[libcamera-devel] [PATCH v2] cam: kms_sink: Remove limitation that camera and display must match

[Kieran Bingham]

Hi Eric,

Quoting Eric Curtin (2022-02-07 15:00:59)
> There is a limitation that requires input and output to be pixel
> for pixel identical in terms of height and width. Remove this
> limitation to enable more hardware that doesn't match exactly in
> terms of pixels. Centralize the image. This works for the case
> where camera output has more pixels than the display and
> vice-versa. In the case where there are too many pixels for the
> display, we take the most central part of the image cropping out
> the border.

Thankyou, I'm very pleased to see this patch, As I'm sure you're aware
from our discussions on IRC.

I haven't actually been able to test direct render with the DRM part
here, so I think this will be really helpful. I can't test this right
now though, but I hope to this week, so just some quick comments while I
skim through.


> Signed-off-by: Eric Curtin <ecurtin at redhat.com>
> ---
> 
> Changes in v2:
> - Tested and support drawing from negative pixel range
>   kernel parameter (video=960x540 at 60) was useful here
> 
>  src/cam/kms_sink.cpp | 32 ++++++++++++++------------------
>  src/cam/kms_sink.h   |  2 ++
>  2 files changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/src/cam/kms_sink.cpp b/src/cam/kms_sink.cpp
> index 973cd370..8eb51454 100644
> --- a/src/cam/kms_sink.cpp
> +++ b/src/cam/kms_sink.cpp
> @@ -113,24 +113,20 @@ int KMSSink::configure(const libcamera::CameraConfiguration &config)
>         const libcamera::StreamConfiguration &cfg = config.at(0);
>  
>         const std::vector<DRM::Mode> &modes = connector_->modes();
> -       const auto iter = std::find_if(modes.begin(), modes.end(),
> -                                      [&](const DRM::Mode &mode) {
> -                                              return mode.hdisplay == cfg.size.width &&
> -                                                     mode.vdisplay == cfg.size.height;
> -                                      });

Hrm, I would maybe expect to see some sort of 'best mode' search here to
find the closest mode that fits the incoming image. I'm sure that might
be a pattern that exists already somewhere.

But I expect being able to draw on any mode, is going to make this work
on more devices than only drawing on an exact mode.


> -       if (iter == modes.end()) {
> -               std::cerr
> -                       << "No mode matching " << cfg.size.toString()
> -                       << std::endl;
> -               return -EINVAL;
> -       }
>  
>         int ret = configurePipeline(cfg.pixelFormat);
>         if (ret < 0)
>                 return ret;
>  
> -       mode_ = &*iter;
> +       mode_ = &modes[0];
>         size_ = cfg.size;
> +
> +       // We need to cast for the case where the camera output has more
> +       // pixels than the display, in this case we start drawing from a
> +       // negative pixel point to crop out the content to display just
> +       // the middle part.

Our code style uses
 /*
  *
  */

For comment blocks. I guess our checkstyle doesn't actually pick up on
that though.


> +       x_ = (mode_->hdisplay - static_cast<int>(size_.width)) / 2;
> +       y_ = (mode_->vdisplay - static_cast<int>(size_.height)) / 2;

We have a Rectangle class in include/libcamera/geometry.h which can
handle centering, and might be useful here.

>         stride_ = cfg.stride;
>  
>         return 0;
> @@ -297,12 +293,12 @@ bool KMSSink::processRequest(libcamera::Request *camRequest)
>                 drmRequest->addProperty(plane_, "CRTC_ID", crtc_->id());
>                 drmRequest->addProperty(plane_, "SRC_X", 0 << 16);
>                 drmRequest->addProperty(plane_, "SRC_Y", 0 << 16);
> -               drmRequest->addProperty(plane_, "SRC_W", mode_->hdisplay << 16);
> -               drmRequest->addProperty(plane_, "SRC_H", mode_->vdisplay << 16);
> -               drmRequest->addProperty(plane_, "CRTC_X", 0);
> -               drmRequest->addProperty(plane_, "CRTC_Y", 0);
> -               drmRequest->addProperty(plane_, "CRTC_W", mode_->hdisplay);
> -               drmRequest->addProperty(plane_, "CRTC_H", mode_->vdisplay);
> +               drmRequest->addProperty(plane_, "SRC_W", size_.width << 16);
> +               drmRequest->addProperty(plane_, "SRC_H", size_.height << 16);
> +               drmRequest->addProperty(plane_, "CRTC_X", x_);
> +               drmRequest->addProperty(plane_, "CRTC_Y", y_);
> +               drmRequest->addProperty(plane_, "CRTC_W", size_.width);
> +               drmRequest->addProperty(plane_, "CRTC_H", size_.height);
>  
>                 flags |= DRM::AtomicRequest::FlagAllowModeset;
>         }
> diff --git a/src/cam/kms_sink.h b/src/cam/kms_sink.h
> index 4a0a872c..2c16182c 100644
> --- a/src/cam/kms_sink.h
> +++ b/src/cam/kms_sink.h
> @@ -61,6 +61,8 @@ private:
>         libcamera::PixelFormat format_;
>         libcamera::Size size_;
>         unsigned int stride_;
> +       int x_;  // Where to start drawing camera output
> +       int y_;  // Where to start drawing camera output

/*  */ comments here too please.
  
>         std::map<libcamera::FrameBuffer *, std::unique_ptr<DRM::FrameBuffer>> buffers_;
>  
> -- 
> 2.34.1
>