1. A non-transitory computer-readable storage medium storing a program that generates an image in which a moving object slides down a slope according to an inclination of a controller, the program causing a computer to function as: an information acquisition section that acquires inclination information that indicates an inclination of the controller based on a detection result of a detection section that detects information that changes according to an inclination of the controller; a shift angle calculation section that calculates a shift angle based on a magnitude of a velocity vector of the moving object and the inclination information, and calculates a direction of the moving object on the slope based on the shift angle and a direction of the velocity vector of the moving object; a first force vector calculation section that calculates a first force vector in a direction intersecting at right angles on the slope with the direction of the moving object on the slope based on the inclination information, the direction intersecting at right angles corresponding to at least a minimum rotation of the moving object around a z-axis of an object space that contains the moving object; a second force vector calculation section that calculates a second force vector based on a slope angle of the slope; a resultant force vector calculation section that calculates a resultant force vector by combining the first force vector and the second force vector; an update section that updates the velocity vector of the moving object based on the resultant force vector, and updates a position of the moving object based on the updated velocity vector; and an image generation section that generates an image including the moving object, wherein the shift angle calculation section changes the shift angle within a first angular range based on a magnitude of the velocity vector of the moving object and the inclination information when a value of the inclination information has not reached a predetermined threshold value, and changes the shift angle to a predetermined angle outside the first angular range when a value of the inclination information has reached the predetermined threshold value.