Question

我试图让球落在随机位置并循环但我的代码中出错了。出现此错误：＆＃39; - =＆＃39; ：左操作数必须是l值。我可以知道我的代码有什么问题吗？

这是我的代码：

const int maxBall = 500;
int ball [maxBall][3];
float ballRadius = 1.0f;
float speed=0.010f;

void initBall()
{
for (int i=0; i<=maxBall -1;i++)
{
ball[i][0] = rand() % maxBall-maxBall / 2;
ball[i][1] = rand() % maxBall-maxBall / 2;
}
}

void updateBallPos(int value)
{
glutTimerFunc(10, updateBallPos, 0);
for (int i=0; i<=maxBall - 1; i++)
{
ball[i][1]=ball[i][1] + 2;
if(ball[i][1] > 0 )
ball[i][1] = -maxBall;
}
}

void display ()
{
glClear(GL_COLOR_BUFFER_BIT);
for(int i=0; i<=maxBall - 1; i++)
{
glLoadIdentity();
glTranslatef(0.0f, ball[i][1], 0.0f);
glPushMatrix();
 glBegin(GL_TRIANGLE_FAN);
  glColor3f(0.0f, 0.0f, 1.0f);  // Blue
  glVertex2f(0.0f, 0.0f);       // Center of circle
  int numSegments = 100;
  float angle;
  for (int i = 0; i <= numSegments; i++) { // Last vertex same as first          vertex
     angle = i * 2.0f * PI / numSegments;  // 360 deg for all segments
     glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
  }
glEnd();
glPopMatrix();
}
glutSwapBuffers();

ball -= speed;
glFlush();
}
void reshape(int x, int y)
{
glViewport(0, 0, x, y);
//Create projection matrix, 60 degree field of view, near clip plane at 1,    far clip plane at 1000
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective (60, (1.0*x) / y, 1, 1000);  
glMatrixMode(GL_MODELVIEW);
}

Answer 1

C和C ++是极简主义语言，它们的运算符非常低级（您可以在C ++中重载运算符）。 ball是一个数组，-运算符不对数组进行操作，就像它们是向量一样（元素减法）。所以ball -= speed事情并不合适。

你必须迭代数组的元素并按元素执行减法元素。

OpenGL随机位置和循环

1 个答案: