H緩衝暫存器:利用歷史記錄及溢出分享之有效率透明畫格儲存方法

Abstract

圖形繪製往往需要大量的資料暫存空間，也因此限制了在以輕薄為特色的嵌入式裝置上之發展。為了解決此問題，此發明著重在減少暫存透明網格的空間需求。此設計是建構在以下的概念：除了極少數場景在做切換的畫面，決大多數的畫面其每一個畫面座標所擁有的透明網格數量都相當接近。因此我們提出了一個歷史根基透明網格暫存緩衝器－H暫存緩衝器。由於透明網格以任意順序進入H暫存緩衝器做儲存，因此主要面對的挑戰為如何減少其記憶體內部碎裂，並有效率儲存透明網格。在此設計中，我們會去記錄每一張畫面座標上面的透明網格數量，並且用來做為下一張畫面在繪圖時，使用透明網格暫存緩衝器空間大小的依據。一旦遇到透明網格暫存緩衝器空間不夠，我們會將透明網格存放到溢出空間，並且讓多個畫面座標可以共用此空間以減少因內部碎裂所造成的空間浪費。我們測試了連續５００張 QUAKE4 及 DOOM3 畫面，並且與目前所需空間最小的T暫存緩衝器做比較。在QUAKE4中，我們的設計比T暫存緩衝器少了約25％的透明網格儲存空間需求，而在DOOM3中，少了約20％的透明網格儲存空間需求。

Graphics rendering requires various huge amounts of temporary data storages, prohibiting this feature from being implemented on slim embedded devices. To overcome this difficulty, we focus our effort on storage of transparent fragments after rasterization stage. We base our design on the fact that: successive frames typically will have the same or very similar number of transparent fragments located at the same screen pixel location, except in the rare case of scene change. We propose a history based transparent fragment buffer called H-Buffer. Note that transparent fragments arrive in any arbitrary order, making the design challenging. And the storage pressure comes from necessary storage plus internal fragmentation, the latter being resulted from fix-size storage allocation and can be reduced. In this design, transparent fragment counts at all pixel locations are collected for every frame, and be used for storage allocation for the next frame. For the unavoidable case of insufficient storage allocation, our overflow storage allocation assigns neighbor pixel locations to share a given overflow area, in an attempt to reduce internal fragmentation. Easy management and quick access are two major concerns in our design. In evaluation, we used 500 frames from QUAKE4 and DOOM3. Storage requirements are compared against the W-buffer, and the T buffer methods. Compared with the strongest competitor, the T-buffer, results show that our method reduces storage pressure by 25% in QUAKE4 benchmark, and 20% in DOOM3 benchmark. This design idea can be extended to applications where the load change is typically mild and only occasionally abrupt.