RenderState(RenderContext renderContext, [ Matrix matrix, num alpha, BlendMode blendMode ])

Source 

RenderState(RenderContext renderContext, [Matrix matrix, num alpha, BlendMode blendMode]) :
  _renderContext = renderContext,
  _firstContextState = new _ContextState(null) {

  _currentContextState = _firstContextState;

  if (matrix is Matrix) _firstContextState.matrix.copyFrom(matrix);
  if (alpha is num) _firstContextState.alpha = alpha;
  if (blendMode is BlendMode) _firstContextState.blendMode = blendMode;
}