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libsst-wm/EventQueue.h

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+/*
+	EventQueue.h
+	Author: Patrick Baggett <ptbaggett@762studios.com>
+	Created: 6/18/2012
+
+	Purpose: 
+
+	Common event queue code for libsst-wm implementations
+
+	License:
+
+	This program is free software. It comes without any warranty, to
+	the extent permitted by applicable law. You can redistribute it
+	and/or modify it under the terms of the Do What The Fuck You Want
+	To Public License, Version 2, as published by Sam Hocevar. See
+	http://sam.zoy.org/wtfpl/COPYING for more details.
+
+*/
+
+#pragma once
+
+#ifndef _EVENTQUEUE_H
+#define _EVENTQUEUE_H
+
+#include <SST/SST_WMEvent.h>
+#include <SST/SST_Build.h>
+#include <stdlib.h>
+
+typedef struct EventQueue
+{
+	SST_WMEvent* events;
+	size_t head;	/* Index of next item to add (i.e. unused slot) */
+	size_t tail;	/* Index of next item to remove (i.e. used slot) */
+	size_t count;	/* Number of items in the queue */
+	size_t storageSize; /* Size of the backing storage */
+} EventQueue;
+
+#define EQ_DEFAULT_SIZE 32 /* Default capacity of the event queue. It may grow beyond this. */
+
+/*************************************************************************/
+
+/* Initialize an event queue structure, returning non-zero if successful */
+static INLINE int InitEQ(EventQueue* q)
+{
+	/* Allocate raw storage for event queue */
+	q->events = (SST_WMEvent*)malloc(EQ_DEFAULT_SIZE * sizeof(SST_WMEvent));
+	if(q->events == NULL)
+		return 0;
+
+	/* Initialize storage */
+	q->head = 0;
+	q->tail = 0;
+	q->count = 0;
+	q->storageSize = EQ_DEFAULT_SIZE;
+
+	return 1;
+}
+
+/*************************************************************************/
+
+/* Allocate a slot from the queue (as if adding) and return pointer. This manually
+eliminates copying a SST_WMEvent structure that most "enqueue" operation require.  */
+static INLINE SST_WMEvent* AllocSlotInEQ(EventQueue* q)
+{
+	SST_WMEvent* slot;
+
+	/* Need to increase capacity? */
+	if(q->head == q->tail && q->count == q->storageSize)
+	{
+		const size_t newSize = q->storageSize * 2;
+		SST_WMEvent* events;
+
+		/* Expand the queue */
+		events = realloc(q->events, newSize * sizeof(SST_WMEvent));
+		if(events == NULL)
+			return NULL;
+
+		/* All 'count' items from [0,tail] need to be moved to [oldSize, oldSize+count] */
+		if(q->tail != 0)
+		{
+			/*
+				1) A full queue
+				       v--h
+				[G][H][A][B][C][D][E][F]
+				       ^--t
+
+				2) Resized
+				       v--h
+				[G][H][A][B][C][D][E][F][ ][ ][ ][ ][ ][ ][ ][ ]
+				       ^--t
+
+				3) Shift elements from 0 to tail to end, update head ptr
+				                               v--h
+				[ ][ ][A][B][C][D][E][F][G][H][ ][ ][ ][ ][ ][ ]
+				       ^--t
+
+		   */
+
+			/* Shift elements */
+			memmove(&events[q->storageSize], &events[0], q->tail * sizeof(SST_WMEvent));
+			
+		}
+
+		/* Adjust head pointer to point to next empty slot */
+		q->head = q->tail + q->storageSize;
+
+		/* Update storage fields */
+		q->storageSize = newSize;
+		q->events = events;
+	} /* if(needed to increase capacity) */
+
+	/* Get the pointer to the slot where the event may be stored */
+	slot = &q->events[q->head];
+
+	/* Advance the head pointer by 1 */
+	q->head = (q->head + 1) % q->storageSize;
+	q->count += 1;
+
+	/* Return the slot */
+	return slot;
+}
+
+static INLINE int RemoveFromEQ(EventQueue* q, SST_WMEvent* event)
+{
+	/* Completely empty? */
+	if(q->head == q->tail && q->count != q->storageSize)
+		return 0;
+
+	/* Copy the structure */
+	*event = q->events[q->tail];
+
+	/* Advance the tail pointer by 1 */
+	q->tail = (q->tail + 1) % q->storageSize;
+	q->count -= 1;
+
+	/* OK */
+	return 1;
+}
+
+static INLINE void DestroyEQ(EventQueue* q)
+{
+	if(q->events != NULL)
+		free(q->events);
+}
+
+#endif
+