《基于MFC的OpenGL编程》Part 4.pdf

《基于MFC的OpenGL编程》Part4DrawingSimple3D
objects

5D开心SEO博客http://blog.5dkx.com收集整理
视见体ViewingVolumeisnothingbuttheregionof3DCartesianspacein
thatwilloccupythewindow.Itisnothingbuttheminimumandmaximumx,y
andzvaluesthatareinsidethewindow.Soifavertexisoutsidethisrangeofx,
yandzvaluesthentheyareclippedbyOpenGLbeforerenderingcanoccur.
ZBuffer
Thenewtermwehavetodealwithinadditiontowidthandheightofan
objectin3Dgraphicsisdepth.Thedepthofanobjectisitsdistancefromthe
viewpoint.Theviewpointisthelocationfromwhichwearelookingatthatpoint.
ThisdepthvaluegoesintothedepthorZ-buffer.Ifwearedrawing2objectsthat
havesomepixelsthatoverlap,thefirstobjectwillafteritisrenderedhaveits
depthvalueinthedepthbuffer.Whenthenextobjectisrendered,OpenGLwill
checktoseewhetherthepixelit’sabouttodrawisinfrontof(withrespectto
theviewpoint)anypixelfromthefirstobjectthat’salreadydrawn.Itdoesthis
bycheckingtheZvalueofthecurrentpixelwiththevaluethatisalreadyinthe
buffer.Ifthenewpixelisclosertotheviewpoint,OpenGLplacesitsdepthvalue
inthedepthbuffer.ThisishowtheZ-bufferworks.
正交投影和透视投影
Onetermweneedtounderstandverywelltolearn3DGraphicswellis
projection.Well,computergraphicsatitssimplestisallaboutsettingacolorto
apixelonscreen.Andapixelonascreencanhaveonlytwodimensions.So3D
graphicsismerelyanillusion.The3Dcoordinatesthatwespecifywillhavetobe
projectedontoa2Dsurfacetocreatethisillusionforus.Andwehavetospecify
howthisprojectionworks.Byspecifyingaprojectionwespecifytheclippingor
viewingvolume.
基本3D图形绘制
1,在CCY457OpenGLView.h中加入下列变量

BOOLm_bPoint;//StatusofPoint
BOOLm_bLine;//StatusofLine
BOOLm_bPolygon;//StatusofPolygon
BOOLm_bTriangle;//StatusofTriangle

并且在构造函数中初始化

CCY457OpenGLView::CCY457OpenGLView()
{
m_bPoint=FALSE;
m_bLine=FALSE;
m_bPolygon=FALSE;
m_bTriangle=FALSE;
m_bCube=FALSE;
m_bTorus=FALSE;
m_bTeapot=FALSE;
m_bIcosahedron=FALSE;
m_bSimpleCube=FALSE;
}

2,加入五个菜单项及其对应的事件处理程序。

voidCCY457OpenGLView::OnObjectsTeapot()
{//画茶壶
m_bCube=FALSE;
m_bTorus=FALSE;
m_bTeapot=TRUE;
m_bIcosahedron=FALSE;
m_bSimpleCub