[libcamera-devel] [PATCH 3/3] cam: kms_sink: Scale the frame buffer to full screen if supported

[Kieran Bingham]

Quoting Laurent Pinchart via libcamera-devel (2022-08-07 19:01:00)
> The KMS sink currently displays the frame buffer on the top-left corner
> of the screen, resulting in either a black area on the bottom and right
> sides (if the frame buffer is smaller than the display resolution) of in
> a restricted field of view (if the frame buffer is larger than the
> display resolution). Improve this by scaling the frame buffer to full
> screen if supported, and aligning the crop rectangle to the frame buffer
> center if the field of view needs to be restricted.
> 
> The implementation test three possible composition options, from best to
> worst. The tests are performed when the camera is started, as testing
> atomic commits requires access to frame buffer objects, which are not
> available at configure time. Changing this would require either a large
> refactoring of the cam application to provide frame buffers earlier, or
> extending the KMS API to support testing commits with dummy buffer
> objects. Both are candidates for later development.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/cam/kms_sink.cpp | 92 ++++++++++++++++++++++++++++++++++++++++----
>  src/cam/kms_sink.h   |  8 ++++
>  2 files changed, 92 insertions(+), 8 deletions(-)
> 
> diff --git a/src/cam/kms_sink.cpp b/src/cam/kms_sink.cpp
> index 16435ede6b6a..2f306955cf51 100644
> --- a/src/cam/kms_sink.cpp
> +++ b/src/cam/kms_sink.cpp
> @@ -284,6 +284,77 @@ int KMSSink::stop()
>         return FrameSink::stop();
>  }
>  
> +bool KMSSink::testModeSet(DRM::FrameBuffer *drmBuffer,
> +                         const libcamera::Rectangle &src,
> +                         const libcamera::Rectangle &dst)
> +{
> +       DRM::AtomicRequest drmRequest{ &dev_ };
> +
> +       drmRequest.addProperty(connector_, "CRTC_ID", crtc_->id());
> +
> +       drmRequest.addProperty(crtc_, "ACTIVE", 1);
> +       drmRequest.addProperty(crtc_, "MODE_ID", mode_->toBlob(&dev_));
> +
> +       drmRequest.addProperty(plane_, "CRTC_ID", crtc_->id());
> +       drmRequest.addProperty(plane_, "FB_ID", drmBuffer->id());
> +       drmRequest.addProperty(plane_, "SRC_X", src.x << 16);
> +       drmRequest.addProperty(plane_, "SRC_Y", src.y << 16);
> +       drmRequest.addProperty(plane_, "SRC_W", src.width << 16);
> +       drmRequest.addProperty(plane_, "SRC_H", src.height << 16);
> +       drmRequest.addProperty(plane_, "CRTC_X", dst.x);
> +       drmRequest.addProperty(plane_, "CRTC_Y", dst.y);
> +       drmRequest.addProperty(plane_, "CRTC_W", dst.width);
> +       drmRequest.addProperty(plane_, "CRTC_H", dst.height);
> +
> +       return !drmRequest.commit(DRM::AtomicRequest::FlagAllowModeset |
> +                                 DRM::AtomicRequest::FlagTestOnly);
> +}
> +
> +bool KMSSink::setupComposition(DRM::FrameBuffer *drmBuffer)
> +{
> +       /*
> +        * Test composition options, from most to least desirable, to select the
> +        * best one.
> +        */
> +       const libcamera::Rectangle framebuffer{ size_ };
> +       const libcamera::Rectangle display{ 0, 0, mode_->hdisplay, mode_->vdisplay };
> +
> +       /* 1. Scale the frame buffer to full screen. */

Can we preserve aspect ratio?

That might mean two tests. One that checks if we can 'scale' and center
to fit the screen (with black/white/whatever) boundaries on the edges of
either horizontal or vertical.

Then one which scales and crops to fit without borders...


