draw_boid.cpp

#include <glm/glm.hpp>
#include <GLFW/glfw3.h>

void draw_boid(const glm::vec3& position, const glm::vec3& speed) {   
    const glm::vec3& speed_dir = glm::normalize(speed);
    const glm::vec3 color (0.5 * (1 + speed_dir.x),
                           0.5 * (1 + speed_dir.y),
                           0.5 * (1 + speed_dir.z));
    glPushMatrix();
    glTranslatef(position.x, position.y, position.z);
    
    // Rotate around normal of the plane containing both X-Axis and boid speed
    glm::vec3 axeRot = glm::cross(glm::vec3(1.0f, 0.0f, 0.0f), speed);
    const float angle = glm::degrees(std::atan2(glm::length(axeRot), speed.x));
    glRotatef(angle, axeRot.x, axeRot.y, axeRot.z);
    
    draw_box(glm::vec3(0.6, 0.1, 0.1), color);
    glTranslatef(0.6, 0, 0);
    draw_pyramid(glm::vec3(0.4, 0.1, 0.1), glm::vec3(1.0, 1.0, 0.0));
    glPopMatrix();
}