軌道球應該在中心立方體上投射聚光燈

[英]Orbiting sphere should cast spot light on central cube


I'm writing a program that draws a rotating cube (with texture) in the middle of the screen followed by a small yellow sphere that orbits around the cube. The idea is to make the sphere as a spot light source that illuminates the cube.

我正在編寫一個程序,在屏幕中間繪制一個旋轉的立方體(帶有紋理),然后是一個圍繞立方體旋轉的小黃色球體。我們的想法是將球體作為照亮立方體的聚光源。

Here is the problem: as you can see in the images below, I'm failing to achieve the spot light effect. It seems that the entire cube gets lighted:

問題出在這里:正如您在下面的圖片中看到的那樣,我無法實現聚光燈效果。似乎整個立方體都被點亮了:

I'm setting GL_SPOT_DIRECTION to be the cube position. I didn't set surface normals because I'm struggling to understand how to compute them for the cube, and I'm not sure a simple graphic application like this really requires it.

我將GL_SPOT_DIRECTION設置為立方體位置。我沒有設置表面法線,因為我很難理解如何為立方體計算它們,我不確定像這樣的簡單圖形應用程序真的需要它。

I'm sharing the code below:

我正在分享以下代碼:

main.cpp:

main.cpp中:

#include <QApplication>
#include "glwidget.h"

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    GLWidget gl_widget;
    gl_widget.show();

    return app.exec();
}

GLWidget.h:

GLWidget.h:

#pragma once
#include <QGLWidget>
#include <QImage>

class GLWidget : public QGLWidget
{
    Q_OBJECT
public:
    explicit GLWidget(QWidget* parent = 0);
    virtual ~GLWidget();

    void _draw_texture_cube(int w, int h);
    void _draw_light();

    /* OpenGL initialization, viewport resizing, and painting */

    void initializeGL();
    void paintGL();
    void resizeGL( int width, int height);

    /* enable the user to interact directly with the scene using the keyboard */

    void keyPressEvent(QKeyEvent *e);

private:
    int _width;
    int _height;
    QImage* _img;
    GLuint  _texture;
    float xrot;
    float yrot;
    float zrot;
    bool _light_on;
    bool _must_rotate;
    bool _pause_light;
    GLfloat _light_pos[3];
    GLfloat _cube_pos[3];
    GLUquadricObj* _quadratic;

protected slots:
    void _tick();
};

GLWidget.cpp:

GLWidget.cpp:

#include "GLWidget.h"

#include <iostream>
#include <QKeyEvent>
#include <QTimer>

#include <cmath>

#define LIGHT_MOVEMENT_SPEED    20.0f           // Degrees per second
#define pi                      3.141592654f

GLWidget::GLWidget(QWidget *parent)
: QGLWidget(parent), _img(NULL), _light_on(true), _must_rotate(true),
  _pause_light(false), _quadratic(NULL)
{
    _width = 0;
    _height = 0;
    _texture = 0;

    xrot = 0.f;
    yrot = 0.f;
    zrot = 0.f;

    // Set central cube position
    _cube_pos[0] = 0.0f;
    _cube_pos[1] = 0.0f;
    _cube_pos[2] = -7.0f;

    // Set light position
    _light_pos[0] = 0.5f;
    _light_pos[1] = 0.5f;
    _light_pos[2] = -7.0f;
}

GLWidget::~GLWidget()
{
    if (_img)
        delete _img;

    glDeleteTextures(1, &_texture);
}

void GLWidget::_tick()
{
    update(); // triggers paintGL()

    QTimer::singleShot(33, this, SLOT(_tick()));
}

void GLWidget::initializeGL()
{
    std::cout << "GLWidget::initializeGL" << std::endl;
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);       // Black Background

    glEnable(GL_CULL_FACE);

    /* Load bitmap */

    glEnable(GL_TEXTURE_RECTANGLE_ARB);
    glPixelStorei (GL_UNPACK_ALIGNMENT, 1);

    if (!_img)
    {
        std::cout << "GLWidget::paintGL: loading image" << std::endl;

        QImage tmp(":/crate.jpg");
        if (tmp.isNull())
        {
            std::cout << "GLWidget::paintGL: !!! Failed QImage #1" << std::endl;
            return;
        }

        _img = new QImage(QGLWidget::convertToGLFormat(tmp));
    }

    /* Convert bitmap into texture */

    // Create The Texture
    glGenTextures(1, &_texture);

