如何绘制所有面都具有不同纹理的立方体？

Question

I'm trying to move my code over to modern Opengl, but am having trouble. Right now my code will draw a cube and it will put a texture on, but it will only attach the first texture to all of my face. I am also using SOIL to load my textures into my program. What am I doing wrong?

This is my code:

class Rectangle
{
public:
    Rectangle();

    Rectangle(float x, float y, float z, float width, float height, float depth, string frontFace, string backFace, string leftFace, 
            string RightFace, string topFace, string bottomFace);

    void Draw();
private:
   GLuint m_Textures[6];
   string m_TextureNames[6];


   GLfloat m_Vertices[72];   // v0,v1,v2,v3 (front)
    // normal array
    GLfloat m_Normals[72];   // v0,v1,v2,v3 (front)
    // color array
    GLfloat m_Colours[72];   // v0,v1,v2,v3 (front)
    // index array of vertex array for glDrawElements() & glDrawRangeElement()
    GLubyte m_Indices[36];     // front

    GLfloat m_Texcoords[48];
};

Rectangle::Rectangle(float x, float y, float z, float width, float height, float depth, string topFace, string bottomFace, string frontFace, 
            string backFace, string leftFace, string rightFace)
{
    m_CenterX = x;
    m_CenterY = y;
    m_CenterZ = z; 
    m_Width = width;
    m_Height = height;
    m_Depth = depth; 

    m_TextureNames[0] = topFace;
    m_TextureNames[1] = bottomFace;
    m_TextureNames[2] = frontFace;
    m_TextureNames[3] = backFace;
    m_TextureNames[4] = leftFace;
    m_TextureNames[5] = rightFace;
    m_ObjectType = Textured;

    GLfloat tempVert[] = {  // front
    -1.0, -1.0,  1.0,
     1.0, -1.0,  1.0,
     1.0,  1.0,  1.0,
    -1.0,  1.0,  1.0,
    // top
    -1.0,  1.0,  1.0,
     1.0,  1.0,  1.0,
     1.0,  1.0, -1.0,
    -1.0,  1.0, -1.0,
    // back
     1.0, -1.0, -1.0,
    -1.0, -1.0, -1.0,
    -1.0,  1.0, -1.0,
     1.0,  1.0, -1.0,
    // bottom
    -1.0, -1.0, -1.0,
     1.0, -1.0, -1.0,
     1.0, -1.0,  1.0,
    -1.0, -1.0,  1.0,
    // left
    -1.0, -1.0, -1.0,
    -1.0, -1.0,  1.0,
    -1.0,  1.0,  1.0,
    -1.0,  1.0, -1.0,
    // right
     1.0, -1.0,  1.0,
     1.0, -1.0, -1.0,
     1.0,  1.0, -1.0,
     1.0,  1.0,  1.0,
     };

    // normal array
    GLfloat tempNormals[]  = { 0, 0, 1,   0, 0, 1,   0, 0, 1,   0, 0, 1,   // v0,v1,v2,v3 (front)
                            1, 0, 0,   1, 0, 0,   1, 0, 0,   1, 0, 0,   // v0,v3,v4,v5 (right)
                            0, 1, 0,   0, 1, 0,   0, 1, 0,   0, 1, 0,   // v0,v5,v6,v1 (top)
                           -1, 0, 0,  -1, 0, 0,  -1, 0, 0,  -1, 0, 0,   // v1,v6,v7,v2 (left)
                            0,-1, 0,   0,-1, 0,   0,-1, 0,   0,-1, 0,   // v7,v4,v3,v2 (bottom)
                            0, 0,-1,   0, 0,-1,   0, 0,-1,   0, 0,-1 }; // v4,v7,v6,v5 (back)

    // color array
    GLfloat tempColors[]   = { 1, 1, 1,   1, 1, 0,   1, 0, 0,   1, 0, 1,   // v0,v1,v2,v3 (front)
                            1, 1, 1,   1, 0, 1,   0, 0, 1,   0, 1, 1,   // v0,v3,v4,v5 (right)
                            1, 1, 1,   0, 1, 1,   0, 1, 0,   1, 1, 0,   // v0,v5,v6,v1 (top)
                            1, 1, 0,   0, 1, 0,   0, 0, 0,   1, 0, 0,   // v1,v6,v7,v2 (left)
                            0, 0, 0,   0, 0, 1,   1, 0, 1,   1, 0, 0,   // v7,v4,v3,v2 (bottom)
                            0, 0, 1,   0, 0, 0,   0, 1, 0,   0, 1, 1 }; // v4,v7,v6,v5 (back)

