OpenGl 显示动画并绘制文本
OpenGl display animation and draw text
我想展示太阳系并绘制一个简单的文字，上面写着"Hello world"：
下面的代码显示了太阳系，一切正常：
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void OpenGLInit(void);
static void Animate(void );
static void Key_r(void );
static void Key_s(void );
static void Key_up(void );
static void Key_down(void );
static void ResizeWindow(int w, int h);
static void KeyPressFunc( unsigned char Key, int x, int y );
static void SpecialKeyFunc( int Key, int x, int y );
static GLenum spinMode = GL_TRUE;
static GLenum singleStep = GL_FALSE;
// These three variables control the animation's state and speed.
static float HourOfDay = 0.0;
static float DayOfYear = 0.0;
static float AnimateIncrement = 24.0; // Time step for animation (hours)
// glutKeyboardFunc is called below to set this function to handle
// all normal key presses.
static void KeyPressFunc( unsigned char Key, int x, int y )
{
switch ( Key ) {
case 'R':
case 'r':
Key_r();
break;
case 's':
case 'S':
Key_s();
break;
case 27: // Escape key
exit(1);
}
}
// glutSpecialFunc is called below to set this function to handle
// all special key presses. See glut.h for the names of
// special keys.
static void SpecialKeyFunc( int Key, int x, int y )
{
switch ( Key ) {
case GLUT_KEY_UP:
Key_up();
break;
case GLUT_KEY_DOWN:
Key_down();
break;
}
}
static void Key_r(void)
{
if ( singleStep ) { // If ending single step mode
singleStep = GL_FALSE;
spinMode = GL_TRUE; // Restart animation
}
else {
spinMode = !spinMode; // Toggle animation on and off.
}
}
static void Key_s(void)
{
singleStep = GL_TRUE;
spinMode = GL_TRUE;
}
static void Key_up(void)
{
AnimateIncrement *= 2.0; // Double the animation time step
}
static void Key_down(void)
{
AnimateIncrement /= 2.0; // Halve the animation time step
}
/*
* Animate() handles the animation and the redrawing of the
* graphics window contents.
*/
static void Animate(void)
{
// Clear the redering window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (spinMode) {
// Update the animation state
HourOfDay += AnimateIncrement;
DayOfYear += AnimateIncrement/24.0;
HourOfDay = HourOfDay - ((int)(HourOfDay/24))*24;
DayOfYear = DayOfYear - ((int)(DayOfYear/365))*365;
}
// Clear the current matrix (Modelview)
glLoadIdentity();
// Back off eight units to be able to view from the origin.
glTranslatef ( 0.0, 0.0, -8.0 );
// Rotate the plane of the elliptic
// (rotate the model's plane about the x axis by fifteen degrees)
glRotatef( 15.0, 1.0, 0.0, 0.0 );
// Draw the sun -- as a yellow, wireframe sphere
glColor3f( 1.0, 1.0, 0.0 );
glutWireSphere( 1.0, 15, 15 );
// Draw the Earth
// First position it around the sun
// Use DayOfYear to determine its position
glRotatef( 360.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 4.0, 0.0, 0.0 );
glPushMatrix(); // Save matrix state
// Second, rotate the earth on its axis.
// Use HourOfDay to determine its rotation.
glRotatef( 360.0*HourOfDay/24.0, 0.0, 1.0, 0.0 );
// Third, draw the earth as a wireframe sphere.
glColor3f( 0.2, 0.2, 1.0 );
glutWireSphere( 0.4, 10, 10);
glPopMatrix(); // Restore matrix state
// Draw the moon.
// Use DayOfYear to control its rotation around the earth
glRotatef( 360.0*12.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 0.7, 0.0, 0.0 );
glColor3f( 0.3, 0.7, 0.3 );
glutWireSphere( 0.1, 5, 5 );
// Flush the pipeline, and swap the buffers
glFlush();
glutSwapBuffers();
if ( singleStep ) {
spinMode = GL_FALSE;
}
glutPostRedisplay(); // Request a re-draw for animation purposes
}
// Initialize OpenGL's rendering modes
void OpenGLInit(void)
{
glShadeModel( GL_FLAT );
glClearColor( 0.0, 0.0, 0.0, 0.0 );
glClearDepth( 1.0 );
glEnable( GL_DEPTH_TEST );
}
// ResizeWindow is called when the window is resized
static void ResizeWindow(int w, int h)
{
float aspectRatio;
h = (h == 0) ? 1 : h;
w = (w == 0) ? 1 : w;
glViewport( 0, 0, w, h ); // View port uses whole window
aspectRatio = (float)w/(float)h;
// Set up the projection view matrix (not very well!)
