GLUT Tutorials 18：多窗口的rendering

Posted 2021-02-18 flyinggod

博客转自：http://www.lighthouse3d.com/tutorials/glut-tutorial/rendering-to-multiple-subwindows/

Before we start lets recall our callback definitions, as defined when the window and subwindows were created:

• idle function – renderSceneAll
• display func for main window – renderScene
• display func for subwindow 1 – renderScenesw1
• display func for subwindow 2 – renderScenesw2
• display func for subwindow 3 – renderScenesw3

We’ll start by the display functions for each window. The main window is covered with subwindows so we only want to paint it black. Since we are working with multiple windows the first thing we must do is call glutSetWindow with the proper window id. Then we just clear the color buffer with the default color, black.

void renderScene() {
    glutSetWindow(mainWindow);
    glClear(GL_COLOR_BUFFER_BIT);
    glutSwapBuffers();
}

We must define the display function for each subwindow. In our example, the geometry is the same for all windows, the only thing that differs is the viewpoint, or the camera, if you prefer.

The function where the common geometry is rendered is called renderScene2. However, before we call this function we must set the current window to be the respective subwindow, load the identity matrix to clean the MODELVIEW matrix, and set the camera with gluLookAt.

As mentioned before in the initial section covering subwindows we have three subwindows with different perspectives of the same scene. The first subwindow displays the scene from the current point of view, i.e. the main camera. The second displays the same scene from the top, i.e. as if the camera was above the current position looking downwards, and with the same orientation as the line of sigh. The third subwindow behaves like a camera to the right of the current position, and pointing at the current position.

The following code defines the display functions for every window. This code is an extended version of the previous code. If you require more detail just explore the previous sections, namely Moving the Camera II for the keyboard movement, Bitmaps and the Orthogonal View for text display, or Frames per Second for the respective computation.

Note that there are a few differences in the contents of the windows. The top window will display the fps counter using bitmap strings. The two bottom windows will display a red cone at the position of the main camera.

// Common render items for all subwindows
void renderScene2() {

// 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();
            glPopMatrix();
        }
}

// Display func for main window
void renderScene() {
    glutSetWindow(mainWindow);
    glClear(GL_COLOR_BUFFER_BIT);
    glutSwapBuffers();
}

// Display func for sub window 1
void renderScenesw1() {

    glutSetWindow(subWindow1);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x, y, z,
          x + lx,y + ly,z + lz,
          0.0f,1.0f,0.0f);

    renderScene2();

    // display fps in the top window
     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;
    }

    setOrthographicProjection();

    glPushMatrix();
    glLoadIdentity();
    renderBitmapString(5,30,0,GLUT_BITMAP_HELVETICA_12,s);
    glPopMatrix();

    restorePerspectiveProjection();

    glutSwapBuffers();
}

// Display func for sub window 2
void renderScenesw2() {

    glutSetWindow(subWindow2);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x, y+15, z,
          x ,y - 1,z,
          lx,0,lz);

    // Draw red cone at the location of the main camera
    glPushMatrix();
    glColor3f(1.0,0.0,0.0);
    glTranslatef(x,y,z);
    glRotatef(180-(angle+deltaAngle)*180.0/3.14,0.0,1.0,0.0);
    glutSolidCone(0.2,0.8f,4,4);
    glPopMatrix();

    renderScene2();

    glutSwapBuffers();
}

// Display func for sub window 3
void renderScenesw3() {

    glutSetWindow(subWindow3);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x-lz*10 , y, z+lx*10,
          x ,y ,z ,
          0.0f,1.0f,0.0f);

    // Draw red cone at the location of the main camera
    glPushMatrix();
    glColor3f(1.0,0.0,0.0);
    glTranslatef(x,y,z);
    glRotatef(180-(angle+deltaAngle)*180.0/3.14,0.0,1.0,0.0);
    glutSolidCone(0.2,0.8f,4,4);
    glPopMatrix();

    renderScene2();

    glutSwapBuffers();
}

Now all its left to do is to define the global idle function. In our example, this function is renderSceneAll. This function checks if the variables deltaMove or deltaAngle are not zero, and updates the values of the current position, and the line of sight vector.

Afterwards we call the display functions for each of the subwindows. Note that we are not calling the display function for the main window because its contents never change.

// Global idle func
void renderSceneAll() {

    // check for keyboard movement
    if (deltaMove)
        computePos(deltaMove);

    renderScenesw1();
    renderScenesw2();
    renderScenesw3();
}

完整代码如下

#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, ly = 0.0f;

// XZ position of the camera
float x = 0.0f, z = 5.0f, y = 1.75f;

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

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

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

// variables to hold window identifiers
int mainWindow, subWindow1, subWindow2, subWindow3;
//border between subwindows
int border = 6;

void setProjection(int w1, int h1)
{
    float ratio;
    // Prevent a divide by zero, when window is too short
    // (you cant make a window of zero width).
    ratio = 1.0f * w1 / h1;
    // Reset the coordinate system before modifying
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // Set the viewport to be the entire window
    glViewport(0, 0, w1, h1);

