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[solved] Might be a bug for terrain block info building?

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doublue

Post subject: [solved] Might be a bug for terrain block info building?

Posted: 16.04.2008, 05:13

Joined: 16.04.2008, 04:44
Posts: 2
Location: Taiwan

Sources excerpted from terrain.cpp:

Code:

            Vec3f corner0( minU + u * stepU, 0, minV + v * stepV);
            Vec3f corner1( minU + u * stepU, 0, minV + (v + 1) * stepV);
            Vec3f corner2( minU + (u + 1) * stepU, 0, minV + v * stepV);
            Vec3f corner3( minU + (u + 1) * stepU, 0, minV + (v + 1) * stepV);


            ......
            
            Plane tri0( corner0, corner1, corner2 );
            Plane tri1( corner1, corner2, corner3 );

            for( float vv = 0; vv <= stepV; vv += pixelStep )
            {
               for( float uu = 0; uu <= stepU; uu += pixelStep )
               {
                  Plane &curTri = uu <= vv ? tri0 : tri1;

Assume (0,0) to be the left-top corner (or any), as follows:

V0 -------V2
| Tri0 / |
| / |
| / Tri1|
V1--------V3

IMHO for statement curTri = tri0 iff uu <= vv to be true, the tri0 should be (V0, V1, V3) and tri1 (V0, V2, V3). Otherwise different rule for deciding curTri needed.

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Volker

Post subject: Re: Might be a bug for terrain block info building?

Posted: 16.04.2008, 11:39

Tool Developer

Joined: 13.11.2007, 11:07
Posts: 1150
Location: Germany

I've not checked it in detail, but it seems to me that it does not make any difference. But I've found another problem in the terrain rendering.
I can't remember why we had the following statement in the drawTerrainBlock method in terrain.cpp

Code:

float newU = (s * scale + minU) * (terrain->_hmapSize - 1) + 0.4f;
float newV = (t * scale + minV) * (terrain->_hmapSize - 1) + 0.4f;

With this code, the rendering seems not to match with the blockInfo used for the frustum culling (You can check this setting the camera position to x = 278.97134, y = 62.080597, and z = 425.14410 and by adding the following line
to drawTerrainBlock method after the glDrawElements call)

Code:

Modules::renderer().drawDebugAABB(bb.getMinCoords(), bb.getMaxCoords(), true);

If you change it to...

Code:

float newU = (s * scale + minU) * (terrain->_hmapSize - 1) + 0.5f;
float newV = (t * scale + minV) * (terrain->_hmapSize - 1) + 0.5f;

...everything seems to be fine in the terrain example. Maybe someone else can check this. During a quick check it solves the still existing frustum culling problems also mentioned in this thread

Edit: To use the drawDebugAABB method correctly you should insert the following line after the if( saveStates ) statement:

Code:

glUseProgram( shader );

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