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    // Copyright (c) 2017 The vulkano developers
    // Licensed under the Apache License, Version 2.0
    // <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT
    // license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
    // at your option. All files in the project carrying such
    // notice may not be copied, modified, or distributed except
    // according to those terms.

    use std::error;
    use std::fmt;

    use VulkanObject;
    use buffer::BufferAccess;
    use device::DeviceOwned;
    use pipeline::vertex::VertexSource;

    /// Checks whether vertex buffers can be bound.
    ///
    /// # Panic
    ///
    /// - Panics if one of the vertex buffers was not created with the same device as `pipeline`.
    ///
    pub fn check_vertex_buffers<P, V>(pipeline: &P, vertex_buffers: V)
                                      -> Result<CheckVertexBuffer, CheckVertexBufferError>
        where P: DeviceOwned + VertexSource<V>
    {
        let (vertex_buffers, vertex_count, instance_count) = pipeline.decode(vertex_buffers);

        for (num, buf) in vertex_buffers.iter().enumerate() {
            assert_eq!(buf.inner().buffer.device().internal_object(),
                       pipeline.device().internal_object());

            if !buf.inner().buffer.usage_vertex_buffer() {
                return Err(CheckVertexBufferError::BufferMissingUsage { num_buffer: num });
            }
        }

        Ok(CheckVertexBuffer {
               vertex_buffers,
               vertex_count: vertex_count as u32,
               instance_count: instance_count as u32,
           })
    }

    /// Information returned if `check_vertex_buffer` succeeds.
    pub struct CheckVertexBuffer {
        /// The list of vertex buffers.
        pub vertex_buffers: Vec<Box<dyn BufferAccess + Send + Sync>>,
        /// Number of vertices available in the intersection of the buffers.
        pub vertex_count: u32,
        /// Number of instances available in the intersection of the buffers.
        pub instance_count: u32,
    }

    /// Error that can happen when checking whether the vertex buffers are valid.
    #[derive(Debug, Copy, Clone)]
    pub enum CheckVertexBufferError {
        /// The "vertex buffer" usage must be enabled on the buffer.
        BufferMissingUsage {
            /// Index of the buffer that is missing usage.
            num_buffer: usize,
        },
    }

    impl error::Error for CheckVertexBufferError {
        #[inline]
        fn description(&self) -> &str {
            match *self {
                CheckVertexBufferError::BufferMissingUsage { .. } => {
                    "the vertex buffer usage is missing on a vertex buffer"
                },
            }
        }
    }

    impl fmt::Display for CheckVertexBufferError {
        #[inline]
        fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
            write!(fmt, "{}", error::Error::description(self))
        }
    }

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