Impeller supports both Vulkan and Open GL ES rendering on Android. Impeller will prefer rendering with Vulkan and fallback to OpenGL ES 2.0 for compatibility. With both the Vulkan and OpenGL ES, Impeller supports rendering on all existing Android versions supported by Flutter.
The rough logic for backend selection on Android is depicted below.
flowchart TD start[Start] android_api{Check Android API} device_support{Device Supports Vulkan} vulkan_version{Vulkan Version Check} vulkan_exts{Vulkan Supports Extensions} vulkan[Use Vulkan Backend] opengl[Use OpenGL Backend] start-->device_support device_support-->|Yes|android_api device_support-->|No|opengl android_api-->|>= Android 29|vulkan_version android_api-->|< Android 29|opengl vulkan_version-->|>= Vulkan 1.1|vulkan_exts vulkan_version-->|< Vulkan 1.1|opengl vulkan_exts-->|Supports Extensions|vulkan vulkan_exts-->|Doesn't Support Extensions|opengl
For Vulkan, Impeller needs at least Vulkan version 1.1. As of January 06, 2023, this includes 77% of all Android devices per the Android Distribution dashboard.
pie title Vulkan version "No Vulkan Support" : 15 "Vulkan 1.0.3" : 8 "Vulkan 1.1" : 77
Impeller could theoretically support older version of Vulkan but at a significant cost of implementation and for ultimately diminishing returns on investment. The team would rather spend that time improving the OpenGL ES backend.
Besides older devices still in use, devices you can buy new that don't support Vulkan are configurations with 64-bit kernels and 32-bit user-spaces (armv7l) or other RAM constrained devices.
For Vulkan support, Impeller needs at least Android 10, API level 29 (Q, Quince Tart). Cumulative usage of Android 10 as of August 21, 2023 is 78.5% per apilevels.com.
pie title Vulkan version "Android 10 or higher" : 78.5 "Android 9 and lower" : 21.5
Android 9 and older will unconditionally use OpenGL.
Android 10, API level 29 provides necessary support to work with HardwareBuffers efficiently. This is critical to support platform views.
Besides the Vulkan and Android versions. On Android, Impeller needs some extensions for interoperability with the underlying platform to support features like platform views and external texture composition. The expectation is that very Android devices will be filtered out in this check because support for extensions like VK_ANDROID_external_memory_android_hardware_buffer is almost universal on devices with Android 10 and above.
Android Platform Views (i.e. an android.view.View embedded inside a Flutter app) are supported in both GLES and Vulkan backends and the Engine manages this automatically.
Flutter's Java API allows for developers to register custom SurfaceTexture backed textures that can be rendered inside of a Flutter application. See TextureRegistry.registerSurfaceTexture and TextureRegistry.createSurfaceTexture.
There are no issues with SurfaceTextures when using the GLES backend.
We do not currently support rendering these textures when using the Vulkan backend. Supporting this will require adding support for importing GL textures into Vulkan textures which will have performance implications.