My question is very similar to Cost Distance Analyst In QGIS?
However, I'm looking for a means by which I can create a raster displaying the cumulative cost of each pixel to a specified destination rather than simply the least cost path between sets of specified start & end points. In essence, creating a "friction" map in which each raster pixel's value is it's lowest "cost" to get from itself to a specified destination (polygon or single pixel).
I imagine there's a way to do this in QGIS using GRASS operations, but can't figure out how to produce such a map -- does anyone know how? I would imagine it to be the r.cost() function, but without the need to specify start points and stop points.