Display gstreamer video on weston with some transparency

[KATA_KAN]

Hi,all.

Since it was recommended to make another question from the following questions, I made another question.

https://community.nxp.com/t5/i-MX-Processors/Gstreamer-i-MX8MMini-pipeline/m-p/1650686#M205902

I am developing an application that controls the screen display on a board that uses the i.MX8MMini.

What I'm trying to do now is display a video with coordinates and dimensions on top of weston's default screen. I expect weston's default screen to be transparent, except for the video playback area.

Display a transparent image (R, G, B = 0, 0, 0) called invisible.png at 1920x1080, display (x, y) = (640, 0) to 1280x952 videotestsrc on it, and display (R, G,B=0,0,0) can be set as a transparent color, so I built the following pipeline.

gst-launch-1.0 imxcompositor_g2d name=comp \
sink_0::xpos=0 sink_0::ypos=0 sink_0::width=1920 sink_0::height=1080 \
sink_1::xpos=640 sink_1::ypos=0 sink_1::width=1280 sink_1::height=952 ! \
video/x-raw,format=RGB16 ! waylandsink window-width=1920 window-height=1080 \
filesrc location=invisible.png ! pngdec ! alpha method=custom target-r=0 target-b=0 target-g=0 ! imagefreeze ! video/x-raw,width=1920,height=1080,framerate=10/1 ! comp.sink_0 \
videotestsrc ! video/x-raw,width=1280,height=952 ! comp.sink_1

However, I was expecting the default image displayed by weston to be transparent, like the attached image, but it is not transparent and shows a black screen.

Is there anything we can do from here?

[joanxie]

could you explain these pics stand for?

[KATA_KAN]

Sorry, my explanation was lacking.

"gstreamer_test.png" is an image diagram of what you want to display.
"RIMG7765.JPG" is weston's default screen actually shown on the display.
"invisible.png" is the 1980x1080 transparent image you are displaying in the pipeline.

[joanxie]

it seems this is exist bug

https://gstreamer-devel.narkive.com/Tp62Zghb/gstreamer-alpha-channel-on-black