Question

D=(A./B).^n

上面的代码从下至上，从左至右以及从上至下移动一个正方形。背景颜色为蓝色，但是每次碰撞检测后如何更改背景颜色？每次碰撞检测后我要达到的颜色顺序是蓝色，红色和绿色。我已经在背景位置添加了评论。

Answer 1

一个基于state的{{3}}并带有适当的glClearColor() / glColor3f()调用会起作用：

void drawScene()
{
    switch( state )
    {
    case 0: glClearColor( 0.0, 0.0, 0.0, 1.0 ); break;
    case 1: glClearColor( 0.0, 1.0, 0.0, 1.0 ); break;
    case 2: glClearColor( 0.2, 0.0, 0.0, 1.0 ); break;
    case 3: glClearColor( 0.0, 0.0, 1.0, 1.0 ); break;
    }
    glClear( GL_COLOR_BUFFER_BIT );
    ...

演示：

switch()

一起：

#include <cstdio>
#include <GL/glut.h>
#include <cmath>

float squareX = 162.0f;
float squareY = 0.0f;
float squareZ = 0.0f;

void drawShape( void )
{
    float width = 58.0f;
    float height = 40.0f;
    glTranslatef( squareX, squareY, squareZ );
    glBegin( GL_POLYGON );
    glColor3f( 1.0, 0.0, 0.0 );
    glVertex2f( 0, 0 );
    glVertex2f( width, 0 );
    glVertex2f( width, height );
    glVertex2f( 0, height );
    glVertex2f( 0, 0 );
    glEnd();
}

// called when the window is resized
void handleResize( int w, int h )
{
    glViewport( 0, 0, w, h );
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glOrtho( 0.0f, (float)w, 0.0f, (float)h, -1.0f, 1.0f );
}

int state = 1;

void drawScene()
{
    switch( state )
    {
    case 0: glClearColor( 0.0, 0.0, 0.0, 1.0 ); break;
    case 1: glClearColor( 0.0, 1.0, 0.0, 1.0 ); break;
    case 2: glClearColor( 0.2, 0.0, 0.0, 1.0 ); break;
    case 3: glClearColor( 0.0, 0.0, 1.0, 1.0 ); break;
    }
    glClear( GL_COLOR_BUFFER_BIT );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    glPushMatrix();
    drawShape();
    glPushMatrix();
    glFlush();
    glutSwapBuffers();
    glutPostRedisplay();
}

// make the square go up
void update( int value )
{
    // 1 : move up
    if( state == 1 )
    {
        squareY += 1.0f;
        if( squareY > 400.0 )
        {
            state = 2;
            squareX = 0.0f;
            squareY = 180.0f;
        }
    }
    // 2 : move right
    else if( state == 2 )
    {
        squareX += 1.0f;
        if( squareX > 400.0 )
        {
            state = 3;
            squareX = 180.0f;
            squareY = 400.0f;
        }
    }
    // 3 : move down
    else if( state == 3 )
    {
        squareY -= 1.0f;
        if( squareY < 0.0 )
        {
            state = 0;
        }
    }
    glutPostRedisplay();
    glutTimerFunc( 25, update, 0 );
}

int main( int argc, char** argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
    glutInitWindowSize( 400, 400 );
    glutCreateWindow( "Moving Square" );
    glutDisplayFunc( drawScene );
    glutReshapeFunc( handleResize );
    glutTimerFunc( 25, update, 0 );
    glutMainLoop();
    return( 0 );
}

碰撞检测后更改背景颜色？

1 个答案: