Filter › Dither, as Compositor 1.3.3 (12.15)

src/Document/Dither.h

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+#pragma once
+#include "Document/ImageAdjustments.h"
+#include <QImage>
+#include <QString>
+#include <array>
+#include <vector>
+
+// Filter › Dither's looks, in the panel's order and DitherPixels.h's.
+enum class DitherStyle { atkinson, floydSteinberg, bayer2, bayer4, bayer8, dots, lines, diamonds, patterns, ascii };
+inline constexpr std::array allDitherStyles{DitherStyle::atkinson, DitherStyle::floydSteinberg, DitherStyle::bayer2, DitherStyle::bayer4,
+                                            DitherStyle::bayer8,   DitherStyle::dots,           DitherStyle::lines,  DitherStyle::diamonds,
+                                            DitherStyle::patterns, DitherStyle::ascii};
+QString rawValue(DitherStyle style);
+// Swift's groups: diffusion, ordered, halftone, marks.
+int ditherGroup(DitherStyle style);
+// Each pixel's rounding error passes to its neighbours.
+bool diffuses(DitherStyle style);
+// Diffusion and ordered styles have tones; the rest draw marks.
+bool hasTones(DitherStyle style);
+bool isHalftone(DitherStyle style);
+bool drawsMarks(DitherStyle style);
+
+// A chunky pixel: a square, or a dot on dark.
+enum class DitherPixelShape { square, dot };
+inline constexpr std::array allDitherPixelShapes{DitherPixelShape::square, DitherPixelShape::dot};
+QString rawValue(DitherPixelShape shape);
+
+enum class DitherColors { blackWhite, twoColors, original };
+inline constexpr std::array allDitherColors{DitherColors::blackWhite, DitherColors::twoColors, DitherColors::original};
+QString rawValue(DitherColors colors);
+
+// Swift's DitherSettings: the filter's look, in layer pixels.
+struct DitherSettings {
+    static constexpr double pixelSizeLow = 1, pixelSizeHigh = 32;
+    static constexpr double cellSizeLow = 4, cellSizeHigh = 64;
+    static constexpr double levelsLow = 2, levelsHigh = 8;
+    static QString defaultCharacters() { return QStringLiteral(" .:-=+*#%@"); }
+    DitherStyle style = DitherStyle::atkinson;
+    // Each dithered pixel covers this many layer pixels a side.
+    double pixelSize = 2;
+    DitherPixelShape pixelShape = DitherPixelShape::square;
+    // Halftone and character cells, in dithered pixels.
+    double cellSize = 8;
+    // The halftone screen's angle, in degrees.
+    double angle = 45;
+    // Tones per channel; 2 is 1-bit.
+    double levels = 2;
+    // How much error passes on, 0–100%.
+    double diffusion = 100;
+    // −100…100: more ink or less, flatter or punchier.
+    double density = 0;
+    double contrast = 0;
+    DitherColors colors = DitherColors::blackWhite;
+    AdjustmentColor dark = AdjustmentColor(0, 0, 0);
+    AdjustmentColor light = AdjustmentColor(1, 1, 1);
+    // Marks stand for the light tones, lit on the dark.
+    bool lightOnDark = true;
+    // ASCII's characters, sorted by their ink.
+    QString characters = defaultCharacters();
+    DitherSettings normalized() const;
+    QImage apply(const QImage &image) const;
+    friend bool operator==(const DitherSettings &, const DitherSettings &) = default;
+
+    // Each distinct character's coverage map, least ink first.
+    struct Glyphs {
+        std::vector<uint8_t> maps;
+        std::vector<float> coverage;
+    };
+    static Glyphs glyphs(const QString &characters, int cell);
+
+private:
+    QImage dither(const QImage &image) const;
+};