POLYPATH: Supporting Multiple Tradeoffs for Interaction Latency

TL;DR

POLYPATH enables mobile systems to support multiple interaction latency tradeoffs by allowing applications to choose different path designs, notably introducing Presto, which significantly reduces latency without negative visual effects.

Contribution

The paper introduces POLYPATH, a system that supports multiple latency-optimized paths, including a novel fast path called Presto, improving interaction latency in mobile systems.

Findings

Presto reduces touchscreen drawing latency by nearly 50%.

Presto achieves sub-10 ms touch latency with touch prediction.

POLYPATH's approach is orthogonal to other latency reduction methods.

Abstract

Modern mobile systems use a single input-to-display path to serve all applications. In meeting the visual goals of all applications, the path has a latency inadequate for many important interactions. To accommodate the different latency requirements and visual constraints by different interactions, we present POLYPATH, a system design in which application developers (and users) can choose from multiple path designs for their application at any time. Because a POLYPATH system asks for two or more path designs, we present a novel fast path design, called Presto. Presto reduces latency by judiciously allowing frame drops and tearing. We report an Android 5-based prototype of POLYPATH with two path designs: Android legacy and Presto. Using this prototype, we quantify the effectiveness, overhead, and user experience of POLYPATH, especially Presto, through both objective measurements and subjective user assessment. We show that Presto reduces the latency of legacy touchscreen drawing applications by almost half; and more importantly, this reduction is orthogonal to that of other popular approaches and is achieved without any user-noticeable negative visual effect. When combined with touch prediction, Presto is able to reduce the touch latency below 10 ms, a remarkable achievement without any hardware support.