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POproblem with quadTree & union
 

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  1. POproblem with quadTree & union
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    <p>i have the following quadtree-like structure, in which each cell can either be a inner node or a leaf. if it is a leaf, it can store a color. if it is a inner node, it stores pointers to four children (which can be either leaf or inner node):</p> <pre><code>class RenderBucketCell{ public: RenderBucketCell(); RenderBucketCell(float R, float G, float B, float A, unsigned short X, unsigned short Y); ~RenderBucketCell(); void split(); void collapse(); bool isLeaf; RenderBucketCell* neighbours[8]; unsigned short x; unsigned short y; union{ struct{ float r; float g; float b; float a; }; struct{ RenderBucketCell* children[4]; }; }; }; </code></pre> <p>if the cell is is an inner node, then it doesn't need to store a color. if it's a leaf, then it doesn't need to store pointers to children. therefore the color and the children shall share the same memory (union)</p> <p>there is the function split() which transforms a leaf into a inner node and creates for children (leafs) with the same color the current cell has at the moment:</p> <pre><code>void RenderBucketCell::split(){ isLeaf=false; float rt = r;//make backups of the values before setting the children (union) float gt = g; float bt = b; float at = a; unsigned short xt2 = x*2; unsigned short yt2 = y*2; children[0] = new RenderBucketCell(rt,gt,bt,at, xt2, yt2); children[1] = new RenderBucketCell(rt,gt,bt,at, xt2+1, yt2); children[2] = new RenderBucketCell(rt,gt,bt,at, xt2, yt2+1); children[3] = new RenderBucketCell(rt,gt,bt,at, xt2+1, yt2+1); } </code></pre> <p>now i'm debugging the function split(). i set a debug point on the line</p> <pre><code>children[0] = new RenderBucketCell(rt,gt,bt,at, xt2, yt2); </code></pre> <p>so now: the debugger stops at this line and i observe the membervalues. i do a procedurestep, such that the line gets executed (the instruction cursor is now on the next line). After the line has been executed, the pointervalue of children[0] is still the same! instead, the pointervalue of children[2] has changed (along with the float value b)</p> <p>can someone explain me this behaviour?? what am i doing wrong?</p> <p>Thanks!</p>
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    1. USMat
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    1. COIs there any possibility that the `RenderBucketCell` constructor may be calling `split()`? (I assume not, but it's best to check.)
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      1. USdave4420
    2. COhey Dave no - the constructor just sets default values for the fields r, g, b, a, isLeaf, neighbours[8], x and y
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      1. USMat
    3. COAt this point, it's worth asking what compiler and debugger you are using, as your code looks OK. Is split() implemented in a separate file from the rest of RenderBucketCell? It seems it's using different settings for the size of ints/pointers or for alignment.
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      1. USJoh
 

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