如何在openGL中绘制背景

Question

我有一个动画太阳系的程序.该计划吸引太阳和一些轨道行星.我喜欢在背景中放置一个星云像素图,但我不知道该怎么做.我试过的似乎不起作用.这是我尝试过的.

1)使用glDrawPixels绘制像素图.通过这种方法,我能够绘制像素图,但它覆盖了太阳物体.我试图翻译像素图,但这也不起作用.

2)将GL_QUADS绘制为太阳物体后面的平面.这架飞机是一个很小的平行四边形.

据我所知,这可能只是完全错误的做法.如果有人能指出我正确的方向,我将不胜感激.这是方法#1的代码.

    
void
universe::createObj()
{
    QPixmap map ("hst_orion_nebula.jpg");

    glTexImage2D (GL_TEXTURE_2D,0, GL_LUMINANCE, map.width(), map.height(), 0,
                  GL_BGRA,GL_UNSIGNED_BYTE, map.convertToImage().bits());

    callId = glGenLists(itemId::next());

    glNewList(callId, GL_COMPILE);

      glDrawPixels (map.width(), map.height(), GL_RGBA,
         GL_UNSIGNED_BYTE, map.convertToImage().bits());

    glEnable (GL_TEXTURE_2D);
    glEndList();
}

void
universe::draw()
{
   glPushMatrix();
   glPushAttrib (GL_COLOR_BUFFER_BIT | GL_LIGHTING_BIT);

   glCallList (callId);

   glPopMatrix();
   glPopAttrib();
}

/////////////////////////////////
void
sun::createObj()
{
    QPixmap map ("sunmap.jpg");

    glGenTextures (10, canvas::_instance->_texture);
    glBindTexture(GL_TEXTURE_2D, canvas::_instance->_texture[0]);

    glTexImage2D(GL_TEXTURE_2D,0, GL_LUMINANCE, map.width(), map.height(), 0,
                  GL_BGRA,GL_UNSIGNED_BYTE, map.convertToImage().bits());

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    callId = glGenLists(itemId::next());

    glNewList(callId, GL_COMPILE);

    GLUquadricObj *sphere_quadric = gluNewQuadric();
    gluQuadricTexture( sphere_quadric, GL_TRUE );
    gluQuadricDrawStyle(sphere_quadric, (GLenum)GLU_SMOOTH);
    gluSphere(sphere_quadric, 25, 36, 36);

    glEnable (GL_TEXTURE_2D);
    glEndList();
}

void
sun::draw()
{
   glEnable( GL_LIGHTING );

   glPushMatrix();

   glPushAttrib (GL_COLOR_BUFFER_BIT | GL_LIGHTING_BIT);

   GLfloat color1[4] = {1, 0.50, .0, 1 };

   glRotated (_xangle, 1, 0, 0);
   glRotated (_yangle, 0, 1, 0);
   glRotated (_zangle, 0, 0, 1);

    glBindTexture(GL_TEXTURE_2D, canvas::_instance->_texture[0]);
   GLfloat shine[1] = {128};
   glMaterialfv( GL_FRONT_AND_BACK, GL_EMISSION, color1 );
   glMaterialfv( GL_FRONT_AND_BACK, GL_SHININESS, shine );
   glCallList (callId);
   glPopMatrix();
   glPopAttrib();
}

Answer 1

绘制全屏四边形：

glBegin(GL_QUADS);
  glVertex2f(1,1);
  glVertex2f(1,0);
  glVertex2f(0,0);
  glVertex2f(0,1);
glEnd();

首先调用它们，然后调用整个场景。并使用这样的着色器程序：

void main(void){
   gl_Position =  gl_Vertex * 2.0 - 1.0;
   gl_TexCoord[0]  = gl_Vertex;
  }

还要注意，因为 gl_Vertex 已被正式弃用。如果必须使用固定管道的话，就是这样：

glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

glBegin( GL_QUADS );

    glTexCoord2f(0,0);
    glVertex2f(-1.0f, -1.0f);
    glTexCoord2f(1,0);
    glVertex2f(1.0f, -1.0f);
    glTexCoord2f(1,1);
    glVertex2f(1.0f, 1.0f);
    glTexCoord2f(0,1);
    glVertex2f(-1.0f, 1.0f);

glEnd();

glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);