NeHe 系列教程之十一：飘扬的旗帜

英文教程地址：lesson11

本课实现了类似旗帜飘扬的效果， 其要领就是实时循环改变纹理坐标。本课以第六课的代码为基础。

首先是一些全局变量的定义：

namespace {GLfloat     xrot = 0;             // X RotationGLfloat     yrot = 0;             // Y RotationGLfloat     zrot = 0;             // Z Rotationfloat points[45][45][3];     // The Array For The Points On The Grid Of Our "Wave"int wiggle_count = 0;           // Counter Used To Control How Fast Flag WavesGLfloat hold;                   // Temporarily Holds A Floating Point ValueGLuint      texture[1];       // Storage For One Texture ( NEW )
}

加载纹理的过程与第六课类似，略。

然后是初始化过程， 这里重点关注纹理坐标points数据的构造：

void MyGLWidget::initializeGL()
{loadTextures();glEnable(GL_TEXTURE_2D);    // Enable Texture Mapping ( NEW )glShadeModel(GL_SMOOTH);   // Enables Smooth ShadingglClearColor(0.0f, 0.0f, 0.0f, 0.5f);  // Black BackgroundglClearDepth(1.0f);             // Depth Buffer SetupglEnable(GL_DEPTH_TEST);        // Enables Depth TestingglDepthFunc(GL_LEQUAL);        // The Type Of Depth Test To DoglHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Really Nice Perspective CalculationsglPolygonMode( GL_BACK, GL_FILL );      // Back Face Is Filled InglPolygonMode( GL_FRONT, GL_LINE );     // Front Face Is Drawn With Lines// Loop Through The X Planefor(int x=0; x<45; x++) {// Loop Through The Y Planefor(int y=0; y<45; y++) {// Apply The Wave To Our Meshpoints[x][y][0] = float((x/5.0f)-4.5f);points[x][y][1] = float((y/5.0f)-4.5f);points[x][y][2] = float(sin((((x/5.0f)*40.0f)/360.0f)*3.141592654*2.0f));}}
}

最后是绘制代码：

void MyGLWidget::paintGL()
{int x , y;                       // Loop Variablesfloat float_x, float_y, float_xb, float_yb;     // Used To Break The Flag Into Tiny QuadsglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth BufferglLoadIdentity();       // Reset The Current Modelview MatrixglTranslatef(0.0f,0.0f,-15.0f);       // Move Into The Screen 12 UnitsglRotatef(xrot,1.0f,0.0f,0.0f);     // Rotate On The X AxisglRotatef(yrot,0.0f,1.0f,0.0f);   // Rotate On The Y AxisglRotatef(zrot,0.0f,0.0f,1.0f);       // Rotate On The Z AxisglBindTexture(GL_TEXTURE_2D, texture[0]);       // Select Our TextureglBegin(GL_QUADS);for(x = 0; x < 44; x++ ) {for (y = 0; y < 44; y++) {float_x = float(x)/44.0f;       // Create A Floating Point X Valuefloat_y = float(y)/44.0f;       // Create A Floating Point Y Valuefloat_xb = float(x+1)/44.0f;        // Create A Floating Point Y Value+0.0227ffloat_yb = float(y+1)/44.0f;        // Create A Floating Point Y Value+0.0227fglTexCoord2f( float_x, float_y);    // First Texture Coordinate (Bottom Left)glVertex3f( points[x][y][0], points[x][y][1], points[x][y][2] );glTexCoord2f( float_x, float_yb );  // Second Texture Coordinate (Top Left)glVertex3f( points[x][y+1][0], points[x][y+1][1], points[x][y+1][2] );glTexCoord2f( float_xb, float_yb ); // Third Texture Coordinate (Top Right)glVertex3f( points[x+1][y+1][0], points[x+1][y+1][1], points[x+1][y+1][2] );glTexCoord2f( float_xb, float_y );  // Fourth Texture Coordinate (Bottom Right)glVertex3f( points[x+1][y][0], points[x+1][y][1], points[x+1][y][2] );}}glEnd();if( wiggle_count == 2 ) {                // Used To Slow Down The Wave (Every 2nd Frame Only)for( y = 0; y < 45; y++ ) {           // Loop Through The Y Planehold=points[0][y][2];           // Store Current Value One Left Side Of Wavefor( x = 0; x < 44; x++) {    // Loop Through The X Plane// Current Wave Value Equals Value To The Rightpoints[x][y][2] = points[x+1][y][2];}points[44][y][2]=hold;          // Last Value Becomes The Far Left Stored Value}wiggle_count = 0;               // Set Counter Back To Zero}wiggle_count++;                     // Increase The Counterxrot += 0.3f;                             // X Axis Rotationyrot += 0.2f;                             // Y Axis Rotationzrot += 0.4f;                             // Z Axis Rotation
}

运行效果如下所示：