Question

如果我不站在阴影中，阴影效果看起来很完美。但是当我在阴影中时，阴影就消失了。我不知道为什么？

这是我实现阴影效果的代码。

void  CastShadow(SECTOR &sec, float *lp)
{//lp is the relative position to the sec
    unsigned int    i, j, k, jj;
    unsigned int    p1, p2;
    VECTOR          v1, v2;
    float           side;


    for (i=0;i<sec.numplanes;i++)
    {
        side =sec.planes[i].planeeq.a*lp[0]+sec.planes[i].planeeq.b*lp[1]+sec.planes[i].planeeq.c*lp[2]+sec.planes[i].planeeq.d*lp[3];
        if (side>0) 
            sec.planes[i].visible = TRUE;
        else
            sec.planes[i].visible = FALSE;
    }

    glDisable(GL_LIGHTING);
    glDepthMask(GL_FALSE);
    glDepthFunc(GL_LEQUAL);
    glEnable(GL_STENCIL_TEST);
    glColorMask(0, 0, 0, 0);
    glStencilFunc(GL_ALWAYS, 1, 0xffffffff);

    // first pass, stencil operation decreases stencil value
    glFrontFace(GL_CCW);
    glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
    for (i=0; i<sec.numplanes;i++)
    {
        if (sec.planes[i].visible)
            for (j=0;j<3;j++){
                k = sec.planes[i].neigh[j];
                if ((!k) || (!sec.planes[k-1].visible))//如果以第k个点开始的邻边没有相邻平面或者相邻平面不可见
                {
                    // here we have an edge, we must draw a polygon
                    p1 = sec.planes[i].p[j]-1;//邻边的起点
                    jj = (j+1)%3;           
                    p2 = sec.planes[i].p[jj]-1;//邻边的终点

                    //calculate the length of the vector
                    v1.x = (sec.points[p1].vec.x - lp[0])*100;
                    v1.y = (sec.points[p1].vec.y - lp[1])*100;
                    v1.z = (sec.points[p1].vec.z - lp[2])*100;

                    v2.x = (sec.points[p2].vec.x - lp[0])*100;
                    v2.y = (sec.points[p2].vec.y - lp[1])*100;
                    v2.z = (sec.points[p2].vec.z - lp[2])*100;

                    glBegin(GL_TRIANGLE_STRIP);//将光源连到邻边的起点并延长,将光源连到邻边的终点的并延长,最后延长出来的梯形,画了过后模板缓冲区的值加1
                        glVertex3f(sec.points[p1].vec.x,sec.points[p1].vec.y,sec.points[p1].vec.z);
                        glVertex3f(sec.points[p1].vec.x + v1.x,sec.points[p1].vec.y + v1.y,sec.points[p1].vec.z + v1.z);
                        glVertex3f(sec.points[p2].vec.x,sec.points[p2].vec.y,sec.points[p2].vec.z);
                        glVertex3f(sec.points[p2].vec.x + v2.x,sec.points[p2].vec.y + v2.y,sec.points[p2].vec.z + v2.z);
                    glEnd();
                }
            }
    }

    // second pass, stencil operation increases stencil value
    glFrontFace(GL_CW);//这句表示画的多边形,只看到里面
    glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);
    for (i=0; i<sec.numplanes;i++){
        if (sec.planes[i].visible)
            for (j=0;j<3;j++){
                k = sec.planes[i].neigh[j];
                if ((!k) || (!sec.planes[k-1].visible))//如果以第k个点开始的邻边没有相邻平面或者相邻平面不可见
                {
                    // here we have an edge, we must draw a polygon
                    p1 = sec.planes[i].p[j]-1;//邻边的起点
                    jj = (j+1)%3;           
                    p2 = sec.planes[i].p[jj]-1;//邻边的终点

                    //calculate the length of the vector
                    v1.x = (sec.points[p1].vec.x - lp[0])*100;
                    v1.y = (sec.points[p1].vec.y - lp[1])*100;
                    v1.z = (sec.points[p1].vec.z - lp[2])*100;

                    v2.x = (sec.points[p2].vec.x - lp[0])*100;
                    v2.y = (sec.points[p2].vec.y - lp[1])*100;
                    v2.z = (sec.points[p2].vec.z - lp[2])*100;

                    glBegin(GL_TRIANGLE_STRIP);//将光源连到邻边的起点并延长,将光源连到邻边的终点的并延长,最后延长出来的梯形,画了过后模板缓冲区的值加1
                        glVertex3f(sec.points[p1].vec.x,sec.points[p1].vec.y,sec.points[p1].vec.z);
                        glVertex3f(sec.points[p1].vec.x + v1.x,sec.points[p1].vec.y + v1.y,sec.points[p1].vec.z + v1.z);
                        glVertex3f(sec.points[p2].vec.x,sec.points[p2].vec.y,sec.points[p2].vec.z);
                        glVertex3f(sec.points[p2].vec.x + v2.x,sec.points[p2].vec.y + v2.y,sec.points[p2].vec.z + v2.z);
                    glEnd();
                }
            }
    }

    glFrontFace(GL_CCW);
    glColorMask(1, 1, 1, 1);

    //draw a shadowing rectangle covering the entire screen
    glColor4f(0.0f, 0.0f, 0.0f,0.4f);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glStencilFunc(GL_NOTEQUAL, 0, 0xffffffff);
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    glPushMatrix();
    glLoadIdentity();
    glBegin(GL_TRIANGLE_STRIP);
        glVertex3f(-0.1f, 0.1f,-0.0010f);
        glVertex3f(-0.1f,-0.1f,-0.0010f);
        glVertex3f( 0.1f, 0.1f,-0.0010f);
        glVertex3f( 0.1f,-0.1f,-0.0010f);
    glEnd();
    glPopMatrix();
    glDisable(GL_BLEND);

    glDepthFunc(GL_LEQUAL);
    glDepthMask(GL_TRUE);
    glEnable(GL_LIGHTING);
    glDisable(GL_STENCIL_TEST);
    glShadeModel(GL_SMOOTH);

}

并且类SECTOR是这样的：

class SECTOR
{
public:
    int numpoints;
    int numplanes;
    vector<VERTEX> points;
    vector<PLANE> planes;
    MATERIAL material;
    bool read();
    bool loadtexture();
    bool build();
    bool plane_calc();
    void SetConnectivity();
    SECTOR& SECTOR::subdivide(long depth);
    SECTOR(string str1,string str2):modelfilename(str1),texturefilename(str2)
    {
        numpoints=0;
        numplanes=0;

    }
    SECTOR()
    {
        numpoints=0;
        numplanes=0;

    }

private:
    FILE *modelfilein,*texturefilein;
    string modelfilename,texturefilename;
    char oneline[255];
    UINT texturename;
    AUX_RGBImageRec *TextureImage;
};

Answer 1

由于您已经在近剪裁平面上处理了“加盖”阴影体积，因此您可能会遇到摄像机位于相机后面的物体投射的阴影体内的问题。您可以通过移动相机使其位于阴影体内（发生问题的位置）进行测试，然后旋转相机，使对象位于近剪裁平面的前方。

使用“深度失败”算法来处理这种特殊情况更容易，尽管您必须能够为阴影卷的远端计算和渲染上限。您可以在wikipedia上概述阴影卷算法之间的差异。

opengl：当我站在阴影中时为什么阴影会消失？

1 个答案: