## Summary
This pull request introduces custom screen transition animations to
enhance the overall user experience during navigation.
The key change is the implementation of a custom slide/fade effect for
navigating from main screens (i.e., screens hosted in the bottom
navigation bar) to detail screens. Transitions between the bottom
navigation bar tabs themselves retain a simple, clean cross-fade effect
to ensure a fast and smooth user interaction.
This PR also addresses the root cause of an issue where custom
animations were being overridden by the navigation library's defaults.
## Root Cause
During implementation, it was discovered that custom transition
animations defined in the `defaultTransitions` parameter of the
`DestinationsNavHost` in `MainActivity` were not being applied. Instead,
a default fade-in/fade-out animation was always present.
The root cause was traced to the `compose-destinations` KSP (Kotlin
Symbol Processing) code generator. By default, the generator creates a
`NavGraphSpec` (e.g., `RootNavGraph.kt`) that includes its own
`defaultTransitions` property. This property, defined at compile-time
within the generated graph object, has a higher precedence than the
`defaultTransitions` parameter supplied to the `DestinationsNavHost`
composable at runtime.
As a result, our intended custom animations were being ignored and
overridden by the generated default.
## Solution
To resolve this precedence issue permanently, this PR adopts the
official configuration method recommended by the `compose-destinations`
library.
- The following KSP argument has been added to the
`app/build.gradle.kts` file:
```kotlin
ksp {
arg("compose-destinations.defaultTransitions", "none")
}
```
- This argument instructs the code generator to omit the
`defaultTransitions` property from the generated `NavGraphSpec`.
- By removing the higher-priority, generated default, the
`defaultTransitions` parameter on `DestinationsNavHost` now functions as
the effective default, allowing our custom animation logic to execute as
intended.
## Animation Logic Details
The new animation logic is conditional and defined within
`MainActivity`. It distinguishes between two primary navigation types:
- Main Screen → Detail Screen:
- Enter: The new detail screen slides in from the right.
- Exit: The old main screen slides out to the left while fading out.
- Detail Screen → Main Screen (on Pop):
- Pop Enter: The main screen slides back in from the left while fading
in.
- Pop Exit: The detail screen slides out to the right.
- Between Bottom Navigation Tabs:
- A simple cross-fade (`fadeIn`/`fadeOut`) is maintained for these
transitions to provide a quick and non-disruptive experience when
switching between primary sections of the app.
When kernel is compiled with CONFIG_DEBUG_ATOMIC_SLEEP enabled, it
prints the following splat in dmesg during post boot:
[ 6.739169] init: Opening SELinux policy
[ 6.751520] init: Loading SELinux policy
[ 6.894684] SELinux: policy capability network_peer_controls=1 [
6.894688] SELinux: policy capability open_perms=1 [ 6.894690] SELinux:
policy capability extended_socket_class=1 [ 6.894691] SELinux: policy
capability always_check_network=0 [ 6.894693] SELinux: policy capability
cgroup_seclabel=0 [ 6.894695] SELinux: policy capability
nnp_nosuid_transition=1 [ 7.214323] selinux: SELinux: Loaded file
context from: [ 7.214332] selinux:
/system/etc/selinux/plat_file_contexts [ 7.214339] selinux:
/system_ext/etc/selinux/system_ext_file_contexts [ 7.214345] selinux:
/product/etc/selinux/product_file_contexts [ 7.214350] selinux:
/vendor/etc/selinux/vendor_file_contexts [ 7.214356] selinux:
/odm/etc/selinux/odm_file_contexts [ 7.216398] KernelSU:
/system/bin/init argc: 2
[ 7.216401] KernelSU: /system/bin/init first arg: second_stage [
7.216403] KernelSU: /system/bin/init second_stage executed [ 7.216506]
BUG: sleeping function called from invalid context at
security/selinux/ss/hashtab.c:47 [ 7.216512] in_atomic(): 0,
irqs_disabled(): 0, non_block: 0, pid: 1, name: init [ 7.216516]
preempt_count: 0, expected: 0
[ 7.216518] RCU nest depth: 1, expected: 0
[ 7.216524] CPU: 6 PID: 1 Comm: init Not tainted
5.4.289-Scarlet-v2.0-beta3 #1 [ 7.216526] Hardware name: redwood based
Qualcomm Technologies, Inc. SM7325 (DT) [ 7.216528] Call trace:
[ 7.216536] dump_backtrace+0x0/0x210
[ 7.216539] show_stack+0x14/0x20
[ 7.216544] dump_stack+0x9c/0xec
[ 7.216548] __might_resched+0x1f0/0x210
[ 7.216552] hashtab_insert+0x38/0x230
[ 7.216557] add_type+0xd4/0x2e0
[ 7.216559] ksu_type+0x24/0x60
[ 7.216562] apply_kernelsu_rules+0xa8/0x650
[ 7.216565] ksu_handle_execveat_ksud+0x2a8/0x460
[ 7.216568] ksu_handle_execveat+0x2c/0x60
[ 7.216571] __arm64_sys_execve+0xe8/0xf0
[ 7.216574] el0_svc_common+0xf4/0x1a0
[ 7.216577] do_el0_svc+0x2c/0x40
[ 7.216579] el0_sync_handler+0x18c/0x200
[ 7.216582] el0_sync+0x140/0x180
This is because apply_kernelsu_rules() uses rcu_read_lock() to protect
SELinux policy modifications. However, cond_resched() from
hashtab_insert() at security/selinux/ss/hashtab.c is internally called
and it sleeps which is illegal under an RCU read-side critical section.
While replacing it with a spinlock would suppress the warning, this is
fundamentally incorrect because sleeping is illegal while holding a
spinlock and spinlock would turn off preemption which isn't an ideal
solution since it intentionally turns off rescheduling, and can lead to
deadlocks.
Instead, replace the RCU lock with a mutex lock. Mutex lock allows
sleeping when necessary, which is appropriate here because
apply_kernelsu_rules() runs in process context, not in atomic or
interrupt context. As apply_kernelsu_rules() is invoked only once during
post boot (SYSTEM_RUNNING), the mutex lock does not introduce any major
runtime performance regression and provides correct synchronization.
Fixes: https://github.com/tiann/KernelSU/issues/2637
Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
