OpenGL入门笔记（三）

今天主要学习二维图形的着色和旋转。

intDrawGLScene(GLvoid)//Here'sWhereWeDoAllTheDrawing
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);//ClearScreenAndDepthBuffer
glLoadIdentity();
glTranslatef(-1.5f,0.0f,-6.0f);//MoveLeft1.5UnitsAndIntoTheScreen6.0
glRotatef(rtri,0.0f,1.0f,0.0f);
glBegin(GL_TRIANGLES);//DrawingUsingTriangles
glColor3f(1.0f,0.0f,0.0f);
glVertex3f(0.0f,1.0f,0.0f);//Top
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(-1.0f,-1.0f,0.0f);//BottomLeft
glColor3f(0.0f,0.0f,1.0f);
glVertex3f(1.0f,-1.0f,0.0f);//BottomRight
glEnd();//FinishedDrawingTheTriangle
glLoadIdentity();
glTranslatef(1.5f,0.0f,-6.0f);//MoveRight3Units
glRotatef(rquad,1.0f,0.0f,0.0f);
glBegin(GL_QUADS);//DrawAQuad
glColor3f(1.0f,0.0f,0.0f);
glVertex3f(-1.0f,1.0f,0.0f);//TopLeft
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(1.0f,1.0f,0.0f);//TopRight
glColor3f(0.0f,0.0f,1.0f);
glVertex3f(1.0f,-1.0f,0.0f);//BottomRight
glColor3f(1.0f,1.0f,1.0f);
glVertex3f(-1.0f,-1.0f,0.0f);//BottomLeft
glEnd();//DoneDrawingTheQuad//ResetTheCurrentModelviewMatrix
rtri+=0.2f;
rquad-=0.15f;
returnTRUE;//EverythingWentOK
}

glColor<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><chmetcnv unitname="F" sourcevalue="3" hasspace="False" negative="False" numbertype="1" tcsc="0" w:st="on">3f</chmetcnv>(r,g,b)。括号中的三个参数依次是红、绿、蓝三色分量。取值范围可以从0,<chmetcnv unitname="F" sourcevalue="0" hasspace="False" negative="False" numbertype="1" tcsc="0" w:st="on">0f</chmetcnv>到<chmetcnv unitname="F" sourcevalue="1" hasspace="False" negative="False" numbertype="1" tcsc="0" w:st="on"><span lang="EN-US" style="FONT-SIZE: 10pt; FONT-FAMILY: Verdana">1.0f</span></chmetcnv>。因为每个顶点有不同的颜色，因此看起来颜色从每个角喷出，并刚好在三角形的中心汇合，三种颜色相互混合。<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

glRotatef(Angle,Xvector,Yvector,Zvector)负责让对象绕某个轴旋转。这个命令有很多用处。Angle通常是个变量代表对象转过的角度。Xvector、Yvector、Zvector三个参数则共同决定旋转轴的方向。比如(1,0,0)所描述的矢量经过X坐标轴的1个单位处并且方向向右。(-1,0,0)所描述的矢量经过X坐标轴的1个单位处，但方向向左。

代码中我们增加了另一个glLoadIdentity()调用。目的是为了重置模型观察矩阵。如果我们没有重置，直接调用glTranslate的话，会出现意料之外的结果。