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aa wire box neat tricks?


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#1 fir   Members   

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Posted 15 June 2014 - 09:36 AM

im often a little upset writing this thing (all this + - (or +0) combinations to set a 12 line segmants to draw a box)  but i from time to time do that

void DrawAAWireBox3d(float x, float y, float z, float h, unsigned colr)
{
 
 DrawLine3d(x-h,y-h,z-h,   x+h,y-h,z-h,   colr);
 DrawLine3d(x+h,y-h,z-h,   x+h,y+h,z-h,   colr);
 DrawLine3d(x+h,y+h,z-h,   x-h,y+h,z-h,   colr);
 DrawLine3d(x-h,y+h,z-h,   x-h,y-h,z-h,   colr);
 
 DrawLine3d(x-h,y-h,z+h,   x+h,y-h,z+h,   colr);
 DrawLine3d(x+h,y-h,z+h,   x+h,y+h,z+h,   colr);
 DrawLine3d(x+h,y+h,z+h,   x-h,y+h,z+h,   colr);
 DrawLine3d(x-h,y+h,z+h,   x-h,y-h,z+h,   colr);
 
 DrawLine3d(x-h,y-h,z-h,   x-h,y-h,z+h,   colr);
 DrawLine3d(x+h,y-h,z-h,   x+h,y-h,z+h,   colr);
 DrawLine3d(x+h,y+h,z-h,   x+h,y+h,z+h,   colr);
 DrawLine3d(x-h,y+h,z-h,   x-h,y+h,z+h,   colr);
 
}

are there maybe some neat tricks that would help to wrote this quickier or make shorter code here?
also could some one improve it stylistically?

Edited by fir, 15 June 2014 - 10:01 AM.


#2   Members   

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Posted 15 June 2014 - 09:55 AM

To improve it stylistically, you could consider editing your post to use the forum code tags. 


“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”


#3 fir   Members   

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Posted 15 June 2014 - 09:57 AM

To improve it stylistically, you could consider editing your post to use the forum code tags. 

i did it and it ate second part of the text - still present bug

 

Other question is that this code colorisation here is ugly, sometimes it looks worse than black font



#4   Members   

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Posted 15 June 2014 - 10:39 AM

You can imagine a box as a min and max vector in some space, and the edges of the box are the lines between any two verts that differ in only one axis. Not sure you'll think this is much of an improvement, but it's an alternative nonetheless.

void DrawAAWireBox3d(float x, float y, float z, float h, unsigned colr)
{
    Vector3 min(x-h, y-h, z-h);
    Vector3 max(x+h, y+h, z+h);

    for (int i = 0; i < 8; i++) {
        for (int j = i + 1; j < 8; j++) {
            int diff = i ^ j; // determine number of axes these verts differ in
            if (NumberOfBitsSet(diff) == 1) { // if it's only one axis then draw a line
                Vector3 a((i & 1) ? max.x, min.x,
                          (i & 2) ? max.y, min.y,
                          (i & 4) ? max.z, min.z);
                Vector3 b((j & 1) ? max.x, min.x,
                          (j & 2) ? max.y, min.y,
                          (j & 4) ? max.z, min.z);

                DrawLine3d(a.x, a.y, a.z, b.x, b.y, b.z, colr);
            }
        }
    }
}


#5   Prime Members   

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Posted 15 June 2014 - 11:23 AM

 It's this sort of thing that makes me wish there were a GL_LINE_FAN primitive type in OpenGL



#6 fir   Members   

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Posted 15 June 2014 - 11:41 AM

 

You can imagine a box as a min and max vector in some space, and the edges of the box are the lines between any two verts that differ in only one axis. Not sure you'll think this is much of an improvement, but it's an alternative nonetheless.

void DrawAAWireBox3d(float x, float y, float z, float h, unsigned colr)
{
    Vector3 min(x-h, y-h, z-h);
    Vector3 max(x+h, y+h, z+h);

    for (int i = 0; i < 8; i++) {
        for (int j = i + 1; j < 8; j++) {
            int diff = i ^ j; // determine number of axes these verts differ in
            if (NumberOfBitsSet(diff) == 1) { // if it's only one axis then draw a line
                Vector3 a((i & 1) ? max.x, min.x,
                          (i & 2) ? max.y, min.y,
                          (i & 4) ? max.z, min.z);
                Vector3 b((j & 1) ? max.x, min.x,
                          (j & 2) ? max.y, min.y,
                          (j & 4) ? max.z, min.z);

                DrawLine3d(a.x, a.y, a.z, b.x, b.y, b.z, colr);
            }
        }
    }
}

huh, this is strange :U though at leas something (bit hard tu understand for me) - maybe something simpler? it seem that there should be something simpler



#7 fir   Members   

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Posted 15 June 2014 - 11:48 AM

 It's this sort of thing that makes me wish there were a GL_LINE_FAN primitive type in OpenGL

if this would be about line segments it wouldnt called a fan i think ;\

though this is good idea, define array of 8 vertices, then do some for loop that would draw a pairs of it

 

table[8] = {000,001,011,010, ...}

 

nay it wouldnt strictly work, as wirebox canot be construct this way without reapiting....


Edited by fir, 15 June 2014 - 11:48 AM.


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Posted 15 June 2014 - 12:07 PM

You basically need a list of the edges and then loop over them to render lines.

 

You could abstract this into a some sort of generic "geometry class" that describes a shape (box, pyramid, whatever else you have) and can give you:

-List of vertices

-List of edges (index to start and index to end vertex)

-List of surfaces

etc.

 

If using C++ I would make one class for each shape and then use templates to make a wiremesh renderer that can draw any shape (basically compile time polymorphism, you dont probably like runtime overhead...):

template T
void drawGenericShape(T shape)
{
    for each edge in shape.getEdges() do
    {
        drawLine(shape.getVertex(edge.A),shape.getVertex(edge.B))
    }
}

However, to create the specific shape class to represent a box, I would still just manually hardcode the vertices. This is because unless you want it to support 2 and 4 dimensional boxes too, its not really a useful target for a generalization. And youll have to use a different approach for every type of shape anyways. So yeah, I would just make an array of vertices and an array of edges and an array of surfaces.


o3o


#9 fir   Members   

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Posted 15 June 2014 - 12:27 PM

You basically need a list of the edges and then loop over them to render lines.

 

You could abstract this into a some sort of generic "geometry class" that describes a shape (box, pyramid, whatever else you have) and can give you:

-List of vertices

-List of edges (index to start and index to end vertex)

-List of surfaces

etc.

 

If using C++ I would make one class for each shape and then use templates to make a wiremesh renderer that can draw any shape (basically compile time polymorphism, you dont probably like runtime overhead...):

template T
void drawGenericShape(T shape)
{
    for each edge in shape.getEdges() do
    {
        drawLine(shape.getVertex(edge.A),shape.getVertex(edge.B))
    }
}

However, to create the specific shape class to represent a box, I would still just manually hardcode the vertices. This is because unless you want it to support 2 and 4 dimensional boxes too, its not really a useful target for a generalization. And youll have to use a different approach for every type of shape anyways. So yeah, I would just make an array of vertices and an array of edges and an array of surfaces.

 

iterating on array by for (than hardkoding 12 callls is good, but feeling it with hand returns us almost back to the first problem - There would be for example some need for formula to make up this array instead of feeling it by hand (those feeling it with hand is most troublesome,

copy and paste calls is easy)






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