gvr_blitframebuffer.rs

if self.fbo_texture != layer.texture_id {
    // Attach external texture to the used later in BlitFramebuffer.
    gl::BindFramebuffer(gl::FRAMEBUFFER, self.fbo_id);
    gl::FramebufferTexture2D(gl::FRAMEBUFFER, gl::COLOR_ATTACHMENT0, gl::TEXTURE_2D, layer.texture_id,    0);
    self.fbo_texture = layer.texture_id;
}

let texture_size = layer.texture_size.unwrap_or_else(|| {
    (self.render_size.width as u32, self.render_size.height as u32)
});

// BlitFramebuffer: external texture to gvr pixel buffer.
gvr::gvr_frame_bind_buffer(self.frame, 0);
gl::BindFramebuffer(gl::READ_FRAMEBUFFER, self.fbo_id);
gl::BlitFramebuffer(0, 0, texture_size.0 as i32, texture_size.1 as i32,
                    0, 0, self.render_size.width, self.render_size.height,
                    gl::COLOR_BUFFER_BIT, gl::LINEAR);
gvr::gvr_frame_unbind(self.frame);

// Set up uvs.
gvr::gvr_buffer_viewport_set_source_uv(self.left_eye_vp, gvr_texture_bounds(&layer.left_bounds));
gvr::gvr_buffer_viewport_set_source_uv(self.right_eye_vp, gvr_texture_bounds(&layer.right_bounds));

// Submit frame.
gvr::gvr_frame_submit(mem::transmute(&self.frame), self.viewport_list, self.synced_head_matrix);

// Restore bound fbo.
gl::BindFramebuffer(gl::FRAMEBUFFER, current_fbo as u32);