创造雨滴

Question

#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;
}

我正在尝试创建从屏幕顶部落下并散开的雨滴，但雨滴无法正常下落。它应该像真正的雨一样落下。我试图弄清楚问题是什么，但我一直在让它变得更糟。如果您能帮助我并告诉我问题所在，我将不胜感激。

它是如何工作的：

我希望它如何工作（上图编辑）：

Answer 1

您必须在每帧的开头通过glClear 清除默认帧缓冲区（“窗口”）的颜色平面。请注意，只要您不明确更改帧缓冲区的内容，它就不会更改。您绘制的所有内容都会保留，直到它被清除或覆盖。

进一步不要重绘idle中的窗口，而是通过glutPostRedisplay将当前窗口标记为需要在display中重新显示。 GLUT 事件处理循环将为您调用display：

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

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