Matrix4 Camera::CreatePerspectiveMatrix_() {
// http://www.gamedev.net/topic/264248-building-a-projection-matrix-without-api/
const Vector2 frustumOffset(0.0f, 0.0f);
Matrix4 retval = Matrix4::ZERO;
Radian thetaY (field_of_view_ * 0.5f);
float32 tanThetaY = std::tan(thetaY.ValueRadians());
float32 tanThetaX = tanThetaY * aspect_ratio_;
float32 nearFocal = near_distance_ / focal_length_;
float32 nearOffsetX = frustumOffset.x * nearFocal;
float32 nearOffsetY = frustumOffset.y * nearFocal;
float32 half_w = tanThetaX * near_distance_;
float32 half_h = tanThetaY * near_distance_;
float32 left = - half_w + nearOffsetX;
float32 right = + half_w + nearOffsetX;
float32 bottom = - half_h + nearOffsetY;
float32 top = + half_h + nearOffsetY;
// The code below will dealing with general projection
// parameters, similar glFrustum and glOrtho.
// Doesn't optimize manually except division operator, so the
// code self-explanatory.
float32 inv_w = 1 / (right - left);
float32 inv_h = 1 / (top - bottom);
float32 inv_d = 1 / (far_distance_ - near_distance_);
// Calc matrix elements
float32 A = 2 * near_distance_ * inv_w;
float32 B = 2 * near_distance_ * inv_h;
float32 C = (right + left) * inv_w;
float32 D = (top + bottom) * inv_h;
float32 q, qn;
if (far_distance_ == 0) {
// Infinite far plane
q = Frustum::INFINITE_FAR_PLANE_ADJUST - 1;
qn = near_distance_ * (Frustum::INFINITE_FAR_PLANE_ADJUST - 2);
} else {
q = - (far_distance_ + near_distance_) * inv_d;
qn = -2 * (far_distance_ * near_distance_) * inv_d;
}
// NB: This creates 'uniform' perspective projection matrix,
// which depth range [-1,1], right-handed rules
//
// [ A 0 C 0 ]
// [ 0 B D 0 ]
// [ 0 0 q qn ]
// [ 0 0 -1 0 ]
//
// A = 2 * near / (right - left)
// B = 2 * near / (top - bottom)
// C = (right + left) / (right - left)
// D = (top + bottom) / (top - bottom)
// q = - (far + near) / (far - near)
// qn = - 2 * (far * near) / (far - near)
retval[0][0] = A;
retval[0][2] = C;
retval[1][1] = B;
retval[1][2] = D;
retval[2][2] = q;
retval[2][3] = qn;
retval[3][2] = -1;
return retval;
}
