OpenGL 使用 GLUT 处理键盘输入

Tag: OpenGl opengl-2d-graphic-tutorial Posted on 2020-04-12 16:02:11 Edited on 2020-04-12 19:00:13 Views: 5

OpenGL 二维图形学教程系列

此系列翻译自:OpenGL Tutorial An Introduction on OpenGL with 2D Graphics

  1. OpenGl 环境搭建与介绍
  2. OpenGl 顶点,图元以及颜色
  3. OpenGL 裁剪区域与视口
  4. OpenGl 平移和旋转
  5. OpenGl 动画
  6. OpenGL 使用 GLUT 处理键盘输入
  7. OpenGL 使用 GLUT 处理鼠标输入

7. 使用 GLUT 处理键盘输入

我们可以分别为常规按键和特殊按键分别组成回调函数。

  • glutKeyboardFunc 函数:注册处理键盘输入事件的回调函数

    void glutKeyboardFunc (void (*func)(unsigned char key, int x, int y)
       // key is the char pressed, e.g., 'a' or 27 for ESC
       // (x, y) is the mouse location in Windows' coordinates
  • glutSpecialFunc 函数:注册处理特殊按键(例如箭头按键和功能键)事件的回调函数

    void glutSpecialFunc (void (*func)(int specialKey, int x, int y)
       // specialKey: GLUT_KEY_* (* for LEFT, RIGHT, UP, DOWN, HOME, END, PAGE_UP, PAGE_DOWN, F1,...F12). 
       // (x, y) is the mouse location in Windows' coordinates

7.1 例子 8:在全屏模式和窗口模式之间进行切换(GL08FullScreen.cpp)

对于上述的弹跳小球程序,下述程序实现了使用 F1 键将其从全屏模式以及窗口模式之间进行切换的功能。

/*
 * GL08FullScreen.cpp: Switching between full-screen mode and windowed-mode
 */
#include <windows.h>  // for MS Windows
#include <GL/glut.h>  // GLUT, includes glu.h and gl.h
#include <Math.h>     // Needed for sin, cos
#define PI 3.14159265f

// Global variables
char title[] = "Full-Screen & Windowed Mode";  // Windowed mode's title
int windowWidth  = 640;     // Windowed mode's width
int windowHeight = 480;     // Windowed mode's height
int windowPosX   = 50;      // Windowed mode's top-left corner x
int windowPosY   = 50;      // Windowed mode's top-left corner y

GLfloat ballRadius = 0.5f;   // Radius of the bouncing ball
GLfloat ballX = 0.0f;         // Ball's center (x, y) position
GLfloat ballY = 0.0f;
GLfloat ballXMax, ballXMin, ballYMax, ballYMin; // Ball's center (x, y) bounds
GLfloat xSpeed = 0.02f;      // Ball's speed in x and y directions
GLfloat ySpeed = 0.007f;
int refreshMillis = 30;      // Refresh period in milliseconds

// Projection clipping area
GLdouble clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop;

bool fullScreenMode = true; // Full-screen or windowed mode?

/* Initialize OpenGL Graphics */
void initGL() {
   glClearColor(0.0, 0.0, 0.0, 1.0); // Set background (clear) color to black
}

/* Callback handler for window re-paint event */
void display() {
   glClear(GL_COLOR_BUFFER_BIT);  // Clear the color buffer
   glMatrixMode(GL_MODELVIEW);    // To operate on the model-view matrix
   glLoadIdentity();              // Reset model-view matrix

   glTranslatef(ballX, ballY, 0.0f);  // Translate to (xPos, yPos)
   // Use triangular segments to form a circle
   glBegin(GL_TRIANGLE_FAN);
      glColor3f(0.0f, 0.0f, 1.0f);  // Blue
      glVertex2f(0.0f, 0.0f);       // Center of circle
      int numSegments = 100;
      GLfloat angle;
      for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
         angle = i * 2.0f * PI / numSegments;  // 360 deg for all segments
         glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
      }
   glEnd();

   glutSwapBuffers();  // Swap front and back buffers (of double buffered mode)

   // Animation Control - compute the location for the next refresh
   ballX += xSpeed;
   ballY += ySpeed;
   // Check if the ball exceeds the edges
   if (ballX > ballXMax) {
      ballX = ballXMax;
      xSpeed = -xSpeed;
   } else if (ballX < ballXMin) {
      ballX = ballXMin;
      xSpeed = -xSpeed;
   }
   if (ballY > ballYMax) {
      ballY = ballYMax;
      ySpeed = -ySpeed;
   } else if (ballY < ballYMin) {
      ballY = ballYMin;
      ySpeed = -ySpeed;
   }
}

/* Call back when the windows is re-sized */
void reshape(GLsizei width, GLsizei height) {
   // Compute aspect ratio of the new window
   if (height == 0) height = 1;                // To prevent divide by 0
   GLfloat aspect = (GLfloat)width / (GLfloat)height;

   // Set the viewport to cover the new window
   glViewport(0, 0, width, height);

   // Set the aspect ratio of the clipping area to match the viewport
   glMatrixMode(GL_PROJECTION);  // To operate on the Projection matrix
   glLoadIdentity();             // Reset the projection matrix
   if (width >= height) {
      clipAreaXLeft   = -1.0 * aspect;
      clipAreaXRight  = 1.0 * aspect;
      clipAreaYBottom = -1.0;
      clipAreaYTop    = 1.0;
   } else {
      clipAreaXLeft   = -1.0;
      clipAreaXRight  = 1.0;
      clipAreaYBottom = -1.0 / aspect;
      clipAreaYTop    = 1.0 / aspect;
   }
   gluOrtho2D(clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop);
   ballXMin = clipAreaXLeft + ballRadius;
   ballXMax = clipAreaXRight - ballRadius;
   ballYMin = clipAreaYBottom + ballRadius;
   ballYMax = clipAreaYTop - ballRadius;
}

/* Called back when the timer expired */
void Timer(int value) {
   glutPostRedisplay();    // Post a paint request to activate display()
   glutTimerFunc(refreshMillis, Timer, 0); // subsequent timer call at milliseconds
}

/* Callback handler for special-key event */
void specialKeys(int key, int x, int y) {
   switch (key) {
      case GLUT_KEY_F1:    // F1: Toggle between full-screen and windowed mode
         fullScreenMode = !fullScreenMode;         // Toggle state
         if (fullScreenMode) {                     // Full-screen mode
            windowPosX   = glutGet(GLUT_WINDOW_X); // Save parameters for restoring later
            windowPosY   = glutGet(GLUT_WINDOW_Y);
            windowWidth  = glutGet(GLUT_WINDOW_WIDTH);
            windowHeight = glutGet(GLUT_WINDOW_HEIGHT);
            glutFullScreen();                      // Switch into full screen
         } else {                                         // Windowed mode
            glutReshapeWindow(windowWidth, windowHeight); // Switch into windowed mode
            glutPositionWindow(windowPosX, windowPosX);   // Position top-left corner
         }
         break;
   }
}

/* Main function: GLUT runs as a console application starting at main() */
int main(int argc, char** argv) {
   glutInit(&argc, argv);            // Initialize GLUT
   glutInitDisplayMode(GLUT_DOUBLE); // Enable double buffered mode
   glutInitWindowSize(windowWidth, windowHeight);  // Initial window width and height
   glutInitWindowPosition(windowPosX, windowPosY); // Initial window top-left corner (x, y)
   glutCreateWindow(title);      // Create window with given title
   glutDisplayFunc(display);     // Register callback handler for window re-paint
   glutReshapeFunc(reshape);     // Register callback handler for window re-shape
   glutTimerFunc(0, Timer, 0);   // First timer call immediately
   glutSpecialFunc(specialKeys); // Register callback handler for special-key event
   glutFullScreen();             // Put into full screen
   initGL();                     // Our own OpenGL initialization
   glutMainLoop();               // Enter event-processing loop
   return 0;
}

