[{"id":27582,"web_url":"https://patchwork.libcamera.org/comment/27582/","msgid":"","date":"2023-07-18T11:49:55","subject":"Re: [libcamera-devel] [PATCH v3 06/10] libcamera: transform: Invert\n\toperator*() operands","submitter":{"id":42,"url":"https://patchwork.libcamera.org/api/people/42/","name":"David Plowman","email":"david.plowman@raspberrypi.com"},"content":"Hi Jacopo\n\nThanks for doing this!\n\nOn Tue, 18 Jul 2023 at 11:52, Jacopo Mondi\n wrote:\n>\n> The current definition of operator*(Transform t1, Transform t0) follows\n> the function composition notion, where t0 is applied first then t1 is\n> applied last.\n>\n> In order to introduce operator*(Orientation, Transform) where a\n> Transform is applied on top of an Orientation, invert the operand order\n> of operator*(Transform, Transform) so that usage of operator* with both\n> Orientation and Transform can be made associative.\n>\n> For example:\n>\n> Orientation o;\n> Transform t = t1 * t2\n> Transform t3 = o * t\n\nStrictly, o * t gives us an orientation and not a transform. But\notherwise I agree!\n\nReviewed-by: David Plowman \n\nThanks!\nDavid\n\n> = o * (t1 * t2) = (o * t1) * t2 = o * t1 * t2\n>\n> Signed-off-by: Jacopo Mondi \n> ---\n> src/libcamera/camera_sensor.cpp | 4 ++--\n> src/libcamera/transform.cpp | 19 +++++++++++--------\n> 2 files changed, 13 insertions(+), 10 deletions(-)\n>\n> diff --git a/src/libcamera/camera_sensor.cpp b/src/libcamera/camera_sensor.cpp\n> index 3ba364c44a40..038d8b959072 100644\n> --- a/src/libcamera/camera_sensor.cpp\n> +++ b/src/libcamera/camera_sensor.cpp\n> @@ -1051,7 +1051,7 @@ Transform CameraSensor::validateTransform(Transform *transform) const\n> * Combine the requested transform to compensate the sensor mounting\n> * rotation.\n> */\n> - Transform combined = *transform * rotationTransform_;\n> + Transform combined = rotationTransform_ * *transform;\n>\n> /*\n> * We combine the platform and user transform, but must \"adjust away\"\n> @@ -1080,7 +1080,7 @@ Transform CameraSensor::validateTransform(Transform *transform) const\n> * If the sensor can do no transforms, then combined must be\n> * changed to the identity. The only user transform that gives\n> * rise to this is the inverse of the rotation. (Recall that\n> - * combined = transform * rotationTransform.)\n> + * combined = rotationTransform * transform.)\n> */\n> *transform = -rotationTransform_;\n> combined = Transform::Identity;\n> diff --git a/src/libcamera/transform.cpp b/src/libcamera/transform.cpp\n> index c70cac3f14ee..d192d63d9290 100644\n> --- a/src/libcamera/transform.cpp\n> +++ b/src/libcamera/transform.cpp\n> @@ -189,14 +189,17 @@ Input image | | goes to output image | |\n> */\n>\n> /**\n> - * \\brief Compose two transforms together\n> - * \\param[in] t1 The second transform\n> - * \\param[in] t0 The first transform\n> + * \\brief Compose two transforms by applying \\a t0 first then \\a t1\n> + * \\param[in] t0 The first transform to apply\n> + * \\param[in] t1 The second transform to apply\n> + *\n> + * Compose two transforms by applying \\a t1 after \\a t0. The operation\n> + * is conceptually equivalent to the canonical notion of function composition,\n> + * with inverse order of operands. If in the canonical function composition\n> + * notation \"f * g\" equals to \"f(g())\", the notation for Transforms composition\n> + * \"t0 * t1\" equals to \"t1(t0()))\" where \\a t0 is applied first, then \\a t1.\n> *\n> - * Composing transforms follows the usual mathematical convention for\n> - * composing functions. That is, when performing `t1 * t0`, \\a t0 is applied\n> - * first, and then \\a t1.\n> - * For example, `Transpose * HFlip` performs `HFlip` first and then the\n> + * For example, `HFlip * Transpose` performs `HFlip` first and then the\n> * `Transpose` yielding `Rot270`, as shown below.\n> ~~~\n> A-B B-A B-D\n> @@ -206,7 +209,7 @@ Input image | | -> HFLip -> | | -> Transpose -> | | = Rot270\n> * Note that composition is generally non-commutative for Transforms,\n> * and not the same as XOR-ing the underlying bit representations.\n> */\n> -Transform operator*(Transform t1, Transform t0)\n> +Transform operator*(Transform t0, Transform t1)\n> {\n> /*\n> * Reorder the operations so that we imagine doing t0's transpose\n> --\n> 2.40.1\n>","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 75E25BDB1C\n\tfor ;\n\tTue, 18 Jul 2023 11:50:09 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id D0A3C628C0;\n\tTue, 18 Jul 2023 13:50:08 +0200 (CEST)","from mail-oi1-x22f.google.com (mail-oi1-x22f.google.com\n\t[IPv6:2607:f8b0:4864:20::22f])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id EC42A61E2B\n\tfor ;\n\tTue, 18 Jul 2023 13:50:07 +0200 (CEST)","by mail-oi1-x22f.google.com with SMTP id\n\t5614622812f47-3a46da5cd6dso738951b6e.0\n\tfor ;\n\tTue, 18 Jul 2023 04:50:07 -0700 (PDT)"],"DKIM-Signature":["v=1; 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charset=\"UTF-8\"","Subject":"Re: [libcamera-devel] [PATCH v3 06/10] libcamera: transform: Invert\n\toperator*() operands","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","From":"David Plowman via libcamera-devel ","Reply-To":"David Plowman ","Cc":"libcamera-devel@lists.libcamera.org","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]