opengl笔记——旋转，一段代码的理解

重看：opengl笔记——OpenGL好资料备忘

在找到这段代码，对理解opengl旋转很有帮助

...
glPushMatrix();

// initialze ModelView matrix
glLoadIdentity();

// First, transform the camera (viewing matrix) from world space to eye space
// Notice all values are negated, because we move the whole scene with the
// inverse of camera transform

//要理解这段代码：opengl 没有提供操作相机的函数，移动相机就是反向移动模型坐标

//可以理解为：把物体移到视野中去
glRotatef(-cameraAngle[2], 0, 0, 1); // roll
glRotatef(-cameraAngle[1], 0, 1, 0); // heading
glRotatef(-cameraAngle[0], 1, 0, 0); // pitch
glTranslatef(-cameraPosition[0], -cameraPosition[1], -cameraPosition[2]);

// draw the grid at origin before model transform

// 注意：表示

drawGrid();

// transform the object (model matrix)
// The result of GL_MODELVIEW matrix will be:
// ModelView_M = View_M * Model_M
glTranslatef(modelPosition[0], modelPosition[1], modelPosition[2]);
glRotatef(modelAngle[0], 1, 0, 0);
glRotatef(modelAngle[1], 0, 1, 0);
glRotatef(modelAngle[2], 0, 0, 1);

// draw a teapot with model and view transform together
drawTeapot();

glPopMatrix();
...

比较：

// transform the object (model matrix)
// The result of GL_MODELVIEW matrix will be:
// ModelView_M = View_M * Model_M
glTranslatef(modelPosition[0], modelPosition[1], modelPosition[2]);
glRotatef(modelAngle[0], 1, 0, 0);
glRotatef(modelAngle[1], 0, 1, 0);
glRotatef(modelAngle[2], 0, 0, 1);

//放在这，区别：网格随物体移动（当改变modelPosition时）

drawGrid();

// draw a teapot with model and view transform togetherdrawTeapot();

http://www.songho.ca/opengl/gl_transform.html#overview