If your plugin uses its own methods to render a map layer, writing your own layer type based on QgsPluginLayer might be the best way to implement that.
Below is an example of a minimal QgsPluginLayer implementation. It is an excerpt of the Watermark example plugin
class WatermarkPluginLayer(QgsPluginLayer):
LAYER_TYPE="watermark"
def __init__(self):
QgsPluginLayer.__init__(self, WatermarkPluginLayer.LAYER_TYPE, "Watermark plugin layer")
self.setValid(True)
def draw(self, rendererContext):
image = QImage("myimage.png")
painter = rendererContext.painter()
painter.save()
painter.drawImage(10, 10, image)
painter.restore()
return True
Methods for reading and writing specific information to the project file can also be added
def readXml(self, node):
pass
def writeXml(self, node, doc):
pass
When loading a project containing such a layer, a factory class is needed
class WatermarkPluginLayerType(QgsPluginLayerType):
def __init__(self):
QgsPluginLayerType.__init__(self, WatermarkPluginLayer.LAYER_TYPE)
def createLayer(self):
return WatermarkPluginLayer()
You can also add code for displaying custom information in the layer properties
def showLayerProperties(self, layer):
pass