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//! Various options to specify how to combine pixels with what they draw over //! //! GPU blending follows the equation: //! //! `Output = Operation(SourceFunction(Source), DestFunction(Destination))` //! //! The `Operation` is controlled by [`BlendEquation`], and the //! `SourceFunction` and `DestFunction` are controlled by [`BlendFunction`]. Both of these are //! combined to form a [`BlendMode`], which can be applied by [`Context::set_blend_mode`]. //! //! The default [`BlendMode`] produces the result of: //! //! `Output = Source.Alpha * Source + (1 - Source.Alpha) * Destination` //! //! and looks like: //! //! ```no_run //! # use golem::blend::{ //! # BlendMode, BlendInput, BlendFactor, BlendChannel, BlendOperation, BlendEquation, //! # BlendFunction, //! # }; //! # fn test() -> BlendMode { //! BlendMode { //! equation: BlendEquation::Same(BlendOperation::Add), //! function: BlendFunction::Same { //! source: BlendFactor::Color { //! input: BlendInput::Source, //! channel: BlendChannel::Alpha, //! is_inverse: false, //! }, //! destination: BlendFactor::Color { //! input: BlendInput::Source, //! channel: BlendChannel::Alpha, //! is_inverse: true, //! }, //! }, //! global_color: [0.0; 4] //! } //! # } //! ``` //! //! For more information, see the documentation for the individual Blend enums. //! //! [`Context::set_blend_mode`]: crate::Context::set_blend_mode /// The state of the blend pipeline /// /// See [`Context::set_blend_mode`] /// /// [`Context::set_blend_mode`]: crate::Context::set_blend_mode #[derive(Copy, Clone, Debug, PartialEq)] pub struct BlendMode { /// How to combine the source and destination pub equation: BlendEquation, /// How to transform the inputs to the `equation` pub function: BlendFunction, /// A color in blending that's neither the source nor destination, specified as [R, G, B, A] /// /// This provides the value for [`BlendInput::GlobalBlend`] pub global_color: [f32; 4], } impl Default for BlendMode { fn default() -> BlendMode { BlendMode { equation: BlendEquation::default(), function: BlendFunction::default(), global_color: [0.0; 4], } } } /// How to combine the values when blending /// /// Almost all the time you'll want `BlendEquation::Same(BlendOperation::Add)`, but there are cases /// where other blend equatiosn come in handy. #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendEquation { /// Apply the same equation to the color and alpha of the blended pixels Same(BlendOperation), /// Apply a different equation to the color and alpha channel of the blended pixels Separate { color: BlendOperation, alpha: BlendOperation, }, } impl Default for BlendEquation { fn default() -> BlendEquation { BlendEquation::Same(BlendOperation::Add) } } /// The operation to apply to the pixels during blending #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendOperation { /// Output = Source + Destination Add, /// Output = Source - Destination Subtract, /// Output = Destination - Source ReverseSubtract, /// Output = Max(Source, Destination) Max, /// Output = Min(Source, Destination) Min, } impl BlendOperation { pub(crate) fn to_gl(self) -> u32 { use BlendOperation::*; match self { Add => glow::FUNC_ADD, Subtract => glow::FUNC_SUBTRACT, ReverseSubtract => glow::FUNC_REVERSE_SUBTRACT, Max => glow::MAX, Min => glow::MIN, } } } /// The blend function controls how the source and destination are transformed /// /// Before being passed to the [`BlendEquation`], the source and destination are multiplied by the /// value determined by `BlendFunction`. #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendFunction { /// Use the same [`BlendFactor`] on the color and alpha channels Same { source: BlendFactor, destination: BlendFactor, }, /// Use different [`BlendFactor`]s on the color and alpha channels Separate { source_color: BlendFactor, source_alpha: BlendFactor, destination_color: BlendFactor, destination_alpha: BlendFactor, }, } impl Default for BlendFunction { fn default() -> BlendFunction { BlendFunction::Same { source: BlendFactor::Color { input: BlendInput::Source, channel: BlendChannel::Alpha, is_inverse: false, }, destination: BlendFactor::Color { input: BlendInput::Source, channel: BlendChannel::Alpha, is_inverse: true, }, } } } /// The various coefficients to multiply the color inputs by #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendFactor { Zero, One, Color { /// Which source of color input: BlendInput, /// Which channel of the `input` to use channel: BlendChannel, /// Whether to use (1 - Value) instead of Value is_inverse: bool, }, } impl BlendFactor { pub(crate) fn to_gl(self) -> u32 { use BlendChannel::*; use BlendFactor::{Color as Col, One, Zero}; use BlendInput::*; match self { Zero => glow::ZERO, One => glow::ONE, Col { input: Source, channel: Color, is_inverse: false, } => glow::SRC_COLOR, Col { input: Source, channel: Color, is_inverse: true, } => glow::ONE_MINUS_SRC_COLOR, Col { input: Source, channel: Alpha, is_inverse: false, } => glow::SRC_ALPHA, Col { input: Source, channel: Alpha, is_inverse: true, } => glow::ONE_MINUS_SRC_ALPHA, Col { input: Destination, channel: Color, is_inverse: false, } => glow::DST_COLOR, Col { input: Destination, channel: Color, is_inverse: true, } => glow::ONE_MINUS_DST_COLOR, Col { input: Destination, channel: Alpha, is_inverse: false, } => glow::DST_ALPHA, Col { input: Destination, channel: Alpha, is_inverse: true, } => glow::ONE_MINUS_DST_ALPHA, Col { input: GlobalBlend, channel: Color, is_inverse: false, } => glow::CONSTANT_COLOR, Col { input: GlobalBlend, channel: Color, is_inverse: true, } => glow::ONE_MINUS_CONSTANT_COLOR, Col { input: GlobalBlend, channel: Alpha, is_inverse: false, } => glow::CONSTANT_ALPHA, Col { input: GlobalBlend, channel: Alpha, is_inverse: true, } => glow::ONE_MINUS_CONSTANT_ALPHA, } } } /// A color to pull from when blending #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendInput { /// The pixel that is being drawn Source, /// The pixel that is being replaced Destination, /// The color supplied to [`BlendMode::global_color`] GlobalBlend, } /// Which part of the [`BlendInput`] to pull from #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)] pub enum BlendChannel { /// The RGB component when using separate functions, or RGBA otherwise Color, /// The Alpha component Alpha, }