产生雨滴 [英] Creating rain drops

问题描述

#include <stdio.h>  // this library is for standard input and output
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include "glut.h"// this library is for glut the OpenGL Utility Toolkit

#define RAINSIZE 50
int winWidth = 1000, winHeight = 1000;
int counter = 0;
time_t t;
float rotationAngle = 0;

struct drop {
    float x = 400;
    float y = 400;
    float inc = 0.01;
    float radius = 5;
    float scale = 1.0;
    float rotationAngle = 0;
    float rotationInc = 1;
};

drop rain[RAINSIZE];

void initRain() {
    srand((unsigned)time(&t));
    for (int i = 0; i < RAINSIZE; i++) {
        rain[i].x = rand() % winWidth;
        rain[i].y = rand() % winHeight;
        rain[i].inc = 1.5 + (float)(rand() % 100) / 1000.0;
        rain[i].radius = (float)(rand() % 8);
        rain[i].scale = (float)(rand() % 20000) / 1000.0;
        rain[i].rotationAngle = (float)(rand() % 3000) / 1000.0;
        rain[i].rotationInc = (float)(rand() % 100) / 1000.0;
        if ((rand() % 100) > 50) {
            rain[i].rotationInc = -rain[i].rotationInc;
        }
    }
}

void drawParticleShape(int i) {
    glBegin(GL_POINTS);
    glVertex2d(rain[i].x, rain[i].y);
    glEnd();
    glBegin(GL_LINES);
    glVertex2d(rain[i].x, rain[i].y);
    glVertex2d(rain[i].x, rain[i].y + rain[i].radius * 2);
    glEnd();
}

void drawDrop(int i) {
    glColor3f(0.0, 0.0, 1.0);
    glLineWidth(2);
    drawParticleShape(i);
    rain[i].y -= rain[i].inc;
    if (rain[i].y < 0) {
        rain[i].y = winHeight;
    }
}

void drawRain() {
    for (int i = 0; i < RAINSIZE; i++) {
        drawDrop(i);
    }
}

// this is the initialisation function, called once only
void init() {
    glClearColor(0.0, 0.0, 0.0, 0.0); // set what colour you want the background to be
    glMatrixMode(GL_PROJECTION); // set the matrix mode, we will look at this later
    gluOrtho2D(0.0, winWidth, 0.0, winHeight);
}

float elapsedTime = 0, base_time = 0, fps = 0, frames;

void calcFPS() {
    elapsedTime = glutGet(GLUT_ELAPSED_TIME);
    if ((elapsedTime - base_time) > 1000.0) {
        fps = frames * 1000.0 / (elapsedTime - base_time);
        printf("fps: %f", fps);
        base_time = elapsedTime;
        frames = 0;
    }
    frames++;
}

// This is the display function it is called when ever you want to draw something
// all drawing should be called form here
void display() {
   glClear(GL_COLOR_BUFFER_BIT);
   drawRain();
   calcFPS();
   glFlush();
   counter++;
   glutPostRedisplay();
}

// This is the idle function it is called whenever the program is idle
// This has the effect of repeatedly calling the display function
void idle() {
    //display();
}

// As with many programming languages the main() function
// is the entry point for execution of the program
int main(int argc, char** argv) {
    srand(1);
    initRain();
    glutInit(&argc, argv);  //perform the GLUT initialization
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA); // more initialisation
    glutInitWindowSize(winWidth, winHeight); // set window position
    glutInitWindowPosition(0, 0); // set window size
    glutCreateWindow("Hello"); // create a display with a given caption for the title bar
    glEnable(GL_BLEND); //Enable blending.
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); //Set blending function.
    init(); // call init function defined above
    glutIdleFunc(idle); //  define what function to call when the program is idle
    glutDisplayFunc(display); // define what function to call to draw
    // the last function in the program puts the program into infinite loop
    glutMainLoop();
    // this line exits the program
    return 0;
}

我试图使雨滴从屏幕顶部滴下并扩散开，但是雨滴没有适当地滴下.应该像真正的雨一样落下.我试图弄清楚问题出在哪里，但是我一直使问题变得更糟.如果您能帮助我并告诉我问题出在哪里，我将不胜感激.

I am trying to create rain drops falling and spreading from the top of the screen, but the rain does not drop properly. It's supposed to drop like real rain. I have tried to figure out what the problem was, but I kept making it worse. I would appreciate if you could help me and tell me what the problem is.

工作原理:

我希望它如何工作(上图的编辑):

How I want it to work (edit of image above):

推荐答案

您必须在每个帧的开头通过 glClear .注意，只要不显式更改帧缓冲区的内容，它就不会更改.您所绘制的所有内容都将保留，直到被清除或覆盖.

You have to clear the color plane of the default framebuffer (the "window") at the begin of each frame by glClear. Note, the content of the framebuffer won't change as long as you do not explicitly change it. Everything what you have drawn is kept until it s cleared or overwritten.

此外，不要在idle中重新绘制窗口，而是通过display中重新显示. /spec3/node20.html"rel =" nofollow noreferrer> glutPostRedisplay . GLUT事件处理循环将为您执行display调用:

Further don't redraw the window in idle, but mark the current window as needing to be redisplayed in display by glutPostRedisplay. The GLUT event processing loop will do the display call for you:

void display() {
    glClear( GL_COLOR_BUFFER_BIT );
    drawRain();
    calcFPS();
    glFlush();
    counter++;
    glutPostRedisplay();
}

void idle() {
    //display();
}

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