计算机图形图像绘制技术(8)

计算机图形图像绘制技术第8讲上次课内容小结Colorambient,reflection=Colorambient,lightxColorambient,materialColordiffuse,reflection=L.NxColordiffuse,lightxColordiffuse,materialColorspecular,reflection=N.HshininessxColorspecular,lightxColorspecular,material上次课小结物体看上去有颜色，是它被光线照射的结果；如果光是白色的，那么呈现的就是物体本身的颜色，否则会是光色和表面本色综合的结果；物体表面被点光源照射后，会呈现三个区域：高光区、过渡色区和环境色区高光区是镜面反射的结果，亮度特别高，光源越强越明显；过渡色区是漫反射的结果，通常面积较大；与物体本色相一致环境色区则是不受光照部份的颜色，通常较暗；为物体的阴影部分；一个例子GLfloatmat_specular[]={1.0,1.0,1.0,1.0};GLfloatmat_shininess[]={50.0};GLfloatlight_position[]={1.0,1.0,1.0,0.0);glShadeModel(GL_SMOOTH);glMaterialfv(GL_FRONT,GL_SPECULAR,mat_specular);glMaterialfv(GL_FRONT,GL_SHININESS,mat_shininess);glLightfv(GL_LIGHT0,GL_POSITION,light_position);glEnable(GL_LIGHTING);glEnable(GL_LIGHT0);glEnable(GL_DEPTH_TEST);glutSolidSphere(1.0,20,16);光源类型判断以下两图中，哪个图使用的是平行光源？主要内容光强的衰减聚光光源材质的发射光属性光与表面法线透明度雾光强的衰减glLightf(GL_LIGHT0,GL_CONSTANT_ATTENUATION,1.0);//setskcglLightf(GL_LIGHT0,GL_LINEAR_ATTENUATION,0.0);//setsklglLightf(GL_LIGHT0,GL_QUADRATIC_ATTENUATION,0.5);//setskqTIONIC_ATTENUAGL_QUADRATNATTENUATIOGL_LINEAR_IONT_ATTENUATGL_CONSTAN12qlcqlckkkddkdkk光源与目标点的距离衰减因子voidglLight{if}[v](GLenumlight,GLenumpname,TYPEparam);GLfloatamb_color[]={0.2,0.2,0.2,1.0};GLfloatdiff_color[]={1.0,1.0,1.0,1.0};GLfloatspec_color[]={1.0,1.0,1.0,1.0};GLfloatpos[]={0.0,1.0,0.0,1.0};//pointlightsourceat(0,1,0)glLightfv(GL_LIGHT1,GL_AMBIENT,amb_color);glLightfv(GL_LIGHT1,GL_DIFFUSE,diff_color);glLightfv(GL_LIGHT1,GL_SPECULAR,spec_color);glLightfv(GL_LIGHT1,GL_POSITION,pos);glLightf(GL_LIGHT1,GL_CONSTANT_ATTENUATION,1.0);//setsk0glLightf(GL_LIGHT1,GL_LINEAR_ATTENUATION,0.0);//setsk1glLightf(GL_LIGHT1,GL_QUADRATIC_ATTENUATION,0.5);//setsk2glEnable(GL_LIGHT1);例子程序启用衰减与未启用衰减的比较未启用衰减启用衰减聚光源光锥半角GL_SPOT_CUTOFF光锥方向GL_SPOT_DIRECTION光锥强度分布GL_EXPONENT衰减因子GL_SPOT_CUTOFFGL_SPOT_DIRECTIONfloatlightDirection[]={-1.0,-2.5,0.0};glLightf(GL_LIGHT2,GL_SPOT_CUTOFF,10.0);glLightfv(GL_LIGHT2,GL_SPOT_DIRECTION,lightDirection);glLightf(GL_LIGHT2,GL_SPOT_EXPONENT,5.0);一个聚光灯的例子floatLightPos[]={5.0,10,0,1};floatlightDiffuse[]={1.0f,.0f,1.0f};floatlightSpecular[]={0.92f,0.92f,0.92f};floatlightDirection[]={-1.0,-2.5,0.0};glEnable(GL_LIGHTING);glEnable(GL_LIGHT2);glLightfv(GL_LIGHT2,GL_POSITION,LightPos);//设置光源位置glLightfv(GL_LIGHT2,GL_DIFFUSE,lightDiffuse);//设置散射光颜色glLightfv(GL_LIGHT2,GL_SPECULAR,lightSpecular);//设置镜面反射光颜色glLightf(GL_LIGHT2,GL_SPOT_CUTOFF,10.0);glLightfv(GL_LIGHT2,GL_SPOT_DIRECTION,lightDirection