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective( 60.0, aspectRatio, 1.0, 30.0 );
// Select the Modelview matrix
glMatrixMode( GL_MODELVIEW );
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
// Initialize OpenGL.
OpenGLInit();
// Set up callback functions for key presses
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
// Set up the callback function for resizing windows
glutReshapeFunc( ResizeWindow );
// Callback for graphics image redrawing
glutDisplayFunc( Animate );
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}
下面的代码绘制文本" 你好世界 "并且也可以工作：
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void drawBitmapText(char *string,float x,float y,float z)
{
char *c;
glRasterPos3f(x, y,z);
for (c=string; *c != ' '; c++)
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_10, *c);
}
}
void drawStrokeText(char*string,int x,int y,int z)
{
char *c;
glPushMatrix();
glTranslatef(x, y+8,z);
// glScalef(0.09f,-0.08f,z);
for (c=string; *c != ' '; c++)
{
glutStrokeCharacter(GLUT_STROKE_ROMAN , *c);
}
glPopMatrix();
}
void reshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,w,h,0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void render(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glColor3f(0,1,0);
drawBitmapText("Hello world",200,200,0);
glutSwapBuffers();
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
glutDisplayFunc(render);
glutIdleFunc(render);
glutReshapeFunc(reshape);
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}
我试图将它们一起使用来显示太阳系并绘制文本，但是
我得到一个空白的黑屏：
#include <iostream>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
void OpenGLInit(void);
static void Animate(void );
static void Key_r(void );
static void Key_s(void );
static void Key_up(void );
static void Key_down(void );
static void ResizeWindow(int w, int h);
static void KeyPressFunc( unsigned char Key, int x, int y );
static void SpecialKeyFunc( int Key, int x, int y );
static GLenum spinMode = GL_TRUE;
static GLenum singleStep = GL_FALSE;
// These three variables control the animation's state and speed.
static float HourOfDay = 0.0;
static float DayOfYear = 0.0;
static float AnimateIncrement = 24.0; // Time step for animation (hours)
// glutKeyboardFunc is called below to set this function to handle
// all normal key presses.
static void KeyPressFunc( unsigned char Key, int x, int y )
{
switch ( Key ) {
case 'R':
case 'r':
Key_r();
break;
case 's':
case 'S':
Key_s();
break;
case 27: // Escape key
exit(1);
}
}
// glutSpecialFunc is called below to set this function to handle
// all special key presses. See glut.h for the names of
// special keys.
static void SpecialKeyFunc( int Key, int x, int y )
{
switch ( Key ) {
case GLUT_KEY_UP:
Key_up();
break;
case GLUT_KEY_DOWN:
Key_down();
break;
}
}
static void Key_r(void)
{
if ( singleStep ) { // If ending single step mode
singleStep = GL_FALSE;
spinMode = GL_TRUE; // Restart animation
}
else {
spinMode = !spinMode; // Toggle animation on and off.
}
}
static void Key_s(void)
{
singleStep = GL_TRUE;
spinMode = GL_TRUE;
}
static void Key_up(void)
{
AnimateIncrement *= 2.0; // Double the animation time step
}
static void Key_down(void)
{
AnimateIncrement /= 2.0; // Halve the animation time step
}
/*
* Animate() handles the animation and the redrawing of the
* graphics window contents.
*/
static void Animate(void)
{
// Clear the redering window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (spinMode) {
// Update the animation state
HourOfDay += AnimateIncrement;
DayOfYear += AnimateIncrement/24.0;
HourOfDay = HourOfDay - ((int)(HourOfDay/24))*24;
DayOfYear = DayOfYear - ((int)(DayOfYear/365))*365;
}
// Clear the current matrix (Modelview)
glLoadIdentity();
// Back off eight units to be able to view from the origin.
glTranslatef ( 0.0, 0.0, -8.0 );
// Rotate the plane of the elliptic
// (rotate the model's plane about the x axis by fifteen degrees)
glRotatef( 15.0, 1.0, 0.0, 0.0 );
// Draw the sun -- as a yellow, wireframe sphere
glColor3f( 1.0, 1.0, 0.0 );
glutWireSphere( 1.0, 15, 15 );
// Draw the Earth
// First position it around the sun
// Use DayOfYear to determine its position
glRotatef( 360.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 4.0, 0.0, 0.0 );
glPushMatrix(); // Save matrix state
// Second, rotate the earth on its axis.
