Class EXTBufferAge
The aim of this extension is to expose enough information to applications about how the driver manages the set of front and back buffers associated with a given surface to allow applications to re-use the contents of old frames and minimize how much must be redrawn for the next frame.
There are lots of different ways for a driver to manage these buffers, from double buffering, different styles of triple buffering and even n-buffering or simply single buffer rendering. We also need to consider that power management events or memory pressure events might also result in some of the buffers not currently in-use being freed.
This extension lets applications query the age of the back buffer contents for an EGL surface as the number of frames elapsed since the contents were most recently defined. The back buffer can either be reported as invalid (has an age of 0) or it may be reported to contain the contents from n frames prior to the current frame.
Once the application has queried the buffer age, the age of contents remains valid until the end of the frame for all pixels that continue to pass the pixel ownership test.
For many use-cases this extension can provide an efficient alternative to using the EGL_BUFFER_PRESERVED swap behaviour. The EGL_BUFFER_PRESERVED swap behaviour adds a direct dependency for any frame n on frame n - 1 which can affect the pipelining of multiple frames but also implies a costly copy-back of data to initialize the back-buffer at the start of each frame.
For example if you consider a double buffered application drawing a small spinning icon, but everything else in the scene is static. If we know that 2 buffers are continuously being recycled each time eglSwapBuffers is called then even though 100s of frames may need to be drawn to animate the icon it can be seen that the two buffers are remaining unchanged except within the bounds of the icon. In this scenario ideally the application would simply perform an incremental update of the old buffer instead of redundantly redrawing all the static parts of the scene. The problem up until now though has been that EGL doesn't report how buffers may be recycled so it wasn't safe for applications to try and reuse their contents. Now applications can keep track of all the regions that have changed over the last n frames and by knowing the age of the buffer they know how to efficiently repair buffers that are re-cycled instead of redrawing the entire scene.
Requires EGL 1.4.
-
Field Summary
Fields -
Method Summary
-
Field Details
-
EGL_BUFFER_AGE_EXT
public static final int EGL_BUFFER_AGE_EXT- See Also:
-