Method DrawEllipticArc

Rendering/ContextOpenGL2/vtkOpenGLContextDevice2D.cxx:1521–1576

------------------------------------------------------------------------------

//------------------------------------------------------------------------------
void vtkOpenGLContextDevice2D::DrawEllipticArc(
  float x, float y, float rX, float rY, float startAngle, float stopAngle)
{
  assert("pre: positive_rX" && rX >= 0);
  assert("pre: positive_rY" && rY >= 0);

  if (SkipDraw())
  {
    return;
  }

  if (rX == 0.0f && rY == 0.0f)
  {
    // we make sure maxRadius will never be null.
    return;
  }

  // If the 'arc' is actually a full circle, gl2ps can just insert a circle
  // instead of using a polygonal approximation.
  if (IsFullCircle(startAngle, stopAngle))
  {
    vtkOpenGLGL2PSHelper* gl2ps = vtkOpenGLGL2PSHelper::GetInstance();
    if (gl2ps && gl2ps->GetActiveState() == vtkOpenGLGL2PSHelper::Capture)
    {
      this->DrawCircleGL2PS(x, y, rX, rY);
      return;
    }
  }

  vtkOpenGLClearErrorMacro();

  int iterations = this->GetNumberOfArcIterations(rX, rY, startAngle, stopAngle);

  float* p = new float[2 * (iterations + 1)];

  // step in radians.
  double step = vtkMath::RadiansFromDegrees(stopAngle - startAngle) / (iterations);

  // step have to be lesser or equal to maxStep computed inside
  // GetNumberOfIterations()
  double rstart = vtkMath::RadiansFromDegrees(startAngle);

  // we are iterating counterclockwise
  for (int i = 0; i <= iterations; ++i)
  {
    double a = rstart + i * step;
    p[2 * i] = rX * cos(a) + x;
    p[2 * i + 1] = rY * sin(a) + y;
  }

  this->DrawPolygon(p, iterations + 1);
  this->DrawPoly(p, iterations + 1);
  delete[] p;

  vtkOpenGLCheckErrorMacro("failed after DrawEllipseArc");
}

//------------------------------------------------------------------------------