OPENGL的纹理.doc

OPENGL的纹理在3D图形中，纹理映射是广泛使用的。纹理映射也是相当复杂的过程：一 定义纹理二 控制滤波三 说明映射方式四 绘制场景给出顶点的纹理坐标和几何坐标注意！纹理映射只能在RGBA模式下使用，不适用于颜色索引模式1.纹理定义void glTexImage2D( GLenum target, GLint level, GLint components,GLsizei width, GLsizei height, GLint border,GLenum format, GLenum type, const GLvoid *pixels );定义一个二维纹理映射。target是常数 GL_TEXTURE_2Dlevel表示多级分辨率的纹理图象的级数。若只有一种分辨率，level为0。components是从1到4的整数，1：选择R；2：选择R A；3：选择R G B；4：选择R G B A；width height是纹理的尺寸。format和type描述映射格式和数据类型。它们与前面讲的glDrawPixels()中OPENGL的纹理在3D图形中，纹理映射是广泛使用的。纹理映射也是相当复杂的过程：一 定义纹理二 控制滤波三 说明映射方式四 绘制场景给出顶点的纹理坐标和几何坐标注意！纹理映射只能在RGBA模式下使用，不适用于颜色索引模式1.纹理定义void glTexImage2D( GLenum target, GLint level, GLint components,GLsizei width, GLsizei height, GLint border,GLenum format, GLenum type, const GLvoid *pixels );定义一个二维纹理映射。target是常数 GL_TEXTURE_2Dlevel表示多级分辨率的纹理图象的级数。若只有一种分辨率，level为0。components是从1到4的整数，1：选择R；2：选择R A；3：选择R G B；4：选择R G B A；width height是纹理的尺寸。format和type描述映射格式和数据类型。它们与前面讲的glDrawPixels()中GL_NEAREST_MIPMAP_NEARESTGL_NEAREST_MIPMAP_LINEARGL_LINEAR_MIPMAP_NEARESTGL_LINEAR_MIPMAP_LINEAR2.1 滤波原始纹理图象是个方形图象，把它映射到奇形怪状的物体上，一般不可能图象上的一个象素对应屏幕的一个象素。因此局部放大缩小时，就要定义合适的滤波方式（以2D为例）：void glTexParameter(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);void glTexParameter(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);前者是放大滤波（GL_TEXTURE_MAG_FILTER），后者是缩小滤波（GL_TEXTURE_MIN_FILTER）；另外，GL_NEAREST是利用最坐标最靠近象素中心的纹理元素，这有可能使图样走型，但计算速度快；GL_LINEAR利用线形插值，效果好但计算量大。.2重复与缩限纹理映射可以重复映射或者缩限映射，重复映射时纹理可以在自己的坐标S T方向重复。对于重复映射：void glTexParameterfv(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_REPEAT);void glTexParameterfv(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_REPEAT);参数GL_REPEAT改为GL_CLAMP，则缩限，所有大于1的纹理元素值置为1。所有小于0的纹理元素值置为0。0的纹理元素值置为0。3. 映射方式处理纹理本身图案颜色和物体本身颜色的关系：void glTexEnvifv(GLenum target,GLenum pname,TYPE param);target必须是GL_TEXTURE_ENV;pname是GL_TEXTURE_ENV_MODE，则param可以是 GL_DECAL GL_MODULATE或GL_BLEND，说明纹理值与原来颜色不同的处理方式。pname是GL_TEXTURE_ENV_COLOR，则参数param是包含4个浮点数（R、G、B、A）的数组。这些值只在采用GL_BLEND纹理函数时才采用。4. 纹理坐标坐标的定义：纹理图象是方形的，纹理坐标可定义成s,t,r,q坐标，仿照齐次坐标系的x,y,z,w坐标。void glTexCoord1234sifdv(TYPE coords)；设置当前纹理坐标，此后调用glVertex*()所产生的顶点都赋予当前的纹理坐标。5. 坐标自动产生有时不需要为每个物体顶点赋予纹理坐标，可以使用void glTexGenif(GLenum coord,GLenum pname,TYPE param);coord为：GL_S GL_T GL_R或GL_Q，指明哪个坐标自动产生pname为GL_TEXTURE_GEN_MODE时param为常数：GL_OBJECT_LINEAR GL_EYE_LINEAR或GL_SPHERE_MAP，它们决定用哪个函数来产生纹理坐标pname为GL_OBJECT_PLANE或GL_EYE_PLANE，param时一个指向参数数组的指针。