Efficient compositing strategies for automotive HMI systems

The relevance of graphical functions in vehicular applications has increased significantly during the last years. Modern cars are equipped with multiple displays used by different applications such as speedometer, navigation system, or media players. The rendered output of the applications is stored in so-called off-screen buffers and then bitblitted to the screen buffer at the respective window sizes and positions. To guarantee the visibility of the potentially overlapping windows, the compositing has to match the z-order of the windows. To this end, two common compositing strategies Tile compositing and Full compositing are used, each having performance issues depending on how windows overlap. Since automotive embedded platforms are restricted in power consumption, installation space, and hardware cost, their performance is limited which effectuates the need for highly efficient bitblitting. In order to increase the performance in compositing the windows, we propose Hybrid Compositing which predicts the required bitblitting time and chooses the most efficient strategy for each pair of overlapping windows. Using various scenarios we show that our approach is faster than the other strategies. In addition, we propose CacheHybrid Compositing which reduces the CPU execution time of our approach by up to 66 %. In case of an automotive scenario we show that our optimized approach saves up to 51% bitblitting time compared to existing approaches.