    // index array of vertex array for glDrawElements() & glDrawRangeElement()
    GLubyte tempIndices[]  = { 0, 1, 2,   2, 3, 0,      // front
                           4, 5, 6,   6, 7, 4,      // right
                           8, 9,10,  10,11, 8,      // top
                          12,13,14,  14,15,12,      // left
                          16,17,18,  18,19,16,      // bottom
                          20,21,22,  22,23,20 };    // back

    GLfloat tempTexcoords[2*4*6] = {
    // front
    0.0, 0.0,
    1.0, 0.0,
    1.0, 1.0,
    0.0, 1.0,
  };
  for (int i = 1; i < 6; i++)
    memcpy(&tempTexcoords[i*4*2], &tempTexcoords[0], 2*4*sizeof(GLfloat));


    copy(tempVert, tempVert + 72, m_Vertices);
    copy(tempNormals, tempNormals + 72, m_Normals);
    copy(tempColors, tempColors + 72, m_Colours);

    copy(tempIndices, tempIndices + 36, m_Indices);
    std::copy(tempTexcoords, tempTexcoords + 48, m_Texcoords);

    LoadTexture(m_TextureNames);
}

void Rectangle::LoadTexture(string TextureName[6])          
{
    // Create texture index array.
    glGenTextures(6, m_Textures); 


    for(int i = 0 ; i < 1 ; i++)
    {
        glBindTexture(GL_TEXTURE_2D, m_Textures[i]);
        // Set our texture parameters
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        // Set texture filtering
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);  // NOTE the GL_NEAREST Here! 
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);  // NOTE the GL_NEAREST Here! 

        std::string fileType;
        fileType.append(m_TextureNames[i], m_TextureNames[i].size()-3,3);

        if(fileType == "jpg")
        {
            m_Textures[i] = SOIL_load_OGL_texture // load an image file directly as a new OpenGL texture
            (
                m_TextureNames[i].c_str(),
                SOIL_LOAD_AUTO,
                SOIL_CREATE_NEW_ID,
                SOIL_FLAG_MIPMAPS | SOIL_FLAG_INVERT_Y | SOIL_FLAG_NTSC_SAFE_RGB | SOIL_FLAG_COMPRESS_TO_DXT
            );
            // allocate a texture name
        }
        else
        {
            m_Textures[i] = SOIL_load_OGL_texture // load an image file directly as a new OpenGL texture
            (
                m_TextureNames[i].c_str(),
                SOIL_LOAD_AUTO,
                SOIL_CREATE_NEW_ID,
                SOIL_FLAG_MIPMAPS | SOIL_FLAG_NTSC_SAFE_RGB | SOIL_FLAG_COMPRESS_TO_DXT
            );
            // allocate a texture name
        }

    }
}

// Function to draw Sphere.
void Rectangle::Draw()
{
        // enable and specify pointers to vertex arrays
        glEnableClientState(GL_NORMAL_ARRAY);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
        glEnableClientState(GL_COLOR_ARRAY);
        glEnableClientState(GL_VERTEX_ARRAY);
        glNormalPointer(GL_FLOAT, 0, m_Normals);
        glTexCoordPointer(2, GL_FLOAT, 0, m_Texcoords);
        glColorPointer(3, GL_FLOAT, 0, m_Colours);
        glVertexPointer(3, GL_FLOAT, 0, m_Vertices);

        for (int i=0;i<6;i++)
        {
        glPushMatrix();
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, m_Textures[i]);

            glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_BYTE, m_Indices);
        glPopMatrix();
        }

        glDisableClientState(GL_VERTEX_ARRAY);  // disable vertex arrays
        glDisableClientState(GL_TEXTURE_COORD_ARRAY);
        glDisableClientState(GL_COLOR_ARRAY);
        glDisableClientState(GL_NORMAL_ARRAY);
}


Rectangle testRect;