先请看一个简单的例子：/sample.cpp#include glos.h#include #include #include windows.hvoid myinit(void);void CALLBACK display(void);void CALLBACK reshape(GLsizei w,GLsizei h);/创建纹理图象的子程序#define TEXTUREWIDTH 64#define TEXTUREHEIGHT 64GLubyte TextureTEXTUREWIDTHTEXTUREHEIGHT3;void makeTexture(void)void makeTexture(void)int i,j,r,g,b;for(i=0;iTEXTUREWIDTH;i+)for(j=0;jTEXTUREHEIGHT;j+)r=(i*j)%255;g=(4*i)%255;b=(4*j)%255;Textureij0 =(GLubyte)r;Textureij1 =(GLubyte)g;Textureij2 =(GLubyte)b;void myinit(void)auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);auxInitPosition(0,0,500,500);auxInitWindow(sample1);auxInitWindow(sample1);glClearColor(0.0,0.0,0.0,0.0);glClear(GL_COLOR_BUFFER_BIT);/创建纹理图象的原始数据保存在Texture中makeTexture();glPixelStorei(GL_UNPACK_ALIGNMENT,1);/定义二维纹理glTexImage2D(GL_TEXTURE_2D,0,3,TEXTUREWIDTH,TEXTUREHEIGHT,0,GL_RGB,GL_UNSIGNED_BYTE,&Texture000);/控制滤波glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_CLAMP);glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_CLAMP);glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);glTexParameterf(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);/说明映射方式glTexEnvf(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_DECAL);/这个应该很熟了，启用纹理模式glEnable(GL_TEXTURE_2D);glEnable(GL_TEXTURE_2D);/ glShadeModel(GL_FLAT);void CALLBACK reshape(GLsizei w,GLsizei h)glViewport(0,0,w,h);glMatrixMode(GL_PROJECTION);glLoadIdentity();/定义立体视景体gluPerspective(60.0,1.0*(GLfloat)w/(GLfloat)h,1.0,30.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();glTranslatef(0.0,0.0,-3.6);void CALLBACK display(void)glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);glBegin(GL_QUADS);/绘制四边形/先绘制正方形，用来显示实际未变形的纹理图样/先绘制正方形，用来显示实际未变形的纹理图样glTexCoord2f(0.0,0.0);glVertex3f(-2.0,-1.0,0.0);glTexCoord2f(0.0,1.0);glVertex3f(-2.0,1.0,0.0);glTexCoord2f(1.0,1.0);glVertex3f(0.0,1.0,0.0);glTexCoord2f(1.0,0.0);glVertex3f(0.0,-1.0,0.0);/绘制一个不规则四边形，用来显示纹理是如何随物体形状而变形的。glTexCoord2f(0.0,0.0);glVertex3f(0.0,-1.0,0.0);glTexCoord2f(0.0,1.0);glVertex3f(0.0,1.0,0.0);glTexCoord2f(1.0,1.0);glVertex3f(1.41421,1.0,-1.41421);glTexCoord2f(1.0,0.0);glVertex3f(1.41421,-1.0,-1.41421);glEnd();glFlush();void main(void)myinit();auxReshapeFunc(reshape);auxMainLoop(display);/end of sample从例子来看，除了纹理的定义和控制比较麻烦和不容易理解外，其应用是十分方便的。只须从纹理的坐标系选出合适点附在实际物体顶点上即可。对于复杂的纹理定义和控制，你也可以自行改变一些参数，看看效果如何。例如把GL_LINEAR改成GL_NEAREST，则纹理的明显变的粗糙，但计算结果却快的多。你也可以改动glTexCoord2f()的参数，看看如何选定纹理的一部分（例子中是选定全部纹理）来贴图。例如1.0改成0.5则选择实际纹理的左上1/4部分来贴图。下次将给出一个更复杂的纹理应用的例子和说明。18:03 98-1-21这次将结束纹理的内容。紧接上次，在上次平面纹理贴图中，我们先定义了一个数组（一维或二维.）来定义纹理的数据，所以纹理本身是一个N维空间，有自己的坐标和顶点。在上次的例子中，我们学会了如何把纹理数据中的坐标和屏幕物体坐标相结合，就象把一块布料扯成合适的形状贴在物体表面。而上次唯一没有使用的函数是纹理坐标的自动产生（最后一个给出的函数），它的意义是产生一个环境纹理，所有环境内的物体都赋予此纹理，很象一个特殊光源。