *
 * \var Transform::Identity
 *
 * Identity transform.
~~~
              A-B                          A-B
Input image   | |   goes to output image   | |
              C-D                          C-D
~~~
 * Numeric value: 0 (no bits set).
 *
 * \var Transform::Rot0
 *
 * Synonym for Transform::Identity (zero degree rotation).
 *
 * \var Transform::HFlip
 *
 * Horizontal flip.
~~~
              A-B                          B-A
Input image   | |   goes to output image   | |
              C-D                          D-C
~~~
 * Numeric value: 1 (horizontal flip bit set only).
 *
 * \var Transform::VFlip
 *
 * Vertical flip.
~~~
              A-B                          C-D
Input image   | |   goes to output image   | |
              C-D                          A-B
~~~


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