Fixed foveated rendering (FFR)

• Improves framerate in applications with GPU fill bottlenecks.
• Reduces power consumption, and thereby reduces heat and increases battery life.
• Enables applications to increase the resolution of eye textures, which improves the viewing experience, while maintaining performance and power consumption levels.

• FFR may not improve performance in applications with simple shaders.
• Applications using FFR should aim to place high-contrast items, such as text, in the center of the frame. Applications that encourage players to look at the edges of the screen (i.e., by placing user interface on your avatar’s belt) will cause users to notice the degraded image quality.

• White = Full resolution: This is the center of the FOV. Every pixel of the texture is computed independently by the GPU.
• Green = 1/4 resolution: Only one quarter of the pixels are calculated by the GPU.
• Black = no resolution: the GPU does not render anything in this area.

FFR Setting	Left Eye Resolution Multiplier Map	Example Left Eye Tile Map
Low
Medium
High
High Top (VrApi only)

• FFR levels can be changed on a per-frame basis and should be changed according to the content being displayed. Starting a new level, opening/closing menus, and entering new map areas are generally good points to consider changing the FFR setting. However, avoid changing FFR levels frequently within the same scene without another transition as the jump between FFR levels can be fairly noticeable.
  • A simple, effective example would be to turn off FFR on menu screens, where there is performance headroom to spare and a lot of text elements, and then turning it on after loading into the game where the performance is needed.
  • Another example would be to set FFR to high on a complex outdoor scene, then turning it off on a simpler indoors level.
• Applications can use FFR for their in-world scene, but preserve the pixel density of user interfaces on the edge of the frame, by placing user interfaces on Compositor Layers. Compositor layers are not affected by FFR settings.
• The system property debug.oculus.foveation.level is a system-wide FFR setting override that can be used to quickly test different FFR settings without changing, reinstalling, or restarting the app, with 0 = Off, 1 = Low, 2 = Medium, 3 = High, 4 = High Top. For example, adb shell setprop debug.oculus.foveation.level 2 sets the FFR level to medium.
  • When using this system property for debugging, please make sure dynamic foveation is disabled (by adb shell setprop debug.oculus.foveation.dynamic 0). Otherwise you won’t be able to toggle the foveation level by debug.oculus.foveation.level since it is controlling the maximum foveation level when dynamic foveation is enabled.
• Use the VrApi logcat outputs to determine suitable FFR levels. VrApi generates performance information in logcat every second, including FFR level, GPU rendering times, and average FPS. For instance, a VrApi log that shows an app running at 72 fps (FPS=72), with the app’s GPU rendering time at 5.51ms (App=5.51ms), and FFR on high (Fov=3), would indicate more than enough room to turn the FFR level down for a general improvement in the visual quality.
  • When dynamic foveation is enabled, you should see the postfix D like Fov=3D in the VrApi logcat outputs.

• VK_EXT_fragment_density_map — Core fragment density map support
• VK_EXT_fragment_density_map2 — Improved latency for reading fragment density maps on Qualcomm hardware

XrSwapchainCreateInfoFoveationFB foveationCreateInfo = {
    .type = XR_TYPE_SWAPCHAIN_CREATE_INFO_FOVEATION_FB,
    .flags = XR_SWAPCHAIN_CREATE_FOVEATION_FRAGMENT_DENSITY_MAP_BIT_FB,
};

XrSwapchainCreateInfo swapchainCreateInfo = {
    .type = XR_TYPE_SWAPCHAIN_CREATE_INFO,
    .next = &foveationCreateInfo,
    .usageFlags = XR_SWAPCHAIN_USAGE_SAMPLED_BIT | XR_SWAPCHAIN_USAGE_COLOR_ATTACHMENT_BIT,
    .format = vulkanColorFormat,
    .sampleCount = 1,
    .width = width,
    .height = height,
    .faceCount = 1,
    .arraySize = 2,  // multiview
    .mipCount = 1,
};

XrSwapchain swapchain;
xrCreateSwapchain(session, &swapchainCreateInfo, &swapchain);

XrSwapchainImageVulkanKHR colorImages[bufferCount];
XrSwapchainImageFoveationVulkanFB fdmImages[bufferCount];

for (uint32_t i = 0; i < bufferCount; i++) {
    fdmImages[i].type = XR_TYPE_SWAPCHAIN_IMAGE_FOVEATION_VULKAN_FB;
    fdmImages[i].next = NULL;
    fdmImages[i].image = VK_NULL_HANDLE;

    colorImages[i].type = XR_TYPE_SWAPCHAIN_IMAGE_VULKAN_KHR;
    colorImages[i].next = &fdmImages[i];
}

xrEnumerateSwapchainImages(swapchain, bufferCount, &bufferCount,
    (XrSwapchainImageBaseHeader*)colorImages);

