QGIS custom legend + legend node

gistfile1.py

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from qgis.core import *

# iface.activeLayer().setLegend(RasterRampLegend(iface.activeLayer()))

# nodeLayer = QgsProject.instance().layerTreeRoot().children()[0]


class RasterRampLegend(QgsMapLayerLegend):
  def __init__(self, rlayer):
    QgsMapLayerLegend.__init__(self)
    self.rlayer = rlayer

  def createLayerTreeModelLegendNodes(self, nodeLayer):
    r = self.rlayer.renderer()
    if not isinstance(r, QgsSingleBandPseudoColorRenderer):
      return []

    items = r.shader().rasterShaderFunction().colorRampItemList()
    vMin, vMax = items[0].value, items[-1].value
    stops = [ QgsGradientStop( (item.value-vMin) / (vMax-vMin), item.color ) for item in items[1:-1] ]
    ramp = QgsVectorGradientColorRampV2(items[0].color, items[-1].color, False, stops)
    return [RasterRampLegendNode(nodeLayer, ramp, self)]


class RasterRampLegendNode(QgsLayerTreeModelLegendNode):
  def __init__(self, nodeLayer, ramp, parent):
    QgsLayerTreeModelLegendNode.__init__(self, nodeLayer, parent)
    self.ramp = ramp

  def data(self, role):
    if role == Qt.DisplayRole:
      return ""
    elif role == Qt.DecorationRole:
      return QgsSymbolLayerV2Utils.colorRampPreviewPixmap(self.ramp, QSize(200,24))
    else:
      return

  def drawSymbol(self, settings, ctx, itemHeight):
    size = settings.symbolSize()
    if ctx:
      pix = QgsSymbolLayerV2Utils.colorRampPreviewPixmap(self.ramp, QSize(500,200))
      ctx.painter.drawPixmap(QRectF(ctx.point.x(),ctx.point.y(),size.width()*4,size.height()), pix, QRectF(0,0,pix.width(),pix.height()))
    return size