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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::Device;
    use device::DeviceOwned;

    /// Checks whether a fill buffer command is valid.
    ///
    /// # Panic
    ///
    /// - Panics if the buffer not created with `device`.
    ///
    pub fn check_fill_buffer<B>(device: &Device, buffer: &B) -> Result<(), CheckFillBufferError>
        where B: ?Sized + BufferAccess
    {
        assert_eq!(buffer.inner().buffer.device().internal_object(),
                   device.internal_object());

        if !buffer.inner().buffer.usage_transfer_destination() {
            return Err(CheckFillBufferError::BufferMissingUsage);
        }

        if buffer.inner().offset % 4 != 0 {
            return Err(CheckFillBufferError::WrongAlignment);
        }

        Ok(())
    }

    /// Error that can happen when attempting to add a `fill_buffer` command.
    #[derive(Debug, Copy, Clone)]
    pub enum CheckFillBufferError {
        /// The "transfer destination" usage must be enabled on the buffer.
        BufferMissingUsage,
        /// The data or size must be 4-bytes aligned.
        WrongAlignment,
    }

    impl error::Error for CheckFillBufferError {
        #[inline]
        fn description(&self) -> &str {
            match *self {
                CheckFillBufferError::BufferMissingUsage => {
                    "the transfer destination usage must be enabled on the buffer"
                },
                CheckFillBufferError::WrongAlignment => {
                    "the offset or size are not aligned to 4 bytes"
                },
            }
        }
    }

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

    #[cfg(test)]
    mod tests {
        use super::*;
        use buffer::BufferUsage;
        use buffer::CpuAccessibleBuffer;

        #[test]
        fn missing_usage() {
            let (device, queue) = gfx_dev_and_queue!();
            let buffer =
                CpuAccessibleBuffer::from_data(device.clone(), BufferUsage::vertex_buffer(), 0u32)
                    .unwrap();

            match check_fill_buffer(&device, &buffer) {
                Err(CheckFillBufferError::BufferMissingUsage) => (),
                _ => panic!(),
            }
        }

        #[test]
        fn wrong_device() {
            let (dev1, queue) = gfx_dev_and_queue!();
            let (dev2, _) = gfx_dev_and_queue!();
            let buffer = CpuAccessibleBuffer::from_data(dev1, BufferUsage::all(), 0u32).unwrap();

            assert_should_panic!({
                                     let _ = check_fill_buffer(&dev2, &buffer);
                                 });
        }
    }

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