android使用OpenGL ES定義圖片形狀

為了能夠開發高端的圖形作品，定義形狀往往是第一步。使用OpenGL ES繪製圖片你不需要知道OpenGL ES怎樣希望你去定義圖片對象。下面介紹協調系統相關的和螢幕，定義了形狀，如三角形和圓形。

定義一個三角形：

OpenGL ES允許你在三維空間定義對象。

class Triangle {

    private FloatBuffer vertexBuffer;

    // number of coordinates per vertex in this array
    static final int COORDS_PER_VERTEX = 3;
    static float triangleCoords[] = { // in counterclockwise order:
         0.0f,  0.622008459f, 0.0f,   // top
        -0.5f, -0.311004243f, 0.0f,   // bottom left
         0.5f, -0.311004243f, 0.0f    // bottom right
    };

    // Set color with red, green, blue and alpha (opacity) values
    float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

    public Triangle() {
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
                // (number of coordinate values * 4 bytes per float)
                triangleCoords.length * 4);
        // use the device hardware's native byte order
        bb.order(ByteOrder.nativeOrder());

        // create a floating point buffer from the ByteBuffer
        vertexBuffer = bb.asFloatBuffer();
        // add the coordinates to the FloatBuffer
        vertexBuffer.put(triangleCoords);
        // set the buffer to read the first coordinate
        vertexBuffer.position(0);
    }

定義一個矩形：

class Square {

    private FloatBuffer vertexBuffer;
    private ShortBuffer drawListBuffer;

    // number of coordinates per vertex in this array
    static final int COORDS_PER_VERTEX = 3;
    static float squareCoords[] = { -0.5f,  0.5f, 0.0f,   // top left
                                    -0.5f, -0.5f, 0.0f,   // bottom left
                                     0.5f, -0.5f, 0.0f,   // bottom right
                                     0.5f,  0.5f, 0.0f }; // top right

    private short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices

    public Square() {
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
        // (# of coordinate values * 4 bytes per float)
                squareCoords.length * 4);
        bb.order(ByteOrder.nativeOrder());
        vertexBuffer = bb.asFloatBuffer();
        vertexBuffer.put(squareCoords);
        vertexBuffer.position(0);

        // initialize byte buffer for the draw list
        ByteBuffer dlb = ByteBuffer.allocateDirect(
        // (# of coordinate values * 2 bytes per short)
                drawOrder.length * 2);
        dlb.order(ByteOrder.nativeOrder());
        drawListBuffer = dlb.asShortBuffer();
        drawListBuffer.put(drawOrder);
        drawListBuffer.position(0);
    }
}