http://d.puremagic.com/issues/show_bug.cgi?id=1190

           Summary: Reference becoming null
           Product: D
           Version: 1.013
          Platform: PC
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: blocker
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: arkangath@gmail.com


The following code is part of a LOD terrain engine I'm coding and the code fails on a split operation, where references to Nodes are updated (copied) to generate child nodes. The code has been ported from C++ (I can post it as well) and all lines has been checked and re-checked for errors on the implementation.

The code has been striped of all unnecessary methods to improve readability and reduce dependencies. When compiled with "dmd -g -debug teste.d" the program fails to generate a viable mesh, crashing on an assert. This assert can be removed and the code would generate a mesh, but with null Nodes, if could not be rendered (Access Violation if attempted).

The assert occurs in both Windows and Linux, the only platforms available for testing.

The line in which the assert fails is 307, when the current node's right neighbor's base neighbor is set to current node's right child node. Before that line, both are asserted as NOT being null. I tried to analyze the disassembled code, but I couldn't find the source of the error.

------------------ teste.d -------------------------
///Contains all declarations concerning the terrain engine
import std.string;
import std.stream;
import std.math;

alias std.string.toString strfy;
alias std.stdio.writefln Log;

private static const ubyte PatchSize=64; //must be power of 2
//const ubyte MAX_DEPTH=cast(ubyte)(2*sqrt(PatchSize)+1);
private static const MaxDepth=4;//17

private struct CamInfo
{
    uint x, y, z;
}

private CamInfo camInfo;

/**
The Terrain engine class.
*/
public final class Terrain
{
    ///The TreeNode class is used to store information about the patch tree
    private final class TreeNode
    {
        private TreeNode lChild, rChild, bNeigh, lNeigh, rNeigh;

        public this()
        {
            reset();
        }

        public void reset()
        {
            lChild=rChild=bNeigh=lNeigh=rNeigh=null;
        }
    }

    ///Patch Class. A terrain is composed of several patches
    private final class Patch
    {
        this (ushort x, ushort y)
        {
            this.x=x; this.y=y;
            visible=true;
            rNode=new TreeNode(); //these never get reassigned
            lNode=new TreeNode(); //they're const, remmember?
            assert(rNode !is null);
            assert(lNode !is null);
            //nodes come already clean
            rNode.bNeigh=lNode;
            lNode.bNeigh=rNode;
            calcError();
        }

        ///Resets the patch. It becomes undivided and ready for the next
tesselation.
        void reset()
        {
            rNode.reset();
            lNode.reset();
            rNode.bNeigh=lNode;
            lNode.bNeigh=rNode;
            //TODO: check visibility here
            visible=true;
        }

        ///Tesselates this patch and it becomes ready for rendering
        void update()
        {
            std.gc.disable();
            cError[]=lError;
            tesselate(lNode, x, cast(ushort)(y+PatchSize),
cast(ushort)(x+PatchSize), y, x, y, 1);
            cError[]=rError;
            tesselate(rNode, cast(ushort)(x+PatchSize), y, x,
cast(ushort)(y+PatchSize),
                cast(ushort)(x+PatchSize), cast(ushort)(y+PatchSize), 1);
            std.gc.enable();
        }

        ///This patch's error measure is updated from the data on hData.
        void calcError()
        {
            Calculate(x, cast(ushort)(y+PatchSize), cast(ushort)(x+PatchSize),
y, x, y, 1);
            lError[]=cError; //copy the error data
            Calculate(cast(ushort)(x+PatchSize), y, x,
cast(ushort)(y+PatchSize),
                cast(ushort)(x+PatchSize), cast(ushort)(y+PatchSize), 1);
            rError[]=cError;
            return;
        }

        ~this()
        {
            delete rNode;
            delete lNode;
        }

        //no need to protect this vars because this class won't be accessed
from the exterior
        const ushort x, y; //coordinates aren't expected to change
        bool visible; ///Result of lastest cull check
        ushort[MaxDepth] lError, rError;
        const TreeNode rNode, lNode;
    }

    public:
    this(in File file, float detail)
    in
    {
        assert(file !is null);
        assert(detail>=0); //negative error values make no sense. 0 values are
purely debugging technices
    }
    body
    {
        debug Log("Creating terrain object");
        this.detail=detail;
        file.read(sizeX);
        file.read(sizeY);
        assert((sizeX>0)&&(sizeY>0));
        HMult=1; //TODO: Replace with resolution from file
        hData=new ushort[][](sizeX, sizeY); //initialize data
        debug Log(" * Loading terrain data...");
        foreach (stripe; hData)
            foreach (inout vertex; stripe)
            {
                file.read(vertex);
                vertex*=HMult;
            }
        maxH=0; //Maximum height present on the map. Used somewhere in debug
code
        foreach (stripe; hData)
            foreach (vertex; stripe)
                if (vertex>maxH) maxH=vertex;
        xPatch=cast(ubyte)(sizeX/PatchSize);
        yPatch=cast(ubyte)(sizeY/PatchSize);
        nodes.length=(sizeX*sizeY/PatchSize);
        debug Log(" * Creating terrain nodes ("~strfy(nodes.length)~")...");
        foreach(inout node; nodes) node=new TreeNode;

        debug Log(" * Creating patches...");
        patches.length=xPatch;//how many columns will we have? Patch[col][row]
        foreach (size_t row, inout Patch[] strip; patches)
        {
            assert(strip.length==0, "Oups! Redefining a length of a strip");
            strip.length=yPatch; //How many rows?
            foreach (size_t col, inout Patch patch; strip)
                patch=new Patch(cast(ushort)(col*PatchSize),
cast(ushort)(row*PatchSize));
        }
        debug Log("Terrain creation complete");
    }

    public float heightAt(in float x, in float y)
    out(result)
    {
        assert((result>=0.0f)||(result==float.nan));
    }
    body
    {
        if ((x<0.0)||(y<0.0f)) return float.nan;
        //triangulate height at the given point
        return 0.0f;
    }

    ///Makes the terrain ready for rendering. Tesselates all the patches.
    void update()
    body
    {
        //reset the engine first
        currNode=0; //reset current node
        foreach (size_t row, inout Patch[] strip; patches)
            foreach (size_t col, inout Patch patch; strip)
            {
                patch.reset(); //Recalculate the visibility flag
                if (patch.visible) //bail on non-visible patches
                {
                    if (col>0) patch.lNode.lNeigh=patches[col-1][row].rNode;
                    else patch.lNode.lNeigh=null;
                    if (col<(xPatch-1))
patch.rNode.lNeigh=patches[col+1][row].lNode;
                    else patch.rNode.lNeigh=null;
                    if (row>0) patch.lNode.rNeigh=patches[col][row-1].rNode;
                    else patch.lNode.rNeigh=null;
                    if (row<(yPatch-1))
patch.rNode.rNeigh=patches[col][row+1].lNode;
                    else patch.rNode.rNeigh=null;
                }
            }
        //Unfloatize camera information. Remember the case in which the coords
are <0
        foreach (Patch[] strip; patches)
            foreach (Patch patch; strip)
                if (patch.visible) patch.update();
        return;
    }

    ~this()
    {
        /*Since the terrain is the last thing to be deleted when a game is
over, a gc.fullCollect()
        will be preformed sometime soon, so it is not necessary to clean up
manually*/
        foreach (inout stripe; hData)
        {
            stripe.length=0; delete stripe;
        }
        hData.length=0;
        foreach (inout Patch[] strip; patches)
            foreach (inout Patch patch; strip)
                delete patch;
        foreach(inout node; nodes) delete node;
        nodes.length=0;
    }

    private:
    ///Returns the next available TreeNode. Creates a new one if there are no
more available.
    TreeNode newNode()
    out(result)
    {
        assert(result !is null, "newNode() attempted to return a null
TreeNode.");
    }
    body
    {
        assert(currNode<=nodes.length, "currNode advanced too much");
        if (currNode==nodes.length)
        {
            nodes~=new TreeNode; //no more nodes available, create another one
            debug Log("Insufficient TreeNodes for current tesselation
(detail="~strfy(detail)~"). Increasing TreeNode pool
(currNode="~strfy(currNode)~").");
        }
        TreeNode ret=nodes[currNode]; //get a new node
        ret.reset(); //clear new node's affiliations
        currNode++;
        return ret;
    }

    ///To be used by functions of the class, returns raw height value.
    ushort heightAt(ushort x, ushort y)
    {
        if ((x==sizeX)||(y==sizeY)) return 0; //Out of bounds values are not
drawn (taken has void in game)
        assert(x<sizeX, "Out of bounds value requested");
        assert(y<sizeY, "Out of bounds value requested");
        return hData[x][y];
    }