    // Typical Texture Generation Using Data From The Bitmap
    glBindTexture(GL_TEXTURE_RECTANGLE_ARB, _texture);

    // Generate The Texture
    glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0,
                 GL_RGBA, _img->width(), _img->height(), 0,
                 GL_RGBA, GL_UNSIGNED_BYTE, _img->bits());

    if (glGetError() != GL_NO_ERROR)
    {
        std::cout << "GLWidget::paintGL: !!! Failed glTexImage2D" << std::endl;
        return;
    }

    /* Setup lighting */

    glShadeModel(GL_SMOOTH);    //Smooth color shading

    // Light properties
    GLfloat AmbientLight[4]      = {0.2, 0.2, 0.2, 1.0};
    GLfloat DiffuseLight[4]      = {0.8, 0.8, 0.8, 1.0};      // color
    GLfloat SpecularLight[4]     = {1.0, 1.0, 1.0, 1.0};      // bright
    GLfloat SpecRef[]            = {0.7f, 0.7f, 0.7f, 1.0f};
    GLubyte Shine                = 60.0;

    //glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, AmbientLight);
    glLightfv(GL_LIGHT0, GL_AMBIENT, AmbientLight);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, DiffuseLight);
    glLightfv(GL_LIGHT0, GL_SPECULAR, SpecularLight);
    glLightfv(GL_LIGHT0, GL_POSITION, _light_pos);

    glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);
    glMaterialfv(GL_FRONT, GL_SPECULAR, SpecRef);           // refletância do material
    glMaterialf(GL_FRONT, GL_SHININESS, Shine);             // concentração do brilho
    glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, 0);
    //glColorMaterial(GL_FRONT,GL_DIFFUSE);

    glEnable(GL_COLOR_MATERIAL);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);

    // Sphere
    _quadratic = gluNewQuadric();               // Create A Pointer To The Quadric Object
    gluQuadricNormals(_quadratic, GLU_SMOOTH);  // Create Smooth Normals
    gluQuadricTexture(_quadratic, GL_TRUE);     // Create Texture Coords

    /* Start the timer */

    _tick();
}

/* Draw the central cube with texture
 */
void GLWidget::_draw_texture_cube(int w, int h)
{
    glPushMatrix();

    glTranslatef(_cube_pos[0], _cube_pos[1], _cube_pos[2]);
    glRotatef ( xrot, 1.0, 0.0, 0.0 );
    glRotatef ( yrot, 0.0, 1.0, 0.0 );
    glRotatef ( zrot, 0.0, 0.0, 1.0 );

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

    glBegin(GL_QUADS);  // Draw A Cube

        // Front Face
        glTexCoord2f(0.0f, 0.0f);           glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(w, 0.0f);              glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(w, h);                 glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, h);              glVertex3f(-1.0f,  1.0f,  1.0f);

        // Back Face
        glTexCoord2f(w, 0.0f);              glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(w, h);                 glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, h);              glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f);           glVertex3f( 1.0f, -1.0f, -1.0f);

        // Top Face
        glTexCoord2f(0.0f, h);              glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f);           glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(w, 0.0f);              glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(w, h);                 glVertex3f( 1.0f,  1.0f, -1.0f);

        // Bottom Face
        glTexCoord2f(w, h);                 glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, h);              glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f);           glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(w, 0.0f);              glVertex3f(-1.0f, -1.0f,  1.0f);

        // Right face
        glTexCoord2f(w, 0.0f);              glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(w, h);                 glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, _img->height()); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 0.0f);           glVertex3f( 1.0f, -1.0f,  1.0f);

        // Left Face
        glTexCoord2f(0.0f, 0.0f);           glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(w, 0.0f);              glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(w, h);                 glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, h);              glVertex3f(-1.0f,  1.0f, -1.0f);

    glEnd();
    glPopMatrix();

    if (_must_rotate)
    {
        xrot += 0.6f;
        yrot += 0.4f;
        zrot += 0.8f;
    }
}

/* Draw light source and light model (sphere)
 */
void GLWidget::_draw_light()
{
    if (_light_on)
    {
        glEnable(GL_LIGHT0);    // enable lights that we use
    }
    else
    {
        glDisable(GL_LIGHT0);
    }

    static float light_angle = 25.0f;
    if (!_pause_light)          // stop moving the light source
    {
        light_angle += LIGHT_MOVEMENT_SPEED * 0.1;
        if (light_angle > 360.0f)
            light_angle -= 360.0f;
    }

