feat(vf): add TileRgb, TileSpec and TilePixel

core/include/vf/TileTexture.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <cstdint>
+
+#include "TilePalette.h"
+
+namespace vf {
+
+// One generated texel. Alpha is either 0 or 255: the atlas is sampled with
+// nearest filtering, so a half transparent edge would only smear.
+struct TilePixel {
+    uint8_t r = 0;
+    uint8_t g = 0;
+    uint8_t b = 0;
+    uint8_t a = 255;
+};
+
+// Everything the generator needs beyond the palette itself. Two samplers built
+// from equal params produce byte identical output; nothing here reads a clock,
+// a global, or the order tiles happen to be generated in.
+struct TileTextureParams {
+    int tileSize = 16;
+    uint32_t noiseSeed = 0x9e3779b9u;
+    // Scales every pixel's distance from its tile's base colour. 1 is the
+    // palette as authored.
+    float contrast = 1.0f;
+};
+
+// Turns a TileSpec into pixels. The sampler owns its palette copy so a caller
+// can hold several with different params without them sharing state, and no
+// allocation happens per pixel or per tile.
+class TileSampler {
+public:
+    explicit TileSampler(const TileTextureParams& params = TileTextureParams{});
+    TileSampler(const TileTextureParams& params, const TilePalette& palette);
+
+    const TileTextureParams& params() const { return settings; }
+    const TilePalette& palette() const { return table; }
+
+    TilePixel pixelAt(int tile, int x, int y) const;
+
+    // Same generator against a spec the palette does not hold, which is how the
+    // pattern layer is tested without the palette's noise in the way.
+    TilePixel pixelOf(const TileSpec& spec, int tileSalt, int x, int y) const;
+
+    // Writes tileSize * tileSize RGBA8 texels, row major, into caller memory.
+    void writeTile(int tile, uint8_t* rgba) const;
+
+private:
+    TileTextureParams settings;
+    TilePalette table;
+};
+
+} // namespace vf