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)来实现此目的。OpenGL ES 提供了额外的功能,可以在三维空间或其他独特方式移动和转换绘制的对象,从而打造富有吸引力的用户体验。

在本课中,您将学习如何通过旋转向形状添加运动,从而向使用 OpenGL ES 更进一步。

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,创建另一个转换矩阵(旋转矩阵),然后将其与投影和相机视图转换矩阵合并:

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,请确保您已注释掉 GLSurfaceView.RENDERMODE_WHEN_DIRTY 设置,如下一部分中所述。

启用连续渲染

对于这一点,如果您已认真遵循此类中的示例代码,请确保注释掉将渲染模式设置为仅在脏时绘制的代码行,否则 OpenGL 仅旋转一个增量,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。准备好取消注释此代码,因为下一课使此调用再次适用。