);glLightf(GL_LIGHT2,GL_SPOT_EXPONENT,5.0);floatshininess=10;floatmaterialDiffuse[]={1.0f,0.0f,1.0f,1.0f};floatmaterialSpecular[]={1.0f,1.0f,1.0f,1.0f};glMaterialfv(GL_FRONT_AND_BACK,GL_DIFFUSE,materialDiffuse);glMaterialfv(GL_FRONT_AND_BACK,GL_SPECULAR,materialSpecular);glMaterialfv(GL_FRONT_AND_BACK,GL_SHININESS,&shininess);glutSolidTeapot(0.6);物体的发光特性M为RGBA强度,andlemissionis为物体发射光属性.•在OpenGL中,物发射光不依赖于其它光源与不作为一个新的光源，它只是计算自己的颜色•.IleMlemission=EmissiveComponentParameterNameDefaultValueMeaningGL_AMBIENT(0.0,0.0,0.0,1.0)ambientRGBAintensityoflightGL_DIFFUSE(1.0,1.0,1.0,1.0)diffuseRGBAintensityoflightGL_SPECULAR(1.0,1.0,1.0,1.0)specularRGBAintensityoflightGL_POSITION(0.0,0.0,1.0,0.0)(x,y,z,w)positionoflightGL_SPOT_DIRECTION(0.0,0.0,-1.0)(x,y,z)directionofspotlightGL_SPOT_EXPONENT0.0spotlightexponentGL_SPOT_CUTOFF180.0spotlightcutoffangleGL_CONSTANT_ATTENUATION1.0constantattenuationfactorGL_LINEAR_ATTENUATION0.0linearattenuationfactorGL_QUADRATIC_ATTENUATION0.0quadraticattenuationfactorvoidglLight{i,f}[v](GLenumlight,GLenumpname,TYPEparam);表面法线与光照光照后的颜色取决于表面法线光源位置视点位置NglNormal3f(x,y,z)多边形面的法线定义法线必须将法线标准化，即让其长度为单位长度；可调用函数glEnable(GL_NORMALIZE)，让opengl自动进行法线的标准化；对于glut和glu库定义的对象，如glutSolidSphere，这些对象定义时已给出了法线。但对于程序员使用GL_TRIANGLES,GL_QUADSandGL_POLYGON生成的面，需要给出法线，才能进行光照计算。glBegin(GL_QUADS);glNormal3f(0,0,1);glVertex3f(0,0,1);glVertex3f(1,0,1);glVertex3f(1,1,1);glVertex3f(0,1,1);glEnd();光照计算总模型102materiallightmodelmaterial0,max**0,max****_*1*nishininessmateriallightmateriallightmateriallightiiqlcnsspecularspecularnLdiffusediffuseambientambienteffectspotlightdkdkkambientambientemissionrvertexcolo符号说明i=光源编号,asin{LIGHT0,LIGHT1,LIGHT2,…LIGHT7}d=所求点与光源的距离kc=GL_CONSTANT_ATTENUATIONkl=GL_LINEAR_ATTENUATIONkq=GL_QUADRATIC_ATTENUATION注意:如果光源为聚光源（spotlight）,衰减因子被忽略spotlight_effect1,如果不是聚光光源0,如果是聚光光源，且顶点位于光照锥外max{vd,0}GL_SPOT_EXPONENT这里的v为单位向量，从聚光源位置指向所求顶点。d为聚光源方向L=单位向量，由所求顶点指向光源位置n=所求顶点的单位法向量s=(顶点与光源位置连线的单位向量)+(顶点与相机连线的单位向量)glLightModel[f,i]v该函数用于设设置光源模型参数voidglLightModel[f,i]v(GLenumpname,constGLfloat*params);参数说明pname表示所设置的光照模型，取值可以为GL_LIGHT_MODEL_AMBIENT//全局环境光GL_LIGHT_MODEL_LOCAL_VIEWER//局部视点GL_LIGHT_MODEL_TWO_SIDE//双面光照param是指定的光照模型的属性值3.4设置光照模型属性全局环境光该光源为场景提供不来自于任何特定光源的全局环境光例如：GLfloatImodel_ambient[]={0.2,0.2,0.2,1.0};glLightModelfv(GL_LIGHT_MODEL_AMBIENT,Imodel_ambient);3.4设置光照模型属性局部视点和无穷远视点镜面面反射的高光受视觉点位置的影响；镜面反射光强不但与顶点的法矢N相关，还与光源方向L和视线方向V密切相关；设置GL_LIGHT_MODEL_LOCAL_VIEWER属性设为GL_TRUE或GL_FALSE，可将场景中的视点定位在坐标原点或无穷远点。gl