Gear VR submit frame

gearvr_display.rs

fn submit_frame(&mut self, layer: &VRLayer) {
    let mut frame_params = ovr::helpers::vrapi_DefaultFrameParms(self.render_ovr_java.handle(),
                                                                 ovr::ovrFrameInit::VRAPI_FRAME_INIT_DEFAULT,
                                                                 self.predicted_display_time,
                                                                 ptr::null_mut());
    frame_params.FrameIndex = self.frame_index;

    let eye_projection = self.eye_projection.get();
    for (i, eye) in self.eye_framebuffers.iter_mut().enumerate() {
        let swap_chain_index = (self.frame_index % eye.swap_chain_length as i64) as i32;
        if self.read_texture != layer.texture_id {
            // Attach external texture to be used later in BlitFramebuffer.
            unsafe {
                gl::BindFramebuffer(gl::FRAMEBUFFER, self.read_fbo);
                gl::FramebufferTexture2D(gl::FRAMEBUFFER,
                                         gl::COLOR_ATTACHMENT0,
                                         gl::TEXTURE_2D,
                                         layer.texture_id, 0);
            }
            self.read_texture = layer.texture_id;
        }

        let texture_size = layer.texture_size.unwrap_or_else(|| {
            (eye.width * 2, eye.height)
        });

        // BlitFramebuffer: external texture to gvr pixel buffer.
        unsafe {
            gl::BindFramebuffer(gl::FRAMEBUFFER, eye.fbos[swap_chain_index as usize]);
            gl::BindFramebuffer(gl::READ_FRAMEBUFFER, self.read_fbo);
            let w = texture_size.0/2;
            let x0 = (i as u32) * w;
            let x1 = x0 + w;
            gl::BlitFramebuffer(x0 as i32, 0, x1 as i32, texture_size.1 as i32,
                                0, 0, eye.width as i32, eye.height as i32,
                                gl::COLOR_BUFFER_BIT, gl::LINEAR);
        }

        let target = &mut frame_params.Layers[0].Textures[i];
        target.ColorTextureSwapChain = eye.swap_chain;
        target.TextureSwapChainIndex = swap_chain_index;
        target.TexCoordsFromTanAngles = ovr::helpers::ovrMatrix4f_TanAngleMatrixFromProjection(&eye_projection);
        target.HeadPose = self.predicted_tracking.HeadPose;
        frame_params.Layers[0].Textures[i].CompletionFence = fence;
    }

    unsafe {
        ovr::vrapi_SubmitFrame(self.ovr, &frame_params);
    }
}