TODO:详细的代码解释

7.2 例子 9:按键控制(GL09KeyControl.cpp)

下述代码实现了使用上/下箭头提高/降低小球的 Y 轴的速度,使用左/右箭头提高/降低小球的 X 轴速度,使用 PageUp/PageDown 提高/降低球的半径。

/*
 * GL09KeyControl.cpp: A key-controlled bouncing ball
 */
#include <windows.h>  // for MS Windows
#include <GL/glut.h>  // GLUT, include glu.h and gl.h
#include <Math.h>     // Needed for sin, cos
#define PI 3.14159265f

// Global variables
char title[] = "Full-Screen & Windowed Mode";  // Windowed mode's title
int windowWidth  = 640;     // Windowed mode's width
int windowHeight = 480;     // Windowed mode's height
int windowPosX   = 50;      // Windowed mode's top-left corner x
int windowPosY   = 50;      // Windowed mode's top-left corner y

GLfloat ballRadius = 0.5f;   // Radius of the bouncing ball
GLfloat ballX = 0.0f;        // Ball's center (x, y) position
GLfloat ballY = 0.0f;
GLfloat ballXMax, ballXMin, ballYMax, ballYMin; // Ball's center (x, y) bounds
GLfloat xSpeed = 0.02f;      // Ball's speed in x and y directions
GLfloat ySpeed = 0.007f;
int refreshMillis = 30;      // Refresh period in milliseconds

// Projection clipping area
GLdouble clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop;

bool fullScreenMode = true; // Full-screen or windowed mode?

/* Initialize OpenGL Graphics */
void initGL() {
   glClearColor(0.0, 0.0, 0.0, 1.0); // Set background (clear) color to black
}

/* Callback handler for window re-paint event */
void display() {
   glClear(GL_COLOR_BUFFER_BIT);  // Clear the color buffer
   glMatrixMode(GL_MODELVIEW);    // To operate on the model-view matrix
   glLoadIdentity();              // Reset model-view matrix

   glTranslatef(ballX, ballY, 0.0f);  // Translate to (xPos, yPos)
   // Use triangular segments to form a circle
   glBegin(GL_TRIANGLE_FAN);
      glColor3f(0.0f, 0.0f, 1.0f);  // Blue
      glVertex2f(0.0f, 0.0f);       // Center of circle
      int numSegments = 100;
      GLfloat angle;
      for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
         angle = i * 2.0f * PI / numSegments;  // 360 deg for all segments
         glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
      }
   glEnd();

   glutSwapBuffers();  // Swap front and back buffers (of double buffered mode)

   // Animation Control - compute the location for the next refresh
   ballX += xSpeed;
   ballY += ySpeed;
   // Check if the ball exceeds the edges
   if (ballX > ballXMax) {
      ballX = ballXMax;
      xSpeed = -xSpeed;
   } else if (ballX < ballXMin) {
      ballX = ballXMin;
      xSpeed = -xSpeed;
   }
   if (ballY > ballYMax) {
      ballY = ballYMax;
      ySpeed = -ySpeed;
   } else if (ballY < ballYMin) {
      ballY = ballYMin;
      ySpeed = -ySpeed;
   }
}

/* Call back when the windows is re-sized */
void reshape(GLsizei width, GLsizei height) {
   // Compute aspect ratio of the new window
   if (height == 0) height = 1;                // To prevent divide by 0
   GLfloat aspect = (GLfloat)width / (GLfloat)height;

   // Set the viewport to cover the new window
   glViewport(0, 0, width, height);

   // Set the aspect ratio of the clipping area to match the viewport
   glMatrixMode(GL_PROJECTION);  // To operate on the Projection matrix
   glLoadIdentity();             // Reset the projection matrix
   if (width >= height) {
      clipAreaXLeft   = -1.0 * aspect;
      clipAreaXRight  = 1.0 * aspect;
      clipAreaYBottom = -1.0;
      clipAreaYTop    = 1.0;
   } else {
      clipAreaXLeft   = -1.0;
      clipAreaXRight  = 1.0;
      clipAreaYBottom = -1.0 / aspect;
      clipAreaYTop    = 1.0 / aspect;
   }
   gluOrtho2D(clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop);
   ballXMin = clipAreaXLeft + ballRadius;
   ballXMax = clipAreaXRight - ballRadius;
   ballYMin = clipAreaYBottom + ballRadius;
   ballYMax = clipAreaYTop - ballRadius;
}

