From caa59f3724100090795ccd99a12327d558c61061 Mon Sep 17 00:00:00 2001
From: Gary Talent <gary@drinkingtea.net>
Date: Sat, 27 Jan 2024 23:52:40 -0600
Subject: [PATCH] [nostalgia/core] Add functions for mapping tile idx to
 subsheet

---
 .../core/include/nostalgia/core/tilesheet.hpp |  6 +++
 src/nostalgia/modules/core/src/tilesheet.cpp  | 38 +++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/src/nostalgia/modules/core/include/nostalgia/core/tilesheet.hpp b/src/nostalgia/modules/core/include/nostalgia/core/tilesheet.hpp
index bad7451c..06beb9c5 100644
--- a/src/nostalgia/modules/core/include/nostalgia/core/tilesheet.hpp
+++ b/src/nostalgia/modules/core/include/nostalgia/core/tilesheet.hpp
@@ -158,6 +158,12 @@ struct TileSheet {
 [[nodiscard]]
 std::size_t idx(TileSheet::SubSheet const&ss, ox::Point const&pt) noexcept;
 
+[[nodiscard]]
+TileSheet::SubSheet const*getSubsheet(TileSheet const&ts, SubSheetId const id) noexcept;
+
+[[nodiscard]]
+size_t getTileIdx(TileSheet const&ts, SubSheetId id) noexcept;
+
 [[nodiscard]]
 uint8_t getPixel4Bpp(TileSheet::SubSheet const&ss, std::size_t idx) noexcept;
 
diff --git a/src/nostalgia/modules/core/src/tilesheet.cpp b/src/nostalgia/modules/core/src/tilesheet.cpp
index 21edc35a..67b2c2e0 100644
--- a/src/nostalgia/modules/core/src/tilesheet.cpp
+++ b/src/nostalgia/modules/core/src/tilesheet.cpp
@@ -14,6 +14,44 @@ std::size_t idx(TileSheet::SubSheet const&ss, ox::Point const&pt) noexcept {
 	return ptToIdx(pt, ss.columns);
 }
 
+static TileSheet::SubSheet const*getSubsheet(TileSheet::SubSheet const&ss, SubSheetId const id) noexcept {
+	if (ss.id == id) {
+		return &ss;
+	}
+	for (auto const&child : ss.subsheets) {
+		if (auto out = getSubsheet(child, id)) {
+			return out;
+		}
+	}
+	return {};
+}
+
+TileSheet::SubSheet const*getSubsheet(TileSheet const&ts, SubSheetId const id) noexcept {
+	return getSubsheet(ts.subsheet, id);
+}
+
+static ox::Optional<size_t> getPixelIdx(
+		TileSheet::SubSheet const&ss,
+		SubSheetId const id,
+		size_t idx,
+		int8_t const bpp) noexcept {
+	for (auto const&child : ss.subsheets) {
+		if (child.id == id) {
+			return ox::Optional<size_t>(ox::in_place, idx);
+		}
+		if (auto out = getPixelIdx(child, id, idx, bpp)) {
+			return out;
+		}
+		idx += pixelCnt(ss, bpp);
+	}
+	return {};
+}
+
+size_t getTileIdx(TileSheet const&ts, SubSheetId const id) noexcept {
+	auto const out = getPixelIdx(ts.subsheet, id, 0, ts.bpp);
+	return out.or_value(0) / PixelsPerTile;
+}
+
 uint8_t getPixel4Bpp(TileSheet::SubSheet const&ss, std::size_t idx) noexcept {
 	if (idx & 1) {
 		return ss.pixels[idx / 2] >> 4;