使用预设程序使物体移动,比如旋转三角形对吸引用户注意非常有用,但是如果想让OpenGL ES图形与用户交互又该怎么做呢?让OpenGL ES 应用能响应触摸交互的关键是继承GLSurfaceView并重写OnTouchEvent()监听触摸事件.
本课将向你展示如何监听触摸事件让用户旋转OpenGL ES的物体.
设置触摸监听
为了让OpenGL ES应用响应触摸事件,你必须实现 GLSurfaceView的onTouchEvent()方法.下面的示例代码展示了如何监听 MotionEvent.ACTION_MOVE 事件,并对图形做旋转变换:
private final float TOUCH_SCALE_FACTOR = 180.0f / 320; private float mPreviousX; private float mPreviousY; @Override public boolean onTouchEvent(MotionEvent e) { // MotionEvent reports input details from the touch screen // and other input controls. In this case, you are only // interested in events where the touch position changed. float x = e.getX(); float y = e.getY(); switch (e.getAction()) { case MotionEvent.ACTION_MOVE: float dx = x - mPreviousX; float dy = y - mPreviousY; // reverse direction of rotation above the mid-line if (y > getHeight() / 2) { dx = dx * -1 ; } // reverse direction of rotation to left of the mid-line if (x < getWidth() / 2) { dy = dy * -1 ; } mRenderer.setAngle( mRenderer.getAngle() + ((dx + dy) * TOUCH_SCALE_FACTOR)); requestRender(); } mPreviousX = x; mPreviousY = y; return true; }
注意:计算旋转角度后,会调用requestRender()方法告诉renderer渲染当前帧.示例中的这种方式是最高效的,因为你不需要重新绘制,除非发生旋转变化.然而,如果你想不影响性能,还必须使用setRenderMode()方法来告诉renderer只有在数据发生变化时才重绘,所以确保rendere中的代码取消了注释:
public MyGLSurfaceView(Context context) { ... // Render the view only when there is a change in the drawing data setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY); }
角度的操作(设置和获取)
上面的示例代码需要你在renderer中添加公开的成员变量.一旦你的rederer代码运行在与主线程分开的单独的线程中,必须将公开变量声明为 volatile.下面的代码声明 变量并提供一对getter和setter方法:
public class MyGLRenderer implements GLSurfaceView.Renderer { ... public volatile float mAngle; public float getAngle() { return mAngle; } public void setAngle(float angle) { mAngle = angle; } }
应用投影
注释随机生成的角度,应用触摸输入生成的角度:
public void onDrawFrame(GL10 gl) { ... float[] scratch = new float[16]; // Create a rotation for the triangle // long time = SystemClock.uptimeMillis() % 4000L; // float angle = 0.090f * ((int) time); Matrix.setRotateM(mRotationMatrix, 0, mAngle, 0, 0, -1.0f); // Combine the rotation matrix with the projection and camera view // Note that the mMVPMatrix factor *must be first* in order // for the matrix multiplication product to be correct. Matrix.multiplyMM(scratch, 0, mMVPMatrix, 0, mRotationMatrix, 0); // Draw triangle mTriangle.draw(scratch); }
完成上面所有步骤,运行程序然后在屏幕上移动手指来旋转三角形:
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