OpenGL Study 3

 Lesson04

实现图形的旋转

bool DrawGLScene(GLvoid)
{
    //clear the screen and the depth buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //reset the current modelview matrix
    glLoadIdentity();

    //move left 1.5 units,deep 6.0 units from current position
    //move the model from (0,0,0) to (-1.5,0.0,-6.0),it can also be implemented by move the view point
    glTranslatef(-1.5f,0.0f,-6.0f);

    //rotate around the y axis
    glRotatef(rtri,0.0f,1.0f,0.0f);

    //draw a triangle,with smooth coloring
    glBegin(GL_TRIANGLES);
        glColor3f(1.0f,0.0f,0.0f);
        glVertex3f(0.0f,1.0f,0.0f);
        glColor3f(0.0f,1.0f,0.0f);
        glVertex3f(-1.0f,-1.0f,0.0f);
        glColor3f(0.0f,0.0f,1.0f);
        glVertex3f(1.0f,-1.0f,0.0f);
    glEnd();

    //reset the current modleview matrix
    glLoadIdentity();

    //move from (0.0,0.0,0.0) to (1.5,0.0,-6.0)
    glTranslatef(1.5f,0.0f,-6.0f);

    //rotate around the x axis
    glRotatef(rquad,1.0f,0.0f,0.0f);

    //draw a quad,the vertex is represented in the model coordinate
    //with flat coloring
    glColor3f(0.5f,0.5f,1.0f);
    glBegin(GL_QUADS);
        glVertex3f(-1.0f,1.0f,0.0f);
        glVertex3f(-1.0f,-1.0f,0.0f);
        glVertex3f(1.0f,-1.0f,0.0f);
        glVertex3f(1.0f,1.0f,0.0f);
    glEnd();

    rtri+=0.2f;
    rquad-=0.15f;
    return true;
}

使用glRotatef(r,x,y,z)使图形绕向量（x，y，z）旋转r弧度，r>0时，正对环绕轴来看，逆时针旋转。

代码中两次出现了glLoadIdentity()函数，在每绘制一个图形之前都将模型视图矩阵置一，然后在移动，旋转进行必要的变换，再绘制图形，这样可以防止不同图形之间变换矩阵的影响。

Lesson05

绘制3D物体

bool DrawGLScene(GLvoid)
{
    //clear the screen and the depth buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //reset the current modelview matrix
    glLoadIdentity();

    //move left 1.5 units,deep 6.0 units from current position
    //move the model from (0,0,0) to (-1.5,0.0,-6.0),it can also be implemented by move the view point
    glTranslatef(-1.5f,0.0f,-6.0f);

    //rotate around the y axis
    glRotatef(rtri,0.0f,1.0f,0.0f);

    //draw a diamond made of 4 triangles,with smooth coloring
    glBegin(GL_TRIANGLES);
        //front
        glColor3f(1.0f,0.0f,0.0f);//red
        glVertex3f(0.0f,1.0f,0.0f);
        glColor3f(0.0f,1.0f,0.0f);//green
        glVertex3f(-1.0f,-1.0f,1.0f);
        glColor3f(0.0f,0.0f,1.0f);//blue
        glVertex3f(1.0f,-1.0f,1.0f);

        //right
        glColor3f(1.0f,0.0f,0.0f);//red
        glVertex3f(0.0f,1.0f,0.0f);
        glColor3f(0.0f,0.0f,1.0f);//blue
        glVertex3f(1.0f,-1.0f,1.0f);
        glColor3f(0.5f,0.5f,0.0f);//rg
        glVertex3f(1.0f,-1.0f,-1.0f);

        //back
        glColor3f(1.0f,0.0f,0.0f);//red
        glVertex3f(0.0f,1.0f,0.0f);
        glColor3f(0.5f,0.5f,0.0f);//rg
        glVertex3f(1.0f,-1.0f,-1.0f);
        glColor3f(0.5f,0.0f,0.5f);//rb
        glVertex3f(-1.0f,-1.0f,-1.0f);

        //back
        glColor3f(1.0f,0.0f,0.0f);//red
        glVertex3f(0.0f,1.0f,0.0f);
        glColor3f(0.5f,0.0f,0.5f);//rb
        glVertex3f(-1.0f,-1.0f,-1.0f);
        glColor3f(0.0f,1.0f,0.0f);//green
        glVertex3f(-1.0f,-1.0f,1.0f);

    glEnd();

    //reset the current modleview matrix
    glLoadIdentity();

    //move from (0.0,0.0,0.0) to (1.5,0.0,-6.0)
    glTranslatef(1.5f,0.0f,-6.0f);

    //rotate around the x axis
    glRotatef(rquad,1.0f,0.0f,0.0f);

    //draw a cubic made of 6 quads,the vertex is represented in the model coordinate
    //with flat coloring
    glBegin(GL_QUADS);
        //top,y=1
        glColor3f(1.0f,0.0f,0.0f);
        glVertex3f(-1.0f,1.0f,1.0f);
        glVertex3f(1.0f,1.0f,1.0f);
        glVertex3f(1.0f,1.0f,-1.0f);
        glVertex3f(-1.0f,1.0f,-1.0f);

        //bottom,y=-1
        glColor3f(0.0f,1.0f,0.0f);
        glVertex3f(-1.0f,-1.0f,1.0f);
        glVertex3f(-1.0f,-1.0f,-1.0f);
        glVertex3f(1.0f,-1.0f,-1.0f);
        glVertex3f(1.0f,-1.0f,1.0f);

        //front,z=1
        glColor3f(0.0f,0.0f,1.0f);
        glVertex3f(-1.0f,-1.0f,1.0f);
        glVertex3f(1.0f,-1.0f,1.0f);
        glVertex3f(1.0f,1.0f,1.0f);
        glVertex3f(-1.0f,1.0f,1.0f);

        //right,x=1
        glColor3f(1.0f,1.0f,0.0f);
        glVertex3f(1.0f,-1.0f,1.0f);
        glVertex3f(1.0f,-1.0f,-1.0f);
        glVertex3f(1.0f,1.0f,-1.0f);
        glVertex3f(1.0f,1.0f,1.0f);

        //back,z=-1
        glColor3f(0.0f,1.0f,1.0f);
        glVertex3f(-1.0f,-1.0f,-1.0f);
        glVertex3f(-1.0f,1.0f,-1.0f);
        glVertex3f(1.0f,1.0f,-1.0f);
        glVertex3f(1.0f,-1.0f,-1.0f);

        //left,x=-1
        glColor3f(1.0f,0.0f,1.0f);
        glVertex3f(-1.0f,-1.0f,1.0f);
        glVertex3f(-1.0f,1.0f,1.0f);
        glVertex3f(-1.0f,1.0f,-1.0f);
        glVertex3f(-1.0f,-1.0f,-1.0f);

    glEnd();

    rtri+=0.2f;
    rquad-=0.15f;
    return true;
}

使用4个三角形组成一个金字塔，采用6个正方形组成一个正方体。