Google 致力于为黑人社区推动种族平等。查看具体举措

添加动画

在屏幕上绘制对象是 OpenGL 的基本功能,但您也可以使用其他 Android 图形框架类(包括 CanvasDrawable 对象)来执行此操作。OpenGL ES 提供了其他功能,能够在三维空间或以其他独特方式移动和转换绘制的对象,从而打造具有吸引力的用户体验。

在本课中,您将学习如何通过旋转为形状添加动画效果,从而进一步利用 OpenGL ES。

旋转形状

使用 OpenGL ES 2.0 旋转绘制的对象相对比较简单。在渲染程序中,再创建一个转换矩阵(旋转矩阵),然后将其与投影和相机视图转换矩阵相结合:

Kotlin

    private val rotationMatrix = FloatArray(16)

    override fun onDrawFrame(gl: GL10) {
        val scratch = FloatArray(16)

        ...

        // Create a rotation transformation for the triangle
        val time = SystemClock.uptimeMillis() % 4000L
        val angle = 0.090f * time.toInt()
        Matrix.setRotateM(rotationMatrix, 0, angle, 0f, 0f, -1.0f)

        // Combine the rotation matrix with the projection and camera view
        // Note that the vPMatrix factor *must be first* in order
        // for the matrix multiplication product to be correct.
        Matrix.multiplyMM(scratch, 0, vPMatrix, 0, rotationMatrix, 0)

        // Draw triangle
        mTriangle.draw(scratch)
    }
    

Java

    private float[] rotationMatrix = new float[16];
    Override
    public void onDrawFrame(GL10 gl) {
        float[] scratch = new float[16];

        ...

        // Create a rotation transformation for the triangle
        long time = SystemClock.uptimeMillis() % 4000L;
        float angle = 0.090f * ((int) time);
        Matrix.setRotateM(rotationMatrix, 0, angle, 0, 0, -1.0f);

        // Combine the rotation matrix with the projection and camera view
        // Note that the vPMatrix factor *must be first* in order
        // for the matrix multiplication product to be correct.
        Matrix.multiplyMM(scratch, 0, vPMatrix, 0, rotationMatrix, 0);

        // Draw triangle
        mTriangle.draw(scratch);
    }
    

如果您的三角形在进行这些更改后没有旋转,请确保已对 GLSurfaceView.RENDERMODE_WHEN_DIRTY 设置取消备注,如下一部分中所述。

启用连续渲染

如果您认真遵循了此类中针对这一点的示例代码,请确保对将渲染模式设置为仅在脏时才进行绘制的行取消备注,否则 OpenGL 仅按一个增量旋转形状,然后就等待从 GLSurfaceView 容器调用 requestRender()

Kotlin

    class MyGLSurfaceView(context: Context) : GLSurfaceView(context) {

        init {
            ...
            // Render the view only when there is a change in the drawing data.
            // To allow the triangle to rotate automatically, this line is commented out:
            //renderMode = GLSurfaceView.RENDERMODE_WHEN_DIRTY
        }
    }
    

Java

    public MyGLSurfaceView(Context context) extends GLSurfaceView {
        ...
        // Render the view only when there is a change in the drawing data.
        // To allow the triangle to rotate automatically, this line is commented out:
        //setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
    }
    

除非您在没有任何用户互动的情况下更改对象,否则通常最好启用此标记。请准备好对此代码取消备注,因为下一课将使此调用再次适用。