[Reverse-engineering] [th01] Items: Structure

Storing bomb and point items not just in separate arrays, but also
using separate *functions* for both?! At least it's only a single
structure for both.

Part of P0158, funded by Yanga.

th01/main/stage/item.cpp

@@ -0,0 +1,50 @@
+extern "C" {
+#include "platform.h"
+#include "pc98.h"
+#include "planar.h"
+#include "th01/formats/ptn.hpp"
+}
+
+/// Constants
+/// ---------
+
+static const pixel_t ITEM_W = PTN_W;
+static const pixel_t ITEM_H = PTN_H;
+/// ---------
+
+/// Structures
+/// ----------
+
+enum item_flag_t {
+	IF_FREE = 0,
+	IF_SPLASH = 1,
+	IF_FALL = 2,
+	IF_BOUNCE = 3,
+	IF_COLLECTED = 99,
+	IF_COLLECTED_OVER_CAP = 100,
+
+	_item_flag_t_FORCE_INT16 = 0x7FFF
+};
+
+union item_flag_state_t {
+	unsigned char splash_radius;	// During IF_SPLASH. In pixels.
+	unsigned char collect_time; 	// During ≥IF_COLLECTED.
+};
+
+struct item_t {
+	// Also overloaded for the text popup shown when the item is collected.
+	screen_x_t left;
+	screen_y_t top;
+	int16_t unknown_zero;
+	pixel_t velocity_y;
+
+	char flag; // item_flag_t
+	item_flag_state_t flag_state;
+};
+
+static const int ITEM_BOMB_COUNT = 4;
+static const int ITEM_POINT_COUNT = 10;
+
+extern item_t items_bomb[ITEM_BOMB_COUNT];
+extern item_t items_point[ITEM_POINT_COUNT];
+/// ----------