在正方形上绘制文本作为纹理不会显示任何内容

Question

我是 OpenGL 新手，正在为 Android 开发增强现实应用程序。

到目前为止，我一直在绘制垂直于相机的白色方块，将用户指向“兴趣点”所在的方向。

现在，我试图在方块中显示一些文本。

我读了很多书，似乎用文本创建纹理是最直接、最简单的方法，所以我在获得兴趣点数据并将它们粘贴到它们的方块上后立即创建纹理。为此，我使用位图。

让我们看一些代码。在我的 onDrawFrame 方法中，我做了这样的事情：

public void onDrawFrame(GL10 gl) {

        // Get sensors matrix
                ...


        //Clear Screen And Depth Buffer
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

        // Load remapped matrix
        gl.glMatrixMode(GL10.GL_MODELVIEW);



        // List of Points of interest (modified when some data is downloaded)
        synchronized (poiList) {

            if(mNewData){  // True if new data has been dowloaded)
                if(textures != null)  // Delete old textures
                    gl.glDeleteTextures(textures.length, textures, 0);

                textures = loadGLTexture(gl, soapPoiList.getPoiList());
                mNewData = false;
            }

            int i = 0;
            // Iterate the list
            for (PointOfInterest c : poiList) {

                         gl.glLoadIdentity();
                 gl.glLoadMatrixf(remappedRotationMatrix, 0);

                 // Get bearing
                             ...

                 // Place polygon in the right place
                 gl.glRotatef(-bearing, 0, 0, 1);
                 gl.glTranslatef(0, ICONS_SIZE_RATIO, 0);

                         // Actually draws the polygon with text
                 c.draw(gl, textures[i]);

                 i++;
            }
        }
    }

其中 loadGLTextures 是：

protected int[] loadGLTexture(GL10 gl, List<PointOfInterest> l){
    int res[] = new int[l.size()];
    gl.glGenTextures(res.length, res, 0);
    int i = 0;

    for(PointOfInterest p : l) {
        Bitmap bitmap = Bitmap.createBitmap(256, 256, Bitmap.Config.RGB_565);
        bitmap.eraseColor(Color.BLACK);

        Canvas canvas = new Canvas(bitmap);

        Paint textPaint = new Paint();
        textPaint.setTextSize(35);
        textPaint.setFakeBoldText(true);
        textPaint.setAntiAlias(true);
        textPaint.setARGB(255, 255, 255, 255);
        // Draw the text centered
        canvas.drawText(Float.toString(p.getDinstanceToOrigin()) + " m.", 10,35, textPaint);

        // Bind the texture to our array
        gl.glBindTexture(GL10.GL_TEXTURE_2D, res[i]);

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

        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE);
        gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE);

        GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

        bitmap.recycle();

        i++;
    }
    return res;
}

它基本上为每个兴趣点创建一个位图，并用它生成一个纹理。稍后纹理将应用在白色方块上，如本课程中所示：

    public class PointOfInterest {

        // MEMBERS ----------------------------------------------------------------
            ....
            ....

        // OpenGL necessary variables
        /** The buffer holding the vertices */
        private FloatBuffer vertexBuffer;

        /** The initial vertex definition */
        private float vertices[] = { 
                                    -1.0f, 0.0f, -1.0f, //Bottom Left   V1
                                    -1.0f, 0.0f,  1.0f, //Top Left      V2
                                     1.0f, 0.0f, -1.0f, //Bottom Right  V3
                                     1.0f, 0.0f,  1.0f, //Top Right     V4
                                   };

        private FloatBuffer textureBuffer;
        private float texture[] = {
                                    0.0f, 0.0f,     // V1
                                    1.0f, 0.0f,     // V3
                                    0.0f, 1.0f,     // V2
                                    1.0f, 1.0f      // V4
        };

        // CONSTRUCTORS -----------------------------------------------------------

        public PointOfInterest(Location originLocation){
            currentLocation = originLocation;

            mPoiLocation = new Location(LocationManager.GPS_PROVIDER);

            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);
        }

        // PUBLIC METHODS ---------------------------------------------------------

        public void draw(GL10 gl, int textureId){
            // Bind the previously generated texture
            gl.glBindTexture(GL10.GL_TEXTURE_2D, textureId);

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

            // set the colour for the square
            //gl.glColor4f(0.0f, 0.1f, 0.0f, 0.5f);

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

            //Point to our vertex buffer
            gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
            gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);

            //Draw the vertices as triangle strip
            gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);

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

        ....
        ....
}

我尝试按照教学内容映射纹理 此处 和 这里没有成功。我真的不知道该怎么做才能在正方形上绘制一些字母，并且在这里真的迷失了...也许文本正在正方形的另一面上绘制，也许纹理没有生成...我不知道。

任何形式的帮助将不胜感激。

Answer 1

好吧，我忘了启用纹理映射。您可以在任何使用 GL10 对象的方法中执行此操作。我更喜欢在对象的绘制方法中执行此操作，因此任何其他对象都不会受到纹理的影响。就这么简单（只改变了两行，即新的！！）：

public void draw(GL10 gl, int textureId){
    gl.glEnable(GL10.GL_TEXTURE_2D);    //NEW !!! Enable Texture Mapping

    // Bind the previously generated texture
    gl.glBindTexture(GL10.GL_TEXTURE_2D, textureId);

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

    // set the colour for the square
    //gl.glColor4f(0.0f, 0.1f, 0.0f, 0.5f);

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

    //Point to our vertex buffer
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
    gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);

    //Draw the vertices as triangle strip
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);

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

    gl.glDisable(GL10.GL_TEXTURE_2D);   ////NEW !!! Disable texture mapping
}