    ushort Calculate(ushort lX, ushort lY, ushort rX, ushort rY, ushort aX,
ushort aY, ushort node)
    {
        //Calculate hipotenuse
        ushort cX=cast(ushort)((rX+lX)/2);
        ushort cY=cast(ushort)((rY+lY)/2);
        ushort cZ=heightAt(cX, cY);
        ushort rZ=heightAt(rX, rY);
        ushort lZ=heightAt(lX, lY);
        ushort errRatio=cast(ushort)abs(cZ-((lZ+rZ)/2)); //this iteraction's
primary error ratio
        if (errRatio==0) return 0; //reached perfectness
        if ((abs((rX-lX))>=2)||(abs(rY-lY))>=2) //smaller than 2x2
        {
            //calculate the error of one of the child triangles
            ushort tempErrRatio=Calculate(aX, aY, lX, lY, cX, cY,
cast(ushort)(node*2));
            if (errRatio<tempErrRatio) errRatio=tempErrRatio; //error is
greater, adopt it
            //and then try the other child
            tempErrRatio=Calculate(rX, rY, aX, aY, cX, cY,
cast(ushort)(node*2+1));
            if (errRatio<tempErrRatio) errRatio=tempErrRatio; //error is
greater, adopt it
        }
        //TODO: this "if" may not need to be here: required for range check,
nothing else
        if (node<MaxDepth) cError[node]=errRatio; //store error ratio as we
descend on the tree
        return errRatio; //return this levels error ratio
    }

    ///Splits a TreeNode, used by Patch sub-class
    void split(inout TreeNode myNode)
    in
    {
        assert(myNode !is null, "Attempted to split a null node");
    }
    body
    {
        if (myNode.lChild !is null) return; //already split
        //Check to see if current triangle is diamond with bNeigh
        if ((myNode.bNeigh !is null)&&(myNode.bNeigh.bNeigh !is myNode))
        {
            split(myNode.bNeigh); //it has to be split, so that current
triangle can be a diamond with it's bNeigh
            assert(myNode.bNeigh.lChild !is null, "Split failed!");
        }

        //asserts that I am a diamond with my bNeigh, or I'm a border node
        assert ((myNode.bNeigh is null)||(myNode.bNeigh.bNeigh is myNode),
"Attempted to split a node that is not part of a diamond");

        myNode.lChild=newNode();
        myNode.rChild=newNode();
        //with (myNode) //in this block, all the relations of myNode are
updated
        {
            myNode.lChild.bNeigh=myNode.lNeigh;
myNode.lChild.lNeigh=myNode.rChild;
            myNode.rChild.bNeigh=myNode.rNeigh;
myNode.rChild.rNeigh=myNode.lChild;

            if (myNode.lNeigh !is null) //I have a left neigh
            {
                if (myNode.lNeigh.bNeigh is myNode)
myNode.lNeigh.bNeigh=myNode.lChild;
                else
                {
                    if (myNode.lNeigh.lNeigh is myNode)
myNode.lNeigh.lNeigh=myNode.lChild;
                    else if (myNode.lNeigh.rNeigh is myNode)
myNode.lNeigh.rNeigh=myNode.lChild;
                }
            }
            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at lNeigh update");

            //The following if block causes the children to become null
            if (myNode.rNeigh !is null) //I have a right neigh
            {
                if (myNode.rNeigh.bNeigh is myNode)
                {
                    assert(myNode.lChild !is null);
                    assert(myNode.rChild !is null);
                    assert(myNode.rNeigh.bNeigh !is null);
                    myNode.rNeigh.bNeigh=myNode.rChild; //This causes the
children (both) to die
                    assert(myNode.lChild !is null); //crash here
                    assert(myNode.rChild !is null);
                }
                else
                {
                    if (myNode.rNeigh.rNeigh is myNode)
myNode.rNeigh.rNeigh=myNode.rChild;
                    else if (myNode.rNeigh.lNeigh is myNode)
myNode.rNeigh.lNeigh=myNode.rChild;
                }
            }
            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at rNeigh update");

            if (myNode.bNeigh !is null) //I have a base neigh
            {
                if (myNode.bNeigh.lChild !is null) //My bNeigh is already split
                {
                    assert(myNode.bNeigh.rChild !is null, "bNeigh is only
partially split, cannot update relations.");
                    myNode.bNeigh.lChild.rNeigh=myNode.rChild;
                    myNode.bNeigh.rChild.lNeigh=myNode.lChild;
                    myNode.lChild.rNeigh=myNode.bNeigh.rChild;
                    myNode.rChild.lNeigh=myNode.bNeigh.lChild;
                }
                else split(myNode.bNeigh); //Split my base. He'll take care of
Neigh relations
            }
            else //I don't have bNeigh
            {
                myNode.lChild.rNeigh=null;
                myNode.rChild.lNeigh=null;
            }
            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at bNeigh update");
        } //updates to myNode are over
        assert((myNode.lChild !is null)&&(myNode.rChild !is null), "Node
children have been lost!");
        return;
    }

