rain_2D_a : make raindrops with openFrameworks which use one parameter.

ofApp.cpp

#include "ofApp.h"

//--------------------------------------------------------------
void ofApp::setup(){
    ofSetFrameRate(60);
    ofSetBackgroundAuto(false);
    ofBackground(0, 0, 0);
    
    ofEnableBlendMode(OF_BLENDMODE_ALPHA);
    
    control = true; //state of log, true -> on; false-> off log画面オンオフの状態 true->あり false->なし
}

//--------------------------------------------------------------
void ofApp::update(){
    
    theta = PI / 2 + PI / 2 / 700 * pos.size();  //theta of raindrops, perpendicular = PI / 2 雨粒が落ちる角度 PI/2が鉛直
    float speed = pos.size() / 15;;    //a speed of raindrops 雨粒が落ちる速度
    
    for(int i = 0; i < pos.size(); i++) {
        //convert speed from vector to x, y 雨粒が落ちる速度に傾きをつけてx,yに変換
        ofVec2f vel;
        vel.x = ofGetHeight() / 2300.0f * (length[i] + speed) * cos(theta + noise[i]);
        vel.y = ofGetHeight() / 2300.0f * (length[i] + speed) * sin(theta + noise[i]);
        
        pos[i].x += vel.x;
        pos[i].y += vel.y;
        
        //if a raindrop reach the bottom of window, it returns first position 画面下まで落ちきった時に上に戻る
        if(pos[i].y - length[i] * sin(theta + noise[i]) > ofGetHeight()){
            pos[i].y = 0;
            pos[i].x -= vel.x * (ofGetHeight() / vel.y);
        }
    }

    
}

//--------------------------------------------------------------
void ofApp::draw(){
    ofSetColor(0, 0, 0, 150);
    ofRect(0, 0, ofGetWidth(), ofGetHeight());  //fadeout フェードアウト
    
    ofSetColor(255, 255, 255);  //color of letters and raindrops 文字と雨粒の色
    for(int i = 0; i < pos.size(); i++) {
        
        //coordinate of a raindrop 雨粒の座標
        float x1 = pos[i].x;
        float y1 = pos[i].y;
        float x2 = pos[i].x - length[i] * cos(theta + noise[i]);
        float y2 = pos[i].y - length[i] * sin(theta + noise[i]);
        
        ofSetLineWidth(length[i] / 40); //width of a raindrop 雨粒の太さ
        ofLine(x1, y1, x2, y2); //draw a raindrop雨粒の描画
    }
        
    
    //log画面
    if(control == true){
        string log;
        log = "raindrops num = " + ofToString(pos.size(), 0) + "\n";
        log += "framerate = " + ofToString(ofGetFrameRate(), 4) + "\n";
        log += "1:add 5 raindrops, 2:subtract 5 raindrops \n";
        log += "c:clear raindrops num, f:fullScreen \n";
        log += "press spacekey to change log on/off";
        ofDrawBitmapString(log, 20, 20);
    }
}

//--------------------------------------------------------------
void ofApp::keyPressed(int key){
    if(key == '1'){
        //add 5 raindrops 雨粒の個数を5ずつ増やす
        for(int i = 0; i < 5; i++){
            //define first position 初期位置
            ofVec2f p;
            float x = ofRandom(ofGetWidth() + ofGetHeight());
            p.set(x, 0);
            pos.push_back(p);
            
            //define length 雨粒の長さ
            float l = ofRandom(ofGetHeight() / 60, ofGetHeight() / 10);
            length.push_back(l);
            
            //define speed 雨粒の速さ
            ofVec2f v;
            float vx = length[length.size() - 1] / 10 * cos(theta);
            float vy = length[length.size() - 1] / 10 * sin(theta);
            v.set(vx, vy);
            velocity.push_back(v);
            
            //define noise of slant 傾きのバラつき具合
            float n;
            n = ofRandom(-PI/90, PI/90);
            noise.push_back(n);
        }
        
    }
    
    if(key == '2'){
        //subtract 5 raindrops 雨粒の個数を5ずつ減らす
        if(pos.size() > 0){
            for(int i = 0; i < 5; i++){
                pos.pop_back();
                length.pop_back();
                velocity.pop_back();
                noise.pop_back();
            }
        }
    }
    
    if(key == 'c'){
        //clear raindrops 雨粒の個数を0個にする
        pos.clear();
        length.clear();
        velocity.clear();
        noise.clear();
    }
    
    if(key == 'f'){
        ofSetFullscreen(true);
    }
    if(key == ' '){
        //state of log logの表示の有無
        control =! control;
    }
}

ofApp.h

#pragma once

#include "ofMain.h"

class ofApp : public ofBaseApp{

	public:
		void setup();
		void update();
		void draw();

		void keyPressed(int key);
		void keyReleased(int key);
		
    vector <ofVec2f> pos;   //a position of the raindrop 雨粒の位置
    vector <float> length;  //a length of the raindop 雨粒の長さ
    vector <ofVec2f> velocity;  //a speed of the raindrop 雨粒の速度
    vector <float> noise;   //a noise of a slant of the raidrop 個々の雨粒の向きのブレ具合
    
    float theta;   //general slamt of raindrops 雨粒の基準の傾き
    
    bool control;   //switch of log log画面のon/off

};