/sample.cpp#include glos.h#include #include #include windows.hvoid myinit(void);void CALLBACK display(void);void CALLBACK reshape(GLsizei w,GLsizei h);/定义一个一维纹理的数据，从生成来看，保持红色、兰色分量255（MAX），/所以是渐变的紫色纹理，饱和度不断变化。/所以是渐变的紫色纹理，饱和度不断变化。#define TEXTUREWIDTH 64GLubyte Texture3*TEXTUREWIDTH;void makeTexture(void)int i;for(i=0;iTEXTUREWIDTH;i+)Texture3*i =255;Texture3*i+1 =255-2*i;Texture3*i+2 =255;GLfloat sgenparams=1.0,1.0,1.0,0.0;void myinit(void)auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);auxInitPosition(0,0,500,500);auxInitWindow(sample1);glClearColor(0.0,0.0,0.0,0.0);glClear(GL_COLOR_BUFFER_BIT);/创建纹理makeTexture();glPixelStorei(GL_UNPACK_ALIGNMENT,1);/控制纹理glTexEnvf(GL_TEXTURE_ENV,GL_TEXTURE_ENV_MODE,GL_MODULATE);glTexParameterf(GL_TEXTURE_1D,GL_TEXTURE_WRAP_S,GL_REPEAT);glTexParameterf(GL_TEXTURE_1D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);glTexParameterf(GL_TEXTURE_1D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);glTexImage1D(GL_TEXTURE_1D,0,3,TEXTUREWIDTH,0,GL_RGB,GL_UNSIGNED_BYTE,Texture);/唯一与前面例子不同的地方：启用纹理坐标自动产生，生成环境纹理/纹理的方向SglTexGeni(GL_S,GL_TEXTURE_GEN_MODE,GL_OBJECT_LINEAR);glTexGenfv(GL_S,GL_OBJECT_PLANE,sgenparams);/启用纹理glEnable(GL_TEXTURE_1D);glEnable(GL_TEXTURE_GEN_S);/启用消隐glEnable(GL_DEPTH_TEST);glDepthFunc(GL_LESS);glDepthFunc(GL_LESS);/一些绘图控制，详细可参阅VC5联机帮助glEnable(GL_CULL_FACE);glEnable(GL_LIGHTING);glEnable(GL_LIGHT0);glEnable(GL_AUTO_NORMAL);glEnable(GL_NORMALIZE);glFrontFace(GL_CW);glCullFace(GL_BACK);glMaterialf(GL_FRONT,GL_SHININESS,64.0);/ glShadeModel(GL_FLAT);void CALLBACK reshape(GLsizei w,GLsizei h)glViewport(0,0,w,h);glMatrixMode(GL_PROJECTION);glLoadIdentity();if(w0，缺省1void glLineWidth(GLfoat width);设置线宽，width0，缺省为1void glLineStipple(GLint factor,GLushort pattern);设置线的模式，factor用于对模式进行拉伸的比例因子，pattern是线的模式例如11001100是虚线（1绘制，0不绘制）必须要启用glEnable(GL_LINE_STIPPLE)才能使用以上函数，不再使用时调用glDisable(GL_LINE_STIPPLE)关闭，这与以前的glEnable();glDisable();的用法都是类似的。请看下面例子：/sample.cpp#include glos.h#include glos.h#include #include #include windows.hvoid myinit(void);void CALLBACK display(void);void CALLBACK reshape(GLsizei w,GLsizei h);void myinit(void)auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);auxInitPosition(0,0,600,500);auxInitWindow(sample1);glClearColor(0.0,0.0,0.0,0.0);glClear(GL_COLOR_BUFFER_BIT);glShadeModel(GL_FLAT);void CALLBACK reshape(GLsizei w,GLsizei h)glViewport(0,0,w,h);glMatrixMode(GL_PROJECTION);glLoadIdentity();if(w=h)glOrtho(-4.0,4.0,-4.0*(GLfloat)h/(GLfloat)w,4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0);else glOrtho(-4.0*(GLfloat)h/(GLfloat)w,4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0,-4.0,4.0);glMatrixMode(GL_MODELVIEW);glLoadIdentity();/自定义的绘制直线的函数，参数为起始点和终止点坐标void