    void tesselate (TreeNode myNode, ushort lX, ushort lY, ushort rX, ushort
rY, ushort aX, ushort aY, ushort node)
    in
    {
        assert(myNode !is null, "Attempted to tesselate a null node");
    }
    body
    {
        //Calculate hipotenuse
        ushort cX=cast(ushort)((rX+lX)/2);
        ushort cY=cast(ushort)((rY+lY)/2);
        ushort cZ=heightAt(cX, cY);
        ulong
distance=(cX-camInfo.x)*(cX-camInfo.x)+(cY-camInfo.y)*(cY-camInfo.y)+(cZ-camInfo.z)*(cZ-camInfo.z);
        ulong threshold=cError[node]*cError[node];

        if ((threshold*detail)>distance) //should this triangle be split?
        {
            split(myNode); //won't fail because TreeNodes will not go out
            //I have children and they aren't too small,
            //TODO: Unnecessary check: split never fails: (myNode.lChild !is
null)&&(myNode.rChild !is null)&&
            if
((node<cast(ushort)(MaxDepth/2))&&((abs(lX-rX)>=2)||(abs(lY-rY)>=2)))
            {
                tesselate(myNode.lChild, aX, aY, lX, lY, cX, cY,
cast(ushort)(node*2));
                tesselate(myNode.rChild, rX, rY, aX, aY, cX, cY,
cast(ushort)(node*2+1));
            }
        }
    }

    const ushort maxH;
    float detail; ///Detail Threshold
    TreeNode nodes[]; ///Node pool
    size_t currNode; ///Current node being assigned
    const ushort sizeX, sizeY;
    const ubyte xPatch, yPatch;
    ushort hData[][]; ///The Height Data
    static ushort[MaxDepth] cError; //error buffer
    const ubyte HMult; ///Height multiplier, determines the resolution of the
terrain
    const Patch patches[][]; ///The pathes that compose the terrain.
}

void main()
{
        File este=new File("novomapa.raw", FileMode.In);
        Terrain terrain=new Terrain(este, 2500);
        delete este;
        std.stdio.writefln("Preparing for rendering...");
        terrain.update();

        delete terrain;
}


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190





------- Comment #1 from arkangath@gmail.com  2007-04-25 08:41 -------
Created an attachment (id=142)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=142&action=view)
This file contains the terrain height data

Unzip this file to the exe's directory.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190


arkangath@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|1.013                       |1.015




------- Comment #2 from arkangath@gmail.com  2007-06-06 11:22 -------
This bug still exists on version 1.15, in spite of the corrections made to the GC.


-- 

d-bugmail@puremagic.com wrote:
> http://d.puremagic.com/issues/show_bug.cgi?id=1190
> 
> 
> arkangath@gmail.com changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>             Version|1.013                       |1.015
> 
> 
> 
> 
> ------- Comment #2 from arkangath@gmail.com  2007-06-06 11:22 -------
> This bug still exists on version 1.15, in spite of the corrections made to the
> GC.
> 
> 

I think the version number is supposed to be set to the oldest version where the bug is known to exist.  This way, Walter will know where to begin looking for changes that might have caused the bug.

http://d.puremagic.com/issues/show_bug.cgi?id=1190





------- Comment #3 from bugzilla@digitalmars.com  2007-06-30 14:41 -------
I'd try:

1) removing the delete statements

-or-

2) disabling the gc

and see if either of those affect the results.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190





------- Comment #4 from arkangath@gmail.com  2007-07-01 17:38 -------
Tried that, didn't work. I also added a debug printf on the TreeNode destructor and it didn't get called.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190


deewiant@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|1.015                       |1.013




------- Comment #5 from deewiant@gmail.com  2007-08-31 12:26 -------
Please keep the version at the oldest possible: http://www.digitalmars.com/d/archives/digitalmars/D/bugs/bugzilla_usage_tips_10071.html


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190


davidl@126.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #6 from davidl@126.com  2007-09-04 03:10 -------
I've noticed that your code create something like :
myNode.rNeigh.bNeigh == myNode
So I assume it's your code fault, if you can't provide a smaller test case.

import std.string;
import std.stream;
import std.math;

alias std.string.toString strfy;
alias std.stdio.writefln Log;
int staticc;

private static const ubyte PatchSize=64; //must be power of 2
//const ubyte MAX_DEPTH=cast(ubyte)(2*sqrt(PatchSize)+1);
private static const MaxDepth=4;//17

private struct CamInfo
{
    uint x, y, z;
}

private CamInfo camInfo;

/**
The Terrain engine class.
*/
public final class Terrain
{
    ///The TreeNode class is used to store information about the patch tree
    private final class TreeNode
    {
        private TreeNode lChild, rChild, bNeigh, lNeigh, rNeigh;

        public this()
        {
            reset();
        }

        public void reset()
        {
            lChild=rChild=bNeigh=lNeigh=rNeigh=null;
        }
    }

