Question

我只想要这样的视频：https://youtu.be/dGWtdYlryQQ 它显示了如何在OpenGL中使用glTranslate，glRotate，gluOrtho2d，但它并没有引导我任何事情

就我而言，我画的是钻石而不是三角形，这是我的条件
条件：

当我按下键盘上的r或R时，菱形将顺时针旋转
当我按下键盘上的t或T时，钻石将移动到右侧
当我按下键盘上的+时，钻石会更大

这是我的代码：

#include <stdlib.h>
#include <windows.h>
#include <GL/glut.h>
#include <iostream>
using namespace std;

float angle = 0;
float t,s=0.5,m=0;

void myinit(void){
    glClearColor(1.0,1.0,1.0,0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0,1.0,0.0,1.0,-1.0,1.0);
}
void keyboard(unsigned char key, int x, int y){
        if(key==27)
        {
            exit(0);

        }else if(key == 82 || key == 114){
            angle-=0.1;

            glRotatef(angle,0,0,1);
            glutPostRedisplay();

        }else if(key == 84 || key == 116 )
        {
             t+=0.01;
             glTranslatef(t,0,0);
             glutPostRedisplay();
        }else if(key == 43){
                 s+=0.01;

               //  m-=0.1;
               //  glTranslatef(m,m,0.0);
                 glScalef(s,s,0);
                 glutPostRedisplay();
        }
        (void)(x);
        (void)(y);
}
void hut(void){

    glClear(GL_COLOR_BUFFER_BIT);

        glBegin(GL_TRIANGLE_FAN);
        glVertex3f(0.5,0.4,0.0);
        glVertex3f(0.42,0.5,0.0);    // GREEN
        glVertex3f(0.44,0.5,0.0);
    glColor3f(1.5,1.0,0.0);
        glVertex3f(0.46,0.5,0.0);
    glColor3f(0.25,0.0,0.0);
        glVertex3f(0.57,0.5,0.0);
        glEnd();
    glFlush();

    glColor3f(1.5,1.0,0.0);
        glBegin(GL_TRIANGLE_FAN);
        glVertex3f(0.44,0.55,0.0);
        glVertex3f(0.42,0.5,0.0);
        glVertex3f(0.46,0.5,0.0);
    glColor3f(0.25,0.0,0.0);
        glVertex3f(0.48,0.55,0.0);
        glEnd();

    glColor3f(1.5,1.0,0.0);
        glBegin(GL_TRIANGLE_FAN);
        glVertex3f(0.48,0.55,0.0);
        glVertex3f(0.46,0.5,0.0);
        glVertex3f(0.50,0.5,0.0);
    glColor3f(0.25,0.0,0.0);
        glVertex3f(0.52,0.55,0.0);
        glEnd();

    glColor3f(1.5,1.0,0.0);
        glBegin(GL_TRIANGLE_FAN);
        glVertex3f(0.52,0.55,0.0);
        glVertex3f(0.50,0.5,0.0);
        glVertex3f(0.54,0.5,0.0);
    glColor3f(0.25,0.0,0.0);
        glVertex3f(0.56,0.55,0.0);
        glEnd();
    glColor3f(1.5,1.0,0.0);
        glBegin(GL_TRIANGLE_FAN);
        glVertex3f(0.56,0.55,0.0);
        glVertex3f(0.54,0.5,0.0);
        glVertex3f(0.57,0.5,0.0);
        glEnd();
    glFlush();

}
int main(int argc,char** argv){
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition(100,100);
    glutInitWindowSize(640,480);
    glutCreateWindow("Polygon with viewport");
    myinit();
    glutDisplayFunc(hut);

    glutKeyboardFunc(keyboard);
    glutMainLoop();
}

这是我的输出：https://drive.google.com/file/d/14HHRiCbOHK9ZSZtDOqSl4GP4aSy7UQLh/view?usp=sharing 它与此https://youtu.be/dGWtdYlryQQ

Answer 1

glRotate围绕原点（0,0）旋转。给定您的投影矩阵（使用glOrtho设置），原点最初位于屏幕的左下角，除非您使用glTranslate。你的钻石不是以原点为中心，而是稍微远离它。您需要做的是更改 void hut（void）方法中的顶点值，使钻石以0,0为中心。然后使用glTranslate将渲染原点（以及钻石）移动到你想要的位置，然后使用glRotate。

Answer 2

矩阵堆栈上的操作基于彼此。每个操作的参考系统是当前的转换。

请参阅glTranslate的文档：

glTranslate按x y z生成翻译。当前矩阵（参见glMatrixMode）乘以此平移矩阵，产品替换当前矩阵，

并查看glRotate的文档：

glRotate围绕向量x y z产生角度旋转。当前矩阵（参见glMatrixMode）乘以旋转矩阵，产品替换当前矩阵。

这意味着glRotate围绕当前本地系统的原点进行旋转。

glRotatetf后跟glTranslatef会导致：

glTranslatef后跟glRotatef会导致：

由于您的对象被移位，您必须以这种方式进行翻译，将旋转点放置在原点：

glTranslatef(-0.5f, -0.5f, 0.0f);

然后你可以讨厌它：

glRotatef(angle, 0.0f, 0.0f, 1.0f);

然后将其移回：

glTranslatef(0.5f, 0.5f, 0.0f);

注意，在Fixed Function Pipeline堆栈上，您必须＆＃34;推送＆＃34;此操作的顺序相反。此外，您应该使用GL_MODELVIEW矩阵堆栈。（见glMatrixMode）。

从函数keyboard 中删除所有矩阵运算，并将followig添加到函数hut中：

void hut(void)
{
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(t, 0.0f, 0.0f);
    glTranslatef(0.5f, 0.5f, 0.0f);
    glRotatef(angle, 0.0f, 0.0f, 1.0f);
    glScalef(s, s, 0.0f);
    glTranslatef(-0.5f, -0.5f, 0.0f);

    .....

此外，您的对象会被视图的宽高比破坏。在设置投影矩阵时，可以通过注意纵横比来解决这个问题：

float w = 640.0f;
float h = 480.0f;
glOrtho(0.0,w/h,0.0,1.0,-1.0,1.0);

如何在openGL中使用glTranslatef，glScalef，glRotatef

2 个答案: