EGL_ANDROID_blob_cache#

Supported Hardware#

Series6, Series6XE, Series6XT

Valid APIs#

EGL 1.4

Descriptions#

Shader compilation and optimization has been a troublesome aspect of OpenGL programming for a long time. It can consume seconds of CPU cycles during application start-up. Additionally, state-based re-compiles done internally by the drivers add an unpredictable element to application performance tuning, often leading to occasional pauses in otherwise smooth animations.

This extension provides a mechanism through which client API implementations may cache shader binaries after they are compiled. It may then retrieve those cached shaders during subsequent executions of the same program. The management of the cache is handled by the application (or middleware), allowing it to be tuned to a particular platform or environment.

While the focus of this extension is on providing a persistent cache for shader binaries, it may also be useful for caching other data. This is perfectly acceptable, but the guarantees provided (or lack thereof) were designed around the shader use case.

Note#

Although this extension is written as if the application implements the caching functionality, on the Android OS it is implemented as part of the Android EGL module. This extension is not exposed to applications on Android but will be used automatically in every application that uses EGL, if it is supported by the underlying device-specific EGL implementation.

On the Android OS, the extension doesn’t provide a mechanism to query the cache size and that the cache size is platform specific. If developers have lots of shaders and want to make sure they are cached, they should cache them manually with GL_OES_get_program_binary in ES 2.0 or glGetProgramBinary() in ES 3.0+.

Example#

void setFunction(const void* key, EGLsizeiANDROID keySize,
           const void* value, EGLsizeiANDROID valueSize)
{
  //set key-value pair into cache
}
EGLsizeiANDROID getFunction(const void* key, EGLsizeiANDROID keySize,
    void* value, EGLsizeiANDROID valueSize)
{
    //get value from cache
}
eglSetBlobCacheFuncsANDROID(eglDisplay, setFunction, getFunction);