change tiles from a texture array to a texture atlas

src/smol-atlas.h

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: MIT OR Unlicense
+// smol-atlas: https://github.com/aras-p/smol-atlas
+
+#pragma once
+
+// 2D rectangular bin packing utility that uses the Shelf Best Height Fit
+// heuristic, and supports item removal. You could also call it a
+// dynamic texture atlas allocator.
+//
+// The shelf packing algorithm works well when there is a high number of items
+// with similar sizes, for example dynamic glyph or thumbnail atlases.
+//
+// - Incoming items are placed into horizontal "shelves" based on item heights.
+// - Within each shelf, there is a sorted list of free spans.
+// - When an item is added, needed portion of the first suitable free span
+//   is used.
+// - When an item is removed, resulting free span is joined with any
+//   neighboring spans.
+// - Shelves, once created, stay at their height and location. Even if they
+//   become empty, they are not removed nor joined with nearby shelves.
+//
+// Implementation uses STL <vector>, and some manual memory allocation
+// with just regular `new` and `delete`. Custom allocators might be nice to
+// do someday.
+//
+// At least C++11 is required.
+
+struct smol_atlas_t;
+struct smol_atlas_item_t;
+
+/// Create atlas of given size.
+smol_atlas_t* sma_atlas_create(int width, int height);
+
+/// Destroy the atlas.
+void sma_atlas_destroy(smol_atlas_t* atlas);
+
+/// Get atlas width.
+int sma_atlas_width(const smol_atlas_t* atlas);
+
+/// Get atlas height.
+int sma_atlas_height(const smol_atlas_t* atlas);
+
+/// Add an item of (width x height) size into the atlas.
+/// Use `sma_item_x` and `sma_item_y` to query the resulting item location.
+/// Item can later be removed with `sma_item_remove`.
+/// Returned pointer is valid until atlas is cleared or destroyed, or the item is removed.
+/// Returns NULL if there is no more space left.
+smol_atlas_item_t* sma_item_add(smol_atlas_t* atlas, int width, int height);
+
+/// Remove a previously added item from the atlas.
+/// The item pointer becomes invalid and can no longer be used.
+void sma_item_remove(smol_atlas_t* atlas, smol_atlas_item_t* item);
+
+/// Clear the atlas. This invalidates any previously returned item pointers.
+/// If passed width and height are positive, the atlas size is also set
+/// to the new values.
+void sma_atlas_clear(smol_atlas_t* atlas, int new_width = 0, int new_height = 0);
+
+/// Get item X coordinate.
+int sma_item_x(const smol_atlas_item_t* item);
+/// Get item Y coordinate.
+int sma_item_y(const smol_atlas_item_t* item);
+/// Get item width.
+int sma_item_width(const smol_atlas_item_t* item);
+/// Get item height.
+int sma_item_height(const smol_atlas_item_t* item);