SVG                   ?= $(filter-out copied-%,$(wildcard *.svg))
COPIED_SVG             = $(addprefix copied-,$(notdir $(SVG)))
GENERATED_WIDTHS      ?= 50 100 200 300 400 500 600 700 800 546
GENERATED_PNG_WIDTHS  ?= $(GENERATED_WIDTHS)
GENERATED_PNGS         = \
	$(foreach w, $(GENERATED_PNG_WIDTHS),$(patsubst %.svg,%-$w.png,$(notdir $(SVG))))
GENERATED_IMAGES       = $(GENERATED_PNGS)

all: $(GENERATED_IMAGES)
install:
clean: clean.images
distclean:

clean.images:
	rm -f $(GENERATED_IMAGES) $(COPIED_SVG)

%.png: $(COPIED_SVG)
	inkscape -w $(shell echo $* | sed 's/.*-//') \
		--export-png=$@ copied-$(shell echo $* | sed 's/-[0-9]\+$$//').svg

copied-%.svg: $(SVG)
	@echo $^
	cp $(filter %$*.svg, $^) $@.tmp
	mv $@.tmp $@