openGL 纹理和颜色

Question

我正在学习如何在 openGL 中应用纹理。 我将纹理应用到立方体的一个面上，并使用原始颜色为其他面着色。 在我应用纹理之前，颜色看起来很好，在应用它之后，它们变得更暗。 怎么了？

void LoadGLTextures() {
    // Load Texture
    Image *image1;
    // allocate space for texture
    image1 = (Image *) malloc(sizeof(Image));
    if (image1 == NULL) {
    printf("Error allocating space for image");
    exit(0);
    }

    if (!ImageLoad("dd.bmp", image1)) {
    exit(1);
    }

    // Create Texture
    glGenTextures(1, &texture[0]);
    glBindTexture(GL_TEXTURE_2D, texture[0]);   // 2d texture (x and y size)

    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // scale linearly when image bigger than texture
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // scale linearly when image smalled than texture

    // 2d texture, level of detail 0 (normal), 3 components (red, green, blue), x size from image, y size from image,
    // border 0 (normal), rgb color data, unsigned byte data, and finally the data itself.
    glTexImage2D(GL_TEXTURE_2D, 0, 3, image1->sizeX, image1->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, image1->data);
}


int main()
{
sf::Window App(sf::VideoMode(600, 600, 32), "SFML OpenGL", sf::Style::Close);
glEnable(GL_DEPTH_TEST);
glDepthMask(GL_TRUE);
glDepthFunc(GL_LEQUAL);
glEnable(GL_TEXTURE_2D);
glShadeModel(GL_SMOOTH);
LoadGLTextures();
glBindTexture(GL_TEXTURE_2D, texture[0]);
while (App.IsOpened())
{
    App.SetActive();
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glBegin(GL_QUADS);
    //back
    glColor3f(0.0f,0.0f,0.0f); //cyan
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f,0.2f,0.2f); //top left
    glTexCoord2f(1.0f, 1.0f); glVertex3f(0.2f,0.2f,0.2f); //top right
    glTexCoord2f(1.0f, 0.0f); glVertex3f(0.2f,-0.2f,0.2f); //bottom right
    glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f,-0.2f,0.2f); //bottom left
    //bottom
    glColor3f(0.0f,1.0f,0.0f); //green
    glVertex3f(0.2f,-0.2f,0.2f); //back right
    glVertex3f(-0.2f,-0.2f,0.2f); //back left
    glVertex3f(-0.2f,-0.2f,-0.2f); //front left
    glVertex3f(0.2f,-0.2f,-0.2f); //front right
    //front
    glColor3f(0.0f,0.0f,1.0f); //blue
    glVertex3f(0.2f,-0.2f,-0.2f); //bottom right
    glVertex3f(-0.2f,-0.2f,-0.2f); //bottom left
    glVertex3f(-0.2f,0.2f,-0.2f); //top left
    glVertex3f(0.2f,0.2f,-0.2f); //top right
    //top
    glColor3f(1.0f,1.0f,0.0f); //yellow
    glVertex3f(0.2f,0.2f,-0.2f); //front right
    glVertex3f(-0.2f,0.2f,-0.2f); //front left
    glVertex3f(-0.2f,0.2f,0.2f); //back left
    glVertex3f(0.2f,0.2f,0.2f); //back right
    //left
    glColor3f(0.0f,1.0f,1.0f); //pink
    glVertex3f(-0.2f,-0.2f,-0.2f); //bottom front
    glVertex3f(-0.2f,-0.2f,0.2f); //bottom back
    glVertex3f(-0.2f,0.2f,0.2f); //top back
    glVertex3f(-0.2f,0.2f,-0.2f); //top front
    //right
    glColor3f(1.0f,0.0f,0.0f); //red
    glVertex3f(0.2f,-0.2f,-0.2f); //bottom front
    glVertex3f(0.2f,-0.2f,0.2f); //bottom back
    glVertex3f(0.2f,0.2f,0.2f); //top back
    glVertex3f(0.2f,0.2f,-0.2f); //top front
    glEnd();

    glFlush();

    App.Display();

    sf::Event Event;
    while (App.GetEvent(Event))
    {
        if (Event.Type == sf::Event::Closed)
            App.Close();
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Escape))
            App.Close();
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Right))
            glRotated(20.0d,0.0d,0.2d,0.0d);
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Left))
            glRotated(-20.0d,0.0d,0.2d,0.0d);
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Up))
            glRotated(20.0d,0.2d,0.0d,0.0d);
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Down))
            glRotated(-20.0d,0.2d,0.0d,0.0d);
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::PageUp))
            glRotated(20.0d,0.0d,0.0d,0.2d);
        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::PageDown))
            glRotated(-20.0d,0.0d,0.0d,0.2d);
    }
}
return EXIT_SUCCESS;
}

