用OpenGL快速给图形添加纹理含圆柱圆锥

这里讨论的是二维纹理

1.图取图像数据

void readimage(char* filename, BYTE* imagedata)//所读图片均为24位bmp,且宽度补齐至四字节边界
{
	BITMAPFILEHEADER bf;  //文件头
	BITMAPINFOHEADER bi;  //信息头
	int     m_ImageWidth;   //图象宽度
	int     m_ImageHeight;  //图象高度
	FILE  *fp1; //文件指针，fp1为源文件
	//打开文件，到文件指针
	if ((fp1 = fopen(filename, "rb")) == NULL)
	{
		MessageBox(NULL, "文件打开错误", "warning", MB_OK);
	}

	fread((LPSTR)&bf, sizeof(BITMAPFILEHEADER), 1, fp1);  //读取文件头，读取以后文件指针在文件头末尾（即信息头）
	fread((LPSTR)&bi, sizeof(BITMAPINFOHEADER), 1, fp1);  //读取信息头
	m_ImageWidth = bi.biWidth;             //给图象宽度赋值
	m_ImageHeight = bi.biHeight;           //给图象高度赋值
	fread(imagedata, m_ImageHeight*m_ImageWidth * 3, 1, fp1);  //读取图象数据
	fclose(fp1);
}

注意：读进来的图像为BGR,要调整为RGB

void adjustimage(BYTE* imagedata, int w, int h)
{
	BYTE temp;
	for (int i = 0; iglEnable(GL_TEXTURE_2D);

temp = imagedata[i * 3];imagedata[i * 3] = imagedata[i * 3 + 2];imagedata[i * 3 + 2] = temp;}}

2.设置纹理（因为一般要用到的纹理比较多，先将所有图片读入，要用到那张时候就使用glBindTexture函数来指定当前所使用的纹理对象）

注意：图像的像素要与数组对应，下面的是256*256

//------------------------设置纹理----------------------------------
void loadtexture()
{           
	glGenTextures(2, &texName);//2表示有两个纹理
	glBindTexture(GL_TEXTURE_2D, texName);
	{
		BYTE imagemoon[256][256][3];			//墙壁2的纹理
		readimage("D:\\wall2.bmp", &imagemoon[0][0][0]);
		adjustimage(&imagemoon[0][0][0], 256, 256);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, imagemoon);
	}
	{
		BYTE imagesky[256][256][3];
		readimage("D:\\wall1.bmp", &imagesky[0][0][0]);//墙壁1的纹理
		adjustimage(&imagesky[0][0][0], 256, 256);
		glBindTexture(GL_TEXTURE_2D, texName + 1);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, imagesky);
	}
}

3.启用纹理

glEnable(GL_TEXTURE_2D);

4.纹理坐标

例子：坐标要对应，纹理用单位表示，（0.0，0.0）表示左下角（1.0,1.0）表示右上角

void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	//printf("At:%.2f %.2f %.2f\n",r*cos(c*du),h,r*sin(c*du)); //这就是视点的坐标
	glLoadIdentity();
	gluLookAt(r*cos(c*du), h, r*sin(c*du), 0, 0, 0, 0, 1, 0); //从视点看远点,y轴方向(0,1,0)是上方向

	glColor3f(1.0f, 0.0f, 0.0f);

	glEnable(GL_TEXTURE_2D);
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

	//地面
	glPushMatrix();
	glBindTexture(GL_TEXTURE_2D, texName + 2);
	glColor3f(0.0, 1.0, 1.0);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0, 0.0); glVertex3f(5.0f,-2.0f,3.0f);
	glTexCoord2f(1.0, 0.0); glVertex3f(-5.0f, -2.0f, 3.0f);
	glTexCoord2f(1.0, 1.0); glVertex3f(-5.0f, -2.0f, -3.0f);
	glTexCoord2f(0.0, 1.0); glVertex3f(5.0f, -2.0f, -3.0f);
	glEnd();

	//左墙
	glPushMatrix();
	glBindTexture(GL_TEXTURE_2D, texName + 1);
	glBegin(GL_POLYGON);
	glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, 0.0, 1.5);
	glTexCoord2f(0.0, 0.66); glVertex3f(-2.0, 2.0, 1.5);
	glTexCoord2f(0.5, 1.0); glVertex3f(-2.0, 3.0, 0.0);
	glTexCoord2f(1.0, 0.66); glVertex3f(-2.0, 2.0, -1.5);
	glTexCoord2f(1.0, 0.0); glVertex3f(-2.0, 0.0, -1.5);
	glEnd();
	glPopMatrix();

	glFlush();
	glutSwapBuffers();

	glDisable(GL_TEXTURE_2D);
}

5.对于圆柱和圆锥

将圆柱和圆锥看做是由很多线组成的，使用三角函数和一个循环就可以画出

        //圆柱
	glTranslatef(-3.0, -2.0, 2.0);
	glPushMatrix();
	glBindTexture(GL_TEXTURE_2D, texName );
    glBegin( GL_QUAD_STRIP);
    double t = 0.0;double dt = 2*PI/nslice;
    for (int j = 0; j <= nslice; ++j) 
	{
       glTexCoord2f( t/(2*PI), 1.0); glVertex3f( cos( t), 2.0, -sin( t));
       glTexCoord2f( t/(2*PI), 0.0); glVertex3f( cos( t), 0.0, -sin( t));
       t = t + dt;
     }
    glEnd();
	glPopMatrix();

	//圆锥
	glPushMatrix();
	glBindTexture(GL_TEXTURE_2D, texName + 4 );
	glBegin( GL_QUAD_STRIP);
    double tt = 0.0;double dtt = 2*PI/nslice;
    for (int j = 0; j <= nslice; ++j) 
	{
       glTexCoord2f( tt/(2*PI), 1.0); glVertex3f( 0.0, 2.0, 0.0);
       glTexCoord2f( tt/(2*PI), 0.0); glVertex3f( cos( tt), 0.0, -sin( tt));
       tt = tt + dtt;
     }
    glEnd();
	glPopMatrix();