_getRenderCacheKey( renderObject, stageVertex, stageFragment ) {

		return stageVertex.id + ',' + stageFragment.id + ',' + this.backend.getRenderCacheKey( renderObject );

	}
Computes a cache key representing a render pipeline.

@private
@param {RenderObject} renderObject - The render object.
@param {ProgrammableStage} stageVertex - The programmable stage representing the vertex shader.
@param {ProgrammableStage} stageFragment - The programmable stage representing the fragment shader.
@return {string} The cache key.