    // Set the clipping volume
    gluPerspective(45, ratio, 0.1, 1000);
    glMatrixMode(GL_MODELVIEW);
}

void changeSize(int w1, int h1) {

    if (h1 == 0)
        h1 = 1;

    // we‘re keeping these values cause we‘ll need them latter
    w = w1;
    h = h1;

    // set subwindow 1 as the active window
    glutSetWindow(subWindow1);
    // resize and reposition the sub window
    glutPositionWindow(border, border);
    glutReshapeWindow(w - 2 * border, h / 2 - border * 3 / 2);
    setProjection(w - 2 * border, h / 2 - border * 3 / 2);

    // set subwindow 2 as the active window
    glutSetWindow(subWindow2);
    // resize and reposition the sub window
    glutPositionWindow(border, (h + border) / 2);
    glutReshapeWindow(w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);
    setProjection(w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);

    // set subwindow 3 as the active window
    glutSetWindow(subWindow3);
    // resize and reposition the sub window
    glutPositionWindow((w + border) / 2, (h + border) / 2);
    glutReshapeWindow(w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);
    setProjection(w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);
}

void drawSnowMan() {

    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(1.0f, 0.5f, 0.5f);
    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 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;
}

// Common Render Items for all subwindows
void renderScene2() {

    // 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
    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();
            glPopMatrix();
        }
}

// Display func for main window
void renderScene() {
    glutSetWindow(mainWindow);
    glClear(GL_COLOR_BUFFER_BIT);
    glutSwapBuffers();
}

// Display func for sub window 1
void renderScenesw1() {

    glutSetWindow(subWindow1);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x, y, z,
        x + lx, y + ly, z + lz,
        0.0f, 1.0f, 0.0f);

    renderScene2();

    // display fps in the top window
    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;
    }

    setOrthographicProjection();

    glPushMatrix();
    glLoadIdentity();
    renderBitmapString(5, 30, 0, GLUT_BITMAP_HELVETICA_12, s);
    glPopMatrix();

    restorePerspectiveProjection();

    glutSwapBuffers();
}

// Display func for sub window 2
void renderScenesw2() {

    glutSetWindow(subWindow2);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x, y + 15, z,
        x, y - 1, z,
        lx, 0, lz);

    // Draw red cone at the location of the main camera
    glPushMatrix();
    glColor3f(1.0, 0.0, 0.0);
    glTranslatef(x, y, z);
    glRotatef(180 - (angle + deltaAngle)*180.0 / 3.14, 0.0, 1.0, 0.0);
    glutSolidCone(0.2, 0.8f, 4, 4);
    glPopMatrix();

    renderScene2();

    glutSwapBuffers();
}

// Display func for sub window 3
void renderScenesw3() {

    glutSetWindow(subWindow3);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();
    gluLookAt(x - lz * 10, y, z + lx * 10,
        x, y, z,
        0.0f, 1.0f, 0.0f);

    // Draw red cone at the location of the main camera
    glPushMatrix();
    glColor3f(1.0, 0.0, 0.0);
    glTranslatef(x, y, z);
    glRotatef(180 - (angle + deltaAngle)*180.0 / 3.14, 0.0, 1.0, 0.0);
    glutSolidCone(0.2, 0.8f, 4, 4);
    glPopMatrix();

    renderScene2();

    glutSwapBuffers();
}

// Global idle func
void renderSceneAll() {

    // check for keyboard movement
    if (deltaMove)
        computePos(deltaMove);

    renderScenesw1();
    renderScenesw2();
    renderScenesw3();
}

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

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

    if (key == 27) {
        glutDestroyWindow(subWindow1);
        glutDestroyWindow(subWindow2);
        glutDestroyWindow(subWindow3);
        glutDestroyWindow(mainWindow);
        exit(0);
    }
}

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;
            deltaAngle = 0.0f;
            xOrigin = -1;
        }
        else  {// state = GLUT_DOWN
            xOrigin = x;

        }
    }
}

// -----------------------------------
//             MAIN and INIT
// -----------------------------------

void init() {

    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

    // register callbacks
    glutIgnoreKeyRepeat(1);
    glutKeyboardFunc(processNormalKeys);
    glutSpecialFunc(pressKey);
    glutSpecialUpFunc(releaseKey);
    glutMouseFunc(mouseButton);
    glutMotionFunc(mouseMove);
}

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

    // init GLUT and create main window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(800, 800);
    mainWindow = glutCreateWindow("Lighthouse3D - GLUT Tutorial");

    // callbacks for main window
    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    glutIdleFunc(renderSceneAll);
    init();

    // sub windows
    subWindow1 = glutCreateSubWindow(mainWindow, border, border, w - 2 * border, h / 2 - border * 3 / 2);
    glutDisplayFunc(renderScenesw1);
    init();

    subWindow2 = glutCreateSubWindow(mainWindow, border, (h + border) / 2, w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);
    glutDisplayFunc(renderScenesw2);
    init();

    subWindow3 = glutCreateSubWindow(mainWindow, (w + border) / 2, (h + border) / 2, w / 2 - border * 3 / 2, h / 2 - border * 3 / 2);
    glutDisplayFunc(renderScenesw3);
    init();

    // enter GLUT event processing cycle
    glutMainLoop();

    return 1;
}

显示效果如下