#ifndef IGL_PROJECTION_CONSTRAINT_H
#define IGL_PROJECTION_CONSTRAINT_H

#include <Eigen/Core>

namespace igl
{
  // Construct two constraint equations of the form:
  //
  //     A z = B
  //
  // with A 2x3 and B 2x1, where z is the 3d position of point in the scene,
  // given the current projection matrix (e.g. gl_proj * gl_modelview), viewport
  // (corner u/v and width/height) and screen space point x,y. Satisfying this
  // equation means that z projects to screen space point (x,y).
  // 
  // Inputs:
  //   UV  2-long uv-coordinates of screen space point
  //   M  4 by 4 projection matrix
  //   VP  4-long viewport: (corner_u, corner_v, width, height)
  // Outputs:
  //   A  2 by 3 system matrix
  //   B  2 by 1 right-hand side
  template <
    typename DerivedUV,
    typename DerivedM,
    typename DerivedVP,
    typename DerivedA,
    typename DerivedB>
  void projection_constraint(
    const Eigen::MatrixBase<DerivedUV> & UV,
    const Eigen::MatrixBase<DerivedM> & M,
    const Eigen::MatrixBase<DerivedVP> & VP,
    Eigen::PlainObjectBase<DerivedA> & A,
    Eigen::PlainObjectBase<DerivedB> & B);
}

#ifndef IGL_STATIC_LIBRARY
#  include "projection_constraint.cpp"
#endif

#endif