c - OpenGL矩形动画

Question

我正在尝试根据随机数输入“动画化”矩形的高度。因此，对于每个新的随机数，都会重新绘制矩形。

我该怎么做？

我的代码:

#include <time.h>
#include <GL/freeglut.h>
#include <GL/gl.h>

float height;
int i;

/* display function - code from:
     http://fly.cc.fer.hr/~unreal/theredbook/chapter01.html
This is the actual usage of the OpenGL library.
The following code is the same for any platform */
void renderFunction()
{
    srand(time(NULL));
    height = rand() % 10;

    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0, 0.0, 1.0);
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
    glBegin(GL_POLYGON);
        glVertex2f(-0.5, -0.5);     // bottom left corner
        glVertex2f(-0.5, height);      // top left corner
        glVertex2f(-0.3, height);      // top right corner
        glVertex2f(-0.3, -0.5);     // bottom right corner
    glEnd();
    glFlush();
}

/* Main method - main entry point of application
the freeglut library does the window creation work for us,
regardless of the platform. */
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE);
    glutInitWindowSize(900,600);
    glutInitWindowPosition(100,100);
    glutCreateWindow("OpenGL - First window demo");

    glutDisplayFunc(renderFunction);
    glutIdleFunc(renderFunction);
    glutReshapeFunc(renderFunction);

    glutMainLoop();

    return 0;
}

虽然程序没有崩溃，但它只是简单地绘制了一个矩形。

Answer 1

鉴于您的尺码在 0.0 <= dimension <= 1.0 范围内并且您计算的高度在 0 <= height <= 9 范围内，您需要像这样缩放随机数:

height = (float)rand() / RAND_MAX;

另请移步srand(time(NULL));来自 renderFunction()至 main()否则你的矩形大小将在每一秒内被限制。