    ///Patch Class. A terrain is composed of several patches
    private final class Patch
    {
        this (ushort x, ushort y)
        {
            this.x=x; this.y=y;
            visible=true;
            rNode=new TreeNode(); //these never get reassigned
            lNode=new TreeNode(); //they're const, remmember?
            assert(rNode !is null);
            assert(lNode !is null);
            //nodes come already clean
            rNode.bNeigh=lNode;
            lNode.bNeigh=rNode;
            calcError();
        }

        ///Resets the patch. It becomes undivided and ready for the next
tesselation.
        void reset()
        {
            rNode.reset();
            lNode.reset();
            rNode.bNeigh=lNode;
            lNode.bNeigh=rNode;
            //TODO: check visibility here
            visible=true;
        }

        ///Tesselates this patch and it becomes ready for rendering
        void update()
        {
            std.gc.disable();
            cError[]=lError;
            tesselate(lNode, x, cast(ushort)(y+PatchSize),
cast(ushort)(x+PatchSize), y, x, y, 1);
            cError[]=rError;
            tesselate(rNode, cast(ushort)(x+PatchSize), y, x,
cast(ushort)(y+PatchSize),
                cast(ushort)(x+PatchSize), cast(ushort)(y+PatchSize), 1);
            std.gc.enable();
        }

        ///This patch's error measure is updated from the data on hData.
        void calcError()
        {
            Calculate(x, cast(ushort)(y+PatchSize), cast(ushort)(x+PatchSize),
y, x, y, 1);
            lError[]=cError; //copy the error data
            Calculate(cast(ushort)(x+PatchSize), y, x,
cast(ushort)(y+PatchSize),
                cast(ushort)(x+PatchSize), cast(ushort)(y+PatchSize), 1);
            rError[]=cError;
            return;
        }

        ~this()
        {
            delete rNode;
            delete lNode;
        }

        //no need to protect this vars because this class won't be accessed
from the exterior
        const ushort x, y; //coordinates aren't expected to change
        bool visible; ///Result of lastest cull check
        ushort[MaxDepth] lError, rError;
        const TreeNode rNode, lNode;
    }

    public:
    this(in File file, float detail)
    in
    {
        assert(file !is null);
        assert(detail>=0); //negative error values make no sense. 0 values are
purely debugging technices
    }
    body
    {
        debug Log("Creating terrain object");
        this.detail=detail;
        file.read(sizeX);
        file.read(sizeY);
        assert((sizeX>0)&&(sizeY>0));
        HMult=1; //TODO: Replace with resolution from file
        hData=new ushort[][](sizeX, sizeY); //initialize data
        debug Log(" * Loading terrain data...");
        foreach (stripe; hData)
            foreach (inout vertex; stripe)
            {
                file.read(vertex);
                vertex*=HMult;
            }
        maxH=0; //Maximum height present on the map. Used somewhere in debug
code
        foreach (stripe; hData)
            foreach (vertex; stripe)
                if (vertex>maxH) maxH=vertex;
        xPatch=cast(ubyte)(sizeX/PatchSize);
        yPatch=cast(ubyte)(sizeY/PatchSize);
        nodes.length=(sizeX*sizeY/PatchSize);
        debug Log(" * Creating terrain nodes ("~strfy(nodes.length)~")...");
        foreach(inout node; nodes) node=new TreeNode;

        debug Log(" * Creating patches...");
        patches.length=xPatch;//how many columns will we have? Patch[col][row]
        foreach (size_t row, inout Patch[] strip; patches)
        {
            assert(strip.length==0, "Oups! Redefining a length of a strip");
            strip.length=yPatch; //How many rows?
            foreach (size_t col, inout Patch patch; strip)
                patch=new Patch(cast(ushort)(col*PatchSize),
cast(ushort)(row*PatchSize));
        }
        debug Log("Terrain creation complete");
    }

    public float heightAt(in float x, in float y)
    out(result)
    {
        assert((result>=0.0f)||(result==float.nan));
    }
    body
    {
        if ((x<0.0)||(y<0.0f)) return float.nan;
        //triangulate height at the given point
        return 0.0f;
    }

