添加动画

在屏幕上绘制对象是 OpenGL 的一个基本功能, Android 图形框架类,包括 CanvasDrawable 对象。OpenGL ES 为 在三维空间内移动和转换绘制的对象,或者以其他独特的方式 打造富有吸引力的用户体验。

在本课中,您将学习如何添加动画效果,从而更进一步使用 OpenGL ES 旋转为一个具有旋转的形状。

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,创建 然后将另一个转换矩阵(旋转矩阵)再与您的投影和 相机视图转换矩阵:

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,请确保您已对 GLSurfaceView.RENDERMODE_WHEN_DIRTY 具体设置,如下一部分所述。

启用连续渲染

如果您到目前为止认真阅读了本课程中的示例代码, 请务必注释掉用于将渲染模式设置为仅在 dirty 时绘制的代码行,否则 OpenGL 将形状仅旋转 1 个增量,然后等待从 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 class 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);
}

除非对象在没有任何用户互动的情况下发生改变,否则通常最好采取以下做法: 标记。请准备好对此代码取消注释,因为下一课会让此调用适用 。