GLUT Tutorials 15：帧率

博客转自：http://www.lighthouse3d.com/tutorials/glut-tutorial/frames-per-second/

How fast is your application really going? Sometimes we make small changes and we can’t be sure of the effect they had on the performance, namely how do they affect the number of displayed frames per second. In this section we’ll see how we can use GLUT to count the number of frames per second. Note that this shouldn’t be considered a true benchmark, just a guide value.

GLUT provides a function that allows us to query many features of the system, one of them being the number of milliseconds from the call to glutInit. The function is glutGet and the syntax is as follows:

int glutGet(GLenum state);

Parameters:
state – specifies the value we want.

 This function can be use for a lot of purposes, for instance getting window coordinates or getting the openGL buffer’s depth. In this section we’ll use it to get the number of milliseconds since the call to glutInit, i.e. the argument state is GLUT_ELAPSED_TIME.

int time；

//todo something 

time = glutGet(GLUT_ELAPSED_TIME);

Ok, now we’re going to use this function to compute the number of frames per second of our application. The frame rate varies from frame to frame, i.e. not all frames take the same time to render because our application is not alone. The operating system takes its toll, and the camera maybe moving thereby changing what’s being rendered. Therefore we’re going to avoid computing the frame rate in each and every frame, and instead we’re going to compute it roughly once per second. This also provides a more accurate figure, since its an average.

We’re going to declare three variables: frame, time, and timebase, where timebase and frame are both initialized to zero.

int frame=0,time,timebase=0;

The meaning of these variables is:

• frame – the number of frames since we last computed the frame rate
• time – the current number of milliseconds
• timebase – the time when we last computed the frame rate

The following piece of code, when placed inside the registered idle function, will do the job (see bellow for a detailed description):

...

    frame++;
    time=glutGet(GLUT_ELAPSED_TIME);

    if (time - timebase > 1000) {
        fps = frame*1000.0/(time-timebase));
         timebase = time;
        frame = 0;
    }
    ...

We start by increasing the number of frames, i.e. increasing the variable frame. We then get the current time into time. Next we compare it with timebase to check if a second has elapsed, i.e. if the difference between time and timebase is greater than 1000 millisecond. If this is not the case then we skip the computation part. However when the difference is larger than one second we’ll do the computation.

Computing the difference between time and timebase gives us the number of milliseconds elapsed since we last computed the number of frames per second. Dividing 1000 by the number of milliseconds elapsed provides the inverse of the number of seconds elapsed. All its left is to multiply this value by the number of frames rendered since the last time the frame rate was computed, and we get the number of frames per second. Finally we reset timebase to the current number of milliseconds, and frame to zero.

Note that when the application starts timebase is zero, you’ll have to wait one second to get the first value. This first few values however are very misleading because they include the time required to initialize the window. If you run some tests you’ll see that this value is much lower than the actual frame rate.

If you want to print the number of frames per second you can use the following piece of code

...
    frame++;
    time=glutGet(GLUT_ELAPSED_TIME);
    if (time - timebase > 1000) {
        sprintf(s,"FPS:%4.2f",
            frame*1000.0/(time-timebase));
        timebase = time;
        frame = 0;
    }

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

    glPushMatrix();
    glLoadIdentity();
    setOrthographicProjection();
    renderBitmapString(30,35,(void *)font,s);
    glPopMatrix();
    restorePerspectiveProjection();

    ...

全部代码如下

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

// angle of rotation for the camera direction
float angle = 0.0f;

// actual vector representing the camera's direction
float lx=0.0f,lz=-1.0f;

// XZ position of the camera
float x=0.0f, z=5.0f;

// the key states. These variables will be zero
//when no key is being presses
float deltaAngle = 0.0f;
float deltaMove = 0;
int xOrigin = -1;

// Constant definitions for Menus
#define RED 1
#define GREEN 2
#define BLUE 3
#define ORANGE 4

#define FILL 1
#define LINE 2

// Pop up menu identifiers
int fillMenu, fontMenu, mainMenu, colorMenu;

// color for the nose
float red = 1.0f, blue=0.5f, green=0.5f;

// scale of snowman
float scale = 1.0f;

// menu status
int menuFlag = 0;

// default font
void *font = GLUT_STROKE_ROMAN;

// width and height of the window
int h,w;

// variables to compute frames per second
int frame;
long time, timebase;
char s[50];

void changeSize(int ww, int hh) {

    h = hh;
    w = ww;
    // Prevent a divide by zero, when window is too short
    // (you cant make a window of zero width).
    if (h == 0)
        h = 1;

    float ratio =  w * 1.0 / h;

    // Use the Projection Matrix
    glMatrixMode(GL_PROJECTION);