/* Called back when the timer expired */
void Timer(int value) {
   glutPostRedisplay();    // Post a paint request to activate display()
   glutTimerFunc(refreshMillis, Timer, 0); // subsequent timer call at milliseconds
}

/* Callback handler for normal-key event */
void keyboard(unsigned char key, int x, int y) {
   switch (key) {
      case 27:     // ESC key
         exit(0);
         break;
   }
}

/* Callback handler for special-key event */
void specialKeys(int key, int x, int y) {
   switch (key) {
      case GLUT_KEY_F1:    // F1: Toggle between full-screen and windowed mode
         fullScreenMode = !fullScreenMode;         // Toggle state
         if (fullScreenMode) {                     // Full-screen mode
            windowPosX   = glutGet(GLUT_WINDOW_X); // Save parameters for restoring later
            windowPosY   = glutGet(GLUT_WINDOW_Y);
            windowWidth  = glutGet(GLUT_WINDOW_WIDTH);
            windowHeight = glutGet(GLUT_WINDOW_HEIGHT);
            glutFullScreen();                      // Switch into full screen
         } else {                                         // Windowed mode
            glutReshapeWindow(windowWidth, windowHeight); // Switch into windowed mode
            glutPositionWindow(windowPosX, windowPosX);   // Position top-left corner
         }
         break;
      case GLUT_KEY_RIGHT:    // Right: increase x speed
         xSpeed *= 1.05f; break;
      case GLUT_KEY_LEFT:     // Left: decrease x speed
         xSpeed *= 0.95f; break;
      case GLUT_KEY_UP:       // Up: increase y speed
         ySpeed *= 1.05f; break;
      case GLUT_KEY_DOWN:     // Down: decrease y speed
         ySpeed *= 0.95f; break;
      case GLUT_KEY_PAGE_UP:  // Page-Up: increase ball's radius
         ballRadius *= 1.05f;
         ballXMin = clipAreaXLeft + ballRadius;
         ballXMax = clipAreaXRight - ballRadius;
         ballYMin = clipAreaYBottom + ballRadius;
         ballYMax = clipAreaYTop - ballRadius;
         break;
      case GLUT_KEY_PAGE_DOWN: // Page-Down: decrease ball's radius
         ballRadius *= 0.95f;
         ballXMin = clipAreaXLeft + ballRadius;
         ballXMax = clipAreaXRight - ballRadius;
         ballYMin = clipAreaYBottom + ballRadius;
         ballYMax = clipAreaYTop - ballRadius;
         break;
   }
}

/* Main function: GLUT runs as a console application starting at main() */
int main(int argc, char** argv) {
   glutInit(&argc, argv);            // Initialize GLUT
   glutInitDisplayMode(GLUT_DOUBLE); // Enable double buffered mode
   glutInitWindowSize(windowWidth, windowHeight);  // Initial window width and height
   glutInitWindowPosition(windowPosX, windowPosY); // Initial window top-left corner (x, y)
   glutCreateWindow(title);      // Create window with given title
   glutDisplayFunc(display);     // Register callback handler for window re-paint
   glutReshapeFunc(reshape);     // Register callback handler for window re-shape
   glutTimerFunc(0, Timer, 0);   // First timer call immediately
   glutSpecialFunc(specialKeys); // Register callback handler for special-key event
   glutKeyboardFunc(keyboard);   // Register callback handler for special-key event   glutFullScreen();             // Put into full screen
   initGL();                     // Our own OpenGL initialization
   glutMainLoop();               // Enter event-processing loop
   return 0;
}

TODO:详细的代码解释

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