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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.

    //! Defines how the color output of the fragment shader is written to the attachment.
    //!
    //! # Blending in details
    //!
    //! There are three kinds of color attachments for the purpose of blending:
    //!
    //! - Attachments with a floating-point, fixed point format.
    //! - Attachments with a (non-normalized) integer format.
    //! - Attachments with a normalized integer format.
    //!
    //! For floating-point and fixed-point formats, the blending operation is applied. For integer
    //! formats, the logic operation is applied. For normalized integer formats, the logic operation
    //! will take precedence if it is activated, otherwise the blending operation is applied.
    //!

    use vk;

    /// Describes how the color output of the fragment shader is written to the attachment. See the
    /// documentation of the `blend` module for more info.
    #[derive(Debug, Clone, PartialEq)]
    pub struct Blend {
        pub logic_op: Option<LogicOp>,

        pub attachments: AttachmentsBlend,

        /// The constant color to use for the `Constant*` blending operation.
        ///
        /// If you pass `None`, then this state will be considered as dynamic and the blend constants
        /// will need to be set when you build the command buffer.
        pub blend_constants: Option<[f32; 4]>,
    }

    impl Blend {
        /// Returns a `Blend` object that directly writes colors and alpha on the surface.
        #[inline]
        pub fn pass_through() -> Blend {
            Blend {
                logic_op: None,
                attachments: AttachmentsBlend::Collective(AttachmentBlend::pass_through()),
                blend_constants: Some([0.0, 0.0, 0.0, 0.0]),
            }
        }

        /// Returns a `Blend` object that adds transparent objects over others.
        #[inline]
        pub fn alpha_blending() -> Blend {
            Blend {
                logic_op: None,
                attachments: AttachmentsBlend::Collective(AttachmentBlend::alpha_blending()),
                blend_constants: Some([0.0, 0.0, 0.0, 0.0]),
            }
        }
    }

    /// Describes how the blending system should behave.
    #[derive(Debug, Clone, PartialEq, Eq)]
    pub enum AttachmentsBlend {
        /// All the framebuffer attachments will use the same blending.
        Collective(AttachmentBlend),

        /// Each attachment will behave differently. Note that this requires enabling the
        /// `independent_blend` feature.
        Individual(Vec<AttachmentBlend>),
    }

    /// Describes how the blending system should behave for an individual attachment.
    #[derive(Debug, Clone, PartialEq, Eq)]
    pub struct AttachmentBlend {
        // TODO: could be automatically determined from the other params
        /// If false, blending is ignored and the output is directly written to the attachment.
        pub enabled: bool,

        pub color_op: BlendOp,
        pub color_source: BlendFactor,
        pub color_destination: BlendFactor,

        pub alpha_op: BlendOp,
        pub alpha_source: BlendFactor,
        pub alpha_destination: BlendFactor,

        pub mask_red: bool,
        pub mask_green: bool,
        pub mask_blue: bool,
        pub mask_alpha: bool,
    }

    impl AttachmentBlend {
        /// Builds an `AttachmentBlend` where blending is disabled.
        #[inline]
        pub fn pass_through() -> AttachmentBlend {
            AttachmentBlend {
                enabled: false,
                color_op: BlendOp::Add,
                color_source: BlendFactor::Zero,
                color_destination: BlendFactor::One,
                alpha_op: BlendOp::Add,
                alpha_source: BlendFactor::Zero,
                alpha_destination: BlendFactor::One,
                mask_red: true,
                mask_green: true,
                mask_blue: true,
                mask_alpha: true,
            }
        }

        /// Builds an `AttachmentBlend` where the output of the fragment shader is ignored and the
        /// destination is untouched.
        #[inline]
        pub fn ignore_source() -> AttachmentBlend {
            AttachmentBlend {
                enabled: true,
                color_op: BlendOp::Add,
                color_source: BlendFactor::Zero,
                color_destination: BlendFactor::DstColor,
                alpha_op: BlendOp::Add,
                alpha_source: BlendFactor::Zero,
                alpha_destination: BlendFactor::DstColor,
                mask_red: true,
                mask_green: true,
                mask_blue: true,
                mask_alpha: true,
            }
        }

        /// Builds an `AttachmentBlend` where the output will be merged with the existing value
        /// based on the alpha of the source.
        #[inline]
        pub fn alpha_blending() -> AttachmentBlend {
            AttachmentBlend {
                enabled: true,
                color_op: BlendOp::Add,
                color_source: BlendFactor::SrcAlpha,
                color_destination: BlendFactor::OneMinusSrcAlpha,
                alpha_op: BlendOp::Add,
                alpha_source: BlendFactor::SrcAlpha,
                alpha_destination: BlendFactor::OneMinusSrcAlpha,
                mask_red: true,
                mask_green: true,
                mask_blue: true,
                mask_alpha: true,
            }
        }

