//primitives
public virtual void begin(IRenderTarget target, GLSortMode mode)
{
if (_begin)
{
throw new InvalidOperationException("You must call end before you can call begin again.");
}
if (_stateStack.Count > 0)
{
throw new InvalidOperationException("State stack was not empty.");
}
if (_clipStack.Count > 0)
{
throw new InvalidOperationException("Clipping stack was not empty.");
}
if (_effectStack.Count > 0)
{
throw new InvalidOperationException("Effect stack was not empty.");
}
_target = target;
_begin = true;
_sortMode = mode;
_renderableIndex = 0;
_clipping = AxisAlignedBox2.Null;
_effect = null;
//_currentMatrix = Matrix3.Identity;
_state = GLState.empty;
_target.enable();
//check other settings
}