Android学习笔记 - 并行计算框架Renderscript

从 Android 12 开始，RenderScript API 已被废弃。

1、RenderScript介绍

        RenderScript 是用于在 Android 上以高性能运行计算密集型任务的框架。RenderScript 主要用于数据并行计算，不过串行工作负载也可以从中受益。RenderScript 运行时可在设备上提供的多个处理器（如多核 CPU 和 GPU）间并行调度工作。这样您就能够专注于表达算法而不是调度工作。RenderScript 对于执行图像处理、计算摄影或计算机视觉的应用来说尤其有用。

         Android 12 中弃用 RenderScript API，Google 在 Android开发者博客中提到，其实早已不建议将RenderScript用于对性能需求至关重要的任务， Android开发者应该转向可在GPU硬件层级上高效运作、且具有出色的跨平台体验的Vulkan API 。并还提供了示例，对比RenderScript 和 Vulkan API 的运行差异。 

        google官方链接

https://developer.android.com/guide/topics/renderscript/computehttps://developer.android.com/guide/topics/renderscript/compute

Renderscript  |  Android 开源项目  |  Android Open Source Projecthttps://source.android.google.cn/devices/architecture/vndk/renderscript.html?hl=zh-cn

2、NV21格式转Bitmap

        使用RenderScript高效的将Camera回调的NV21格式转Bitmap

package com.my.camerademo;

import android.content.Context;
import android.graphics.Bitmap;
import android.renderscript.Allocation;
import android.renderscript.Element;
import android.renderscript.RenderScript;
import android.renderscript.ScriptIntrinsicYuvToRGB;
import android.renderscript.Type;

public class NV21ToBitmap {

    private RenderScript rs;
    private ScriptIntrinsicYuvToRGB yuvToRgbIntrinsic;
    private Type.Builder yuvType, rgbaType;
    private Allocation in, out;

    public NV21ToBitmap(Context context) {
        rs = RenderScript.create(context);
        yuvToRgbIntrinsic = ScriptIntrinsicYuvToRGB.create(rs, Element.U8_4(rs));
    }

    public Bitmap nv21ToBitmap(byte[] nv21, int width, int height){
        if (yuvType == null){
            yuvType = new Type.Builder(rs, Element.U8(rs)).setX(nv21.length);
            in = Allocation.createTyped(rs, yuvType.create(), Allocation.USAGE_SCRIPT);

            rgbaType = new Type.Builder(rs, Element.RGBA_8888(rs)).setX(width).setY(height);
            out = Allocation.createTyped(rs, rgbaType.create(), Allocation.USAGE_SCRIPT);
        }

        in.copyFrom(nv21);

        yuvToRgbIntrinsic.setInput(in);
        yuvToRgbIntrinsic.forEach(out);

        Bitmap bmpout = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        out.copyTo(bmpout);

        return bmpout;

    }

}

3、使用RenderScript实现图片高斯模糊效果

public class BlurBitmap {
     private static final float BITMAP_SCALE = 1.0f;
     private static final float BLUR_RADIUS = 25;

     public static Bitmap blur(Context context, Bitmap image) {
         int width = Math.round(image.getWidth() * BITMAP_SCALE);
         int height = Math.round(image.getHeight() * BITMAP_SCALE);

         Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
         Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

         RenderScript rs = RenderScript.create(context);
         ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
         Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
         Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
         theIntrinsic.setRadius(BLUR_RADIUS);
         theIntrinsic.setInput(tmpIn);
         theIntrinsic.forEach(tmpOut);
         tmpOut.copyTo(outputBitmap);

         return outputBitmap;
     }
 }

4、使用RenderScript进行直方图均衡化（histEq.rs）

#pragma version(1)
#pragma rs_fp_relaxed
#pragma rs java_package_name(com.example.q.renderscriptexample)
#include "rs_debug.rsh"
int32_t histo[256];
float remapArray[256];
int size;
//Method to keep the result between 0 and 1
static float bound (float val) {
    float m = fmax(0.0f, val);
    return fmin(1.0f, m);
}
uchar4 __attribute__((kernel)) root(uchar4 in, uint32_t x, uint32_t y) {
    //Convert input uchar4 to float4
    float4 f4 = rsUnpackColor8888(in);
    //Get YUV channels values
    float Y = 0.299f * f4.r + 0.587f * f4.g + 0.114f * f4.b;
    float U = ((0.492f * (f4.b - Y))+1)/2;
    float V = ((0.877f * (f4.r - Y))+1)/2;
    //Get Y value between 0 and 255 (included)
    int32_t val = Y * 255;
    //Increment histogram for that value
    rsAtomicInc(&histo[val]);
    //Put the values in the output uchar4, note that we keep the alpha value
    return rsPackColorTo8888(Y, U, V, f4.a);
}
uchar4 __attribute__((kernel)) remaptoRGB(uchar4 in, uint32_t x, uint32_t y) {
    //Convert input uchar4 to float4
    float4 f4 = rsUnpackColor8888(in);
    //Get Y value
    float Y = f4.r;
    //Get Y value between 0 and 255 (included)
    int32_t val = Y * 255;
    //Get Y new value in the map array
    Y = remapArray[val];
    //Get value for U and V channel (back to their original values)
    float U = (2*f4.g)-1;
    float V = (2*f4.b)-1;
    //Compute values for red, green and blue channels
    float red = bound(Y + 1.14f * V);
    float green = bound(Y - 0.395f * U - 0.581f * V);
    float blue = bound(Y + 2.033f * U);
    //Put the values in the output uchar4
    return rsPackColorTo8888(red, green, blue, f4.a);
}
void init() {
    //init the array with zeros
    for (int i = 0; i < 256; i++) {
        histo[i] = 0;
        remapArray[i] = 0.0f;
    }
}
void createRemapArray() {
    //create map for y
    float sum = 0;
    for (int i = 0; i < 256; i++) {
        sum += histo[i];
        remapArray[i] = sum / (size);
    }
}

Java调用

public static Bitmap histogramEqualization(Bitmap image, Context context) {
    //Get image size
    int width = image.getWidth();
    int height = image.getHeight();
    //Create new bitmap
    Bitmap res = image.copy(image.getConfig(), true);
    //Create renderscript
    RenderScript rs = RenderScript.create(context);
    //Create allocation from Bitmap
    Allocation allocationA = Allocation.createFromBitmap(rs, res);
    //Create allocation with same type
    Allocation allocationB = Allocation.createTyped(rs, allocationA.getType());
    //Create script from rs file.
    ScriptC_histEq histEqScript = new ScriptC_histEq(rs);
    
    //Set size in script
    histEqScript.set_size(width*height);
    //Call the first kernel.
    histEqScript.forEach_root(allocationA, allocationB);
    //Call the rs method to compute the remap array
    histEqScript.invoke_createRemapArray();
    //Call the second kernel
    histEqScript.forEach_remaptoRGB(allocationB, allocationA);
    //Copy script result into bitmap
    allocationA.copyTo(res);
    //Destroy everything to free memory
    allocationA.destroy();
    allocationB.destroy();
    histEqScript.destroy();
    rs.destroy();
    return res;
}

5、Android高效旋转图片的方式

Android高效旋转图片的方式_Coder蒋的博客-优快云博客_安卓旋转图片