[nostalgia/core/studio] Add scrolling support to TileSheetEditor

src/nostalgia/core/ptidxconv.hpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2016 - 2022 Gary Talent (gary@drinkingtea.net). All rights reserved.
+ */
+
+#pragma once
+
+#include <nostalgia/common/point.hpp>
+
+#include "consts.hpp"
+
+namespace nostalgia::core {
+
+[[nodiscard]]
+constexpr std::size_t pointToIdx(int w, int x, int y) noexcept {
+	constexpr auto colLength = static_cast<std::size_t>(PixelsPerTile);
+	const auto rowLength = static_cast<std::size_t>(static_cast<std::size_t>(w / TileWidth) * colLength);
+	const auto colStart = static_cast<std::size_t>(colLength * static_cast<std::size_t>(x / TileWidth));
+	const auto rowStart = static_cast<std::size_t>(rowLength * static_cast<std::size_t>(y / TileHeight));
+	const auto colOffset = static_cast<std::size_t>(x % TileWidth);
+	const auto rowOffset = static_cast<std::size_t>((y % TileHeight) * TileHeight);
+	return static_cast<std::size_t>(colStart + colOffset + rowStart + rowOffset);
+}
+
+[[nodiscard]]
+constexpr std::size_t ptToIdx(int x, int y, int c) noexcept {
+	return pointToIdx(c * TileWidth, x, y);
+}
+
+[[nodiscard]]
+constexpr std::size_t ptToIdx(common::Point pt, int c) noexcept {
+	return pointToIdx(c * TileWidth, pt.x, pt.y);
+}
+
+[[nodiscard]]
+constexpr common::Point idxToPt(int i, int c) noexcept {
+	const auto t = i / PixelsPerTile; // tile number
+	const auto iti = i % PixelsPerTile; // in tile index
+	const auto tc = t % c; // tile column
+	const auto tr = t / c; // tile row
+	const auto itx = iti % TileWidth; // in tile x
+	const auto ity = iti / TileHeight; // in tile y
+	return {
+		itx + tc * TileWidth,
+		ity + tr * TileHeight,
+	};
+}
+
+static_assert(idxToPt(4, 1) == common::Point{4, 0});
+static_assert(idxToPt(8, 1) == common::Point{0, 1});
+static_assert(idxToPt(8, 2) == common::Point{0, 1});
+static_assert(idxToPt(64, 2) == common::Point{8, 0});
+static_assert(idxToPt(128, 2) == common::Point{0, 8});
+static_assert(idxToPt(129, 2) == common::Point{1, 8});
+static_assert(idxToPt(192, 2) == common::Point{8, 8});
+static_assert(idxToPt(384, 8) == common::Point{48, 0});
+
+}