From 647ad7f254232f59ccba519159b37af4b32de854 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Sun, 13 Sep 2026 20:17:24 +0200
Subject: [PATCH] test: cover luminance and colourDistance

---
 tests/testTileTexture.cpp | 151 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 151 insertions(+)
 create mode 100644 tests/testTileTexture.cpp

diff --git a/tests/testTileTexture.cpp b/tests/testTileTexture.cpp
new file mode 100644
index 0000000..fcba8f7
--- /dev/null
+++ b/tests/testTileTexture.cpp
@@ -0,0 +1,151 @@
+#include <cstdio>
+#include <set>
+#include <vector>
+
+#include "testHarness.h"
+#include "vf/Block.h"
+#include "vf/TileTexture.h"
+
+using namespace vf;
+
+namespace {
+
+int luminance(TilePixel texel) {
+    return (texel.r * 299 + texel.g * 587 + texel.b * 114) / 1000;
+}
+
+int colourDistance(TilePixel texel, TileRgb reference) {
+    int dr = static_cast<int>(texel.r) - reference.r;
+    int dg = static_cast<int>(texel.g) - reference.g;
+    int db = static_cast<int>(texel.b) - reference.b;
+    return dr * dr + dg * dg + db * db;
+}
+
+bool leansToAccent(TilePixel texel, const TileSpec& spec) {
+    return colourDistance(texel, spec.accent) < colourDistance(texel, spec.base);
+}
+
+// The palette owns how many tiles exist. A table short of a row must surface as
+// a reported failure, not as a read past the end of the table proving it.
+int renderedTiles(const TileSampler& sampler) {
+    int held = sampler.palette().size();
+    return held < tileCount ? held : tileCount;
+}
+
+std::vector<uint8_t> renderTile(const TileSampler& sampler, int tile) {
+    int size = sampler.params().tileSize;
+    std::vector<uint8_t> bytes(static_cast<std::size_t>(size) * size * 4);
+    sampler.writeTile(tile, bytes.data());
+    return bytes;
+}
+
+std::vector<uint8_t> renderAtlas(const TileSampler& sampler, bool backwards) {
+    int size = sampler.params().tileSize;
+    std::size_t tileBytes = static_cast<std::size_t>(size) * size * 4;
+    int held = renderedTiles(sampler);
+    std::vector<uint8_t> bytes(tileBytes * static_cast<std::size_t>(held));
+    if (backwards) {
+        for (int tile = held - 1; tile >= 0; --tile) {
+            sampler.writeTile(tile, bytes.data() + tileBytes * static_cast<std::size_t>(tile));
+        }
+    } else {
+        for (int tile = 0; tile < held; ++tile) {
+            sampler.writeTile(tile, bytes.data() + tileBytes * static_cast<std::size_t>(tile));
+        }
+    }
+    return bytes;
+}
+
+// The first row and column carry a deliberate edge darkening, which would hand
+// every tile a luminance spread for free. Contrast is therefore only ever
+// measured inside that border.
+struct LuminanceRange {
+    int lowest = 255;
+    int highest = 0;
+    int spread() const { return highest - lowest; }
+};
+
+LuminanceRange interiorRange(const TileSampler& sampler, int tile) {
+    LuminanceRange range;
+    int size = sampler.params().tileSize;
+    for (int y = 1; y < size; ++y) {
+        for (int x = 1; x < size; ++x) {
+            int value = luminance(sampler.pixelAt(tile, x, y));
+            if (value < range.lowest) range.lowest = value;
+            if (value > range.highest) range.highest = value;
+        }
+    }
+    return range;
+}
+
+TileSpec withoutGrain(TileSpec spec) {
+    spec.noise = 0.0f;
+    return spec;
+}
+
+// Columns in one row that the pattern painted with the accent colour. For a
+// brick tile those are the vertical mortar joints.
+std::vector<int> accentColumns(const TileSampler& sampler, const TileSpec& spec, int tileSalt,
+                               int y) {
+    std::vector<int> columns;
+    for (int x = 0; x < sampler.params().tileSize; ++x) {
+        if (leansToAccent(sampler.pixelOf(spec, tileSalt, x, y), spec)) columns.push_back(x);
+    }
+    return columns;
+}
+
+// A brick course is offset from the one above it, so the set of mortar columns
+// has to differ between courses. Rows that are entirely mortar are the
+// horizontal joints and say nothing about the offset.
+int distinctJointLayouts(const TileSampler& sampler, const TileSpec& spec, int tileSalt) {
+    int size = sampler.params().tileSize;
+    std::set<std::vector<int>> layouts;
+    for (int y = 0; y < size; ++y) {
+        std::vector<int> columns = accentColumns(sampler, spec, tileSalt, y);
+        if (columns.empty()) continue;
+        if (static_cast<int>(columns.size()) > size / 2) continue;
+        layouts.insert(columns);
+    }
+    return static_cast<int>(layouts.size());
+}
+
+TileSpec syntheticBrick() {
+    TileSpec spec;
+    spec.name = "syntheticBrick";
+    spec.pattern = TilePattern::Brick;
+    spec.material = TileMaterial::Stone;
+    spec.base = TileRgb{30, 30, 30};
+    spec.accent = TileRgb{240, 240, 240};
+    spec.noise = 0.0f;
+    spec.scale = 0.40f;
+    spec.density = 0.50f;
+    return spec;
+}
+
+} // namespace
+
+// Same params in, same bytes out. Anything that reached for a clock, a global
+// counter or an uninitialised buffer would show up here first.
+VF_TEST(renderingATileTwiceProducesIdenticalBytes) {
+    TileSampler first;
+    TileSampler second;
+    CHECK_EQ(first.palette().size(), tileCount);
+    for (int tile = 0; tile < renderedTiles(first); ++tile) {
+        std::vector<uint8_t> a = renderTile(first, tile);
+        std::vector<uint8_t> b = renderTile(second, tile);
+        bool identical = a == b;
+        CHECK(identical);
+        if (!identical) std::printf("  tile %d is not reproducible\n", tile);
+    }
+}
+
+// A tile must not care which tiles were generated before it. The atlas built
+// back to front has to match the atlas built front to back byte for byte.
+VF_TEST(theAtlasDoesNotDependOnTheOrderTilesAreGenerated) {
+    TileSampler sampler;
+    std::vector<uint8_t> forwards = renderAtlas(sampler, false);
+    std::vector<uint8_t> backwards = renderAtlas(sampler, true);
+    CHECK_EQ(forwards.size(), backwards.size());
+    CHECK(forwards == backwards);
+}
+