Answer 1

OpenGL 是一个状态机。这意味着最后一个纹理坐标集将应用于所有后续顶点。因此，即使您停止提供纹理坐标，它仍然会在应用于整个面的最后设置的纹理坐标处应用纹理的颜色。

要停止纹理，您必须使用 glDisable(GL_TEXTURE_2D); 禁用纹理，将其放入代码中：

// ...
App.SetActive();
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

glEnable(GL_TEXTURE_2D); // <- enable texturing for the one face
glBegin(GL_QUADS);
//back
glColor3f(0.0f,0.0f,0.0f); //cyan
glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f,0.2f,0.2f); //top left
glTexCoord2f(1.0f, 1.0f); glVertex3f(0.2f,0.2f,0.2f); //top right
glTexCoord2f(1.0f, 0.0f); glVertex3f(0.2f,-0.2f,0.2f); //bottom right
glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f,-0.2f,0.2f); //bottom left
glEnd(); // <- first end the current primitive list

glDisable(GL_TEXTURE_2D); // <- disable texturing for the rest of the faces
glBegin(GL_QUADS);
//bottom
glColor3f(0.0f,1.0f,0.0f); //green
glVertex3f(0.2f,-0.2f,0.2f); //back right
glVertex3f(-0.2f,-0.2f,0.2f); //back left
glVertex3f(-0.2f,-0.2f,-0.2f); //front left
glVertex3f(0.2f,-0.2f,-0.2f); //front right
//front

//...

Answer 2

尝试在绘制纹理面之前启用 GL_TEXTURE2D，并在绘制之后立即禁用它。

...
//back
glEnable(GL_TEXTURE2D);
glBegin(GL_QUADS);
glColor3f(0.0f,0.0f,0.0f); //cyan
glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f,0.2f,0.2f); //top left
glTexCoord2f(1.0f, 1.0f); glVertex3f(0.2f,0.2f,0.2f); //top right
glTexCoord2f(1.0f, 0.0f); glVertex3f(0.2f,-0.2f,0.2f); //bottom right
glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f,-0.2f,0.2f); //bottom left
glEnd();
glDisable(GL_TEXTURE2D);
glBegin(GL_QUADS);
//bottom
...

Answer 3

你是绝对正确的，现在这是正确的代码：

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, texture);
    glBegin(GL_QUADS);
    //back
    glColor3f(1.0f,1.0f,1.0f); //white
    glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f,0.2f,0.2f); //top left
    glTexCoord2f(1.0f, 1.0f); glVertex3f(0.2f,0.2f,0.2f); //top right
    glTexCoord2f(1.0f, 0.0f); glVertex3f(0.2f,-0.2f,0.2f); //bottom right
    glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f,-0.2f,0.2f); //bottom left
    glEnd();
    glDisable(GL_TEXTURE_2D);
    glBegin(GL_QUADS);
    //bottom
    glColor3f(0.0f,1.0f,0.0f); //green
    glVertex3f(0.2f,-0.2f,0.2f); //back right
    glVertex3f(-0.2f,-0.2f,0.2f); //back left
    glVertex3f(-0.2f,-0.2f,-0.2f); //front left
    glVertex3f(0.2f,-0.2f,-0.2f); //front right
    //front
    glColor3f(0.0f,0.0f,1.0f); //blue
    glVertex3f(0.2f,-0.2f,-0.2f); //bottom right
    glVertex3f(-0.2f,-0.2f,-0.2f); //bottom left
    glVertex3f(-0.2f,0.2f,-0.2f); //top left
    glVertex3f(0.2f,0.2f,-0.2f); //top right
    //top
    glColor3f(1.0f,1.0f,0.0f); //yellow
    glVertex3f(0.2f,0.2f,-0.2f); //front right
    glVertex3f(-0.2f,0.2f,-0.2f); //front left
    glVertex3f(-0.2f,0.2f,0.2f); //back left
    glVertex3f(0.2f,0.2f,0.2f); //back right
    //left
    glColor3f(0.0f,1.0f,1.0f); //pink
    glVertex3f(-0.2f,-0.2f,-0.2f); //bottom front
    glVertex3f(-0.2f,-0.2f,0.2f); //bottom back
    glVertex3f(-0.2f,0.2f,0.2f); //top back
    glVertex3f(-0.2f,0.2f,-0.2f); //top front
    //right
    glColor3f(1.0f,0.0f,0.0f); //red
    glVertex3f(0.2f,-0.2f,-0.2f); //bottom front
    glVertex3f(0.2f,-0.2f,0.2f); //bottom back
    glVertex3f(0.2f,0.2f,0.2f); //top back
    glVertex3f(0.2f,0.2f,-0.2f); //top front
    glEnd();