I did some more hacking and got softdevice to a useable state on VDR 2.0.4. My patch against softdevice cvs is attached.
The TL;DR version is that I suspect 2 bugs in VDR 2.0.4:
(1) The bottom 1% lines of the OSD are not being cleared when the OSD extends that low. (I can choose up to 99% height and 0% vertical offset.)
(2) Changes in DVB subtitles will flash the OSD layer (make it empty for a very short time) if an OSD is active. I suppose that DVB subtitles should not be displayed at all when OSD layer is active.
On Mon, Nov 04, 2013 at 10:30:14PM +1000, Torgeir Veimo wrote:
Softdevice had transparency 'dithering' for when there's only 1-bit transparency, did you look at that option?
I am a bit unsure if it really is using 1-bit transparency. The background inside the LCARS main menu is darker (but still translucent) than the area outside the menu borders. Everything else in the OSD layer is opaque.
With "perf top" I noticed that Softdevice was spending a lot of time, scaling the OSD layer down from 1920×1080 to 720×576 that is my video output resolution. So, I hardcoded the OSD size back to 720×576. OSD updates became snappy (fewer pixels to copy to the cSoftOsd::OSD_Bitmap[], and from there it would be a straight memcpy to the video memory). The following problem was unaffected by this fix.
If I set the OSD size to 100% height, then VDR will never clear the very bottom lines at the screen. If I set it to 99% height, everything will be erased properly when I leave the main menu, or the program info at the bottom of the screen is cleared. If I set it to 99% height and 1% vertical offset, the garbage will appear again. My current understanding is that it is VDR 2.0.4 that fails to post a proper draw request to clear the bottom of the screen.
The next problem was related to my patch. It turned out that cSoftOsd::Flush() has to check cOsd::IsTrueColor() and render pixmaps or bitmaps accordingly. This would also explain why I previously never saw any output from the Classic VDR OSD (it is the only non-TrueColor built-in theme).
The garbage-at-bottom problem also affects DVB subtitles. If I move the "Setup.DVB$Subtitle offset" too low, the pixels from the last 4 or so of the 576 lines will never be cleared (only drawn when there is some "y" or "p" or "q" character that extends to to the "garbage area").
A small (old) problem with the Softdevice OSD/subtitles remains. When the OSD is active while the current stream is showing DVB subtitles, the OSD layer will be cleared, but no subtitles will be displayed. Eventually, parts of the OSD will be repainted. It turns out that this problem was emphasized by the cSoftOsd::dirty_lines[] array. If I commit out the dirty_lines[] checks, the OSD will be properly repainted, but the entire OSD layer will be cleared for a few frames whenever the subtitles are about to display. (No subtitles will be actually displayed, because the OSD layer is active.) How to avoid this short OSD flash? I tried commenting out all cSoftOsd::Clear() calls, but that did not help (other than leaving DVB subtitles garbage on the screen when the OSD layer was not active).
Note: I understand that the non-truecolor DVB subtitles are not being alpha-blended to the truecolor OSD layer. It is OK for me not to see subtitles when the OSD is active. But it is not OK that the active OSD layer gets cleared whenever subtitles are attempting to display or clear themselves.
Best regards,
Marko