    // Reset Matrix
    glLoadIdentity();

    // Set the viewport to be the entire window
    glViewport(0, 0, w, h);

    // Set the correct perspective.
    gluPerspective(45.0f, ratio, 0.1f, 100.0f);

    // Get Back to the Modelview
    glMatrixMode(GL_MODELVIEW);
}

void drawSnowMan() {

    glScalef(scale, scale, scale);
    glColor3f(1.0f, 1.0f, 1.0f);

// Draw Body
    glTranslatef(0.0f ,0.75f, 0.0f);
    glutSolidSphere(0.75f,20,20);

// Draw Head
    glTranslatef(0.0f, 1.0f, 0.0f);
    glutSolidSphere(0.25f,20,20);

// Draw Eyes
    glPushMatrix();
    glColor3f(0.0f,0.0f,0.0f);
    glTranslatef(0.05f, 0.10f, 0.18f);
    glutSolidSphere(0.05f,10,10);
    glTranslatef(-0.1f, 0.0f, 0.0f);
    glutSolidSphere(0.05f,10,10);
    glPopMatrix();

// Draw Nose
    glColor3f(red, green, blue);
    glRotatef(0.0f,1.0f, 0.0f, 0.0f);
    glutSolidCone(0.08f,0.5f,10,2);

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

}

void renderBitmapString(
        float x,
        float y,
        float z,
        void *font,
        char *string) {

    char *c;
    glRasterPos3f(x, y,z);
    for (c=string; *c != ''; c++) {
        glutBitmapCharacter(font, *c);
    }
}

void renderStrokeFontString(
        float x,
        float y,
        float z,
        void *font,
        char *string) {  

    char *c;
    glPushMatrix();
    glTranslatef(x, y,z);
    glScalef(0.002f, 0.002f, 0.002f);
    for (c=string; *c != ''; c++) {
        glutStrokeCharacter(font, *c);
    }
    glPopMatrix();
}

void restorePerspectiveProjection() {

    glMatrixMode(GL_PROJECTION);
    // restore previous projection matrix
    glPopMatrix();

    // get back to modelview mode
    glMatrixMode(GL_MODELVIEW);
}

void setOrthographicProjection() {

    // switch to projection mode
    glMatrixMode(GL_PROJECTION);

    // save previous matrix which contains the
    //settings for the perspective projection
    glPushMatrix();

    // reset matrix
    glLoadIdentity();

    // set a 2D orthographic projection
    gluOrtho2D(0, w, h, 0);

    // switch back to modelview mode
    glMatrixMode(GL_MODELVIEW);
}

void computePos(float deltaMove) {

    x += deltaMove * lx * 0.1f;
    z += deltaMove * lz * 0.1f;
}

void renderScene(void) {

    if (deltaMove)
        computePos(deltaMove);

    // Clear Color and Depth Buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Reset transformations
    glLoadIdentity();
    // Set the camera
    gluLookAt(    x, 1.0f, z,
            x+lx, 1.0f,  z+lz,
            0.0f, 1.0f,  0.0f);

// Draw ground

    glColor3f(0.9f, 0.9f, 0.9f);
    glBegin(GL_QUADS);
        glVertex3f(-100.0f, 0.0f, -100.0f);
        glVertex3f(-100.0f, 0.0f,  100.0f);
        glVertex3f( 100.0f, 0.0f,  100.0f);
        glVertex3f( 100.0f, 0.0f, -100.0f);
    glEnd();

// Draw 36 SnowMen
    char number[3];
    for(int i = -3; i < 3; i++)
        for(int j=-3; j < 3; j++) {
            glPushMatrix();
            glTranslatef(i*10.0f, 0.0f, j * 10.0f);
            drawSnowMan();
            sprintf(number,"%d",(i+3)*6+(j+3));
            renderStrokeFontString(0.0f, 0.5f, 0.0f, (void *)font ,number);
            glPopMatrix();
        }

    // Code to compute frames per second
    frame++;

    time=glutGet(GLUT_ELAPSED_TIME);
    if (time - timebase > 1000) {
        sprintf(s,"Lighthouse3D - FPS:%4.2f",
            frame*1000.0/(time-timebase));
        timebase = time;
        frame = 0;
    }

