Optimizing SSAO on Mobile: Introducing EdgeDownSample in MobileSSAO (SmallBurger Assets)

On mobile platforms, SSAO (Screen Space Ambient Occlusion) has always been a performance-intensive visual effect.

In MobileSSAO, we have already optimized the PreDepthNormalPass using MRT (Multiple Render Targets), but under high-quality settings with increased Sample Count, performance bottlenecks can still be noticeable.
This is especially true on mid-to-low-end devices such as the Galaxy S8, where achieving a balance between visual quality and smooth frame rates remains a key challenge.

To address this, we’ve introduced a new feature in this update: EdgeDownSample.
This is a flexible SSAO optimization technique that maintains high Sample Count in the center of the screen, while dynamically reducing SSAO sampling costs along the edges of the screen, resulting in significantly improved performance.

This design concept also aligns well with the current trend of Foveated Rendering, which is widely adopted in VR devices and supported by many modern hardware solutions. It is also highly suitable for portrait-mode mobile games, where UI elements are often positioned around the edges of the screen. In such cases, reducing SSAO sampling precision in these peripheral areas has minimal visual impact but can greatly reduce GPU workload.

Using the EdgeDownSampleScreenSizeRatio parameter, you can easily adjust the size of the edge zone.

This makes the feature especially effective for portrait-mode mobile games, where the main UI is typically placed along the screen edges—perfectly aligning with the principles of Foveated Rendering.

Performance Comparison (Galaxy S8, High-Quality Mode):

Without EdgeDownSample enabled:

With EdgeDownSample enabled:

Related video：

Asset:

MobileSSAO

Other related assets:

SmallBurger Assets