有关irix上OpenGL的Makefile问题！

gunforest

小弟在irix上看了其自带的OpenGL的例子，它的Makefile文件如下：
#!smake

OBJECT_STYLE ?= N32

COMMONPREF = standard
include $(ROOT)/usr/include/make/commondefs
sinclude $(ROOT)/usr/include/make/$(PRODUCT)defs

TARGETS = built.32 built.N32 built.64

GLDEBUG ?= no
#if $(GLDEBUG) != "no"
WOFF =
OPTIMIZER = -g
#endif

TOOLKITDIR ?= /usr/share/src/OpenGL/toolkits

LCINCS = -I$(ROOT)$(TOOLKITDIR)/include
#if $(OBJECT_STYLE) == "64"
LLDLIBS = -L$(ROOT)$(TOOLKITDIR)/lib64
#elif $(OBJECT_STYLE) == "N32"
LLDLIBS = -L$(ROOT)$(TOOLKITDIR)/lib32
#else
LLDLIBS = -L$(ROOT)$(TOOLKITDIR)/lib
#endif
LLDLIBS += -lrgb -lfont -lglut -lGLU -lGL -lXmu -lXext -lX11 -lm

DFILES = \
        1.rgb \
        2.rgb \
        3.rgb \
        $(NULL)

PROGFILES = \
        blendxor.c \
        $(NULL)

default all: $(_FORCE)
        $(MAKE) program;

include $(COMMONRULES)

program: $(_FORCE)
        @if [ ! -d built.$(OBJECT_STYLE) ]; then \
            mkdir built.$(OBJECT_STYLE); \
        fi;
        cd built.$(OBJECT_STYLE); OBJECT_STYLE=$(OBJECT_STYLE) $(MAKE) -f ../Makefile links;
        cd built.$(OBJECT_STYLE); OBJECT_STYLE=$(OBJECT_STYLE) $(MAKE) -f ../Makefile built;

links:
        @for i in $(PROGFILES) $(DFILES); do \
            if [ ! -r $$i ]; then \
                ln -sf ../$$i $$i; \
            fi; \
        done;

built:
        @for i in $(PROGFILES:.c=); do \
            OBJECT_STYLE=$(OBJECT_STYLE) $(MAKE) -f ../Makefile $$i; \
        done;

clean: $(COMMONPREF)$$@
        for i in $(TARGETS); do \
            if [ -d $$i ]; then \
                ( cd $$i; $(MAKE) -f ../Makefile $(COMMONPREF)clean ); \
            fi; \
        done;

clobber: $(COMMONPREF)$$@
        for i in $(TARGETS); do \
            if [ -d $$i ]; then \
                rm -rf $$i; \
            fi; \
        done;

headers exports install: default

$(COMMONTARGS): $(COMMONPREF)$$@

这段代码我看不大懂，请高手指教一下！谢谢