如何以最有效的方式创建多个camera2预览？

Question

我正在尝试根据自己的活动创建4个摄像机预览流。我创建了一个TextureView，将其注册到feed的camera2 API，然后在SurfaceView上设置了一个侦听器，以侦听feed的更改并相应地更新其他3个预览（ImageViews）。您可以在下面的代码中看到：

    private final TextureView.SurfaceTextureListener mSurfaceTextureListener
            = new TextureView.SurfaceTextureListener() {

        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture texture, int width, int height) {
            cameraHandler.openCamera(width, height);
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture texture) {
            return true;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture texture) {
            for (ImageView mSecondaryPreview : mSecondaryPreviews) {
                Bitmap frame = Bitmap.createBitmap(mTextureView.getWidth(), mTextureView.getHeight(), Bitmap.Config.ARGB_8888);
                mTextureView.getBitmap(frame);
                mSecondaryPreview.setImageBitmap(frame);
            }
        }
    };

如您所见，必须从TextureView中读取每一帧，提取位图，然后设置其他3个ImageView流的位图。我最初尝试在速度很慢的UI线程上执行此操作，然后尝试将其提交给具有更好帧速率的后台处理程序，但由于负载导致应用崩溃导致很多问题。

谢谢

Answer 1

因此，如果可以像在GLSurfaceView中那样使this question与照相机预览一起使用，则只需再添加6个多边形，就可以再制作3个副本。让我解释一下它们的布局。 vtmp和ttmp分别以GL_TRIANGLE_STRIP形式描述两个三角形的矢量坐标和纹理坐标：

float[] vtmp = {
    1.0f, 1.0f,    //Top right of screen
    1.0f, -1.0f,    //Bottom right of screen
    -1.0f, 1.0f,    //Top left of screen
    -1.0f, -1.0f    //Bottom left of screen
};

float[] ttmp = {
    1.0f, 1.0f,     //Top right of camera surface
    0.0f, 1.0f,     //Top left of camera surface
    1.0f, 0.0f,     //Bottom right of camera surface
    0.0f, 0.0f      //Bottom left of camera surface
};

步骤1：让我们将原始类型更改为GL_TRIANGLES，因为使用GL_TRIANGLE_STRIP会很困难：

float[] vtmp = {
    //Triangle 1:
    1.0f, 1.0f,
    1.0f, -1.0f,
    -1.0f, 1.0f,

    //Triangle 2:
    -1.0f, 1.0f,
    1.0f, -1.0f,
    -1.0f, -1.0f
};

//I've attempted to fix the left-right inversion here by altering the
//texture X (u) coordinates. Hope I did it right!
float[] ttmp = {
    //Triangle 1:
    0.0f, 1.0f,
    1.0f, 1.0f,
    0.0f, 0.0f,

    //Triangle 2:
    0.0f, 0.0f,
    1.0f, 1.0f,
    1.0f, 0.0f
};

pVertex = ByteBuffer.allocateDirect(12*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
(...)
pTexCoord = ByteBuffer.allocateDirect(12*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
(...)
GLES20.glVertexAttribPointer(ph, 2, GLES20.GL_FLOAT, false, 6*2, pVertex);
GLES20.glVertexAttribPointer(tch, 2, GLES20.GL_FLOAT, false, 6*2, pTexCoord );
(...)
GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 6);    //Careful: Multiple changes on this line
(...)

如果第1步顺利进行，那么在第2步中添加额外的三角形：

float[] vtmp = {
    //Triangle 1:
    0.0f, 1.0f,
    0.0f, 0.0f,
    -1.0f, 1.0f,

    //Triangle 2:
    -1.0f, 1.0f,
    0.0f, 0.0f,
    -1.0f, 0.0f,

    //Triangle 3:
    1.0f, 1.0f,
    1.0f, 0.0f,
    0.0f, 1.0f,

    //Triangle 4:
    0.0f, 1.0f,
    1.0f, 0.0f,
    0.0f, 0.0f,

    //Triangle 5:
    1.0f, 0.0f,
    1.0f, -1.0f,
    0.0f, 0.0f,

    //Triangle 6:
    0.0f, 0.0f,
    1.0f, -1.0f,
    0.0f, -1.0f,

    //Triangle 7:
    0.0f, 0.0f,
    0.0f, -1.0f,
    -1.0f, 0.0f,

    //Triangle 8:
    -1.0f, 0.0f,
    0.0f, -1.0f,
    -1.0f, -1.0f
};

float[] ttmp = {
    //Triangle 1:
    0.0f, 1.0f,
    1.0f, 1.0f,
    0.0f, 0.0f,

    //Triangle 2:
    0.0f, 0.0f,
    1.0f, 1.0f,
    1.0f, 0.0f,

    //Triangle 3:
    0.0f, 1.0f,
    1.0f, 1.0f,
    0.0f, 0.0f,

    //Triangle 4:
    0.0f, 0.0f,
    1.0f, 1.0f,
    1.0f, 0.0f,

    //Triangle 5:
    0.0f, 1.0f,
    1.0f, 1.0f,
    0.0f, 0.0f,

    //Triangle 6:
    0.0f, 0.0f,
    1.0f, 1.0f,
    1.0f, 0.0f,

    //Triangle 7:
    0.0f, 1.0f,
    1.0f, 1.0f,
    0.0f, 0.0f,

    //Triangle 8:
    0.0f, 0.0f,
    1.0f, 1.0f,
    1.0f, 0.0f
};

pVertex = ByteBuffer.allocateDirect(48*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
(...)
pTexCoord = ByteBuffer.allocateDirect(48*4).order(ByteOrder.nativeOrder()).asFloatBuffer();
(...)
GLES20.glVertexAttribPointer(ph, 2, GLES20.GL_FLOAT, false, 24*2, pVertex);
GLES20.glVertexAttribPointer(tch, 2, GLES20.GL_FLOAT, false, 24*2, pTexCoord );
(...)
GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 24);
(...)

我是在没有测试的情况下手工完成的，因此如果出现严重错误，您会原谅我。