第二人生的源码分析 12 天空显示的实现

Posted 2021-02-07 skiwnchh

在虚拟世界里，自然现象的实现是最需要实现的，比如天空的实现，以便反映是白天还是晚上，这样才逼真反映现实世界。在第二人生里实现的天空，还是比较好的，如下图所示：

蔡军生 2008/01/10 QQ:9073204 深圳

从上面的图片里，可以看到太阳在远处，并具有雾化的效果，这是早上太阳升起的效果。看到远处是浅蓝色的天空，与海边连接成一体。在室外场境的模拟中，最重要的就是天空体的实现。目前实现天空体有两种不同的实现方式：天体盒和天空穹。而第二人生里是采用天空盒的实现方式，这种方式是渲染的速度比较快，但纹理需要特别处理，才让人们看到的所有地方一样远的感觉。跟实现地面是一样的，都是使用网格和纹理来实现。下面就来通过代码仔细地分析怎么创建天空盒的网格，以及纹理的坐标设置。

 

#001 

#002 BOOL LLVOSky::updateGeometry(LLDrawable *drawable)

#003 {

#004      if (mFace[FACE_REFLECTION] == NULL)

#005      {

#006             LLDrawPoolWater *poolp = (LLDrawPoolWater*) gPipeline.getPool(LLDrawPool::POOL_WATER);

#007             mFace[FACE_REFLECTION] = drawable->addFace(poolp, NULL);

#008      }

创建反射表面。

 

#009 

#010      mCameraPosAgent = drawable->getPositionAgent();

#011      mEarthCenter.mV[0] = mCameraPosAgent.mV[0];

#012      mEarthCenter.mV[1] = mCameraPosAgent.mV[1];

#013 

#014      LLVector3 v_agent[8];

#015      for (S32 i = 0; i < 8; ++i)

#016      {

#017              F32 x_sgn = (i&1) ? 1.f : -1.f;

#018              F32 y_sgn = (i&2) ? 1.f : -1.f;

#019              F32 z_sgn = (i&4) ? 1.f : -1.f;

#020             v_agent[i] = HORIZON_DIST*0.25f * LLVector3(x_sgn, y_sgn, z_sgn);

#021      }

#022 

#023      LLStrider<LLVector3> verticesp;

#024      LLStrider<LLVector3> normalsp;

#025      LLStrider<LLVector2> texCoordsp;

#026      LLStrider<U32> indicesp;

#027      S32 index_offset;

#028      LLFace *face;     

#029 

 

下面开始创建天空盒的6个平面。

#030      for (S32 side = 0; side < 6; ++side)

#031      {

#032             face = mFace[FACE_SIDE0 + side];

#033 

#034             if (face->mVertexBuffer.isNull())

#035             {

#036                    face->setSize(4, 6);

设置每个表面有4个顶点构成，共有6个索引顶点。

 

#037                    face->setGeomIndex(0);

#038                    face->setIndicesIndex(0);

#039                    face->mVertexBuffer = new LLVertexBuffer(LLDrawPoolSky::VERTEX_DATA_MASK, GL_STREAM_DRAW_ARB);

#040                    face->mVertexBuffer->allocateBuffer(4, 6, TRUE);

上面分配顶点缓冲区和索引缓冲区。

 

#041                   

#042                    index_offset = face->getGeometry(verticesp,normalsp,texCoordsp, indicesp);

#043                   

#044                    S32 vtx = 0;

#045                    S32 curr_bit = side >> 1; // 0/1 = Z axis, 2/3 = Y, 4/5 = X

#046                    S32 side_dir = side & 1; // even - 0, odd - 1

#047                    S32 i_bit = (curr_bit + 2) % 3;

#048                    S32 j_bit = (i_bit + 2) % 3;

#049 

#050                    LLVector3 axis;

#051                    axis.mV[curr_bit] = 1;

