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libcamera: transform: Invert operator*() operands

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The current definition of operator*(Transform t1, Transform t0) follows
the function composition notion, where t0 is applied first then t1 is
applied last.

In order to introduce operator*(Orientation, Transform) where a
Transform is applied on top of an Orientation, invert the operand order
of operator*(Transform, Transform) so that usage of operator* with both
Orientation and Transform can be made associative.

For example:

Orientation o;
Transform t = t1 * t2
Orientation o1 = o * t
	       = o * (t1 * t2) = (o * t1) * t2 = o * t1 * t2

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
This commit is contained in:
Jacopo Mondi
2023-10-19 16:01:27 +02:00
committed by Laurent Pinchart
parent 250577878b
commit b54c935dd7
2 changed files with 13 additions and 13 deletions
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22
src/libcamera/transform.cpp
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@@ -189,24 +189,24 @@ Input image | | goes to output image | |
*/
/**
* \brief Compose two transforms together
* \param[in] t1 The second transform
* \param[in] t0 The first transform
* \brief Compose two transforms by applying \a t0 first then \a t1
* \param[in] t0 The first transform to apply
* \param[in] t1 The second transform to apply
*
* Composing transforms follows the usual mathematical convention for
* composing functions. That is, when performing `t1 * t0`, \a t0 is applied
* first, and then \a t1.
* For example, `Transpose * HFlip` performs `HFlip` first and then the
* `Transpose` yielding `Rot270`, as shown below.
* Compose two transforms into a transform that is equivalent to first applying
* \a t0 and then applying \a t1. For example, `HFlip * Transpose` performs
* `HFlip` first and then the `Transpose` yielding `Rot270`, as shown below.
~~~
A-B B-A B-D
Input image | | -> HFLip -> | | -> Transpose -> | | = Rot270
C-D D-C A-C
~~~
* Note that composition is generally non-commutative for Transforms,
* and not the same as XOR-ing the underlying bit representations.
* Note that composition is generally non-commutative for Transforms, and not
* the same as XOR-ing the underlying bit representations.
*
* \return A Transform equivalent to applying \a t0 and then \a t1
*/
Transform operator*(Transform t1, Transform t0)
Transform operator*(Transform t0, Transform t1)
{
/*
* Reorder the operations so that we imagine doing t0's transpose