我很新的OpenGL和我在做一个非常简单的程序来检查，如果我可以选择在屏幕上呈现的对象，绘制每一个具有独特的色彩。到目前为止，我使2台广场和一个三角形。

I am very new to OpenGL and I'm doing a very simple program to check if I can pick objects rendered on the screen, drawing each one with a unique color. So far, I render 2 flat squares and one triangle.

的问题是，当用户触摸的多边形，我从黑色不同，但颜色指数为三个对象（当它应该是不同的）。

The problem is that when the user touches the polygons, I get a color different from black, but the color index is the same for the three objects (when it should be different).

下面是我的code：

该onDrawFrame方法（我的渲染器内）。这里是我渲染的多边形与当用户触摸屏幕的独特的色彩。

The onDrawFrame method (within my Renderer). Here is where I render the polygons with an unique color when the user is touching the screen.

public void onDrawFrame(GL10 gl) {

    // clear Screen and Depth Buffer
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

    // Reset the Modelview Matrix
    gl.glLoadIdentity();

    if (mGLView.isPickingEnabled()) {
         gl.glDisable(GL10.GL_TEXTURE_2D);
         gl.glDisable(GL10.GL_LIGHTING);
         gl.glDisable(GL10.GL_FOG);

         // draw colored objects  and picking pixel color
         pickingDraw(gl);

         mGLView.mPickingY = (int)(mHeight - mGLView.mPickingY);

         gl.glReadPixels((int) mGLView.mPickingX, 
                 (int) mGLView.mPickingY, 1, 1, 
                 GL10.GL_RGBA, 
                 GL10.GL_UNSIGNED_BYTE, 
                 mGLView.m_PickingPixelBuffer);

         Log.i("RA", "RGBA COLORS: " +
                 (int) mGLView.m_PickingPixelBuffer.get(0) + " , " +
                 (int) mGLView.m_PickingPixelBuffer.get(1) + " , " +
                 (int) mGLView.m_PickingPixelBuffer.get(2) + " , " +
                 (int) mGLView.m_PickingPixelBuffer.get(3) );

         mGLView.disablePicking();

         // Clear BACK BUFFER
         gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    }

    gl.glLoadIdentity();

    // Drawing
    gl.glTranslatef(0.0f, 0.0f, -25.0f);    // move 5 units INTO the screen
                                            // is the same as moving the camera 5 units away
    square.draw(gl);                        // Draw the triangle

    gl.glTranslatef(0.0f, -5.0f, 0.0f);
    square.draw(gl);

    gl.glTranslatef(4.0f, 10.0f, 0.0f);
    triangle.draw(gl);
}

pickingDraw方法如下（我的渲染中也是如此）：

pickingDraw method is the following (within my Renderer too):

private void pickingDraw(GL10 gl) {
    // Drawing
    gl.glTranslatef(0.0f, 0.0f, -25.0f);    // move 5 units INTO the screen
    gl.glColor4f(128, 0, 0, 1);
    square.draw(gl);                        // Draw the triangle

    gl.glTranslatef(0.0f, -5.0f, 0.0f);
    gl.glColor4f(129, 0, 0, 1);
    square.draw(gl);

    gl.glTranslatef(4.0f, 10.0f, 0.0f);
    gl.glColor4f(130, 0, 0, 1);
    triangle.draw(gl);
}

在另一方面，我继承GLSurfaceView这样我就可以处理用户触摸。在这个班，我用这个方法：

On the other hand, I inherited GLSurfaceView so I can handle user touches. Within this class, I use this method:

public boolean onTouchEvent(MotionEvent e) {

    float _iX = e.getX();
    float _iY = e.getY();

    int iIndex = -1;
    int iRed;

    m_PickingPixelBuffer = ByteBuffer.allocateDirect(4);
    m_PickingPixelBuffer.order(ByteOrder.nativeOrder());

    // setting globals for Renderer
    mPickingX = _iX;
    mPickingY = _iY;

    mPickingEnabled = true;
    requestRender();

    // wait for picking process (renderer)
    while(mPickingEnabled);

    iRed = m_PickingPixelBuffer.get(0);
    if(iRed < 0)
    {
       iRed += 256;
    }

    Log.i("RA", "Coordinates: (" + mPickingX + ", " + mPickingY + ")");
    Log.i("RA", "Red Color " + iRed);

    return true;
}

看来它检测到的平方，当我触摸它们的三角形，但我得到了他们三个相同颜色索引。此外，这三个对象具有相同的精确的颜色（我甚至吸引了每一个有红色，绿色和蓝色的值分别为，他们有相同的颜色，这是最后绘制的颜色之一）。

It seems that it detects the squares and the triangle when I touch them, but I get the same color index for the three of them. Plus, the three objects have the same exact color (I even drew each one with a value of red, green and blue respectively and they had the same color, the color of the last one that was drawn).

最后，这是输出我得到的，当我触摸一个平方，然后一个空的空间，而另一方：

Finally, this is the output I get when I touch an square, then an empty space, and another square:

01-19 01:34:23.345: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.355: INFO/RA(11566): Coordinates: (247.81186, 391.0)
01-19 01:34:23.355: INFO/RA(11566): Red Color 255
01-19 01:34:23.385: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.385: INFO/RA(11566): Coordinates: (248.52428, 390.0)
01-19 01:34:23.385: INFO/RA(11566): Red Color 255
01-19 01:34:23.405: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.405: INFO/RA(11566): Coordinates: (248.52428, 390.0)
01-19 01:34:23.405: INFO/RA(11566): Red Color 255
01-19 01:34:24.305: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.315: INFO/RA(11566): Coordinates: (119.571884, 577.0)
01-19 01:34:24.315: INFO/RA(11566): Red Color 0
01-19 01:34:24.335: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.335: INFO/RA(11566): Coordinates: (119.33441, 573.0)
01-19 01:34:24.335: INFO/RA(11566): Red Color 0
01-19 01:34:24.355: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.355: INFO/RA(11566): Coordinates: (119.33441, 573.0)
01-19 01:34:24.355: INFO/RA(11566): Red Color 0
01-19 01:34:25.195: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.195: INFO/RA(11566): Coordinates: (259.80466, 395.0)
01-19 01:34:25.195: INFO/RA(11566): Red Color 255
01-19 01:34:25.215: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.215: INFO/RA(11566): Coordinates: (259.44843, 398.0)
01-19 01:34:25.215: INFO/RA(11566): Red Color 255
01-19 01:34:25.245: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.245: INFO/RA(11566): Coordinates: (259.80466, 395.0)
01-19 01:34:25.245: INFO/RA(11566): Red Color 255

我不知道为什么红色值对每个对象是相同的。

I don't know why the red values are the same for each object.

任何帮助将是AP preciated。谢谢你。

Any help would be appreciated. Thanks.

推荐答案

gl.glColor4f（红，绿，蓝，alpha）;四个参数都浮类型和值应该是0到1，匹配普通的RGB范围为0〜255，因此，如果您设置的R值128，129和130，实际上，它们之间没有什么区别。他们都是255共同RGB范围。

gl.glColor4f(red, green, blue, alpha); the type of the four parameters are float and the value are supposed to be 0 to 1, which match the common RGB range 0 to 255 so if you set the R value 128, 129 and 130, in fact , there is no difference between them. They are all 255 for common RGB range.