c++ - 具有 alpha 和 glColor4f 的 OpenGL 纹理，glColor4f 影响纹理

Question

我想应用包含 alpha 透明度的 .tga 文件中的纹理。当纹理绑定(bind)到对象时，它会显示为对象本身的纯色。我希望颜色消失，或者至少是透明的。如果我将对象颜色更改为透明，那么整个纹理将变得更加透明，这不是我想要的。

有没有办法关闭颜色，或者如何让 glColor4f 不影响纹理？

void Sector::DrawPlanets(double gameTime){
  glEnable(GL_TEXTURE_2D);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  glEnable( GL_BLEND );
  glColor4f(0.0f, 0.0f, 1.0f,0.1f);

  for(std::vector<Planet *>::iterator it = Planets.begin(); it != Planets.end(); it++){
    double x,y,angle;
    (*it)->GetPosition(&x,&y,&angle,gameTime);
    int radius = (*it)->GetRadius();
    glPushMatrix();
    glTranslatef(x,y,0);
    GLUquadricObj * sphere = gluNewQuadric();
    gluQuadricDrawStyle(sphere, GLU_FILL);
    gluQuadricTexture(sphere, GL_TRUE);
    glBindTexture(GL_TEXTURE_2D, get_textures()[static_cast<int>((*it)->GetPlanetZone())]);
    gluSphere(sphere,radius,20,20);
    glPopMatrix();
  }
  glDisable(GL_TEXTURE_2D);
  }

补充信息我已经看到加载纹理的方式也可能是问题的罪魁祸首。我也会包括在内。这是我从类里面获得的代码，这就是我使用 .tga 的原因，因为它已经可用。这是我认为相关的内容，不包括某些功能。

const int num_textures = 5;
static GLuint texName[num_textures];

void InitializeTextures(){
bool repeat[num_textures];
bool border[num_textures];
gliGenericImage *image[num_textures];
int n=0;
repeat[n] = false; border[n] = false;
image[n++] = readImage("ice.tga");
repeat[n] = false; border[n] = false;
image[n++] = readImage("jupiter.tga");
repeat[n] = false; border[n] = false;
image[n++] = readImage("world.tga");
repeat[n] = false; border[n] = false;
image[n++] = readImage("volcanic.tga");
repeat[n] = false; border[n] = false;
image[n++] = readImage("stars.tga");

if(n!=num_textures)
{
    printf("Error: Wrong number of textures\n");
    _getch();
    exit(1);;
}
glGenTextures(num_textures, texName);

for(int i=0; i<num_textures; i++)
{
    glBindTexture(GL_TEXTURE_2D, texName[i]);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    int repeats = repeat[i];
    int needs_border = border[i]; // Needed if clamping and not filling the whole polygon.
    if(repeats)
    {
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    }
    else
    {
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    }
    if(needs_border)
    {
        // set a border.
        SetBorder(image[i]);
    }

    bool mipmaps = false;
    if(!PowerOf2(image[i]->height) || !PowerOf2(image[i]->width))
    {
        // WARNING: Images that do not have width and height as 
        // powers of 2 MUST use mipmaps.
        mipmaps = true; 
    }

    if (mipmaps) 
    {
        gluBuild2DMipmaps(GL_TEXTURE_2D, image[i]->components,
                image[i]->width, image[i]->height,
                image[i]->format, GL_UNSIGNED_BYTE, image[i]->pixels);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                //GL_LINEAR_MIPMAP_LINEAR);
                GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, 
                //GL_LINEAR);
                GL_NEAREST);
    } 
    else 
    {
        glTexImage2D(GL_TEXTURE_2D, 0, image[i]->components,
                image[i]->width, image[i]->height, 0,
                image[i]->format, GL_UNSIGNED_BYTE, image[i]->pixels);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    }
}
}

Answer 1

当您将 TEXTURE_ENV_MODE 设置为 DECAL 时，您得到的是覆盖颜色的纹理:

// This is not what you want
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

您需要 MODULATE，这是默认设置，所以只需删除该行即可。

请注意，MODULATE 会将颜色乘以纹理，因此如果您希望纹理以全亮度显示，请将颜色更改为白色:

glColor4f(1.0f, 1.0f, 1.0f, 1.0f);