    ///Makes the terrain ready for rendering. Tesselates all the patches.
    void update()
    body
    {
        //reset the engine first
        currNode=0; //reset current node
        foreach (size_t row, inout Patch[] strip; patches)
            foreach (size_t col, inout Patch patch; strip)
            {
                patch.reset(); //Recalculate the visibility flag
                if (patch.visible) //bail on non-visible patches
                {
                    if (col>0) patch.lNode.lNeigh=patches[col-1][row].rNode;
                    else patch.lNode.lNeigh=null;
                    if (col<(xPatch-1))
patch.rNode.lNeigh=patches[col+1][row].lNode;
                    else patch.rNode.lNeigh=null;
                    if (row>0) patch.lNode.rNeigh=patches[col][row-1].rNode;
                    else patch.lNode.rNeigh=null;
                    if (row<(yPatch-1))
patch.rNode.rNeigh=patches[col][row+1].lNode;
                    else patch.rNode.rNeigh=null;
                }
            }
        //Unfloatize camera information. Remember the case in which the coords
are <0
        foreach (Patch[] strip; patches)
            foreach (Patch patch; strip)
                if (patch.visible) patch.update();
        return;
    }

    ~this()
    {
        /*Since the terrain is the last thing to be deleted when a game is
over, a gc.fullCollect()
        will be preformed sometime soon, so it is not necessary to clean up
manually*/
        foreach (inout stripe; hData)
        {
            stripe.length=0; delete stripe;
        }
        hData.length=0;
        foreach (inout Patch[] strip; patches)
            foreach (inout Patch patch; strip)
                delete patch;
        foreach(inout node; nodes) delete node;
        nodes.length=0;
    }

    private:
    ///Returns the next available TreeNode. Creates a new one if there are no
more available.
    TreeNode newNode()
    out(result)
    {
        assert(result !is null, "newNode() attempted to return a null
TreeNode.");
    }
    body
    {
        assert(currNode<=nodes.length, "currNode advanced too much");
        if (currNode==nodes.length)
        {
            nodes~=new TreeNode; //no more nodes available, create another one
            debug Log("Insufficient TreeNodes for current tesselation
(detail="~strfy(detail)~"). Increasing TreeNode pool
(currNode="~strfy(currNode)~").");
        }
        TreeNode ret=nodes[currNode]; //get a new node
        ret.reset(); //clear new node's affiliations
        currNode++;
        return ret;
    }

    ///To be used by functions of the class, returns raw height value.
    ushort heightAt(ushort x, ushort y)
    {
        if ((x==sizeX)||(y==sizeY)) return 0; //Out of bounds values are not
drawn (taken has void in game)
        assert(x<sizeX, "Out of bounds value requested");
        assert(y<sizeY, "Out of bounds value requested");
        return hData[x][y];
    }

    ushort Calculate(ushort lX, ushort lY, ushort rX, ushort rY, ushort aX,
ushort aY, ushort node)
    {
        //Calculate hipotenuse
        ushort cX=cast(ushort)((rX+lX)/2);
        ushort cY=cast(ushort)((rY+lY)/2);
        ushort cZ=heightAt(cX, cY);
        ushort rZ=heightAt(rX, rY);
        ushort lZ=heightAt(lX, lY);
        ushort errRatio=cast(ushort)abs(cZ-((lZ+rZ)/2)); //this iteraction's
primary error ratio
        if (errRatio==0) return 0; //reached perfectness
        if ((abs((rX-lX))>=2)||(abs(rY-lY))>=2) //smaller than 2x2
        {
            //calculate the error of one of the child triangles
            ushort tempErrRatio=Calculate(aX, aY, lX, lY, cX, cY,
cast(ushort)(node*2));
            if (errRatio<tempErrRatio) errRatio=tempErrRatio; //error is
greater, adopt it
            //and then try the other child
            tempErrRatio=Calculate(rX, rY, aX, aY, cX, cY,
cast(ushort)(node*2+1));
            if (errRatio<tempErrRatio) errRatio=tempErrRatio; //error is
greater, adopt it
        }
        //TODO: this "if" may not need to be here: required for range check,
nothing else
        if (node<MaxDepth) cError[node]=errRatio; //store error ratio as we
descend on the tree
        return errRatio; //return this levels error ratio
    }

    ///Splits a TreeNode, used by Patch sub-class
    void split(inout TreeNode myNode)
    in
    {
                if (myNode.rNeigh !is null)
                assert(myNode.rNeigh.bNeigh !is myNode);
        assert(myNode !is null, "Attempted to split a null node");
    }
    body
    {
        if (myNode.lChild !is null) return; //already split
        //Check to see if current triangle is diamond with bNeigh
        if ((myNode.bNeigh !is null)&&(myNode.bNeigh.bNeigh !is myNode))
        {
            split(myNode.bNeigh); //it has to be split, so that current
triangle can be a diamond with it's bNeigh
            assert(myNode.bNeigh.lChild !is null, "Split failed!");
        }

