NeHe 系列教程之九： 在3D空间中移动位图

英文教程地址：lesson09

本课基于第一课的代码， 利用颜色混合的方法，将一个黑白纹理与随机颜色进行混合，产生绚丽的效果。

首先是定义相关变量和数据结构，如下所示：

namespace {bool    twinkle;                        // Twinkling Starsbool    tp;                         // 'T' Key Pressed?const   int num = 50;                         // Number Of Stars To Drawtypedef struct                          // Create A Structure For Star{int r, g, b;                        // Stars ColorGLfloat dist;                       // Stars Distance From CenterGLfloat angle;                      // Stars Current Angle}stars;                              // Structures Name Is Starsstars star[num];                    // Make 'star' Array Of 'num' Using Info From The StructureGLfloat zoom=-15.0f;                        // Viewing Distance Away From StarsGLfloat tilt=90.0f;                     // Tilt The ViewGLfloat spin;                           // Spin Twinkling StarsGLuint  loop;                           // General Loop VariableGLuint  texture[1];                     // Storage For One Texture
}

加载纹理的代码跟之前课程代码类似。

然后是初始化代码：

void MyGLWidget::initializeGL()
{loadTextures();glEnable(GL_TEXTURE_2D);glShadeModel(GL_SMOOTH);   // Enables Smooth ShadingglClearColor(0.0f, 0.0f, 0.0f, 0.5f);  // Black BackgroundglClearDepth(1.0f);             // Depth Buffer Setup//   glEnable(GL_DEPTH_TEST);        // Enables Depth Testing//   glDepthFunc(GL_LEQUAL);        // The Type Of Depth Test To DoglHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Really Nice Perspective CalculationsglBlendFunc(GL_SRC_ALPHA,GL_ONE);           // Set The Blending Function For TranslucencyglEnable(GL_BLEND);                 // Enable Blendingfor (loop=0; loop<num; loop++)               // Create A Loop That Goes Through All The Stars{star[loop].angle=0.0f;              // Start All The Stars At Angle Zerostar[loop].dist=(float(loop)/num)*5.0f;     // Calculate Distance From The Centerstar[loop].r=rand()%256;            // Give star[loop] A Random Red Intensitystar[loop].g=rand()%256;            // Give star[loop] A Random Green Intensitystar[loop].b=rand()%256;            // Give star[loop] A Random Blue Intensity}
}

注意，开启混合的时候要关闭深度测试。

接着是绘制代码，如下所示：

void MyGLWidget::paintGL()
{glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth BufferglLoadIdentity();       // Reset The Current Modelview MatrixglBindTexture(GL_TEXTURE_2D, texture[0]);       // Select Our Texturefor (loop=0; loop<num; loop++)               // Loop Through All The Stars{glLoadIdentity();               // Reset The View Before We Draw Each StarglTranslatef(0.0f,0.0f,zoom);           // Zoom Into The Screen (Using The Value In 'zoom')glRotatef(tilt,1.0f,0.0f,0.0f);         // Tilt The View (Using The Value In 'tilt')glRotatef(star[loop].angle,0.0f,1.0f,0.0f); // Rotate To The Current Stars AngleglTranslatef(star[loop].dist,0.0f,0.0f);    // Move Forward On The X PlaneglRotatef(-star[loop].angle,0.0f,1.0f,0.0f);    // Cancel The Current Stars AngleglRotatef(-tilt,1.0f,0.0f,0.0f);        // Cancel The Screen Tiltif (twinkle)                    // Twinkling Stars Enabled{// Assign A Color Using BytesglColor4ub(star[(num-loop)-1].r,star[(num-loop)-1].g,star[(num-loop)-1].b,255);glBegin(GL_QUADS);          // Begin Drawing The Textured QuadglTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,-1.0f, 0.0f);glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,-1.0f, 0.0f);glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 0.0f);glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 0.0f);glEnd();                // Done Drawing The Textured Quad}glRotatef(spin,0.0f,0.0f,1.0f);         // Rotate The Star On The Z Axis// Assign A Color Using BytesglColor4ub(star[loop].r,star[loop].g,star[loop].b,255);glBegin(GL_QUADS);              // Begin Drawing The Textured QuadglTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,-1.0f, 0.0f);glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,-1.0f, 0.0f);glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 0.0f);glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 0.0f);glEnd();                    // Done Drawing The Textured Quadspin+=0.01f;                    // Used To Spin The Starsstar[loop].angle += float(loop)/num;      // Changes The Angle Of A Starstar[loop].dist -= 0.01f;             // Changes The Distance Of A Starif (star[loop].dist<0.0f)            // Is The Star In The Middle Yet{star[loop].dist += 5.0f;          // Move The Star 5 Units From The Centerstar[loop].r = rand()%256;        // Give It A New Red Valuestar[loop].g = rand()%256;        // Give It A New Green Valuestar[loop].b = rand()%256;        // Give It A New Blue Value}}
}

按键T 的处理， 当按下T键时，会有闪烁效果，且亮度更大：

void MyGLWidget::keyReleaseEvent(QKeyEvent *e)
{switch (e->key()) {case Qt::Key_T:tp = false;break;default:QGLWidget::keyReleaseEvent(e);}
}void MyGLWidget::keyPressEvent(QKeyEvent *e)
{switch (e->key()) {case Qt::Key_F:fullscreen = !fullscreen;if (fullscreen) {showFullScreen();} else {resize(640, 480);showNormal();}break;case Qt::Key_T:if (!tp) {tp = TRUE;twinkle = !twinkle;}break;case Qt::Key_Up:tilt -= 0.5f;break;case Qt::Key_Down:tilt += 0.5f;break;case Qt::Key_PageUp:zoom -= 0.2f;break;case Qt::Key_PageDown:zoom += 0.2f;break;case Qt::Key_Escape:QMessageBox::StandardButton reply;reply = QMessageBox::question(NULL, "NeHe","Do you want to exit?",QMessageBox::Yes | QMessageBox::No,QMessageBox::Yes);if (reply == QMessageBox::Yes) {qApp->quit();}break;default:QGLWidget::keyPressEvent(e);break;}
}

运行效果如下所示： （T 键按下）