C语言 OpenGL 从角落移动物体

Question

我有一个使用 GLUT 的 openGL 程序，当我调整窗口大小时，我不得不将其从左上角移动到右下角。我试图降低一个比率，但我无法弄清楚。

#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>
//global variables
GLsizei wh = 500, ww = 500;
double height;
 double width;
double top = 500;
double bottom = 450;
int right = 50;
int left = 0;
double ratiowidth = 500/500;
double ratioheight = 500/500;
void myinit(){
glClearColor (0.0, 0.0, 0.0, 0.0);
}
void reshape(int w, int h){
if(h == 0){
    h = 1;
}
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, (GLsizei) w, 0, (GLsizei)h);
glViewport(0,0,w,h);
glMatrixMode(GL_MODELVIEW);
int difference = h - wh;
int difference2 = w - ww;
left = left + difference2;
right = right + difference2;
wh = (GLsizei)h;
ww = (GLsizei)w;
height = h;
width = w;
}
void mouse(int button, int state, int x, int y){
if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN){
    top = height;
    bottom = height - 50;
    right =  50;
    left = 0;
    ratiowidth = width/height;
    ratioheight = height/width;
}
if(button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN){
    exit(0);
}
}
void display(){
glClear (GL_COLOR_BUFFER_BIT);
glColor3i (rand(), rand(), rand());
glBegin(GL_POLYGON);
  glVertex3f (left,top,0.0);
  glVertex3f (right, top, 0.0);
  glVertex3f (right, bottom, 0.0);
  glVertex3f (left, bottom, 0.0);
glEnd();
if(bottom == 0 || bottom < 0)
   bottom = 0;
else{
   left = left + ratiowidth;
   right = right + ratiowidth;
   top = top - ratioheight;
   bottom = bottom - ratioheight;
}
glutSwapBuffers();
usleep(10000);
glutPostRedisplay();
}
int main(int argc, char** argv) {
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(ww, wh);
glutInitWindowPosition(100,100);
glutCreateWindow("moving Square");
myinit();
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutMainLoop();
return 0;
}

Answer 1

glBegin(GL_POLYGON);
  glVertex3f (left,top,0.0);
  glVertex3f (right, top, 0.0);
  glVertex3f (right, bottom, 0.0);
  glVertex3f (left, bottom, 0.0);
glEnd();

小心您的缠绕顺序。 glFrontFace()默认为 GL_CCW 。 也许你的意思是：

glBegin(GL_POLYGON);
  glVertex3f (left, bottom, 0.0);
  glVertex3f (right, bottom, 0.0);
  glVertex3f (right, top, 0.0);
  glVertex3f (left,top,0.0);
glEnd();

编辑：这就是我认为你想做的：

#include <GL/glut.h>
struct State
{
    double x;       // in units
    double y;    
    double xvel;    // in units per second
    double yvel;  
};
State curState = { 0 };
void myinit()
{
    curState.xvel = 100;
    curState.yvel = 100;
}
void Integrate( State* state, double dt )
{
    state->x += state->xvel * dt;
    state->y += state->yvel * dt;
}
double GetSeconds()
{
    return glutGet(GLUT_ELAPSED_TIME) / 1000.0f;
}
void reshape(int w, int h)
{
    glViewport(0,0,w,h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, (GLsizei)w, 0, (GLsizei)h);
}
void mouse(int button, int state, int x, int y)
{
    if(button == GLUT_LEFT_BUTTON && state == GLUT_UP)
    {
        curState.x = 0;
        curState.y = 0;
    }
    if(button == GLUT_RIGHT_BUTTON && state == GLUT_UP)
    {
        exit(0);
    }
}
void display()
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glClear (GL_COLOR_BUFFER_BIT);
    float w = 20;
    float h = 20;
    float x = curState.x;
    float y = curState.y;
    glColor3ub(rand()%255, rand()%255, rand()%255);
    glBegin(GL_QUADS);
    glVertex2f( x - w/2, y - h/2 );
    glVertex2f( x + w/2, y - h/2 );
    glVertex2f( x + w/2, y + h/2 );
    glVertex2f( x - w/2, y + h/2 );
    glEnd();
    static double lastTime = GetSeconds();
    double curTime = GetSeconds();
    Integrate( &curState, curTime - lastTime );
    lastTime = curTime;
    glutSwapBuffers();
}
void timer(int extra)
{
    glutPostRedisplay();
    glutTimerFunc(16, timer, 0);
}
int main(int argc, char** argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100,100);
    glutCreateWindow("moving Square");
    myinit();
    glutReshapeFunc(reshape);
    glutTimerFunc(0, timer, 0);
    glutDisplayFunc(display);
    glutMouseFunc(mouse);
    glutMainLoop();
    return 0;
}

请注意，那里可能有一些C++主义:)