如何在 Android RenderScript 中同时缩放、裁剪和旋转

Question

是否可以拍摄 Y'UV 格式的相机图像并使用 RenderScript：

将其转换为 RGBA
裁剪到特定区域
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;
}

要设置分配：

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，您可能可以通过移动 LaunchOptions 和变量设置来优化它，这样它们只出现一次（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
    }
}

所有这些看起来有点多，但速度非常快 - 比在 java/kotlin 侧进行旋转要快得多，这要归功于 RenderScript 能够运行核函数在子集上与创建位图然后创建第二个裁剪后的位图相比，它的开销更少。

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 phone.

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。

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