        #[inline]
        pub(crate) fn into_vulkan_state(self) -> vk::PipelineColorBlendAttachmentState {
            vk::PipelineColorBlendAttachmentState {
                blendEnable: if self.enabled { vk::TRUE } else { vk::FALSE },
                srcColorBlendFactor: self.color_source as u32,
                dstColorBlendFactor: self.color_destination as u32,
                colorBlendOp: self.color_op as u32,
                srcAlphaBlendFactor: self.alpha_source as u32,
                dstAlphaBlendFactor: self.alpha_destination as u32,
                alphaBlendOp: self.alpha_op as u32,
                colorWriteMask: {
                    let mut mask = 0;
                    if self.mask_red {
                        mask |= vk::COLOR_COMPONENT_R_BIT;
                    }
                    if self.mask_green {
                        mask |= vk::COLOR_COMPONENT_G_BIT;
                    }
                    if self.mask_blue {
                        mask |= vk::COLOR_COMPONENT_B_BIT;
                    }
                    if self.mask_alpha {
                        mask |= vk::COLOR_COMPONENT_A_BIT;
                    }
                    mask
                },
            }
        }
    }

    /// Which logical operation to apply to the output values.
    ///
    /// The operation is applied individually for each channel (red, green, blue and alpha).
    ///
    /// Only relevant for integer or unsigned attachments.
    ///
    /// Also note that some implementations don't support logic operations.
    #[derive(Debug, Copy, Clone, PartialEq, Eq)]
    #[repr(u32)]
    pub enum LogicOp {
        /// Returns `0`.
        Clear = vk::LOGIC_OP_CLEAR,
        /// Returns `source & destination`.
        And = vk::LOGIC_OP_AND,
        /// Returns `source & !destination`.
        AndReverse = vk::LOGIC_OP_AND_REVERSE,
        /// Returns `source`.
        Copy = vk::LOGIC_OP_COPY,
        /// Returns `!source & destination`.
        AndInverted = vk::LOGIC_OP_AND_INVERTED,
        /// Returns `destination`.
        Noop = vk::LOGIC_OP_NO_OP,
        /// Returns `source ^ destination`.
        Xor = vk::LOGIC_OP_XOR,
        /// Returns `source | destination`.
        Or = vk::LOGIC_OP_OR,
        /// Returns `!(source | destination)`.
        Nor = vk::LOGIC_OP_NOR,
        /// Returns `!(source ^ destination)`.
        Equivalent = vk::LOGIC_OP_EQUIVALENT,
        /// Returns `!destination`.
        Invert = vk::LOGIC_OP_INVERT,
        /// Returns `source | !destination.
        OrReverse = vk::LOGIC_OP_OR_REVERSE,
        /// Returns `!source`.
        CopyInverted = vk::LOGIC_OP_COPY_INVERTED,
        /// Returns `!source | destination`.
        OrInverted = vk::LOGIC_OP_OR_INVERTED,
        /// Returns `!(source & destination)`.
        Nand = vk::LOGIC_OP_NAND,
        /// Returns `!0` (all bits set to 1).
        Set = vk::LOGIC_OP_SET,
    }

    impl Default for LogicOp {
        #[inline]
        fn default() -> LogicOp {
            LogicOp::Noop
        }
    }

    #[derive(Debug, Copy, Clone, PartialEq, Eq)]
    #[repr(u32)]
    pub enum BlendOp {
        Add = vk::BLEND_OP_ADD,
        Subtract = vk::BLEND_OP_SUBTRACT,
        ReverseSubtract = vk::BLEND_OP_REVERSE_SUBTRACT,
        Min = vk::BLEND_OP_MIN,
        Max = vk::BLEND_OP_MAX,
    }

    #[derive(Debug, Copy, Clone, PartialEq, Eq)]
    #[repr(u32)]
    pub enum BlendFactor {
        Zero = vk::BLEND_FACTOR_ZERO,
        One = vk::BLEND_FACTOR_ONE,
        SrcColor = vk::BLEND_FACTOR_SRC_COLOR,
        OneMinusSrcColor = vk::BLEND_FACTOR_ONE_MINUS_SRC_COLOR,
        DstColor = vk::BLEND_FACTOR_DST_COLOR,
        OneMinusDstColor = vk::BLEND_FACTOR_ONE_MINUS_DST_COLOR,
        SrcAlpha = vk::BLEND_FACTOR_SRC_ALPHA,
        OneMinusSrcAlpha = vk::BLEND_FACTOR_ONE_MINUS_SRC_ALPHA,
        DstAlpha = vk::BLEND_FACTOR_DST_ALPHA,
        OneMinusDstAlpha = vk::BLEND_FACTOR_ONE_MINUS_DST_ALPHA,
        ConstantColor = vk::BLEND_FACTOR_CONSTANT_COLOR,
        OneMinusConstantColor = vk::BLEND_FACTOR_ONE_MINUS_CONSTANT_COLOR,
        ConstantAlpha = vk::BLEND_FACTOR_CONSTANT_ALPHA,
        OneMinusConstantAlpha = vk::BLEND_FACTOR_ONE_MINUS_CONSTANT_ALPHA,
        SrcAlphaSaturate = vk::BLEND_FACTOR_SRC_ALPHA_SATURATE,
        Src1Color = vk::BLEND_FACTOR_SRC1_COLOR,
        OneMinusSrc1Color = vk::BLEND_FACTOR_ONE_MINUS_SRC1_COLOR,
        Src1Alpha = vk::BLEND_FACTOR_SRC1_ALPHA,
        OneMinusSrc1Alpha = vk::BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA,
    }

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