1 #ifndef ANDROID_DVR_FIELD_OF_VIEW_H_ 2 #define ANDROID_DVR_FIELD_OF_VIEW_H_ 3 4 #include <cmath> 5 6 #include <private/dvr/eigen.h> 7 8 namespace android { 9 namespace dvr { 10 11 // Encapsulates a generalized, asymmetric field of view with four half angles. 12 // Each half angle denotes the angle between the corresponding frustum plane. 13 // Together with a near and far plane, a FieldOfView forms the frustum of an 14 // off-axis perspective projection. 15 class FieldOfView { 16 public: 17 // The default constructor sets an angle of 0 (in any unit) for all four 18 // half-angles. FieldOfView()19 FieldOfView() : left_(0.0f), right_(0.0f), bottom_(0.0f), top_(0.0f) {} 20 21 // Constructs a FieldOfView from four angles. FieldOfView(float left,float right,float bottom,float top)22 FieldOfView(float left, float right, float bottom, float top) 23 : left_(left), right_(right), bottom_(bottom), top_(top) {} 24 FieldOfView(const float * fov)25 explicit FieldOfView(const float* fov) 26 : FieldOfView(fov[0], fov[1], fov[2], fov[3]) {} 27 28 // Accessors for all four half-angles. GetLeft()29 float GetLeft() const { return left_; } GetRight()30 float GetRight() const { return right_; } GetBottom()31 float GetBottom() const { return bottom_; } GetTop()32 float GetTop() const { return top_; } 33 34 // Setters for all four half-angles. SetLeft(float left)35 void SetLeft(float left) { left_ = left; } SetRight(float right)36 void SetRight(float right) { right_ = right; } SetBottom(float bottom)37 void SetBottom(float bottom) { bottom_ = bottom; } SetTop(float top)38 void SetTop(float top) { top_ = top; } 39 GetProjectionMatrix(float z_near,float z_far)40 Eigen::AffineMatrix<float, 4> GetProjectionMatrix(float z_near, 41 float z_far) const { 42 float x_left = -std::tan(left_) * z_near; 43 float x_right = std::tan(right_) * z_near; 44 float y_bottom = -std::tan(bottom_) * z_near; 45 float y_top = std::tan(top_) * z_near; 46 47 float zero = 0.0f; 48 if (x_left == x_right || y_bottom == y_top || z_near == z_far || 49 z_near <= zero || z_far <= zero) { 50 return Eigen::AffineMatrix<float, 4>::Identity(); 51 } 52 53 float x = (2 * z_near) / (x_right - x_left); 54 float y = (2 * z_near) / (y_top - y_bottom); 55 float a = (x_right + x_left) / (x_right - x_left); 56 float b = (y_top + y_bottom) / (y_top - y_bottom); 57 float c = (z_near + z_far) / (z_near - z_far); 58 float d = (2 * z_near * z_far) / (z_near - z_far); 59 60 // Note: Eigen matrix initialization syntax is always 'column-major' 61 // even if the storage is row-major. Or in other words, just write the 62 // matrix like you'd see in a math textbook. 63 Eigen::AffineMatrix<float, 4> result; 64 result.matrix() << x, 0, a, 0, 65 0, y, b, 0, 66 0, 0, c, d, 67 0, 0, -1, 0; 68 return result; 69 } 70 FromProjectionMatrix(const Eigen::AffineMatrix<float,4> & m)71 static FieldOfView FromProjectionMatrix( 72 const Eigen::AffineMatrix<float, 4>& m) { 73 // Compute tangents. 74 float tan_vert_fov = 1.0f / m(1, 1); 75 float tan_horz_fov = 1.0f / m(0, 0); 76 float t = (m(1, 2) + 1.0f) * tan_vert_fov; 77 float b = (m(1, 2) - 1.0f) * tan_vert_fov; 78 float l = (m(0, 2) - 1.0f) * tan_horz_fov; 79 float r = (m(0, 2) + 1.0f) * tan_horz_fov; 80 81 return FieldOfView(std::atan(-l), std::atan(r), std::atan(-b), 82 std::atan(t)); 83 } 84 85 private: 86 float left_; 87 float right_; 88 float bottom_; 89 float top_; 90 }; 91 92 } // namespace dvr 93 } // namespace android 94 95 #endif // ANDROID_DVR_FIELD_OF_VIEW_H_ 96