feat(vf): add BrushParams and BrushResult

core/include/vf/Brush.h

@@ -0,0 +1,105 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#include "Block.h"
+#include "EditHistory.h"
+#include "Math.h"
+#include "Selection.h"
+#include "World.h"
+
+namespace vf {
+
+enum class BrushKind : uint8_t {
+    Sphere = 0,
+    Cylinder = 1,
+    Replace = 2,
+    Smooth = 3,
+    Erode = 4,
+    Overlay = 5,
+    Naturalize = 6,
+    Gradient = 7,
+};
+
+// Everything a stroke needs. One struct for all brushes: a kind reads the
+// fields that apply to it and ignores the rest, which keeps a brush preset a
+// plain value that can be stored, copied and replayed.
+struct BrushParams {
+    enum class VolumeMode : uint8_t {
+        Fill = 0,
+        Hollow = 1,
+        Shell = 2,
+    };
+
+    BrushKind kind = BrushKind::Sphere;
+    VolumeMode mode = VolumeMode::Fill;
+
+    Vec3i center{0, 0, 0};
+    int radius = 3;
+    int height = 4;
+    int shellThickness = 1;
+
+    Block block = Block::Stone;
+    Block secondaryBlock = Block::Dirt;
+
+    // Empty means "every non-air block"; otherwise only the listed types are
+    // touched, which is what makes a replace brush safe to drag over terrain.
+    std::vector<Block> onlyReplace;
+
+    int freeNeighbourThreshold = 3;
+    int soilDepth = 3;
+    Block surfaceBlock = Block::Grass;
+    Block soilBlock = Block::Dirt;
+    Block deepBlock = Block::Stone;
+
+    uint32_t seed = 0u;
+
+    int worldMinY = 0;
+    int worldMaxY = 256;
+
+    std::string label;
+};
+
+struct BrushResult {
+    std::size_t changed = 0;
+    std::size_t visited = 0;
+    bool outsideLoadedWorld = false;
+    bool clippedAtHeightLimit = false;
+    bool recorded = false;
+};
+
+// Applies brushes to a world through an EditHistory. One call to apply() is one
+// batch, so every stroke - including the ones that touch thousands of blocks -
+// undoes in a single step.
+class BrushStroke {
+public:
+    BrushStroke(World& world, EditHistory& history);
+
+    BrushResult apply(const BrushParams& params, uint64_t tick);
+    BrushResult applyWithin(const BrushParams& params, const Selection& limit, uint64_t tick);
+
+    // The volume a brush covers when no selection restricts it.
+    static Selection regionOf(const BrushParams& params);
+    static const char* kindName(BrushKind kind);
+
+    const BrushResult& lastResult() const { return previous; }
+
+private:
+    void write(const BrushParams& params, const Vec3i& cell, Block block, BrushResult& outcome);
+    void paintVolume(const BrushParams& params, const Selection& limit, BrushResult& outcome);
+    void paintReplace(const BrushParams& params, const Selection& limit, BrushResult& outcome);
+    void paintSmooth(const BrushParams& params, const Selection& limit, BrushResult& outcome);
+    void paintNeighbourRule(const BrushParams& params, const Selection& limit, bool erode,
+                            BrushResult& outcome);
+    void paintNaturalize(const BrushParams& params, const Selection& limit, BrushResult& outcome);
+    void paintGradient(const BrushParams& params, const Selection& limit, BrushResult& outcome);
+
+    World& world;
+    EditHistory& history;
+    BrushResult previous;
+};
+
+} // namespace vf