Add tilemap to texture array conversion to pipeline

pipeline/main.zig

@@ -103,7 +103,7 @@ fn visit(assets_dir: std.fs.Dir, library_dir: std.fs.Dir, allocator: std.mem.All
         };
         defer allocator.free(outbuf);
 
-        @memcpy(outbuf, img.data);
+        rearrange(grid_w, grid_h, tile_w, tile_h, img.data, outbuf);
 
         const out_name = std.fs.path.stem(entry.name);
 
@@ -116,6 +116,42 @@ fn visit(assets_dir: std.fs.Dir, library_dir: std.fs.Dir, allocator: std.mem.All
     }
 }
 
+fn rearrange(grid_w: u32, grid_h: u32, tile_w: u32, tile_h: u32, inbuf: []const u8, outbuf: []u8) void {
+    std.log.debug("rearrange: {}×{} grid of {}×{} tiles", .{ grid_w, grid_h, tile_w, tile_h });
+
+    const row_size = 4 * tile_w;
+    const row_stride = row_size * grid_w;
+    const tile_stride = row_stride * tile_h;
+
+    std.debug.assert(inbuf.len == tile_stride * grid_h);
+    std.debug.assert(outbuf.len == tile_stride * grid_h);
+
+    var outptr: usize = 0;
+
+    var tile_y: u32 = 0;
+    while (tile_y < grid_h) : (tile_y += 1) {
+        const tile_byte_offset = tile_y * tile_stride;
+
+        var tile_x: u32 = 0;
+        while (tile_x < grid_w) : (tile_x += 1) {
+            const column_byte_offset = tile_x * row_size;
+
+            var row: u32 = 0;
+            while (row < tile_h) : (row += 1) {
+                const row_byte_offset = row * row_stride + tile_byte_offset;
+                const byte_offset = row_byte_offset + column_byte_offset;
+
+                @memcpy(
+                    outbuf[outptr .. outptr + row_size],
+                    inbuf[byte_offset .. byte_offset + row_size],
+                );
+
+                outptr += row_size;
+            }
+        }
+    }
+}
+
 fn openDirOrExit(dir: std.fs.Dir, sub_path: []const u8, args: std.fs.Dir.OpenOptions) std.fs.Dir {
     return dir.openDir(sub_path, args) catch |err| {
         std.log.err("Could not open \"{s}\" directory: {s}", .{ sub_path, @errorName(err) });