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Blender to Directx exporter... works, but i think its too hacky


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#1 NightcrawlerEX   Members   -  Reputation: 108

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Posted 25 January 2013 - 09:18 AM

Hi all,

 

I have been working on a simple model exporter and have been having proplems with my UV coordinates.

 

When i exported from blender a textured cube the texture would not map properly. After a small search I realised that this was beacuse blender stores UV coordinates in relation to the the origin being at the bottom left and directx uses the top left. I then edited my exporter by changing...


V = V

 

to

 

V = 1 - V

 

This sort of worked but it ended up with the textures being displayed backwards....

 

001.png

 

 

 

I then started reading through a directx exporter I found that it used some code to turn triangles backward (vertindex = vertindex[::-1])

e.g.

vert1 = 3 

vert2 = 2

vert3 = 1

 

so I gave that a try to see how it affected everything and it yeilded this result...

 

002.png

 

so I changed the rasterizer settings to cull the front of triangles and display the back...

 

003.png

 

This worked!

But I can't help feeling that this is the wrong way to do things.

 

Am I missing a more simple, less hacky way to do things here?

 

does it by chance have anything to do with the fact that blender uses different XYZ coordinates to directx

[Blender]

X = left/right

Y = forward/back

Z = up/down

 

[DirectX]

X = left/right

Y = up/down

Z = foward/back

 

 

Any help would be greatly appreciated, I think it is something I am doing wrong beacuse anything I have read so far on this topic has ended with the answer simply being to invert the V coord. This does not work for me so I assume that I am doing something fundementally wrong

 

btw here is my texture...

 

004.png



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#2 Zaoshi Kaba   Crossbones+   -  Reputation: 4111

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Posted 25 January 2013 - 10:10 AM

Have you tried U = 1-U? You mirrored UVs vertically, why not to do same for other axis?

Edited by Zaoshi Kaba, 25 January 2013 - 10:10 AM.


#3 eppo   Crossbones+   -  Reputation: 2367

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Posted 25 January 2013 - 01:40 PM

does it by chance have anything to do with the fact that blender uses different XYZ coordinates to directx


Yes, it does. In your importer you can transform all vertices by a matrix that translates vertices between coordinate systems.

Positions need to be rotated 90 degrees around the x-axis, and mirrored/scaled along the z-axis (depending on whether you use a left- or right handed coordinate system).

Matrix xfrm = MatrixRotationAxis(X_AXIS, PI * 0.5) * MatrixScaling(Vec3(1.0, 1.0, -1.0)).

You can then use that matrix to transform other vertex components (like normals) as well.

For UVs, '1.0f - V' will work.

Edited by eppo, 25 January 2013 - 01:54 PM.


#4 NightcrawlerEX   Members   -  Reputation: 108

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Posted 28 January 2013 - 05:40 AM

Positions need to be rotated 90 degrees around the x-axis, and mirrored/scaled along the z-axis (depending on whether you use a left- or right handed coordinate system).

 

Thanks, that was indeed my problem. All I had to do was create the rotation/scale matrix and apply it to all the vertices on export and also turn my indices for each triangle backward






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