renderscript - 如何在 Android RenderScript 中同时缩放、裁剪和旋转

Question

是否可以使用 RenderScript 拍摄 Y'UV 格式的相机图像:

1. 将其转换为 RGBA
2. 裁剪到特定区域
3. 必要时旋转它

Answer 1

是的!我想出了如何并认为我会与他人分享。 RenderScript 有一点学习曲线，更简单的示例似乎会有所帮助。

裁剪时，您仍然需要设置输入和输出分配以及脚本本身的分配。一开始可能看起来很奇怪，但输入和输出分配必须具有相同的大小，因此如果您正在裁剪，则需要设置另一个分配来写入裁剪后的输出。稍后会详细介绍。

#pragma version(1)
#pragma rs java_package_name(com.autofrog.chrispvision)
#pragma rs_fp_relaxed

/*
 * This is mInputAllocation
 */
rs_allocation gInputFrame;

/*
 * This is where we write our cropped image
 */
rs_allocation gOutputFrame;

/*
 * These dimensions define the crop region that we want
 */
uint32_t xStart, yStart;
uint32_t outputWidth, outputHeight;

uchar4 __attribute__((kernel)) yuv2rgbFrames(uchar4 in, uint32_t x, uint32_t y)
{
    uchar Y = rsGetElementAtYuv_uchar_Y(gInputFrame, x, y);
    uchar U = rsGetElementAtYuv_uchar_U(gInputFrame, x, y);
    uchar V = rsGetElementAtYuv_uchar_V(gInputFrame, x, y);

    uchar4 rgba = rsYuvToRGBA_uchar4(Y, U, V);

    /* force the alpha channel to opaque - the conversion doesn't seem to do this */
    rgba.a = 0xFF;

    uint32_t translated_x = x - xStart;
    uint32_t translated_y = y - yStart;

    uint32_t x_rotated = outputWidth - translated_y;
    uint32_t y_rotated = translated_x;

    rsSetElementAt_uchar4(gOutputFrame, rgba, x_rotated, y_rotated);
    return rgba;
}

设置分配:

private fun createAllocations(rs: RenderScript) {

    /*
     * The yuvTypeBuilder is for the input from the camera.  It has to be the
     * same size as the camera (preview) image
     */
    val yuvTypeBuilder = Type.Builder(rs, Element.YUV(rs))
    yuvTypeBuilder.setX(mImageSize.width)
    yuvTypeBuilder.setY(mImageSize.height)
    yuvTypeBuilder.setYuvFormat(ImageFormat.YUV_420_888)
    mInputAllocation = Allocation.createTyped(
        rs, yuvTypeBuilder.create(),
        Allocation.USAGE_IO_INPUT or Allocation.USAGE_SCRIPT)

    /*
     * The RGB type is also the same size as the input image.  Other examples write this as
     * an int but I don't see a reason why you wouldn't be more explicit about it to make
     * the code more readable.
     */
    val rgbType = Type.createXY(rs, Element.RGBA_8888(rs), mImageSize.width, mImageSize.height)

    mScriptAllocation = Allocation.createTyped(
        rs, rgbType,
        Allocation.USAGE_SCRIPT)

    mOutputAllocation = Allocation.createTyped(
        rs, rgbType,
        Allocation.USAGE_IO_OUTPUT or Allocation.USAGE_SCRIPT)

    /*
     * Finally, set up an allocation to which we will write our cropped image.  The
     * dimensions of this one are (wantx,wanty)
     */
    val rgbCroppedType = Type.createXY(rs, Element.RGBA_8888(rs), wantx, wanty)
    mOutputAllocationRGB = Allocation.createTyped(
        rs, rgbCroppedType,
        Allocation.USAGE_SCRIPT)
}

最后，由于您正在裁剪，因此需要在调用之前告诉脚本要做什么。如果图像大小没有改变，您可以通过移动 LaunchOptions 和变量设置来优化它，使它们只出现一次(而不是每次)，但我将它们留在这里作为我的示例以使其更清楚。

override fun onBufferAvailable(a: Allocation) {
    // Get the new frame into the input allocation
    mInputAllocation!!.ioReceive()

    // Run processing pass if we should send a frame
    val current = System.currentTimeMillis()
    if (current - mLastProcessed >= mFrameEveryMs) {
        val lo = Script.LaunchOptions()

        /*
         * These coordinates are the portion of the original image that we want to
         * include.  Because we're rotating (in this case) x and y are reversed
         * (but still offset from the actual center of each dimension)
         */

        lo.setX(starty, endy)
        lo.setY(startx, endx)

        mScriptHandle.set_xStart(lo.xStart.toLong())
        mScriptHandle.set_yStart(lo.yStart.toLong())

        mScriptHandle.set_outputWidth(wantx.toLong())
        mScriptHandle.set_outputHeight(wanty.toLong())

        mScriptHandle.forEach_yuv2rgbFrames(mScriptAllocation, mOutputAllocation, lo)

        val output = Bitmap.createBitmap(
            wantx, wanty,
            Bitmap.Config.ARGB_8888
        )

        mOutputAllocationRGB!!.copyTo(output)

        /* Do something with the resulting bitmap */
        listener?.invoke(output)

        mLastProcessed = current
    }
}

所有这一切可能看起来有点多，但它非常快 - 比在 java/kotlin 端进行旋转快得多，并且由于 RenderScript 能够在图像的子集上运行内核函数，它比创建的开销更少一个位图，然后创建第二个裁剪后的位图。

对我来说，所有的旋转都是必要的，因为 RenderScript 看到的图像从相机旋转了 90 度。有人告诉我这是拥有三星手机的某种特殊性。

RenderScript 起初令人生畏，但一旦您习惯了它的功能，它就没那么糟糕了。我希望这对某人有帮助。