Detecting screen orientation chage

[TheMostDiligent]

Hello!

I was reading an article about surface rotation, and it was very helpful - thank you. However, I am struggling with rotation detection. The article suggests to handle APP_CMD_CONTENT_RECT_CHANGED event, however if you take a look at native_app_glue.c file from the most recent NDK (21.1), you will find out that the event is never generated. Similarly, APP_CMD_WINDOW_RESIZED is also a dead event.
The only one that is really generated is APP_CMD_CONFIG_CHANGED, but this one is very inconsistent: on some devices it is generated before the surface has been rotated, on others - after.
I was trying to compare window dimensions, but, again, on some devices the window size changes before the surface size changes.

I can handle SUBOPTIMAL error code, but I am looking for the method that will also work for GLES.

Thank you!

[PavelRudko-ARM]

Hi!
Yes APP_CMD_CONTENT_RECT_CHANGED is not generated by default. This is already reported here and looks like it will work properly in NDK 22.
However, this works:
app->activity->callbacks->onContentRectChanged = on_content_rect_changed;
You can see this in our AndroidPlatform class. In this callback the event APP_CMD_CONTENT_RECT_CHANGED is then dispatched and handled in on_app_cmd.
So try using onContentRectChanged.
Please note, that this repository is now moved to KhronosGroup/Vulkan-Samples.
The tutorial and code was updated, so check out the new repository.
I have also created an issue related to your question.
Hope that helps!

[TheMostDiligent]

@PavelRudko-ARM Thanks, this is very useful! Is APP_CMD_CONTENT_RECT_CHANGED guaranteed to be generated after the surface orientation has actually changed so that the swap chain can be resized?

[TomAtkinsonArm]

Hi @TheMostDiligent, onContentRectChanged Is called when "The rectangle in the window in which content should be placed has changed."

onContentRectChanged is transformed to APP_CMD_CONTENT_RECT_CHANGED by android_native_app_glue.h in ndk version 22+. If you would like to still use APP_CMD_CONTENT_RECT_CHANGED you could always re-implement the ndk 22 version for older versions of the ndk. It would require a check to see if the callback is set, if not then set the re-implemented version :)

[TomAtkinsonArm]

So to answer your question. When this event fires the Swapchain can be resized

[TomAtkinsonArm]

This said after reviewing both the ndk implementation and the on_content_rect_changed implementation in this project both methods are effectively doing the same thing