Method ComputeProjectionTransform

Rendering/Core/vtkCamera.cxx:1060–1149

------------------------------------------------------------------------------ Compute the projection transform matrix. This is used in converting between view and world coordinates.

// Compute the projection transform matrix. This is used in converting
// between view and world coordinates.
void vtkCamera::ComputeProjectionTransform(double aspect, double nearz, double farz)
{
  this->ProjectionTransform->Identity();

  // apply user defined transform last if there is one
  if (this->UserTransform)
  {
    this->ProjectionTransform->Concatenate(this->UserTransform->GetMatrix());
  }

  if (this->UseExplicitProjectionTransformMatrix)
  {
    assert(this->ExplicitProjectionTransformMatrix != nullptr);
    this->ProjectionTransform->Concatenate(this->ExplicitProjectionTransformMatrix);
    return;
  }

  if (this->UseExplicitAspectRatio)
  {
    aspect = this->ExplicitAspectRatio;
  }

  // adjust Z-buffer range
  this->ProjectionTransform->AdjustZBuffer(-1, +1, nearz, farz);

  if (this->ParallelProjection)
  {
    // set up a rectangular parallelipiped

    double width = this->ParallelScale * aspect;
    double height = this->ParallelScale;

    double xmin = (this->WindowCenter[0] - 1.0) * width;
    double xmax = (this->WindowCenter[0] + 1.0) * width;
    double ymin = (this->WindowCenter[1] - 1.0) * height;
    double ymax = (this->WindowCenter[1] + 1.0) * height;

    this->ProjectionTransform->Ortho(
      xmin, xmax, ymin, ymax, this->ClippingRange[0], this->ClippingRange[1]);
  }
  else if (this->UseOffAxisProjection)
  {
    this->ComputeOffAxisProjectionFrustum();
  }
  else
  {
    // set up a perspective frustum

    double tmp = tan(vtkMath::RadiansFromDegrees(this->ViewAngle) / 2.);
    double width;
    double height;
    if (this->UseHorizontalViewAngle)
    {
      width = this->ClippingRange[0] * tmp;
      height = this->ClippingRange[0] * tmp / aspect;
    }
    else
    {