LV overlays issues for D678 Photo mode

General issues (Digic 6)

D6.. winsys_sem (Semaphore_Winsys_v aka vsync semaphore) DNE on 750, but it exists on 5D4 (and D.78X)
- Usage in D6.. removed in bae1c85d185e1850ad795caa7c5f10fdf106b4b8
- Without semaphore, screen tearing is possible while redrawing ML GUI.
- TODO: Investigate when it was introduced by Canon, adapt code accordingly.

General issues (Digic 6 and up):

D678 Even when no Canon overlays are visible, Canon will draw some on actions (eg. shutter speed change)
- Canon overlays will flicker as we actively overdraw whole screen while zebra_should_run() (94c0e0325235e437fb707a57bf5a2acc1d1d661e)
- To be investigated: possibility to kill Canon GUI drawing in this mode
- Guess: this was achieved by bmp_on() / bmp_off() on D45
- In FEATURE_COMPOSITOR_XCM we could just mute Canon layer(s), but there should be more generic solution.
D678: HTP can have multiple levels now. Adapt to same style display as ALO.

General issues (Digic 8):

D..8 PROP_LENS_DYNAMIC_DATA / lens struct size issues
- RAW values (and field sizes) for ISO, AV, TV had changed.
D..8 CONFIG_COMPOSITOR_DEDICATED_LAYER implementation for EOS RP and up (code to setup our own layer)
- R code is specific to R; RP, 250D and even R6 (Digic X) seems to have unified code
- Different structures are used to setup GUI layers
- Can be probably achieved using just XCM function calls, without touching RENDERER / VMIX structs.
- Refer to Chapter 4 for clues: Compositors, layers, contexts in RGB and YUV - How Digic 7(6?)+ draw GUI
D..8 Most dial modes are displayed properly except Fv + SCN + Movie Mode are displayed as ?

Partially fixed:

D..8 338dd8efe13de19ec8844bf90cea0cde75f13ddd Detection if overlays are clear to draw is broken:
- TODO: check possibility to improve delay by handling props from 958c07fdd8cb36399d62eda309f7145d589db620
D678 Many (not yet enabled) code paths search for dialog struct in a broken way
- Addressed for enabled cases by 338caa19453fb26807e6df8699fa6967523c1385
- New implementation checks if given handler is not null, instead of checking gui_task_list topmost window
- Require expansion with each new case enabled
- TODO: check if it can be backported to D45
- There's a brief moment on app transitions (eg LV->Main menu) where old code crashes, probably due to gui_task_list.current being null (see below)
```
struct gui_task * current = gui_task_list.current;
struct dialog * dialog = current->priv;
```

Fixed issues:

750D 618e5c2e55b3d251a0ae1f295b595df8a44a1ebf GUI modes are wrong
D67. 939a14cda37491d1b7e4dda36ce771dee0fbb47d PROP_LV_LENS: PROP_LV_LENS_D67 added, new method of data fetching needed
D..8 fa47a5399ad76fed35a6d5d8180d79ee715706bc PROP_LENS_STATIC_DATA has different lengths on R/RP/250D/M50.
D..8 103f33d2d68191df67af7aa54a57804b487edf70 With CONFIG_COMPOSITOR_DEDICATED_LAYER our LV overlays wont disappear unless ML menu open/close.
D..8 dc65526f33e82fa6e3d1ba6fa6a6e1861ed00153 PROP_PIC_QUALITY2 decoding data fails on R.
D..8 aa8eabeaa48db91759ca6af93537348f6a7a317f dialog_struct needs update for other cameras than R.
D..8 aa3f67de4676eaa27d5b5e058a82b6cc9ed24bd1 On start camera will not display any Canon GUI (black screen, only ML GUI is visible).
D..8 aa3f67de4676eaa27d5b5e058a82b6cc9ed24bd1 With CONFIG_COMPOSITOR_DEDICATED_LAYER screen sometimes is left not cleaned.
D..8 aa3f67de4676eaa27d5b5e058a82b6cc9ed24bd1 Rewrite R compositor support, leave space for RP+ and Ximr implementations.
D678 338caa19453fb26807e6df8699fa6967523c1385 After exit ML menu in LV mode, LV becomes black until Canon menu is open and closed.
D678 338caa19453fb26807e6df8699fa6967523c1385 liveview_display_idle() dialog handlers based LV detection is fundamentally broken.

reticulatedpines / magiclantern_simplified