二维几何变换相比三维略简单一点但原理基本一致，下列代码实现了平移、缩放、旋转变换，并有一个复合变换矩阵保存所有变换计算后的结果，方便用其结果在OpenGL进行渲染

#include 
     
      #include 
      
       class wcPt2D {public:	GLfloat x, y;};typedef GLfloat Matrix3x3[3][3];const GLdouble pi = 3.14159;Matrix3x3 matComposite;void matrix3x3SetIdentity(Matrix3x3 &matIdent3x3){	GLint row, col;	for (row = 0; row < 3; ++row)	{		for (col = 0; col < 3; ++col)		{			matIdent3x3[row][col] = (row == col);		}	}}void matrix3x3PreMultiply(Matrix3x3 m1, Matrix3x3 m2){	GLint row, col;	Matrix3x3 matTemp;	for (row = 0; row < 3; ++row)	{		for (col = 0; col < 3; ++col)		{			matTemp[row][col] = m1[row][0] * m2[0][col] + m1[row][1] *				m2[1][col] + m1[row][2] * m2[2][col];		}	}	for (row = 0; row < 3; ++row)	{		for (col = 0; col < 3; ++col)		{			m2[row][col] = matTemp[row][col];		}	}}void translate2D(GLfloat tx, GLfloat ty){	Matrix3x3 matTransl;	matrix3x3SetIdentity(matTransl);	matTransl[0][2] = tx;	matTransl[1][2] = ty;	matrix3x3PreMultiply(matTransl, matComposite);}void rotate2D(wcPt2D pivotPt, GLfloat theta){	Matrix3x3 matRot;	matrix3x3SetIdentity(matRot);	matRot[0][0] = cos(theta);	matRot[0][1] = -sin(theta);	matRot[0][2] = pivotPt.x * (1 - cos(theta)) + pivotPt.y * sin(theta);	matRot[1][0] = sin(theta);	matRot[1][1] = cos(theta);	matRot[1][2] = pivotPt.y * (1 - cos(theta)) - pivotPt.x * sin(theta);	matrix3x3PreMultiply(matRot, matComposite);}void scale2D(GLfloat sx, GLfloat sy, wcPt2D fixedPt){	Matrix3x3 matScale;	matrix3x3SetIdentity(matScale);	matScale[0][0] = sx;	matScale[0][2] = (1 - sx) * fixedPt.x;	matScale[1][1] = sy;	matScale[1][2] = (1 - sy) * fixedPt.y;	matrix3x3PreMultiply(matScale, matComposite);}void transformVerts2D(GLint nVerts, wcPt2D *verts){	GLint k;	GLfloat temp;	for (k = 0; k < nVerts; ++k)	{		temp = matComposite[0][0] * verts[k].x + matComposite[0][1] *			verts[k].y + matComposite[0][2];		verts[k].y = matComposite[1][0] * verts[k].x + matComposite[1][1] *			verts[k].y + matComposite[1][2];		verts[k].x = temp;	}}