// Drawing routine.
void drawScene(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

   glLoadIdentity();

   testRect.Draw();

   glutSwapBuffers();
}

// Initialization routine.
void setup(void) 
{
   glClearColor(0.0, 0.0, 0.0, 0.0); 
   testRect = Rectangle(2, 0.0, 0.0, 1, 2, 1, "grass.bmp","grass.bmp", "grass.bmp", "launch.png", "launch.png", "launch.png");

   // Turn on OpenGL texturing.
   glEnable(GL_TEXTURE_2D);

   glShadeModel (GL_SMOOTH);
}

Answer 1

The posted code has a few issues:

• It's loading only one texture:

   glGenTextures(6, m_Textures); for(int i = 0 ; i < 1 ; i++) { glBindTexture(GL_TEXTURE_2D, m_Textures[i]); ... 

  If you want to load 6 textures, like the rest of the code suggests, you'll have to use 6 for the end value of the loop:

   for(int i = 0 ; i < 6 ; i++) 

• It's creating texture ids twice, and sets parameters with the wrong texture bound. At the start of LoadTexture() , it generates 6 texture ids:

   glGenTextures(6, m_Textures); 

  and then binds them, and makes glTexParameteri() to set various parameters on them. But then it calls SOIL_load_ogl_texture() with a flag asking it to create a new id again, and then stores that one away:

   m_Textures[i] = SOIL_load_OGL_texture( m_TextureNames[i].c_str(), SOIL_LOAD_AUTO, SOIL_CREATE_NEW_ID, SOIL_FLAG_MIPMAPS | SOIL_FLAG_INVERT_Y | SOIL_FLAG_NTSC_SAFE_RGB | SOIL_FLAG_COMPRESS_TO_DXT ); 

  To fix this, you can omit the gGenTextures() call, and move the code to bind the texture and call glTexParameteri() after the SOIL_load_ogl_texture() call. Also, this uses a flag to generate mipmaps, but sets the texture filters to not use mipmapping.

• In the draw function, it loops over the 6 faces, but then draws the entire cube each time:

   for (int i=0;i<6;i++) { glPushMatrix(); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, m_Textures[i]); glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_BYTE, m_Indices); glPopMatrix(); } 

  The second argument to glDrawElements() specifies the number of vertices to be rendered. With the value 36, all vertices will be used (6 sides of the cube, with 2 triangles each, with 3 vertices each.

  Also, the glPushMatrix() / glPopMatrix() serves absolutely no purpose. The draw loop should look something like this:

   glActiveTexture(GL_TEXTURE0); for (int i=0;i<6;i++) { glBindTexture(GL_TEXTURE_2D, m_Textures[i]); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, m_Indices + i * 6); } 

• I don't see the depth test being enabled anywhere. Add this to setup() :

   glEnable(GL_DEPTH_TEST); 

Answer 2

I do it a little differently that works, so maybe the issue is in the difference.

I would bind each texture to a different GL_Texture (GL_Texture0, GL_Texture1...) so that each texture has it's own data. I don't know how SOIL works, but in my case for the first texture after:

glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);

I would include a call:

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texture1Width, texture1Height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmapData);

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_Textures[0]);

And I would repeat this process for each of the 6 textures.

Then I would draw each face:

// First face
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_Textures[0]);

glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_BYTE, m_Indices);

// Second face
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, m_Textures[1]);

glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_BYTE, m_Indices);

And so on for each face.

EDIT:

I did some checking about SOIL, and it looks to me like (using SOIL) you would:

GLuint m_Textures[6];  
int img_width, img_height;

glGenTextures(6, m_Textures);

// For each texture

unsigned char* img = SOIL_load_image(m_TextureNames[0].c_str(), &img_width, &img_height, NULL, 0); // or m_TextureNames[1].c_str() ...

glBindTexture(GL_TEXTURE_2D, m_Textures[0]); // or m_textures[1]...
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// Set texture filtering
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);  // NOTE the GL_NEAREST Here! 
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);  // NOTE the GL_NEAREST Here! 

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img_width, img_height, 0, GL_RGB, GL_UNSIGNED_BYTE, img);

glActiveTexture(GL_TEXTURE0); // or GL_TEXTURE1....
glBindTexture(GL_TEXTURE_2D, m_Textures[0]); // or m_Textures[1]...