计算机图形学——OpenGL学习系列之Graphics3D
计算机图形学——OpenGL学习系列之Graphics3D
一、OpenGl中的坐标系
跟数学中常见的坐标系有点不同，Z轴垂直纸面，反正我刚开始是不习惯的
二、OpenGl中的几何变换
在OpenGl中，无论2D还是3D都可以进行几何变换，实现原理就是调用函数生成变换矩阵：
| glMatrixMode(GL_MODEL_VIEW) |
选中矩阵为后续矩阵操作对象 |
| glTranslate(x,y,z) |
构造一个平移矩阵，和当前选中矩阵相乘 |
| glRotate(th_rad,vx,vy,vz) |
构造一个旋转矩阵，一参为旋转弧度 |
| glScale(x,y,z) |
构造一个缩放矩阵，和当前选中矩阵相乘 |
| glLoadIdentity() |
设置当前矩阵为单位矩阵 |
| glPushMatrix() |
将选中矩阵压栈 |
| glPopMatrix() |
将栈顶矩阵弹出设为选中矩阵 |
三、使用OpenGl绘制长方体
这是一个简单的程序，原理很简单，就是对于长方体的6个面分别绘制就行，然后旋转一定的角度就可以有立体感了。#include
//6个面的绘制顺序,存储的是顶点的下标
static const GLint quads[][4] = {
0, 2, 3, 1,
0, 4, 6, 2,
0, 1, 5, 4,
4, 5, 7, 6,
1, 3, 7, 5,
2, 6, 7, 3,
};
void draw_cube(GLfloat x,GLfloat y,GLfloat z){
//8个顶点
static const GLfloat vetexs[][3] = {
0.0,0.0,0.0,
x,0.0,0.0,
0.0,y,0.0,
x,y,0.0,
0.0,0.0,z,
x,0.0,z,
0.0,y,z,
x,y,z
};
glClear(GL_COLOR_BUFFER_BIT);
glFrontFace(GL_CCW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
glRotated(15,1,0,0);
glRotated(15,0,1,0);
glTranslatef(-x/2,-y/2,-z/2); //平移至中心
//画立方体
for(int i = 0;i<6;i++){
glBegin(GL_QUADS);
glVertex3f(vetexs[quads[i][0]][0],vetexs[quads[i][0]][1],vetexs[quads[i][0]][2]);
glVertex3f(vetexs[quads[i][1]][0],vetexs[quads[i][1]][1],vetexs[quads[i][1]][2]);
glVertex3f(vetexs[quads[i][2]][0],vetexs[quads[i][2]][1],vetexs[quads[i][2]][2]);
glVertex3f(vetexs[quads[i][3]][0],vetexs[quads[i][3]][1],vetexs[quads[i][3]][2]);
glEnd();
}
}
void mydisplay(){
draw_cube(1.0,0.2,0.8);
glFlush();
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(100, 100);
glutInitWindowSize(600, 600);
glutCreateWindow("HelloOpenGL");
glutDisplayFunc(&mydisplay);
glutMainLoop();
return 0;
}