[aquaria] [PATCH] Fix logic bugs in reordering of RenderObjects within a layer.

[Andrew Church]

# HG changeset patch
# User Andrew Church <achurch at achurch.org>
# Date 1313581717 -32400
# Node ID 9c350f140a62de19546039b36d88fd8e0e7d3442
# Parent  5542b94cae02a6333845854bbbd1abe0a259f1a4
Fix logic bugs in reordering of RenderObjects within a layer.

This patch fixes logic bugs with state management for the array-based
RenderObjectLayer implementation which could cause crashes when an
object was moved to the back of the layer.

This is the correct fix for the bug worked around in r199 (b00e51cba5bc).

diff -r 5542b94cae02 -r 9c350f140a62 BBGE/RenderObjectLayer.cpp
--- a/BBGE/RenderObjectLayer.cpp	Mon Aug 01 14:16:11 2011 -0400
+++ b/BBGE/RenderObjectLayer.cpp	Wed Aug 17 20:48:37 2011 +0900
@@ -229,8 +229,8 @@
 		renderObjects[curIdx] = 0;
 		renderObjects[newIdx] = r;
 		r->setIdx(newIdx);
-		if (firstFreeIdx == newIdx)
-			firstFreeIdx++;
+		if (firstFreeIdx > curIdx)
+			firstFreeIdx = curIdx;
 	}
 	else if (objectCount == size)
 	{
@@ -242,7 +242,7 @@
 		r->setIdx(size);
 		for (int i = size+1; i < newSize; i++)
 			renderObjects[i] = 0;
-		firstFreeIdx = size+1;
+		firstFreeIdx = curIdx;
 	}
 	else
 	{
@@ -254,18 +254,16 @@
 			if (!renderObjects[lastFree])
 				break;
 		}
-
 		for (int i = lastFree + 1; i <= lastUsed; i++)
 		{
 			renderObjects[i-1] = renderObjects[i];
-			if(renderObjects[i-1])
-				renderObjects[i-1]->setIdx(i-1);
+			renderObjects[i-1]->setIdx(i-1);  // Known to be non-NULL.
 		}
-
 		renderObjects[lastUsed] = r;
 		r->setIdx(lastUsed);
-		if (firstFreeIdx == lastFree)
-			firstFreeIdx = lastUsed + 1;
+		firstFreeIdx = curIdx;
+		while (renderObjects[firstFreeIdx])
+			firstFreeIdx++;
 	}
 #endif  // RLT_FIXED
 #ifdef RLT_DYNAMIC
@@ -298,7 +296,9 @@
 		renderObjects[curIdx] = 0;
 		renderObjects[newIdx] = r;
 		r->setIdx(newIdx);
-		if (firstFreeIdx == newIdx)
+		// firstFreeIdx must be 0 here; if we filled slot 0, then
+		// scan forward for the next empty element.
+		while (renderObjects[firstFreeIdx])
 			firstFreeIdx++;
 	}
 	else if (objectCount == size)
@@ -312,8 +312,7 @@
 		for (int i = newSize - 1; i >= sizeDiff; i--)
 		{
 			renderObjects[i] = renderObjects[i - sizeDiff];
-			if(renderObjects[i])
-				renderObjects[i]->setIdx(i);
+			renderObjects[i]->setIdx(i);  // Known to be non-NULL.
 		}
 		for (int i = 0; i < newIdx; i++)
 			renderObjects[i] = 0;
@@ -329,8 +328,7 @@
 		for (int i = firstFreeIdx; i > 0; i--)
 		{
 			renderObjects[i] = renderObjects[i-1];
-			if(renderObjects[i])
-				renderObjects[i]->setIdx(i);
+			renderObjects[i]->setIdx(i);  // Known to be non-NULL.
 		}
 		renderObjects[0] = r;
 		r->setIdx(0);