Walk Cycle Zoetrope

Published on 2025-09-29 09:15 by Zachary Leong

About

My creation for the scene graph assignment for CIS 4600 (intro to graphics).

What is a scene graph?

A scene graph is a set of nodes that hold transformation matrix data and pointers to other nodes and geometry. Traverse a directed tree of transformations to render shapes.

Implementation

The joint angles are set procedurally using sin and cos functions offset by their rotation around the center pivot.

After much experimentation, theses are the numbers I came up with that create a decent walk cycle.

"""
This code is iterated N times in a for loop
"""

// root
float time = 1.f / N * i;
float pivot_angle = 2.f * PI * time;

// Controllers

// arms
float u_arm_angle = PI / 8.f * sin(time * 2 * PI);
float l_arm_angle1 = PI / 16.f * (sin(time * 2 * PI + PI / 4.f - PI) - 1);
float l_arm_angle2 = PI / 16.f * (sin(time * 2 * PI + PI / 4.f) - 1);

float uArm_ang1 = -PI / 2.f + u_arm_angle;
float lArm_ang1 = -l_arm_angle1;

float uArm_ang2 = -PI / 2.f - u_arm_angle;
float lArm_ang2 = -l_arm_angle2;

// legs
float u_leg_angle = PI / 6.f * cos(time * 2 * PI + 2 * PI / 6.f);
float l_leg_angle = PI / 12.f * (cos(time * 4 * PI + 3 * PI / 6.f) - 1.2f);

float uLeg_ang1 = -PI / 1.8f + PI / 8.f + u_leg_angle;
float lLeg_ang1 = l_leg_angle;

float uLeg_ang2 = -PI / 1.8f + PI / 8.f - u_leg_angle;
float lLeg_ang2 = l_leg_angle;

// body/head
float body_offset = 0.1f * cos(time * 4 * PI);
float head_offset = 0.02f * cos(time * 4 * PI + PI / 12);

float body_Offy = body_offset;
float head_Offy = head_offset;