line2i(GLint x1,GLint y1,GLint x2,GLint y2)glBegin(GL_LINES);glVertex2f(x1,y1);glVertex2f(x2,y2);glEnd();glEnd();void CALLBACK display(void)glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);/首先绘制一系列点，点的大小不断增加int i;glColor3f(0.8,0.6,0.4);for(i=1;i=10;i+)glPointSize(i*2);glBegin(GL_POINTS);glVertex2f(30.0+(GLfloat)i*50.0),330.0);glEnd();/再绘制两条虚线，第二条比第一条松散一些，由pattern参数即可看出glEnable(GL_LINE_STIPPLE);glLineStipple(1,0x0101);/间隔1位glColor3f(1.0,0.0,0.0);line2i(20,250,250,250);glLineStipple(1,0x00ff);/间隔2位glLineStipple(1,0x00ff);/间隔2位glColor3f(0.0,0.0,1.0);line2i(300,250,550,250);/改变线的绘制宽度的效果-加宽/重新画出上面两条虚线glLineWidth(5.0);glEnable(GL_LINE_STIPPLE);glLineStipple(1,0x0101);glColor3f(1.0,0.0,0.0);line2i(50,150,250,150);glLineStipple(1,0x00ff);glColor3f(0.0,0.0,1.0);line2i(300,150,550,150);glFlush();void main(void)myinit();/ auxReshapeFunc(reshape);auxMainLoop(display);auxMainLoop(display);/end of sample2.多边形void glPolygonMode(GLenum face,GLenum mode);控制多边形指定面的绘图模式，face为：GL_FRONT GL_BACK或GL_FRONT_AND BACKmode为：GL_POINT GL_LINE或GL_FILL表示多边型的轮廓点、轮廓线和填充模式的绘制方式。缺省是填充方式。void glPolygonStipple(const GLubyte *mask);其中mask必须是指向32*32的位图指针，1是绘制、0不绘制使用上述函数也要调用：glEnable(GL_POLYGON-STIPPLE);glDisable(GL_POLYGON_STIPPLE);请看下面例子：/sample.cpp#include glos.h#include #include #include #include windows.hvoid myinit(void);void CALLBACK display(void);void CALLBACK reshape(GLsizei w,GLsizei h);/定义填充模式32*32点阵GLubyte pattern=0x00,0x01,0x80,0x00,0x00,0x03,0xc0,0x00,0x00,0x07,0xe0,0x00,0x00,0x0f,0xf0,0x00,0x00,0x1f,0xf8,0x00,0x00,0x3f,0xfc,0x00,0x00,0x7f,0xfe,0x00,0x00,0xff,0xff,0x00,0x01,0xff,0xff,0x80,0x03,0xff,0xff,0xc0,0x07,0xff,0xff,0xe0,0x0f,0xff,0xff,0xf0,0x1f,0xff,0xff,0xf8,0x3f,0xff,0xff,0xfc,0x3f,0xff,0xff,0xfc,0x7f,0xff,0xff,0xfe,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0x7f,0xff,0xff,0xfe,0x3f,0xff,0xff,0xfc,0x1f,0xff,0xff,0xf8,0x0f,0xff,0xff,0xf0,0x07,0xff,0xff,0xe0,0x03,0xff,0xff,0xc0,0x01,0xff,0xff,0x80,0x00,0xff,0xff,0x00,0x00,0x7f,0xfe,0x00,0x00,0x3f,0xfc,0x00,0x00,0x1f,0xf8,0x00,0x00,0x0f,0xf0,0x00,0x00,0x07,0xe0,0x00,0x00,0x03,0xc0,0x00,0x00,0x01,0x80,0x00;void myinit(void)void myinit(void)auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);auxInitPosition(0,0,400,400);auxInitWindow(sample1);glClearColor(0.0,0.0,0.0,0.0);glClear(GL_COLOR_BUFFER_BIT);glShadeModel(GL_FLAT);void CALLBACK reshape(GLsizei w,GLsizei h)glViewport(0,0,w,h);glMatrixMode(GL_PROJECTION);glLoadIdentity();if(w=h) glOrtho(-4.0,4.0,-4.0*(GLfloat)h/(GLfloat)w,4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0);else glOrtho