tiny_skia/
blend_mode.rs

1use crate::pipeline;
2
3/// A blending mode.
4#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
5pub enum BlendMode {
6    /// Replaces destination with zero: fully transparent.
7    Clear,
8    /// Replaces destination.
9    Source,
10    /// Preserves destination.
11    Destination,
12    /// Source over destination.
13    SourceOver,
14    /// Destination over source.
15    DestinationOver,
16    /// Source trimmed inside destination.
17    SourceIn,
18    /// Destination trimmed by source.
19    DestinationIn,
20    /// Source trimmed outside destination.
21    SourceOut,
22    /// Destination trimmed outside source.
23    DestinationOut,
24    /// Source inside destination blended with destination.
25    SourceAtop,
26    /// Destination inside source blended with source.
27    DestinationAtop,
28    /// Each of source and destination trimmed outside the other.
29    Xor,
30    /// Sum of colors.
31    Plus,
32    /// Product of premultiplied colors; darkens destination.
33    Modulate,
34    /// Multiply inverse of pixels, inverting result; brightens destination.
35    Screen,
36    /// Multiply or screen, depending on destination.
37    Overlay,
38    /// Darker of source and destination.
39    Darken,
40    /// Lighter of source and destination.
41    Lighten,
42    /// Brighten destination to reflect source.
43    ColorDodge,
44    /// Darken destination to reflect source.
45    ColorBurn,
46    /// Multiply or screen, depending on source.
47    HardLight,
48    /// Lighten or darken, depending on source.
49    SoftLight,
50    /// Subtract darker from lighter with higher contrast.
51    Difference,
52    /// Subtract darker from lighter with lower contrast.
53    Exclusion,
54    /// Multiply source with destination, darkening image.
55    Multiply,
56    /// Hue of source with saturation and luminosity of destination.
57    Hue,
58    /// Saturation of source with hue and luminosity of destination.
59    Saturation,
60    /// Hue and saturation of source with luminosity of destination.
61    Color,
62    /// Luminosity of source with hue and saturation of destination.
63    Luminosity,
64}
65
66impl Default for BlendMode {
67    fn default() -> Self {
68        BlendMode::SourceOver
69    }
70}
71
72impl BlendMode {
73    pub(crate) fn should_pre_scale_coverage(self) -> bool {
74        // The most important things we do here are:
75        //   1) never pre-scale with rgb coverage if the blend mode involves a source-alpha term;
76        //   2) always pre-scale Plus.
77        //
78        // When we pre-scale with rgb coverage, we scale each of source r,g,b, with a distinct value,
79        // and source alpha with one of those three values. This process destructively updates the
80        // source-alpha term, so we can't evaluate blend modes that need its original value.
81        //
82        // Plus always requires pre-scaling as a specific quirk of its implementation in
83        // RasterPipeline. This lets us put the clamp inside the blend mode itself rather
84        // than as a separate stage that'd come after the lerp.
85        //
86        // This function is a finer-grained breakdown of SkBlendMode_SupportsCoverageAsAlpha().
87        matches!(
88            self,
89            BlendMode::Destination |        // d              --> no sa term, ok!
90            BlendMode::DestinationOver |    // d + s*inv(da)  --> no sa term, ok!
91            BlendMode::Plus |               // clamp(s+d)     --> no sa term, ok!
92            BlendMode::DestinationOut |     // d * inv(sa)
93            BlendMode::SourceAtop |         // s*da + d*inv(sa)
94            BlendMode::SourceOver |         // s + d*inv(sa)
95            BlendMode::Xor // s*inv(da) + d*inv(sa)
96        )
97    }
98
99    pub(crate) fn to_stage(self) -> Option<pipeline::Stage> {
100        match self {
101            BlendMode::Clear => Some(pipeline::Stage::Clear),
102            BlendMode::Source => None, // This stage is a no-op.
103            BlendMode::Destination => Some(pipeline::Stage::MoveDestinationToSource),
104            BlendMode::SourceOver => Some(pipeline::Stage::SourceOver),
105            BlendMode::DestinationOver => Some(pipeline::Stage::DestinationOver),
106            BlendMode::SourceIn => Some(pipeline::Stage::SourceIn),
107            BlendMode::DestinationIn => Some(pipeline::Stage::DestinationIn),
108            BlendMode::SourceOut => Some(pipeline::Stage::SourceOut),
109            BlendMode::DestinationOut => Some(pipeline::Stage::DestinationOut),
110            BlendMode::SourceAtop => Some(pipeline::Stage::SourceAtop),
111            BlendMode::DestinationAtop => Some(pipeline::Stage::DestinationAtop),
112            BlendMode::Xor => Some(pipeline::Stage::Xor),
113            BlendMode::Plus => Some(pipeline::Stage::Plus),
114            BlendMode::Modulate => Some(pipeline::Stage::Modulate),
115            BlendMode::Screen => Some(pipeline::Stage::Screen),
116            BlendMode::Overlay => Some(pipeline::Stage::Overlay),
117            BlendMode::Darken => Some(pipeline::Stage::Darken),
118            BlendMode::Lighten => Some(pipeline::Stage::Lighten),
119            BlendMode::ColorDodge => Some(pipeline::Stage::ColorDodge),
120            BlendMode::ColorBurn => Some(pipeline::Stage::ColorBurn),
121            BlendMode::HardLight => Some(pipeline::Stage::HardLight),
122            BlendMode::SoftLight => Some(pipeline::Stage::SoftLight),
123            BlendMode::Difference => Some(pipeline::Stage::Difference),
124            BlendMode::Exclusion => Some(pipeline::Stage::Exclusion),
125            BlendMode::Multiply => Some(pipeline::Stage::Multiply),
126            BlendMode::Hue => Some(pipeline::Stage::Hue),
127            BlendMode::Saturation => Some(pipeline::Stage::Saturation),
128            BlendMode::Color => Some(pipeline::Stage::Color),
129            BlendMode::Luminosity => Some(pipeline::Stage::Luminosity),
130        }
131    }
132}
tiny_skia/blend_mode.rs

tiny_skia/
blend_mode.rs
