Scrolling-Aware Rendering to Reduce Frame Rates on Smartphones

One of the major sources of power drain in smartphones is a frame rendering and display process called graphics pipeline, in which power consumption depends largely on frame rendering operations per second (fps), known as the frame rate, and the quantity of UI content to be rendered. We discovered a major problem causing power consumption upon a scrolling operation: The Android graphics pipeline renders all or a large portion of the content displayed most recently at a frame rate of nearly 60 fps. This paper proposes a scrolling-aware rendering (SCAR) scheme to reduce the frame rate caused by a scrolling. When rendering a frame for UI content to be displayed, SCAR pre-renders UI content that is likely to be displayed soon in any subsequent scrolling operation. This frame is extended to place the pre-rendered UI content contiguously with the UI content to be displayed. Upon a subsequent scrolling, SCAR repositions the extended frame on screen by a scrolling distance instead of rendering a new frame. Our experiments on a smartphone show that SCAR reduced frame rates to below one fps in scrolling, thus saving power by up to 30%