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    // Copyright (c) 2016 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::cmp;
    use std::error;
    use std::fmt;

    use VulkanObject;
    use buffer::TypedBufferAccess;
    use device::Device;
    use device::DeviceOwned;

    /// Checks whether a copy buffer command is valid.
    ///
    /// # Panic
    ///
    /// - Panics if the source and destination were not created with `device`.
    ///
    pub fn check_copy_buffer<S, D, T>(device: &Device, source: &S, destination: &D)
                                      -> Result<CheckCopyBuffer, CheckCopyBufferError>
        where S: ?Sized + TypedBufferAccess<Content = T>,
              D: ?Sized + TypedBufferAccess<Content = T>,
              T: ?Sized
    {
        assert_eq!(source.inner().buffer.device().internal_object(),
                   device.internal_object());
        assert_eq!(destination.inner().buffer.device().internal_object(),
                   device.internal_object());

        if !source.inner().buffer.usage_transfer_source() {
            return Err(CheckCopyBufferError::SourceMissingTransferUsage);
        }

        if !destination.inner().buffer.usage_transfer_destination() {
            return Err(CheckCopyBufferError::DestinationMissingTransferUsage);
        }

        let copy_size = cmp::min(source.size(), destination.size());

        if source.conflicts_buffer(&destination) {
            return Err(CheckCopyBufferError::OverlappingRanges);
        } else {
            debug_assert!(!destination.conflicts_buffer(&source));
        }

        Ok(CheckCopyBuffer { copy_size })
    }

    /// Information returned if `check_copy_buffer` succeeds.
    pub struct CheckCopyBuffer {
        /// Size of the transfer in bytes.
        ///
        /// If the size of the source and destination are not equal, then the value is equal to the
        /// smallest of the two.
        pub copy_size: usize,
    }

    /// Error that can happen from `check_copy_buffer`.
    #[derive(Debug, Copy, Clone)]
    pub enum CheckCopyBufferError {
        /// The source buffer is missing the transfer source usage.
        SourceMissingTransferUsage,
        /// The destination buffer is missing the transfer destination usage.
        DestinationMissingTransferUsage,
        /// The source and destination are overlapping.
        OverlappingRanges,
    }

    impl error::Error for CheckCopyBufferError {
        #[inline]
        fn description(&self) -> &str {
            match *self {
                CheckCopyBufferError::SourceMissingTransferUsage => {
                    "the source buffer is missing the transfer source usage"
                },
                CheckCopyBufferError::DestinationMissingTransferUsage => {
                    "the destination buffer is missing the transfer destination usage"
                },
                CheckCopyBufferError::OverlappingRanges => {
                    "the source and destination are overlapping"
                },
            }
        }
    }

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

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