    /* Set light source position */

    _light_pos[0] = 4.0f * (float) cos(light_angle * pi / 180.0f);
    _light_pos[1] = 4.0f * (float) sin(light_angle * pi / 180.0f);
    _light_pos[2] = -7;
    glLightfv(GL_LIGHT0, GL_POSITION, _light_pos);

    GLfloat SpotDir[] = {_cube_pos[0], _cube_pos[1], _cube_pos[2], 0.0 };
    glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, SpotDir);

    glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 150.0);
    glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, 15.0);

    /* Set the light model position to be the same as the light source */

    glPushMatrix();
        glTranslatef(_light_pos[0], _light_pos[1], _light_pos[2]);
        glColor3ub(255, 255, 0);                // yellow
        gluSphere(_quadratic, 0.2f, 32, 32);    // draw sphere
    glPopMatrix();
}

void GLWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer

    glMatrixMode   ( GL_MODELVIEW );    // Select The Model View Matrix
    glLoadIdentity();                   // Reset The Current Modelview Matrix

    /* Draw central cube */

    glEnable(GL_TEXTURE_RECTANGLE_ARB);
    glBindTexture(GL_TEXTURE_RECTANGLE_ARB, _texture);       // Select Our Texture
    _draw_texture_cube(_img->width(), _img->height());
    glDisable(GL_TEXTURE_RECTANGLE_ARB);

    /* Draw light source and light model*/

    _draw_light();
}

void GLWidget::resizeGL( int w, int h)
{
    _width = w;
    _height = h;
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);    // Select The Projection Matrix
    glLoadIdentity();               // Reset The Projection Matrix
    if (h == 0)                     // Calculate The Aspect Ratio Of The Window
       gluPerspective ( 60, ( float ) w, 0.4, 500.0 );
    else
       gluPerspective ( 60, ( float ) w / ( float ) h, 0.4, 500.0 );

    glMatrixMode   ( GL_MODELVIEW );  // Select The Model View Matrix
    glLoadIdentity ( );    // Reset The Model View Matrix
    gluLookAt(0.0,  0.0, 2.0,   // eye
              0.0,  0.0, 0.0,   // center
              0.0,  1.0, 0.0);  // up
}

void GLWidget::keyPressEvent(QKeyEvent *e)
{
    switch (e->key())
    {
        case Qt::Key_L:
            if (_light_on)
                _light_on = false;
            else
                _light_on = true;
        break;

        case Qt::Key_P:
            if (_pause_light)
                _pause_light = false;
            else
                _pause_light = true;
        break;

        case Qt::Key_R:
            if (_must_rotate)
               _must_rotate = false;
            else
               _must_rotate = true;
        break;

        default:
        break;
    }
}

Lighting.pro:

Lighting.pro:

QT += core gui opengl

SOURCES += \
    GLWidget.cpp \
    main.cpp

HEADERS += \
    GLWidget.h

RESOURCES += \
    resource.qrc

What needs to be changed in this application in order to achieve the desired effect?

為了達到預期的效果,需要在此應用程序中進行哪些更改?

1 个解决方案

#1


3  

You do not specify any normals for your cube faces. As OpenGL is a state machine, it will use the default surface normal for all vertices, hence all of your faces. As the normal vector is crucial for the lighting, all of your faces will be lit almost identical (vertex postions still are different, but the effect is weak).

您沒有為立方體面指定任何法線。由於OpenGL是狀態機,它將使用所有頂點的默認曲面法線,因此所有面都使用。由於法線向量對於光照是至關重要的,因此所有的面都會被點亮幾乎相同(頂點位置仍然不同,但效果很弱)。

You should also be aware that the fixed function lighting of OpenGL is done per vertex. If you really want to see a good spotlight on the cuve, you would either need to tessalate it so more vertices are used where the lighting equation is actually evaluated, or use shaders for per-fragment lighting.

您還應該知道OpenGL的固定功能照明是按頂點完成的。如果你真的想要在cuve上看到一個好的聚光燈,你需要對它進行討論,以便在實際評估光照方程的地方使用更多的頂點,或者為每個片段的光照使用着色器。


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