#052                    face->mCenterAgent = (F32)((side_dir << 1) - 1) * axis * HORIZON_DIST;

#053 

#054                    vtx = side_dir << curr_bit;

#055                    *(verticesp++) = v_agent[vtx];

#056                    *(verticesp++) = v_agent[vtx | 1 << j_bit];

#057                    *(verticesp++) = v_agent[vtx | 1 << i_bit];

#058                    *(verticesp++) = v_agent[vtx | 1 << i_bit | 1 << j_bit];

上面计算4个顶点坐标。

 

#059 

#060                    *(texCoordsp++) = TEX00;

#061                    *(texCoordsp++) = TEX01;

#062                    *(texCoordsp++) = TEX10;

#063                    *(texCoordsp++) = TEX11;

#064 

设置4个顶点的纹理坐标。

 

#065                    // Triangles for each side

#066                    *indicesp++ = index_offset + 0;

#067                    *indicesp++ = index_offset + 1;

#068                    *indicesp++ = index_offset + 3;

#069 

#070                    *indicesp++ = index_offset + 0;

#071                    *indicesp++ = index_offset + 3;

#072                    *indicesp++ = index_offset + 2;

上面设置每个表面由两个三角形构成索引。

 

#073             }

#074      }

#075 

#076      const LLVector3 &look_at = gCamera->getAtAxis();

#077      LLVector3 right = look_at % LLVector3::z_axis;

#078      LLVector3 up = right % look_at;

#079      right.normVec();

#080      up.normVec();

#081 

#082      const static F32 elevation_factor = 0.0f/sResolution;

#083      const F32 cos_max_angle = cosHorizon(elevation_factor);

#084      mSun.setDraw(updateHeavenlyBodyGeometry(drawable, FACE_SUN, TRUE, mSun, cos_max_angle, up, right));

#085      mMoon.setDraw(updateHeavenlyBodyGeometry(drawable, FACE_MOON, FALSE, mMoon, cos_max_angle, up, right));

#086 

#087      const F32 water_height = gAgent.getRegion()->getWaterHeight() + 0.01f;

#088             // gWorldPointer->getWaterHeight() + 0.01f;

#089      const F32 camera_height = mCameraPosAgent.mV[2];

#090      const F32 height_above_water = camera_height - water_height;

#091 

#092      BOOL sun_flag = FALSE;

#093 

#094      if (mSun.isVisible())

#095      {

#096             if (mMoon.isVisible())

#097             {

#098                    sun_flag = look_at * mSun.getDirection() > 0;

#099             }

#100             else

#101             {

#102                    sun_flag = TRUE;

#103             }

#104      }

#105     

#106      if (height_above_water > 0)

#107      {

#108 #if 1 //1.9.1

#109             BOOL render_ref = gPipeline.getPool(LLDrawPool::POOL_WATER)->getVertexShaderLevel() == 0;

#110 #else

#111             BOOL render_ref = !(gPipeline.getVertexShaderLevel(LLPipeline::SHADER_ENVIRONMENT) >= LLDrawPoolWater::SHADER_LEVEL_RIPPLE);

#112 #endif

#113             if (sun_flag)

#114             {

#115                    setDrawRefl(0);

#116                    if (render_ref)

#117                    {

#118                           updateReflectionGeometry(drawable, height_above_water, mSun);

#119                    }

#120             }

#121             else

#122             {

#123                    setDrawRefl(1);

#124                    if (render_ref)

#125                    {

#126                           updateReflectionGeometry(drawable, height_above_water, mMoon);

#127                    }

#128             }

#129      }

#130      else

#131      {

#132             setDrawRefl(-1);

#133      }

#134 

#135 

#136      LLPipeline::sCompiles++;

#137      return TRUE;

#138 }

#139 

上面计算太阳和月亮的出现位置以及光照效果。

 

通过上面的分析，了解天空体的网格创建，纹理坐标的设置，以及太阳、月亮的效果计算。

 

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