opengl APIdemo学习1

主要看了api中的2个例子：第一个：2个乱转的立方体第二个：也是2个乱转的立方体，不过带有透明背景

1、在activity的onResume和onPause方法中，调用了GLSurfaceView的相应方法，让其生命周期适应于activity的生命周期

2、画了2个四边形，但只是实例化了一个Cube对象，因为2个对象是完全一样，仅仅是角度和位置不一致。

  public CubeRenderer(boolean useTranslucentBackground) {
        mTranslucentBackground = useTranslucentBackground;
        mCube = new Cube();
	}

3、渲染类的onsurfaceCreate和onsurfacechanged做一些初始化工作

    public void onSurfaceChanged(GL10 gl, int width, int height) {
         gl.glViewport(0, 0, width, height);
         float ratio = (float) width / height;
         gl.glMatrixMode(GL10.GL_PROJECTION);
         gl.glLoadIdentity();
         gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);
    }

    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        gl.glDisable(GL10.GL_DITHER);
        gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,
                 GL10.GL_FASTEST);

         if (mTranslucentBackground) {
             gl.glClearColor(0,0,0,0);
         } else {
             gl.glClearColor(1,1,1,1);
         }
         gl.glEnable(GL10.GL_CULL_FACE);
         gl.glShadeModel(GL10.GL_SMOOTH);
         gl.glEnable(GL10.GL_DEPTH_TEST);
	}

4、实时画的方法，会一直调用

   public void onDrawFrame(GL10 gl) {
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
        gl.glMatrixMode(GL10.GL_MODELVIEW);
        gl.glLoadIdentity();
        gl.glTranslatef(0, 0, -3.0f);
        gl.glRotatef(mAngle,        0, 1, 0);
        gl.glRotatef(mAngle*0.25f,  1, 0, 0);

        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glEnableClientState(GL10.GL_COLOR_ARRAY);

        mCube.draw(gl);

        gl.glRotatef(mAngle*2.0f, 0, 1, 1);
        gl.glTranslatef(0.5f, 0.5f, 0.5f);

        mCube.draw(gl);

        mAngle += 1.2f;
    }

5、Cube类，opengl中，经常将需要描绘的实体抽象到一个类中

该类只是需要在render类中进行初始化，进而在onDrawFrame中调用其draw()方法即可

    public Cube()
    {
        int one = 0x10000;
        int vertices[] = {
                -one, -one, -one,
                one, -one, -one,
                one,  one, -one,
                -one,  one, -one,
                -one, -one,  one,
                one, -one,  one,
                one,  one,  one,
                -one,  one,  one,
        };

        int colors[] = {
                0,    0,    0,  one,
                one,    0,    0,  one,
                one,  one,    0,  one,
                0,  one,    0,  one,
                0,    0,  one,  one,
                one,    0,  one,  one,
                one,  one,  one,  one,
                0,  one,  one,  one,
        };

        byte indices[] = {
                0, 4, 5,    0, 5, 1,
                1, 5, 6,    1, 6, 2,
                2, 6, 7,    2, 7, 3,
                3, 7, 4,    3, 4, 0,
                4, 7, 6,    4, 6, 5,
                3, 0, 1,    3, 1, 2
        };

        // Buffers to be passed to gl*Pointer() functions
        // must be direct, i.e., they must be placed on the
        // native heap where the garbage collector cannot
        // move them.
        //
        // Buffers with multi-byte datatypes (e.g., short, int, float)
        // must have their byte order set to native order

        ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4);
        vbb.order(ByteOrder.nativeOrder());
        mVertexBuffer = vbb.asIntBuffer();
        mVertexBuffer.put(vertices);
        mVertexBuffer.position(0);

        ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length*4);
        cbb.order(ByteOrder.nativeOrder());
        mColorBuffer = cbb.asIntBuffer();
        mColorBuffer.put(colors);
        mColorBuffer.position(0);

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

    public void draw(GL10 gl)
    {
        gl.glFrontFace(gl.GL_CW);
        gl.glVertexPointer(3, gl.GL_FIXED, 0, mVertexBuffer);
        gl.glColorPointer(4, gl.GL_FIXED, 0, mColorBuffer);
        gl.glDrawElements(gl.GL_TRIANGLES, 36, gl.GL_UNSIGNED_BYTE, mIndexBuffer);
    }

6、背景透明：定义透明风格，进而在activity上使用该风格

    <!-- A theme that has a translucent background.  Here we explicitly specify
         that this theme is to inherit from the system's translucent theme,
         which sets up various attributes correctly. -->
    <style name="Theme.Translucent" parent="android:style/Theme.Translucent">
        <item name="android:windowBackground">@drawable/translucent_background</item>
        <item name="android:windowNoTitle">true</item>
        <item name="android:colorForeground">#fff</item>
    </style>

<resources>
    <drawable name="translucent_background">#e0000000</drawable>
</resources>

2.在程序中的oncreate方法中加入2行代码，其余和上一个一样

   // We want an 8888 pixel format because that's required for
        // a translucent window.
        // And we want a depth buffer.
        mGLSurfaceView.setEGLConfigChooser(8, 8, 8, 8, 16, 0);
        // Tell the cube renderer that we want to render a translucent version
        // of the cube:
        mGLSurfaceView.setRenderer(new CubeRenderer(true));
        // Use a surface format with an Alpha channel:
       mGLSurfaceView.getHolder().setFormat(PixelFormat.TRANSLUCENT);

如果缺少以上2个中的任何一个，结果都是黑色背景