1つのボールがふらふら動く

#include "ofApp.h"

float loc_x;
float loc_y;

float speed_x;
float speed_y;
float acc_x;
float acc_y;

//--------------------------------------------------------------
void ofApp::setup(){

	ofBackground(0, 0, 0); //背景色の設定
	ofSetColor(255, 255, 0); //描画色の設定
	ofSetCircleResolution(64);//円の解像度
	ofEnableAlphaBlending();  //アルファチャンネルを有効にする
	ofSetBackgroundAuto(false); //背景色での塗りつぶしなし
	ofSetFrameRate(30); //フレームレイト設定

	loc_x = 500;
	loc_y = 500;
	speed_x = 7;
	speed_y = 4;

	acc_x = 0;
	acc_y = 0;
}

//--------------------------------------------------------------
void ofApp::update(){

	acc_x = ofRandom(-0.8,0.8);
	acc_y = ofRandom(-0.8,0.8);

	speed_x = speed_x + acc_x;
	speed_y = speed_y + acc_y;

	if( loc_x > ofGetWidth() ){
		speed_x = speed_x * -1;
	}
	if( loc_x < 0 ){
		speed_x = speed_x * -1;
	}

	if( loc_y > ofGetHeight() ){
		speed_y = speed_y * -1;
	}
	if( loc_y < 0 ){
		speed_y = speed_y * -1;
	}

	loc_x = loc_x + speed_x;
	loc_y = loc_y + speed_y;
}

//--------------------------------------------------------------
void ofApp::draw(){

	//全画面を半透明の黒でフェード
	ofSetColor(0, 0, 0, 10);
	ofRect(0, 0, ofGetWidth(), ofGetHeight());

	ofSetColor(31, 63, 255);
	ofCircle(loc_x,loc_y, 40);
}

参考

生命情報アート論