如何在 OpenGL ES 1.1 上用不同的纹理填充立方体的每一面？

请，我需要教程/代码示例，了解如何在 OpenGL ES 1.1 上用不同的纹理填充立方体的每一面

我找到了很多教程，但没有一个教程清楚地解释了如何在每个面上放置不同的纹理，也没有一个提供简单的代码示例来说明如何做到这一点。

我的实际代码（来自 nehe 示例）绘制了每个面上具有相同纹理的立方体：

public class Cube {

/** The buffer holding the vertices */
private FloatBuffer vertexBuffer;
/** The buffer holding the texture coordinates */
private FloatBuffer textureBuffer;
/** The buffer holding the indices */
private ByteBuffer indexBuffer;

/** Our texture pointer */
private int[] textures = new int[1];

/** 
 * The initial vertex definition
 * 
 * Note that each face is defined, even
 * if indices are available, because
 * of the texturing we want to achieve 
 */ 
private float vertices[] = {
                    //Vertices according to faces
                    -1.0f, -1.0f, 1.0f, //Vertex 0
                    1.0f, -1.0f, 1.0f,  //v1
                    -1.0f, 1.0f, 1.0f,  //v2
                    1.0f, 1.0f, 1.0f,   //v3

                    1.0f, -1.0f, 1.0f,  //...
                    1.0f, -1.0f, -1.0f,         
                    1.0f, 1.0f, 1.0f,
                    1.0f, 1.0f, -1.0f,

                    1.0f, -1.0f, -1.0f,
                    -1.0f, -1.0f, -1.0f,            
                    1.0f, 1.0f, -1.0f,
                    -1.0f, 1.0f, -1.0f,

                    -1.0f, -1.0f, -1.0f,
                    -1.0f, -1.0f, 1.0f,         
                    -1.0f, 1.0f, -1.0f,
                    -1.0f, 1.0f, 1.0f,

                    -1.0f, -1.0f, -1.0f,
                    1.0f, -1.0f, -1.0f,         
                    -1.0f, -1.0f, 1.0f,
                    1.0f, -1.0f, 1.0f,

                    -1.0f, 1.0f, 1.0f,
                    1.0f, 1.0f, 1.0f,           
                    -1.0f, 1.0f, -1.0f,
                    1.0f, 1.0f, -1.0f,
                                        };

/** The initial texture coordinates (u, v) */   
private float texture[] = {         
                    //Mapping coordinates for the vertices
                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f, 

                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,

                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,

                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,

                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,

                    0.0f, 0.0f,
                    0.0f, 1.0f,
                    1.0f, 0.0f,
                    1.0f, 1.0f,

                                        };

/** The initial indices definition */   
private byte indices[] = {
                    //Faces definition
                    0,1,3, 0,3,2,           //Face front
                    4,5,7, 4,7,6,           //Face right
                    8,9,11, 8,11,10,        //... 
                    12,13,15, 12,15,14,     
                    16,17,19, 16,19,18,     
                    20,21,23, 20,23,22,     
                                        };

/**
 * The Cube constructor.
 * 
 * Initiate the buffers.
 */
public Cube() {
    //
    ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4);
    byteBuf.order(ByteOrder.nativeOrder());
    vertexBuffer = byteBuf.asFloatBuffer();
    vertexBuffer.put(vertices);
    vertexBuffer.position(0);

    //
    byteBuf = ByteBuffer.allocateDirect(texture.length * 4);
    byteBuf.order(ByteOrder.nativeOrder());
    textureBuffer = byteBuf.asFloatBuffer();
    textureBuffer.put(texture);
    textureBuffer.position(0);

    //
    indexBuffer = ByteBuffer.allocateDirect(indices.length);
    indexBuffer.put(indices);
    indexBuffer.position(0);
}

/**
 * The object own drawing function.
 * Called from the renderer to redraw this instance
 * with possible changes in values.
 * 
 * @param gl - The GL Context
 */
public void draw(GL10 gl) {
    //Bind our only previously generated texture in this case
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

    //Point to our buffers
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

    //Set the face rotation
    gl.glFrontFace(GL10.GL_CCW);

    //Enable the vertex and texture state
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
    gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);

    //Draw the vertices as triangles, based on the Index Buffer information
    gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_BYTE, indexBuffer);

    //Disable the client state before leaving
    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
}

/**
 * Load the textures
 * 
 * @param gl - The GL Context
 * @param context - The Activity context
 */
public void loadGLTexture(GL10 gl, Context context) {
    //Get the texture from the Android resource directory
    InputStream is = context.getResources().openRawResource(R.drawable.nehe);
    Bitmap bitmap = null;
    try {
        //BitmapFactory is an Android graphics utility for images
        bitmap = BitmapFactory.decodeStream(is);

    } finally {
        //Always clear and close
        try {
            is.close();
            is = null;
        } catch (IOException e) {
        }
    }

    //Generate one texture pointer...
    gl.glGenTextures(1, textures, 0);
    //...and bind it to our array
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

    //Create Nearest Filtered Texture
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

    //Different possible texture parameters, e.g. GL10.GL_CLAMP_TO_EDGE
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT);
    gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT);

    //Use the Android GLUtils to specify a two-dimensional texture image from our bitmap
    GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

    //Clean up
    bitmap.recycle();
}
}

要使每个面具有不同的纹理，您需要单独渲染立方体的每个面。这意味着您需要为每个面设置纹理，然后渲染该面（使用glDrawArrays or glDrawElements）。所以它看起来像：

glEnable(GL_TEXTURE_2D);
...                        //maybe other state setup (like buffer bindings)
glVertexPointer(...);
glEnableClientState(GL_VERTEX_ARRAY);
...

for each(face of cube)
{
    glBindTexture(GL_TEXTURE_2D, <face_texture>);
    glDrawArrays(...) or glDrawElements(...);      //draw only a single face
}

glDisableClientState(GL_VERTEX_ARRAY);
...
glDisable(GL_TEXTURE_2D);
...                         //maybe other state cleanup

如果立方体的所有面需要不同的纹理，则无法在一次调用中渲染它们。但是您当然仍然可以将它们全部保存在一个数组/VBO 中，并且只需使用参数glDrawArrays or glDrawElements选择相应的面，如上所示。

这是一个相当简化的伪代码示例，如果这一切对您来说听起来很陌生，您应该更深入地研究 OpenGL，并将不同的纹理应用于立方体的每个面是您最不关心的问题。

EDIT:好的，根据您更新的代码：首先，由于所有顶点的位置和 texCoords 都存储在相同的数组中，因此我们不需要更改每个面的这些值。此外，您的索引数组似乎包含所有面，每个面连续存储为 6 个索引（2 个三角形）。这一切使得整个情况变得非常容易。只需替换您现有的glDrawElements在所有面上循环调用：

for(i=0; i<6; ++i)
{
    gl.glBindTexture(GL10.GL_TEXTURE_2D, texture[i]);   //use texture of ith face
    indexBuffer.position(6*i);                          //select ith face

    //draw 2 triangles making up this face
    gl.glDrawElements(GL10.GL_TRIANGLES, 6, GL10.GL_UNSIGNED_BYTE, indexBuffer);
}

因此，对于每个面，我们选择其纹理并仅绘制与该面相对应的 2 个三角形。

一般来说，在学习代码示例时，而不是书本或类似的东西，您至少应该确保您理解每一行代码和每个函数参数的含义。只有这样，您才能自由地调整代码以满足您的需求并开发问题的解决方案。