Richard Linklater is back with the rotoscope equipment he employed in “Waking Life,” but this time he applies it not to “Slacker”-style stream-of-consciousness philosophical ramblings but to an adaptation of Philip K. Dick’s 1977 novel, a combination of sci-fi noodling and paranoid thriller, about a bunch of druggies (including a double-dealing undercover agent) living the low life in a Big Brotherish, corporate-controlled society.

The picture’s concern with intrusive government surveillance is certainly topical in today’s political climate, but situating that theme within the story of a bunch of hapless hop-heads really dates it; the tale might have a certain cult status, but it feels every one of its thirty-odd years in this telling, especially because Linklater’s take on it is so determinedly faithful to his source. The plot, to be blunt, doesn’t make a whole lot of sense, since both Dick and Linklater appear to prize the appearance of coolness over coherence, but it has to do with the increasing availability of a dangerous drug known as Substance D, the source of which is what undercover government agent (Keanu Reeves), operating under the name of Robert Arctor, is assigned to track down. To complete the mission, he’s romancing Donna (Winona Ryder), a dealer, while linking up with addicts Fleck (Rory Cochrane), Barris (Robert Downey, Jr.) and Luckman (Woody Harrelson), the latter two of whom actually live in his dumpy suburban house. And he’s become an addict himself–something obviously unknown to his superiors. Back at work, he’s assigned to oversee the surveillance of his own place, because “Arctor” is suspected of being an important cog in the drug distribution operation–an idea that Barris, offering to turn informant, is peddling to Arctor’s own office. Arctor’s mental deterioration eventually allows him to work his way to the source of Substance D, but as might be expected, “the system” is involved in the trade.

If this summary seems a trifle vague, rest assured the picture is, too; the goal appears to be to keep the viewer in the same semi-conscious, befuddled state a drug-user like Arctor would exist in, and Linklater succeeds all too well in maintaining a frustratingly oblique, enigmatic atmosphere in which questions are never fully answered. The fact that Arctor narrates much of the film, like the protagonists of the old noir thrillers often did, keeps things muddled, too, since he’s operating in a perperual haze himself. The rotoscoping also accentuates the blurred effect, in which nothing is ever entirely clear, but otherwise the technique of layering animation over real locations and live performances dulls the impact, with only two exceptions–an opening sequence in which Freck hallucinates that his room is infested with insects, and the recurrent image of Arctor’s ever-changing suit, which alters his appearance continuously so that his identity can’t be pinned down. (Just call it “Robert and the Amazing Multiple-Identity Dreamcoat.”) And the somber, featureless visuals have a negative impact on the performances; perhaps as a result (and probably because of the pulpy character of the writing), the actors tend to come on very strong. One also has to wonder about the tastefulness of assigning Downey the part of a wildly unbalanced, paranoid drug abuser. It cuts awfully close to the bone.

If, finally, the reader will permit a complaint from an old Latinist, at one point in his interminable narration Arctor remarks that he finds it ironic that the Latin for “make” is “facere,” which sounds so close to the four-letter Anglo-Saxon word commonly used in impolite society nowadays. Unfortunately, he mispronounces it, putting the accent on the second syllable rather than the first. Erudition works only if you get it right, fellas. But even if “A Scanner Darkly” were perfect in such a totally insignificant respect, its frantic but flat effect would make the picture what it definitely is–a bummer clearly.