Instead of using glTex{Sub}Image2D() to refresh the textures, we're using an EGLImageKHR object
backed up by a gralloc buffer. The data is updated using memcpy(). This is faster than
glTex{Sub}Image2D() because the texture is not swizzled. It also uses less memory because
EGLImageKHW is not limited to power-of-two dimensions.
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