Libgdx ModelBuilder.createRect only visible from one side

问题

In my first libgdx 3D game i now switched from createBox to createRect, to create only the visible faces (if a wall is on the left side of another wall, its right face is not visible...). I am creating 4 models:

frontFace
backFace
rightFace
leftFace

They are almost drawn how they actually should. But there is one big issue: The side faces are only visible if i look in the positive z-Direction. If i look the other side (negative z-Direction), they don't draw. The front and back faces only draw, if i look to them in negative x-Direction. Has this something to do with the normals? I have set them to:

normal.x = 0;
normal.y = 1;
normal.z = 0;

Is that the error? How should i set the normals? What do they stand for? I have some basic idea about normal mapping for lighting, is that the same?

Important note: I have disabled backface culling, but it did not make any difference. View frustum culling is turned on. If any more informations are needed please post a comment and i will add them as soon as possible. Thanks

回答1:

Perhaps not directly related, but still important to note: don't use createRect or createBox for anything other than debugging/testing. Instead combine multiple shapes into a single model/node/part. Or even better, use a modeling application where possible.

You didn't specify how you disabled backface culling. But keep in mind that you should not change the opengl state outside the shader/rendercontext (doing so will result in unpredicted behavior). To disable backface culling you can either specify it using the material attribute IntAttribute.CullFace (see: https://github.com/libgdx/libgdx/wiki/Material-and-environment#wiki-intattribute), the DefaultShader (or default ModelBatch) Config defaultCullFace member (see http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/graphics/g3d/shaders/DefaultShader.Config.html#defaultCullFace) or the (deprecated) static DefaultShader#defaultCullFace member (see http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/graphics/g3d/shaders/DefaultShader.html#defaultCullFace).

Whether a face is front or back is based on the vertex winding. Or in other words: the order in which you provide the corners of the rectangle is used to decide which side is front and which side is back. If you use one of the rect methods, you'll notice the arguments have either the 00, 01, 10 or 11 suffix. Here, when looking at the face, 00 is lower-left, 01 upper-left, 11 is upper-right and 10 is lower-right.

For a rectangle, it's normal is the perpendicular facing outwards the rectangle. For example if you have a rectangle on XZ plane with it front face on the top, then its normal is X=0,Y=1,Z=0. If its front face it facing the bottom, then its normal is X=0,Y=-1,Z=0. Likewise if you have a rectangle on XY plane, its normal is either X=0,Y=0,Z=1 or X=0,Y=0,Z=-1. Note that the normal is not used for face culling, it's most commonly used for lighting etc. Specifying an incorrect/opposite normal will not cause the face to be culled (it might cause incorrect/black lighting though).

回答2:

For your purpose I'd recommend you to use Decal class. Decals are bitmap sprites that exist in a 3D scene. This article is about using of decals in LibGDX. I hope it is what you wanted.

来源：https://stackoverflow.com/questions/22089088/libgdx-modelbuilder-createrect-only-visible-from-one-side

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java

libgdx

culling