Action film is a film genre in which the protagonist or protagonists are thrust into a series of events that typically include violence, extended fighting, physical feats, rescues and frantic chases. Action films tend to feature a mostly resourceful hero struggling against incredible odds, which include life-threatening situations, a dangerous villain, or a pursuit which usually concludes in victory for the hero. Advancements in computer-generated imagery (CGI) have made it cheaper and easier to create action sequences and other visual effects that required the efforts of professional stunt crews in the past. However, reactions to action films containing significant amounts of CGI have been mixed, as films that use computer animations to create unrealistic, highly unbelievable events are often met with criticism. While action has long been a recurring component in films, the "action film" genre began to develop in the 1970s along with the increase of stunts and special effects. Common tropes of the genre include explosions, car chases, fistfights and shootouts.