1 // Gets the three coefficients of a plane equation given three points on the plane. 2 void gltGetPlaneEquation(GLTVector3 vPoint1, GLTVector3 vPoint2, GLTVector3 vPoint3, GLTVector3 vPlane) 3 { 4     // Get normal vector from three points. The normal vector is the first three coefficients 5     // to the plane equation... 6     gltGetNormalVector(vPoint1, vPoint2, vPoint3, vPlane); 7      8     // Final coefficient found by back substitution 9     vPlane[3] = -(vPlane[0] * vPoint3[0] + vPlane[1] * vPoint3[1] + vPlane[2] * vPoint3[2]);10 }11     12 void gltMakeShadowMatrix(GLTVector3 vPoints[3], GLTVector4 vLightPos, GLTMatrix destMat)13 {14     GLTVector4 vPlaneEquation;15     GLfloat dot;16 17     gltGetPlaneEquation(vPoints[0], vPoints[1], vPoints[2], vPlaneEquation);18   19     // Dot product of plane and light position20     dot =   vPlaneEquation[0]*vLightPos[0] + 21             vPlaneEquation[1]*vLightPos[1] + 22             vPlaneEquation[2]*vLightPos[2] + 23             vPlaneEquation[3]*vLightPos[3];24 25     26     // Now do the projection27     // First column28     destMat[0] = dot - vLightPos[0] * vPlaneEquation[0];29     destMat[4] = 0.0f - vLightPos[0] * vPlaneEquation[1];30     destMat[8] = 0.0f - vLightPos[0] * vPlaneEquation[2];31     destMat[12] = 0.0f - vLightPos[0] * vPlaneEquation[3];32 33     // Second column34     destMat[1] = 0.0f - vLightPos[1] * vPlaneEquation[0];35     destMat[5] = dot - vLightPos[1] * vPlaneEquation[1];36     destMat[9] = 0.0f - vLightPos[1] * vPlaneEquation[2];37     destMat[13] = 0.0f - vLightPos[1] * vPlaneEquation[3];38 39     // Third Column40     destMat[2] = 0.0f - vLightPos[2] * vPlaneEquation[0];41     destMat[6] = 0.0f - vLightPos[2] * vPlaneEquation[1];42     destMat[10] = dot - vLightPos[2] * vPlaneEquation[2];43     destMat[14] = 0.0f - vLightPos[2] * vPlaneEquation[3];44 45     // Fourth Column46     destMat[3] = 0.0f - vLightPos[3] * vPlaneEquation[0];47     destMat[7] = 0.0f - vLightPos[3] * vPlaneEquation[1];48     destMat[11] = 0.0f - vLightPos[3] * vPlaneEquation[2];49     destMat[15] = dot - vLightPos[3] * vPlaneEquation[3];50 }

 1 // Given three points on a plane in counter clockwise order, calculate the unit normal 2 void gltGetNormalVector(const GLTVector3 vP1, const GLTVector3 vP2, const GLTVector3 vP3, GLTVector3 vNormal) 3     { 4     GLTVector3 vV1, vV2; 5      6     gltSubtractVectors(vP2, vP1, vV1); 7     gltSubtractVectors(vP3, vP1, vV2); 8      9     gltVectorCrossProduct(vV1, vV2, vNormal);10     gltNormalizeVector(vNormal);11     }

 1 第二种 2 /** 创建投射矩阵 */ 3 void CPlanarShadow::CreateShadowMatrix(float m[16], Vector3 point, Vector3 normal, float lp[4]) 4 { 5     /** 计算顶点到平面的距离 */ 6     float d = - ((normal.x * point.x) + (normal.y * point.y) + (normal.z * point.z)); 7      8     /** 计算光源向量和法向量的点积 */ 9     float dot = normal.x*lp[0]  + normal.y*lp[1] + normal.z*lp[2] + d*lp[3];10 11     /** 设置矩阵元素值 */12     m[0]  = dot - lp[0]*normal.x;  m[1]  =       -lp[1]*normal.x;     m[2]  =      -lp[2]*normal.x;  m[3]  =        -lp[3]*normal.x;13     m[4]  =         -lp[0]*normal.y;  m[5]  = dot -lp[1]*normal.y;  m[6]  =      -lp[2]*normal.y;  m[7]  =        -lp[3]*normal.y;14     m[8]  =         -lp[0]*normal.z;  m[9]  =       -lp[1]*normal.z;     m[10] = dot  - lp[2]*normal.z; m[11] =        -lp[3]*normal.z;15     m[12] =         -lp[0]*d;           m[13] =       -lp[1]*d;         m[14] =      -lp[2]*d;            m[15] = dot -lp[3]*d;16 }