        //asserts that I am a diamond with my bNeigh, or I'm a border node
        assert ((myNode.bNeigh is null)||(myNode.bNeigh.bNeigh is myNode),
"Attempted to split a node that is not part of a diamond");

        myNode.lChild=newNode();
        myNode.rChild=newNode();
        //with (myNode) //in this block, all the relations of myNode are
updated
        {
            myNode.lChild.bNeigh=myNode.lNeigh;
myNode.lChild.lNeigh=myNode.rChild;
            myNode.rChild.bNeigh=myNode.rNeigh;
myNode.rChild.rNeigh=myNode.lChild;

            if (myNode.lNeigh !is null) //I have a left neigh
            {
                if (myNode.lNeigh.bNeigh is myNode)
myNode.lNeigh.bNeigh=myNode.lChild;
                else
                {
                    if (myNode.lNeigh.lNeigh is myNode)
myNode.lNeigh.lNeigh=myNode.lChild;
                    else if (myNode.lNeigh.rNeigh is myNode)
myNode.lNeigh.rNeigh=myNode.lChild;
                }
            }

            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at lNeigh update");

            //The following if block causes the children to become null
            if (myNode.rNeigh !is null) //I have a right neigh
            {
                if (myNode.rNeigh.bNeigh is myNode)
                {
                    assert(myNode.lChild !is null);
                    assert(myNode.rChild !is null);
                    assert(myNode.rNeigh.bNeigh !is null);
                                        assert(myNode.rNeigh.bNeigh !is
myNode);
                        myNode.rNeigh.bNeigh=myNode.rChild; //This causes the
children (both) to die
                                        assert(myNode.lChild !is
myNode.rNeigh.bNeigh);
                    assert(myNode.lChild !is null); //crash here
                    assert(myNode.rChild !is null);
                }
                else
                {
                    if (myNode.rNeigh.rNeigh is myNode)
myNode.rNeigh.rNeigh=myNode.rChild;
                    else if (myNode.rNeigh.lNeigh is myNode)
myNode.rNeigh.lNeigh=myNode.rChild;
                }
            }
            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at rNeigh update");

            if (myNode.bNeigh !is null) //I have a base neigh
            {
                if (myNode.bNeigh.lChild !is null) //My bNeigh is already split
                {
                    assert(myNode.bNeigh.rChild !is null, "bNeigh is only
partially split, cannot update relations.");
                    myNode.bNeigh.lChild.rNeigh=myNode.rChild;
                    myNode.bNeigh.rChild.lNeigh=myNode.lChild;
                    myNode.lChild.rNeigh=myNode.bNeigh.rChild;
                    myNode.rChild.lNeigh=myNode.bNeigh.lChild;
                }
                else split(myNode.bNeigh); //Split my base. He'll take care of
Neigh relations
            }
            else //I don't have bNeigh
            {
                myNode.lChild.rNeigh=null;
                myNode.rChild.lNeigh=null;
            }
            assert((myNode.lChild !is null)&&(myNode.rChild !is null),
"Children died at bNeigh update");
        } //updates to myNode are over
        assert((myNode.lChild !is null)&&(myNode.rChild !is null), "Node
children have been lost!");
        return;
    }

    void tesselate (TreeNode myNode, ushort lX, ushort lY, ushort rX, ushort
rY, ushort aX, ushort aY, ushort node)
    in
    {
                if (myNode.rNeigh !is null)
                assert(myNode.rNeigh.bNeigh !is myNode);
        assert(myNode !is null, "Attempted to tesselate a null node");
    }
    body
    {
        //Calculate hipotenuse
        ushort cX=cast(ushort)((rX+lX)/2);
        ushort cY=cast(ushort)((rY+lY)/2);
        ushort cZ=heightAt(cX, cY);
        ulong
distance=(cX-camInfo.x)*(cX-camInfo.x)+(cY-camInfo.y)*(cY-camInfo.y)+(cZ-camInfo.z)*(cZ-camInfo.z);
        ulong threshold=cError[node]*cError[node];

        if ((threshold*detail)>distance) //should this triangle be split?
        {
            split(myNode); //won't fail because TreeNodes will not go out
            //I have children and they aren't too small,
            //TODO: Unnecessary check: split never fails: (myNode.lChild !is
null)&&(myNode.rChild !is null)&&
            if
((node<cast(ushort)(MaxDepth/2))&&((abs(lX-rX)>=2)||(abs(lY-rY)>=2)))
            {
                tesselate(myNode.lChild, aX, aY, lX, lY, cX, cY,
cast(ushort)(node*2));
                tesselate(myNode.rChild, rX, rY, aX, aY, cX, cY,
cast(ushort)(node*2+1));
            }
        }
    }

    const ushort maxH;
    float detail; ///Detail Threshold
    TreeNode nodes[]; ///Node pool
    size_t currNode; ///Current node being assigned
    const ushort sizeX, sizeY;
    const ubyte xPatch, yPatch;
    ushort hData[][]; ///The Height Data
    static ushort[MaxDepth] cError; //error buffer
    const ubyte HMult; ///Height multiplier, determines the resolution of the
terrain
    const Patch patches[][]; ///The pathes that compose the terrain.
}

void main()
{
        File este=new File("novomapa.raw", FileMode.In);
        Terrain terrain=new Terrain(este, 2500);
        delete este;
        std.stdio.writefln("Preparing for rendering...");
        terrain.update();

        delete terrain;
}


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190


arkangath@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |




------- Comment #7 from arkangath@gmail.com  2007-09-04 07:43 -------
(In reply to comment #6)
> I've noticed that your code create something like :
> myNode.rNeigh.bNeigh == myNode
> So I assume it's your code fault, if you can't provide a smaller test case.

There is no such comparison on the code. All comparisons between nodes are made
with the "is" keyword. No "==" comparisons are performed on references and you
can confirm by searching all "==" on the code.
And as I said on the main post, I have tracked the problem to a single line
(marked in the source as "//This causes the
children (both) to die"). Decompilation of the source lines gives out

terrain.d:334                 assert(myNode.rChild !is null);
00403402: 8b5d08                  mov ebx, [ebp+0x8]
00403405: 8b0b                    mov ecx, [ebx]
00403407: 83790c00                cmp dword [ecx+0xc], 0x0
0040340b: 750a                    jnz 0x403417  MFKC7terrain7Terrain8TreeNodeZv
terrain.Terrain.split terrain.d:336

0040340d: b84e010000              mov eax, 0x14e
00403412: e849040000              call 0x403860 void terrain.__assert(int)
terrain.d:423
terrain.d:336                 myNode.rNeigh.bNeigh=myNode.rChild;
00403417: 8b13                    mov edx, [ebx]
00403419: 8b720c                  mov esi, [edx+0xc]
0040341c: 8b7a18                  mov edi, [edx+0x18]
0040341f: 897710                  mov [edi+0x10], esi
terrain.d:337                 assert(myNode.rChild !is null);
00403422: 8b0b                    mov ecx, [ebx]
00403424: 83790c00                cmp dword [ecx+0xc], 0x0
00403428: 750a                    jnz 0x403434  MFKC7terrain7Terrain8TreeNodeZv
terrain.Terrain.split terrain.d:337

0040342a: b851010000              mov eax, 0x151
0040342f: e82c040000              call 0x403860 void terrain.__assert(int)
terrain.d:423
00403434: eb3c                    jmp 0x403472  MFKC7terrain7Terrain8TreeNodeZv
terrain.Terrain.split terrain.d:342

terrain.d:339             else if (myNode.rNeigh.rNeigh is myNode)
myNode.rNeigh.rNeigh=myNode.rChild;
00403436: 8b5508                  mov edx, [ebp+0x8]
00403439: 8b1a                    mov ebx, [edx]
0040343b: 8b7318                  mov esi, [ebx+0x18]
0040343e: 8b4e18                  mov ecx, [esi+0x18]
00403441: 3bcb                    cmp ecx, ebx
00403443: 7510                    jnz 0x403455  MFKC7terrain7Terrain8TreeNodeZv
terrain.Terrain.split terrain.d:340

00403445: 8b4508                  mov eax, [ebp+0x8]
00403448: 8b10                    mov edx, [eax]
0040344a: 8b5a0c                  mov ebx, [edx+0xc]
0040344d: 8b7218                  mov esi, [edx+0x18]
00403450: 895e18                  mov [esi+0x18], ebx
00403453: eb1d                    jmp 0x403472  MFKC7terrain7Terrain8TreeNodeZv
terrain.Terrain.split terrain.d:342

You can confirm the code with ddbg.
The problem isn't with my code, as I have said on the original post, the code
was copied from my functional implementation on C (which I can provide if
necessary) and I have confimed that EVERY LINE was been correctly ported. A
single "copy" operation is cause two references to become null, references
which are only read, not written to, on the faulty operation.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1190





------- Comment #8 from wbaxter@gmail.com  2007-09-04 11:43 -------
This seems to be a bad interaction between inout parameters and a tangly web of pointers.  In your case, I don't think you need to pass the TreeNode by reference (inout) to split, because nowhere in that function is the parameter assigned to directly.  So I think just removing "inout" on that function will fix your problem.  (I got another error after removing it, but it got past the trouble spot).

But this still may be a bug.
You've got a graph like this basically:

                   bNeigh----->
    null<---rNeigh[root]      [tree]bNeigh---> null
                       <------rNeigh

and you pass in root.bNeigh by reference, then you try to set tree.rNeigh.bNeigh, which is the same as tree.

I'll attach a simplified test case.


--