openGL 2D 移动和对象 1 个单位

Question

我有一些关于如何通过按键移动对象的问题。我要做的就是按下键盘上的向上按钮，让对象移动一个单位。

void display(){

    //Clear Window
    glClear(GL_COLOR_BUFFER_BIT);

    glPushMatrix();
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex2f(-0.1, -0.2);
    glVertex2f(-0.1, 0.2);
    glVertex2f(0.1, 0.2);
    glVertex2f(0.1, -0.2);
    glEnd();
    glPopMatrix();
    glFlush();
}


void keyboardListener(int key)
{  
    if( key == GLUT_KEY_UP) 
    {
        glTranslatef(1.0, 0.0, 0.0);
        glutPostRedisplay(); 
    }
}

缺少什么或我不理解什么概念？

Answer 1

使用这个：

#include <stdio.h>
#include <gl/glut.h>

GLfloat rotation = 90.0;
float posX = 0, posY = 0, posZ = 0;

void reshape(int width, int heigth){
    /* window ro reshape when made it bigger or smaller*/

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //clip the windows so its shortest side is 2.0
    if (width < heigth) {
        glOrtho(-2.0, 2.0, -2.0 * (GLfloat)heigth / (GLfloat)width, 2.0 * (GLfloat)heigth / (GLfloat)width, 2.0, 2.0);
    }
    else{
        glOrtho(-2.0, 2.0, -2.0 * (GLfloat)width / (GLfloat)heigth, 2.0 * (GLfloat)width / (GLfloat)heigth,2.0 , 2.0);
    }
    // set viewport to use the entire new window
    glViewport(0, 0, width, heigth);
}

void rect(){
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex2f(-0.1, -0.2);
    glVertex2f(-0.1, 0.2);
    glVertex2f(0.1, 0.2);
    glVertex2f(0.1, -0.2);
    glEnd();

}

void display(){
    //Clear Window
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glPushMatrix();
    glTranslatef(posX,posY,posZ);
    rect();
    glPopMatrix();
    glFlush();
}


void init(){
    // set clear color to black
    glClearColor(0.0, 0.0, 0.0, 0.0);

    // set fill color to white
    glColor3f(1.0, 1.0, 1.0);

    //set up standard orthogonal view with clipping
    //box as cube of side 2 centered at origin
    //This is the default view and these statements could be removed
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-1.0, 1.0, -1.0, 1.0);

}
float move_unit = 0.1f;
void keyboardown(int key, int x, int y)
{
    switch (key){
        case GLUT_KEY_RIGHT:
            posX+=move_unit;;
            break;

        case GLUT_KEY_LEFT:
            posX-=move_unit;;
        break;

        case GLUT_KEY_UP:
            posY+=move_unit;;
            break;

        case GLUT_KEY_DOWN:
            posY-=move_unit;;
        break;

        default:
         break;
    }
    glutPostRedisplay();
}


int main(int argc, char** argv){

    //initialize mode and open a windows in upper left corner of screen
    //Windows tittle is name of program

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(500,500);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Practice 1");
    glutDisplayFunc(display);
    init();
    glutSpecialFunc(keyboardown);
    glutMainLoop();

}

Answer 2

最简单的方法就是这样做

float posX = 0, posY = 0, posZ = 0;

void display(){
  glClear(GL_COLOR_BUFFER_BIT);
  glTranslate(posX,posY,posZ);
  drawPolygon();
  //...
}


void keyboardListener(int key){
  if(key == GLUT_KEY_RIGHT){ posX++; }
  else if(key == GLUT_KEY_LEFT){ posX--; }
  //..similar for up/down
  glutPostRedisplay();
}

Answer 3

此代码绘制一个圆圈，并在按下左、右、上或下键时移动。

#include <cmath>
#include <stdio.h>
float posX = 0.01, posY = -0.1, posZ = 0;

void circ() {
    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLE_FAN);
    for (int i = 0; i <= 300; i++) {
        angle = 2 * PI * i / 300;
        x = cos(angle) / 20;
        y = sin(angle) / 20;
        glVertex2d(x, y);
    }
    glEnd();
}


void display() {
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-1.0, 1.0, -1.0, 1.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glPushMatrix();
    glTranslatef(posX, posY, posZ);
    circ();
    glPopMatrix();

    glutSwapBuffers();
}

**float move_unit = 0.02f;
void keyboardown(int key, int x, int y) {
    switch (key) {
    case GLUT_KEY_RIGHT:
        posX += move_unit;
        break;
    case GLUT_KEY_LEFT:
        posX -= move_unit;
        break;
    case GLUT_KEY_UP:
        posY += move_unit;
        break;
    case GLUT_KEY_DOWN:
        posY -= move_unit;
        break;
    default:
        break;
    }
glutPostRedisplay();
}**



int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(600, 500);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Example");
    glutDisplayFunc(display);
    glutSpecialFunc(keyboardown);
    glutMainLoop();
}