--- a/newgrf_spritegroup.c	Thu Apr 27 18:28:56 2006 +0000
+++ b/newgrf_spritegroup.c	Thu Apr 27 19:53:58 2006 +0000
@@ -2,8 +2,10 @@
 
 #include "stdafx.h"
 #include "openttd.h"
+#include "variables.h"
+#include "macros.h"
 #include "pool.h"
-#include "sprite.h"
+#include "newgrf_spritegroup.h"
 
 enum {
 	SPRITEGROUP_POOL_BLOCK_SIZE_BITS = 4, /* (1 << 4) == 16 items */
@@ -67,3 +69,178 @@
 
 	_spritegroup_count = 0;
 }
+
+
+static const SpriteGroup *ResolveReal(const SpriteGroup *group, ResolverObject *object)
+{
+	bool in_motion;
+	uint set;
+
+	set = object->ResolveReal(object, group->g.real.num_loaded, group->g.real.num_loading, &in_motion);
+
+	assert((in_motion && set < group->g.real.num_loaded) || (!in_motion && set < group->g.real.num_loading));
+
+	return Resolve(in_motion ? group->g.real.loaded[set] : group->g.real.loading[set], object);
+}
+
+
+static uint32 GetVariable(const ResolverObject *object, byte variable, byte parameter)
+{
+	/* Return common variables */
+	switch (variable) {
+		case 0x00: return _date;
+		case 0x01: return _cur_year;
+		case 0x02: return _cur_month;
+		case 0x03: return _opt.landscape;
+		case 0x09: return _date_fract;
+		case 0x0A: return _tick_counter;
+		case 0x0C: return object->callback;
+		case 0x10: return object->callback_param1;
+		case 0x11: return 0;
+		case 0x18: return object->callback_param2;
+		case 0x1A: return -1;
+		case 0x1B: return GB(_display_opt, 0, 6);
+		case 0x1C: return object->last_value;
+		case 0x20: return _opt.landscape == LT_HILLY ? _opt.snow_line : 0xFF;
+
+		/* Not a common variable, so evalute the feature specific variables */
+		default: return object->GetVariable(object, variable, parameter);
+	}
+}
+
+
+/* Evaluate an adjustment for a variable of the given size. This is a bit of
+ * an unwieldy macro, but it saves triplicating the code. */
+#define BUILD_EVAL_ADJUST(size, usize) \
+static size EvalAdjust_ ## size(const DeterministicSpriteGroupAdjust *adjust, size last_value, size value) \
+{ \
+	value >>= adjust->shift_num; \
+	value  &= adjust->and_mask; \
+\
+	if (adjust->type != DSGA_TYPE_NONE) value += (size)adjust->add_val; \
+\
+	switch (adjust->type) { \
+		case DSGA_TYPE_DIV:  value /= (size)adjust->divmod_val; break; \
+		case DSGA_TYPE_MOD:  value %= (size)adjust->divmod_val; break; \
+		case DSGA_TYPE_NONE: break; \
+	} \
+\
+	switch (adjust->operation) { \
+		case DSGA_OP_ADD:  return last_value + value; \
+		case DSGA_OP_SUB:  return last_value - value; \
+		case DSGA_OP_SMIN: return min(last_value, value); \
+		case DSGA_OP_SMAX: return max(last_value, value); \
+		case DSGA_OP_UMIN: return min((usize)last_value, (usize)value); \
+		case DSGA_OP_UMAX: return max((usize)last_value, (usize)value); \
+		case DSGA_OP_SDIV: return last_value / value; \
+		case DSGA_OP_SMOD: return last_value % value; \
+		case DSGA_OP_UDIV: return (usize)last_value / (usize)value; \
+		case DSGA_OP_UMOD: return (usize)last_value % (usize)value; \
+		case DSGA_OP_MUL:  return last_value * value; \
+		case DSGA_OP_AND:  return last_value & value; \
+		case DSGA_OP_OR:   return last_value | value; \
+		case DSGA_OP_XOR:  return last_value ^ value; \
+		default:           return value; \
+	} \
+}
+
+
+BUILD_EVAL_ADJUST(int8, uint8)
+BUILD_EVAL_ADJUST(int16, uint16)
+BUILD_EVAL_ADJUST(int32, uint32)
+
+
+static const SpriteGroup *ResolveVariable(const SpriteGroup *group, ResolverObject *object)
+{
+	static SpriteGroup nvarzero;
+	const SpriteGroup *target;
+	int32 last_value = object->last_value;
+	int32 value = -1;
+	uint i;
+
+	object->scope = group->g.determ.var_scope;
+
+	for (i = 0; i < group->g.determ.num_adjusts; i++) {
+		DeterministicSpriteGroupAdjust *adjust = &group->g.determ.adjusts[i];
+		value = GetVariable(object, adjust->variable, adjust->parameter);
+		switch (group->g.determ.size) {
+			case DSG_SIZE_BYTE:  value = EvalAdjust_int8(adjust, last_value, value); break;
+			case DSG_SIZE_WORD:  value = EvalAdjust_int16(adjust, last_value, value); break;
+			case DSG_SIZE_DWORD: value = EvalAdjust_int32(adjust, last_value, value); break;
+			default: NOT_REACHED(); break;
+		}
+		last_value = value;
+	}
+
+	if (value == -1) {
+		/* Unsupported property */
+		target = group->g.determ.num_ranges > 0 ? group->g.determ.ranges[0].group : group->g.determ.default_group;
+	} else {
+		if (group->g.determ.num_ranges == 0) {
+			/* nvar == 0 is a special case -- we turn our value into a callback result */
+			nvarzero.type = SGT_CALLBACK;
+			nvarzero.g.callback.result = GB(value, 0, 15) | 0x8000;
+			return &nvarzero;
+		}
+
+		target = group->g.determ.default_group;
+		for (i = 0; i < group->g.determ.num_ranges; i++) {
+			if (group->g.determ.ranges[i].low <= (uint32)value && (uint32)value <= group->g.determ.ranges[i].high) {
+				target = group->g.determ.ranges[i].group;
+				break;
+			}
+		}
+	}
+
+	return Resolve(target, object);
+}
+
+
+static const SpriteGroup *ResolveRandom(const SpriteGroup *group, ResolverObject *object)
+{
+	byte mask;
+	byte index;
+
+	object->scope = group->g.random.var_scope;
+
+	if (object->trigger != 0) {
+		/* Handle triggers */
+		/* Magic code that may or may not do the right things... */
+		byte waiting_triggers = object->GetTriggers(object);
+		byte match = group->g.random.triggers & (waiting_triggers | object->trigger);
+		bool res;
+
+		res = (group->g.random.cmp_mode == RSG_CMP_ANY) ?
+			(match != 0) : (match == group->g.random.triggers);
+
+		if (res) {
+			waiting_triggers &= ~match;
+			object->reseed |= (group->g.random.num_groups - 1) << group->g.random.lowest_randbit;
+		} else {
+			waiting_triggers |= object->trigger;
+		}
+
+		object->SetTriggers(object, waiting_triggers);
+	}
+
+	mask  = (group->g.random.num_groups - 1) << group->g.random.lowest_randbit;
+	index = (object->GetRandomBits(object) & mask) >> group->g.random.lowest_randbit;
+
+	return Resolve(group->g.random.groups[index], object);
+}
+
+
+/* ResolverObject (re)entry point */
+const SpriteGroup *Resolve(const SpriteGroup *group, ResolverObject *object)
+{
+	/* We're called even if there is no group, so quietly return nothing */
+	if (group == NULL) return NULL;
+
+	switch (group->type) {
+		case SGT_REAL:          return ResolveReal(group, object);
+		case SGT_DETERMINISTIC: return ResolveVariable(group, object);
+		case SGT_RANDOMIZED:    return ResolveRandom(group, object);
+		default:                return group;
+	}
+}
+

--- a/newgrf_spritegroup.h	Thu Apr 27 18:28:56 2006 +0000
+++ b/newgrf_spritegroup.h	Thu Apr 27 19:53:58 2006 +0000
@@ -154,4 +154,39 @@
 SpriteGroup *AllocateSpriteGroup(void);
 void InitializeSpriteGroupPool(void);
 
+
+typedef struct ResolverObject {
+	byte callback;
+	uint32 callback_param1;
+	uint32 callback_param2;
+
+	byte trigger;
+	uint32 last_value;
+	uint32 reseed;
+	VarSpriteGroupScope scope;
+
+	union {
+		struct {
+			const struct Vehicle *self;
+			const struct Vehicle *parent;
+		} vehicle;
+		struct {
+			TileIndex tile;
+			const struct Station *st;
+			const struct StationSpec *statspec;
+		} station;
+	};
+
+	uint32 (*GetRandomBits)(const struct ResolverObject*);
+	uint32 (*GetTriggers)(const struct ResolverObject*);
+	void (*SetTriggers)(const struct ResolverObject*, int);
+	uint32 (*GetVariable)(const struct ResolverObject*, byte, byte);
+	uint32 (*ResolveReal)(const struct ResolverObject*, uint, uint, bool*);
+} ResolverObject;
+
+
+/* Base sprite group resolver */
+const SpriteGroup *Resolve(const SpriteGroup *group, ResolverObject *object);
+
+
 #endif /* NEWGRF_SPRITEGROUP_H */