> +       libcamera::Rectangle src = libcamera::Rectangle{ size_ };
> +       libcamera::Rectangle dst = display;
> +
> +       if (testModeSet(drmBuffer, src, dst)) {
> +               std::cout << "KMS: full-screen scaled output" << std::endl;
> +               src_ = src;
> +               dst_ = dst;
> +               return true;
> +       }
> +
> +       /* 2. Center the frame buffer on the display. */
> +       src = display.size().centeredTo(framebuffer.center()).boundedTo(framebuffer);
> +       dst = framebuffer.size().centeredTo(display.center()).boundedTo(display);
> +
> +       if (testModeSet(drmBuffer, src, dst)) {
> +               std::cout << "KMS: centered output" << std::endl;
> +               src_ = src;
> +               dst_ = dst;
> +               return true;
> +       }
> +
> +       /* 3. Align the frame buffer on the top-left of the display. */
> +       src = framebuffer.boundedTo(display);
> +       dst = display.boundedTo(framebuffer);
> +
> +       if (testModeSet(drmBuffer, src, dst)) {
> +               std::cout << "KMS: top-left aligned output" << std::endl;
> +               src_ = src;
> +               dst_ = dst;
> +               return true;
> +       }
> +
> +       return false;
> +}
> +
>  bool KMSSink::processRequest(libcamera::Request *camRequest)
>  {
>         /*
> @@ -307,20 +378,25 @@ bool KMSSink::processRequest(libcamera::Request *camRequest)
>  
>         if (!active_ && !queued_) {
>                 /* Enable the display pipeline on the first frame. */
> +               if (!setupComposition(drmBuffer)) {
> +                       std::cerr << "Failed to setup composition" << std::endl;
> +                       return true;
> +               }
> +
>                 drmRequest->addProperty(connector_, "CRTC_ID", crtc_->id());
>  
>                 drmRequest->addProperty(crtc_, "ACTIVE", 1);
>                 drmRequest->addProperty(crtc_, "MODE_ID", mode_->toBlob(&dev_));
>  
>                 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", size_.width << 16);
> -               drmRequest->addProperty(plane_, "SRC_H", size_.height << 16);
> -               drmRequest->addProperty(plane_, "CRTC_X", 0);
> -               drmRequest->addProperty(plane_, "CRTC_Y", 0);
> -               drmRequest->addProperty(plane_, "CRTC_W", size_.width);
> -               drmRequest->addProperty(plane_, "CRTC_H", size_.height);
> +               drmRequest->addProperty(plane_, "SRC_X", src_.x << 16);
> +               drmRequest->addProperty(plane_, "SRC_Y", src_.y << 16);
> +               drmRequest->addProperty(plane_, "SRC_W", src_.width << 16);
> +               drmRequest->addProperty(plane_, "SRC_H", src_.height << 16);
> +               drmRequest->addProperty(plane_, "CRTC_X", dst_.x);
> +               drmRequest->addProperty(plane_, "CRTC_Y", dst_.y);
> +               drmRequest->addProperty(plane_, "CRTC_W", dst_.width);
> +               drmRequest->addProperty(plane_, "CRTC_H", dst_.height);
>  
>                 flags |= DRM::AtomicRequest::FlagAllowModeset;
>         }
> diff --git a/src/cam/kms_sink.h b/src/cam/kms_sink.h
> index 8f5f08667cea..76c4e611bf85 100644
> --- a/src/cam/kms_sink.h
> +++ b/src/cam/kms_sink.h
> @@ -50,6 +50,11 @@ private:
>  
>         int selectPipeline(const libcamera::PixelFormat &format);
>         int configurePipeline(const libcamera::PixelFormat &format);
> +       bool testModeSet(DRM::FrameBuffer *drmBuffer,
> +                        const libcamera::Rectangle &src,
> +                        const libcamera::Rectangle &dst);
> +       bool setupComposition(DRM::FrameBuffer *drmBuffer);
> +
>         void requestComplete(DRM::AtomicRequest *request);
>  
>         DRM::Device dev_;
> @@ -63,6 +68,9 @@ private:
>         libcamera::Size size_;
>         unsigned int stride_;
>  
> +       libcamera::Rectangle src_;
> +       libcamera::Rectangle dst_;
> +
>         std::map<libcamera::FrameBuffer *, std::unique_ptr<DRM::FrameBuffer>> buffers_;
>  
>         std::mutex lock_;
> -- 
> Regards,
> 
> Laurent Pinchart
>