This sample demonstrates SecureMR readback on global tensor by both CPU buffers and GPU textures (Vulkan / OpenGL ES). It acquires the VST camera frame via a SecureMR pipeline and exports a PNG file to the app’s external storage for quick verification.

• After camera permission is granted, the app initializes the SecureMR pipeline.
• On each successful readback, a output.png is written to external storage.
• Exports PNG in external storage.

• readback_cpu: uses XrReadbackTensorBufferPICO to read back CPU buffer data
• readback_vulkan: uses XrReadbackTexturePICO and Vulkan
• readback_opengl: uses XrReadbackTexturePICO and OpenGL ES

• CPU buffer:

./gradlew :samples:readback:installReadback_cpuDebug

• Vulkan texture:

./gradlew :samples:readback:installReadback_vulkanDebug

• OpenGL ES texture:

./gradlew :samples:readback:installReadback_openglDebug

The Gradle flavors configure CMake flags automatically:

• readback_vulkan: -DREADBACK_USE_GPU=1 -DREADBACK_USE_VULKAN=1
• readback_opengl: -DREADBACK_USE_GPU=1 -DREADBACK_USE_OPENGL=1

• Launch the installed app on the device.
• Grant camera permission when prompted.
• After the pipeline initializes, the app saves a PNG to external storage.

• The exported file is written to the app’s external files directory:
  • Example: /sdcard/Android/data/com.bytedance.pico.secure_mr_demo.readback/files/output.png

• Core controller: readback.h
• Sample logic and pipeline setup: readback_file.cpp
• OpenGL ES export: readback_opengl.cpp
• Vulkan export: readback_vulkan.cpp

• Global tensor holding the latest left‑eye VST RGB frame.
• Dimensions: 512×512, Channels: 3.
  CPU mode: XR_SECURE_MR_TENSOR_DATA_TYPE_UINT8_PICO.
  GPU mode: usage XR_SECURE_MR_TENSOR_TYPE_MAT_DYNAMIC_TEXTURE_PICO, data type XR_SECURE_MR_TENSOR_DATA_TYPE_DYNAMIC_TEXTURE_UINT8_PICO.

• Controller initialization
  • In the readback.cpp constructor, readback-related OpenXR PICO extension function pointers are fetched via FrameworkSession (e.g., xrCreateBufferFromGlobalTensorAsyncPICO, xrCreateTextureFromGlobalTensorAsyncPICO).
  • Graphics context is initialized in readback_vulkan.cpp or readback_opengl.cpp depending on the build backend.
• CPU buffer readback
  • Issue: RequestReadbackBuffer(...)
  • Acquire: TryAcquireReadbackBuffer(...) uses xrCreateBufferFromGlobalTensorCompletePICO in two call idiom (query size, then allocate and read).
  • Export: OutputReadbackBufferToFile(...) writes RGB data using stbi_write_png.
• GPU texture readback
  • Issue: RequestReadbackTexture(...)
  • Acquire: TryAcquireReadbackTexture(...) returns an XrReadbackTexturePICO.
  • Export:
    • Vulkan: OutputReadbackTextureToPath(...) copies from VkImage to a staging buffer and saves RGBA PNG.
    • OpenGL ES: OutputReadbackTextureToPath(...) attaches texture to an FBO, glReadPixels RGBA, then saves PNG.