第四章 图元的属性 曾智勇 软件学院

颜色和灰度 OpenGL几何图元和属性 Point Line polygon Character Antialiasing Glut函数

颜色和灰度 颜色空间: RGB HSV HLS Lab

灰度:当RGB函数中指定相同量的红色,绿色和蓝色时,结果是某种程度的灰色.

其它的颜色参数 强度(Intensity) ：物理学术语,用来量化一个时间段中在特定方向的光能辐射. 光亮度( Luminance ): 心理学术语,用来描述感觉光亮的特征.

颜色存储 RGB Index (color lookup table ;color map)

OpenGL颜色函数 设定颜色显示模型 glutInitDisplayMode(modeparameters); 帧缓存模式: GLUT_SINGLE ,GLUT_DOUBLE 颜色模式: GLUT_RGB(defualt), GLUT_RGBA , GLUT_INDEX

指定当前颜色分量 glColor*(colorcomponents); glColor3f(0.0,1.0,0.0); glColor3fv(colorArray); glColor3i(0,255,255); glIndex(colorIndex);

Set_current_color(red); Draw_object(A); Draw_object(B); Set_current_color(blue); Set_current_color(green); Draw_object(c)

显示窗口RGB颜色分量的设置 显示场景的当前刷新缓存的设置 glClearColor(red,green,blue,alpha); glClear(buffer-name); GL_COLOR_BUFFER_BIT;GL_DPTH_BUFFER_BIT;GL_ACCUM_BUFFER_BIT;GL_STENCIL_BUFFER_BIT

图元的绘制 在函数glBegin()和glEnd()之间是顶点函数的集合.glBegin()的参数决定了顶点构造的图元的种类.

顶点 glVertex{234}{sifd}[v](DataType coords);

点 glBegin(GL_POINTS); glVertex*(point-coordinate); …. glEnd();

属性: Color Size glPointSize(GLfloat size-float);

线 GL_LINES GL_LINE_STRIP GL_LINE_LOOP

线 p1 p3 glBegin(GL_LINES); glVertex*(point1-coordinate); glEnd();

p1 p3 p2 p4 glBegin(GL_LINE_STRIP); glVertex*(point1-coordinate); glVertex*(point2-coordinate); glVertex*(point3-coordinate); glVertex*(point4-coordinate); glVertex*(point5-coordinate); glEnd(); p5

p1 p3 p2 p4 glBegin(GL_LINE_LOOP); glVertex*(point1-coordinate); glVertex*(point2-coordinate); glVertex*(point3-coordinate); glVertex*(point4-coordinate); glVertex*(point5-coordinate); glEnd(); p5

属性 Color Width style

Width glLineWidth(GLfloat width); style glLineStripple(Glint repeatFactor,GLushort pattern); 参数 pattern是一个描述如何显示线段的一个16位整数,值为1的位对应一个“开”象素,值为0的位对应一个“关”象素.改模式从低位开始应用于线路径,默认模式为0xFFFF(每一位的值为1 ),它生成实线.整数参数repeatFactor说明模式中每一位重复应用多少次才轮到下一位.默认的重复值是1. glEnable(GL_LINE_STIPPLE); glDisable(GL_LINE_STIPPLE);

Dotted: 0x0101 1 Dashed: 0x00FF 1 Dash/dot/dash: 0x1C47 1

多边形 多边形的限制 多边形的边不能相交. OpenGL多边形必须是凸多边形.

glBegin(GL_POLYGON); glVertex2i(180,15); glVertex2i(10,145); glVertex2i(100,145); glVertex2i(10,15); glEnd(); glBegin(GL_POLYGON); glVertex2i(180,15); glVertex2i(10,145); glVertex2i(180,145); glVertex2i(170,140); glEnd();

多边形的绘制 填充 实填充 某种样式填充. 轮廓线 顶点上的点

设置前向面 glFrontFace(GLenum mode); 如果mode的值是GL_CCW, 窗口坐标系投影多边形的顶点顺序是逆时针方向. 如果mode的值为GL_CW,窗口坐标系投影多边形的顶点顺序是顺时针方向.

设置多边形模式 glPolygonMode(GLenum face, GLenum mode); 控制多边形前向面或后向面的绘制方式. 参数face的值可为:GL_FRONT_AND_BACK, GL_FRONT, 或GL_BACK; 参数mode 可以取GL_POINT, GL_LINE, GL_FILL 以表示多边形被绘制的样式.

glBegin(GL_POLYGON); glVertex2i(150,15); glVertex2i(180,50); glPolygonMode(GL_FRONT,GL_POINT); glPointSize(5); glBegin(GL_POLYGON); glVertex2i(150,15); glVertex2i(180,50); glVertex2i(150,100); glVertex2i(100,100); glVertex2i(50,50); glVertex2i(100,15); glEnd();

glPolygonMode(GL_FRONT,GL_LINE); glBegin(GL_POLYGON); glVertex2i(150,15); glVertex2i(180,50); glVertex2i(150,100); glVertex2i(100,100); glVertex2i(50,50); glVertex2i(100,15); glEnd();

//glPolygonMode(GL_FRONT,GL_FILL); glBegin(GL_POLYGON); glVertex2i(150,15); glVertex2i(180,50); glVertex2i(150,100); glVertex2i(100,100); glVertex2i(50,50); glVertex2i(100,15); glEnd();

设置多边形的填充图案 glPolygonStipple(const GLubyte *mask); - glEnable(GL_POLYGON_STIPPLE); - glDisable(GL_POLYGON_STIPPLE);

字符 glutBitmapCharacter(font,character); glutStrokeCharacter(font,character);

反走样 glEnable(PrimitiveType); PrimitiveType: GL_POINT_SMOOTH GL_LINE_SMOOTH GL_POLYGON_SMOOTH

Glut函数 glutDisplayFunc(void (*func)(void)) glutReshapeFunc(void(*func)(int w,int h)) glutKeyboardFunc(void(*func)(unsigned char key,int x,int y)) glutMouseFunc(void(*func)(int button,int state,int x,int y))