        // Code to display a string (fps) with bitmap fonts
    setOrthographicProjection();

    glPushMatrix();
    glLoadIdentity();
    renderBitmapString(5,30,0,GLUT_BITMAP_HELVETICA_18,s);
    glPopMatrix();

    restorePerspectiveProjection();

    glutSwapBuffers();
}

// -----------------------------------
//             KEYBOARD
// -----------------------------------

void processNormalKeys(unsigned char key, int xx, int yy) {

    switch (key) {
        case 27:
            glutDestroyMenu(mainMenu);
            glutDestroyMenu(fillMenu);
            glutDestroyMenu(colorMenu);
            glutDestroyMenu(fontMenu);
            exit(0);
            break;
    }
}

void pressKey(int key, int xx, int yy) {

    switch (key) {
        case GLUT_KEY_UP : deltaMove = 0.5f; break;
        case GLUT_KEY_DOWN : deltaMove = -0.5f; break;
    }
}

void releaseKey(int key, int x, int y) {

    switch (key) {
        case GLUT_KEY_UP :
        case GLUT_KEY_DOWN : deltaMove = 0;break;
    }
}

// -----------------------------------
//             MOUSE
// -----------------------------------

void mouseMove(int x, int y) {

    // this will only be true when the left button is down
    if (xOrigin >= 0) {

        // update deltaAngle
        deltaAngle = (x - xOrigin) * 0.001f;

        // update camera's direction
        lx = sin(angle + deltaAngle);
        lz = -cos(angle + deltaAngle);
    }
}

void mouseButton(int button, int state, int x, int y) {

    // only start motion if the left button is pressed
    if (button == GLUT_LEFT_BUTTON) {

        // when the button is released
        if (state == GLUT_UP) {
            angle += deltaAngle;
            xOrigin = -1;
        }
        else  {// state = GLUT_DOWN
            xOrigin = x;
        }
    }
}

// -----------------------------------
//             MENUS
// -----------------------------------

void processMenuStatus(int status, int x, int y) {

    if (status == GLUT_MENU_IN_USE)
        menuFlag = 1;
    else
        menuFlag = 0;
}

void processMainMenu(int option) {

    // nothing to do in here
    // all actions are for submenus
}

void processFillMenu(int option) {

    switch (option) {

        case FILL: glPolygonMode(GL_FRONT, GL_FILL); break;
        case LINE: glPolygonMode(GL_FRONT, GL_LINE); break;
    }
}

void processFontMenu(int option) {

    switch (option) {
        case 1: font = GLUT_STROKE_ROMAN;
            break;
        case 2: font = GLUT_STROKE_MONO_ROMAN;
            break;
    }
}

void processColorMenu(int option) {

    switch (option) {
        case RED :
            red = 1.0f;
            green = 0.0f;
            blue = 0.0f; break;
        case GREEN :
            red = 0.0f;
            green = 1.0f;
            blue = 0.0f; break;
        case BLUE :
            red = 0.0f;
            green = 0.0f;
            blue = 1.0f; break;
        case ORANGE :
            red = 1.0f;
            green = 0.5f;
            blue = 0.5f; break;
    }
}

void createPopupMenus() {

    fontMenu = glutCreateMenu(processFontMenu);

        glutAddMenuEntry("STROKE_ROMAN",1 );
        glutAddMenuEntry("STROKE_MONO_ROMAN",2 );
    fillMenu = glutCreateMenu(processFillMenu);

    glutAddMenuEntry("Fill",FILL);
    glutAddMenuEntry("Line",LINE);

    colorMenu = glutCreateMenu(processColorMenu);
    glutAddMenuEntry("Red",RED);
    glutAddMenuEntry("Blue",BLUE);
    glutAddMenuEntry("Green",GREEN);
    glutAddMenuEntry("Orange",ORANGE);

    mainMenu = glutCreateMenu(processMainMenu);

    glutAddSubMenu("Polygon Mode", fillMenu);
    glutAddSubMenu("Color", colorMenu);
    glutAddSubMenu("Font",fontMenu);
    // attach the menu to the right button
    glutAttachMenu(GLUT_RIGHT_BUTTON);

    // this will allow us to know if the menu is active
    glutMenuStatusFunc(processMenuStatus);
}

// -----------------------------------
//             MAIN
// -----------------------------------

int main(int argc, char **argv) {

    // init GLUT and create window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100,100);
    glutInitWindowSize(320,320);
    glutCreateWindow("Lighthouse3D - GLUT Tutorial");

    // register callbacks
    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    glutIdleFunc(renderScene);

    glutIgnoreKeyRepeat(1);
    glutKeyboardFunc(processNormalKeys);
    glutSpecialFunc(pressKey);
    glutSpecialUpFunc(releaseKey);

    // here are the two new functions
    glutMouseFunc(mouseButton);
    glutMotionFunc(mouseMove);

    // OpenGL init
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

    // init Menus
    createPopupMenus();

    // enter GLUT event processing cycle
    glutMainLoop();
    
    return 1;
}

显示效果如下