// Use HourOfDay to determine its rotation.
glRotatef( 360.0*HourOfDay/24.0, 0.0, 1.0, 0.0 );
// Third, draw the earth as a wireframe sphere.
glColor3f( 0.2, 0.2, 1.0 );
glutWireSphere( 0.4, 10, 10);
glPopMatrix(); // Restore matrix state
// Draw the moon.
// Use DayOfYear to control its rotation around the earth
glRotatef( 360.0*12.0*DayOfYear/365.0, 0.0, 1.0, 0.0 );
glTranslatef( 0.7, 0.0, 0.0 );
glColor3f( 0.3, 0.7, 0.3 );
glutWireSphere( 0.1, 5, 5 );
// Flush the pipeline, and swap the buffers
glFlush();
glutSwapBuffers();
if ( singleStep ) {
spinMode = GL_FALSE;
}
glutPostRedisplay(); // Request a re-draw for animation purposes
}
// Initialize OpenGL's rendering modes
void OpenGLInit(void)
{
glShadeModel( GL_FLAT );
glClearColor( 0.0, 0.0, 0.0, 0.0 );
glClearDepth( 1.0 );
glEnable( GL_DEPTH_TEST );
}
// ResizeWindow is called when the window is resized
static void ResizeWindow(int w, int h)
{
float aspectRatio;
h = (h == 0) ? 1 : h;
w = (w == 0) ? 1 : w;
glViewport( 0, 0, w, h ); // View port uses whole window
aspectRatio = (float)w/(float)h;
// Set up the projection view matrix (not very well!)
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective( 60.0, aspectRatio, 1.0, 30.0 );
// Select the Modelview matrix
glMatrixMode( GL_MODELVIEW );
}
void drawBitmapText(char *string,float x,float y,float z)
{
char *c;
glRasterPos3f(x, y,z);
for (c=string; *c != ' '; c++)
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_10, *c);
}
}
void drawStrokeText(char*string,int x,int y,int z)
{
char *c;
glPushMatrix();
glTranslatef(x, y+8,z);
// glScalef(0.09f,-0.08f,z);
for (c=string; *c != ' '; c++)
{
glutStrokeCharacter(GLUT_STROKE_ROMAN , *c);
}
glPopMatrix();
}
void reshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,w,h,0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void render(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glColor3f(0,1,0);
drawBitmapText("Hello world",200,200,0);
glutSwapBuffers();
}
// Main routine
// Set up OpenGL, hook up callbacks, and start the main loop
int main( int argc, char** argv )
{
// Need to double buffer for animation
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
// Create and position the graphics window
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( 600, 360 );
glutCreateWindow( "Solar System Demo" );
// Initialize OpenGL.
OpenGLInit();
// Set up callback functions for key presses
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
// Set up the callback function for resizing windows
glutReshapeFunc( ResizeWindow );
// Callback for graphics image redrawing
glutDisplayFunc( Animate );
glutDisplayFunc(render);
glutIdleFunc(render);
glutReshapeFunc(reshape);
// Start the main loop. glutMainLoop never returns.
glutMainLoop( );
return(0); // Compiler requires this to be here. (Never reached)
}
main（） 中的这些行会导致问题：
glutKeyboardFunc( KeyPressFunc );
glutSpecialFunc( SpecialKeyFunc );
glutReshapeFunc( ResizeWindow );
glutDisplayFunc( Animate );
glutDisplayFunc(render);
glutIdleFunc(render);
glutDisplayFunc（） 覆盖 GLUT 内部的函数指针。所以只有 render（） 函数被调用，而不是 Animate（）。
这里的第二个问题：Idle 函数也是 render（），所以它被调用了两次。与重塑功能相同。
您需要组合 ResizeWindow（） 和 reshape（） 函数，然后是 render（）和 Animate（） 函数，然后删除 glutIdleFunc 调用，因为它一切都已经在 render（） 中完成。
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