// fdmImages[i].image now contains the VkImage for the fragment density map
// fdmImages[i].width and fdmImages[i].height contain the FDM dimensions

// Get function pointers
PFN_xrCreateFoveationProfileFB xrCreateFoveationProfileFB;
PFN_xrDestroyFoveationProfileFB xrDestroyFoveationProfileFB;
PFN_xrUpdateSwapchainFB xrUpdateSwapchainFB;
xrGetInstanceProcAddr(instance, "xrCreateFoveationProfileFB",
    (PFN_xrVoidFunction*)&xrCreateFoveationProfileFB);
xrGetInstanceProcAddr(instance, "xrDestroyFoveationProfileFB",
    (PFN_xrVoidFunction*)&xrDestroyFoveationProfileFB);
xrGetInstanceProcAddr(instance, "xrUpdateSwapchainFB",
    (PFN_xrVoidFunction*)&xrUpdateSwapchainFB);

// Create a foveation level profile
XrFoveationLevelProfileCreateInfoFB levelProfile = {
    .type = XR_TYPE_FOVEATION_LEVEL_PROFILE_CREATE_INFO_FB,
    .level = XR_FOVEATION_LEVEL_HIGH_FB,  // NONE, LOW, MEDIUM, or HIGH
    .verticalOffset = 0.0f,
    .dynamic = XR_FOVEATION_DYNAMIC_LEVEL_ENABLED_FB,  // or DISABLED
};

XrFoveationProfileCreateInfoFB profileCreateInfo = {
    .type = XR_TYPE_FOVEATION_PROFILE_CREATE_INFO_FB,
    .next = &levelProfile,
};

XrFoveationProfileFB foveationProfile;
xrCreateFoveationProfileFB(session, &profileCreateInfo, &foveationProfile);

// Apply the profile to the swapchain
XrSwapchainStateFoveationFB foveationState = {
    .type = XR_TYPE_SWAPCHAIN_STATE_FOVEATION_FB,
    .profile = foveationProfile,
};
xrUpdateSwapchainFB(swapchain, (XrSwapchainStateBaseHeaderFB*)&foveationState);

• Performance: Reduces the amount of data that must be copied from GPU memory to main memory, saving bandwidth.
• Visual quality: Sampling at the original render resolution produces a less aliased result — bilinear filtering works on the actual rendered pixels rather than stretched ones, eliminating the blocky artifacts visible in the peripheral regions without subsampled layout.

// Request foveation with fragment density map
XrSwapchainCreateInfoFoveationFB foveationCreateInfo = {
    .type = XR_TYPE_SWAPCHAIN_CREATE_INFO_FOVEATION_FB,
    .flags = XR_SWAPCHAIN_CREATE_FOVEATION_FRAGMENT_DENSITY_MAP_BIT_FB,
};

// Pass the subsampled bit to the Vulkan image
XrVulkanSwapchainCreateInfoMETA vulkanCreateInfo = {
    .type = XR_TYPE_VULKAN_SWAPCHAIN_CREATE_INFO_META,
    .additionalCreateFlags = VK_IMAGE_CREATE_SUBSAMPLED_BIT_EXT,
    .additionalUsageFlags = 0,
};

// Chain: swapchainCreateInfo -> foveationCreateInfo -> vulkanCreateInfo
foveationCreateInfo.next = &vulkanCreateInfo;

XrSwapchainCreateInfo swapchainCreateInfo = {
    .type = XR_TYPE_SWAPCHAIN_CREATE_INFO,
    .next = &foveationCreateInfo,
    .usageFlags = XR_SWAPCHAIN_USAGE_SAMPLED_BIT | XR_SWAPCHAIN_USAGE_COLOR_ATTACHMENT_BIT,
    .format = vulkanColorFormat,
    .sampleCount = 1,
    .width = width,
    .height = height,
    .faceCount = 1,
    .arraySize = 2,
    .mipCount = 1,  // must be 1 for subsampled images
};

XrSwapchain swapchain;
xrCreateSwapchain(session, &swapchainCreateInfo, &swapchain);

• Mip count must be 1: Subsampled images do not support multiple mipmap levels.
• Immutable samplers: Samplers used with subsampled images must be immutable samplers⁠ bound at descriptor set layout creation time via pImmutableSamplers. Create the sampler with VK_SAMPLER_CREATE_SUBSAMPLED_BIT_EXT.
• Sampler configuration: Use VK_FILTER_LINEAR, VK_SAMPLER_MIPMAP_MODE_NEAREST, and clamp LOD to [0, 0].
• Device support: The runtime checks device capability at swapchain creation. If the device does not support subsampled layout, the flag is silently ignored.

adb shell setprop debug.oculus.foveation.subsampled 1  # force on
adb shell setprop debug.oculus.foveation.subsampled 0  # force off