1 files changed, 141 insertions, 0 deletions
diff --git a/subprojects/pixpat/pixpat-native/src/layout.h b/subprojects/pixpat/pixpat-native/src/layout.h
new file mode 100644
index 0000000..d092bb1
--- /dev/null
+++ b/subprojects/pixpat/pixpat-native/src/layout.h
@@ -0,0 +1,141 @@
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <tuple>
+
+namespace pixpat
+{
+
+enum class ColorKind { RGB, YUV };
+
+// Normalized inter-stage pixel types. 16-bit-per-component integer.
+// N-bit storage values bit-replicate up to normalized 16-bit (so
+// N-bit max maps to 0xFFFF); encoding back is a truncating
+// `normalized >> (16 - N)`. See io/detail.h for the round-trip
+// argument. Sources without an A component emit a=0; cross-color-kind
+// ColorXfm resets a=0xFFFF; sinks with X write 0, sinks with A
+// encode `a`.
+struct RGB16 {
+	static constexpr ColorKind kind = ColorKind::RGB;
+	uint16_t r, g, b, a;
+};
+
+struct YUV16 {
+	static constexpr ColorKind kind = ColorKind::YUV;
+	uint16_t y, u, v, a;
+};
+
+inline constexpr uint16_t kNormMax = 0xFFFF;
+
+enum class C : uint8_t { X, A, R, G, B, Y, U, V };
+
+struct Comp {
+	C c;
+	uint8_t bits;
+	uint8_t shift;
+};
+
+template <typename Storage, Comp... Cs>
+struct Plane {
+	using storage_t = Storage;
+
+	static constexpr size_t num_comps = sizeof...(Cs);
+	static constexpr std::array<Comp, num_comps> comps{ Cs ... };
+	static constexpr size_t total_bits = (size_t(Cs.bits) + ... + 0);
+	static constexpr size_t storage_bits = sizeof(Storage) * 8;
+	static constexpr size_t bytes_per_pixel = (total_bits + 7) / 8;
+
+	static_assert(total_bits <= storage_bits, "components overflow storage word");
+
+	// Index of the n-th component matching Tag, or num_comps if absent.
+	template <C Tag>
+	static constexpr size_t find_pos(size_t n = 0)
+	{
+		for (size_t i = 0; i < num_comps; ++i) {
+			if (comps[i].c == Tag) {
+				if (n == 0)
+					return i;
+				--n;
+			}
+		}
+		return num_comps;
+	}
+
+	// Count of components matching Tag. Used to derive
+	// pixels_per_word for multi-pixel-per-storage formats (XYYY2101010,
+	// P030, ...).
+	template <C Tag>
+	static constexpr size_t component_count()
+	{
+		size_t cnt = 0;
+		for (size_t i = 0; i < num_comps; ++i)
+			if (comps[i].c == Tag)
+				++cnt;
+		return cnt;
+	}
+
+	// Mask each input value to its bit-width and OR-shift it into the
+	// storage word. The loop trip count and the comps[i] reads are
+	// compile-time constant, so the optimizer unrolls and folds.
+	static constexpr Storage pack(const std::array<uint16_t, num_comps>& v) noexcept
+	{
+		Storage out{};
+		for (size_t i = 0; i < num_comps; ++i) {
+			const Storage mask = (Storage{ 1 } << comps[i].bits) - 1;
+			out |= Storage(v[i] & mask) << comps[i].shift;
+		}
+		return out;
+	}
+
+	// Mirror of `pack`.
+	static constexpr std::array<uint16_t, num_comps> unpack(Storage word) noexcept
+	{
+		std::array<uint16_t, num_comps> out{};
+		for (size_t i = 0; i < num_comps; ++i) {
+			const Storage mask = (Storage{ 1 } << comps[i].bits) - 1;
+			out[i] = uint16_t((word >> comps[i].shift) & mask);
+		}
+		return out;
+	}
+};
+
+template <ColorKind Kind, size_t Hsub, size_t Vsub, typename ... Planes>
+struct Layout {
+	static constexpr ColorKind kind = Kind;
+	static constexpr size_t h_sub = Hsub;
+	static constexpr size_t v_sub = Vsub;
+	static constexpr size_t num_planes = sizeof...(Planes);
+
+	template <size_t N>
+	using plane = std::tuple_element_t<N, std::tuple<Planes...> >;
+
+	// Index of the first plane containing component Tag, or num_planes
+	// if no plane has it. Lets PlanarSource/Sink map C::U / C::V to a
+	// plane regardless of YUV vs YVU ordering.
+	// Comma-fold over plane indices: for each plane I check if it has
+	// Tag, and on the first hit assign `found = I`. Subsequent hits are
+	// suppressed by the `found == num_planes` guard. The whole fold
+	// evaluates to a discarded list of int 0s; the `found` capture
+	// carries the result out.
+	template <C Tag>
+	static constexpr size_t find_plane()
+	{
+		return [&]<size_t... I>(std::index_sequence<I...>) {
+			       size_t found = num_planes;
+			       ((plane<I>::template find_pos<Tag>() < plane<I>::num_comps
+			         ? (found == num_planes ? (found = I, 0) : 0)
+			         : 0), ...);
+			       return found;
+		} (std::make_index_sequence<num_planes>{});
+	}
+};
+
+template <size_t N>
+struct Buffer {
+	std::array<uint8_t*, N> data;
+	std::array<size_t,   N> stride;
+};
+
+} // namespace pixpat