The author's themes of surveillance, paranoia and fear attracted the Oscar-nominated actress to the film, she said.
"All this stuff is actually happening right now," she said.
Ryder, 34, knew Dick personally through her godfather, Timothy Leary, the 1960s American psychologist and author who came up with the phrase, "question authority."
Based on Dick's life, "A Scanner Darkly" deals with the issue of drug use. Ryder's character may be on cocaine or just faking it, The Independent reported.
"I feel if we were making this movie forever I don't know if we'd ever fully grasp it," Ryder said. "You don't know who's telling the truth, who's working for whom, who's screwing who over."
"Blade Runner," "Total Recall" and "Minority Report" became big-budget blockbusters.