JNA库截图比机器人类慢？

Question

由于 Robot.createScreenCaputure() 方法很慢，我决定使用本机库。我搜索并找到了这个论坛并找到了一个特定的代码片段使用JNA 图书馆。这是一个旧版本，所以我重写了代码：

import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.DataBuffer;
import java.awt.image.DataBufferInt;
import java.awt.image.DataBufferUShort;
import java.awt.image.DirectColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;

import com.sun.jna.Native;
import com.sun.jna.win32.W32APIOptions;
import com.sun.jna.platform.win32.WinDef;
import com.sun.jna.platform.win32.WinNT;
import com.sun.jna.platform.win32.WinGDI;

public class JNAScreenShot {

    public static BufferedImage getScreenshot(Rectangle bounds) {
        WinDef.HDC windowDC = GDI.GetDC(USER.GetDesktopWindow());
        WinDef.HBITMAP outputBitmap =
                GDI.CreateCompatibleBitmap(windowDC,
                bounds.width, bounds.height);
        try {
            WinDef.HDC blitDC = GDI.CreateCompatibleDC(windowDC);
            try {
                WinNT.HANDLE oldBitmap =
                        GDI.SelectObject(blitDC, outputBitmap);
                try {
                    GDI.BitBlt(blitDC,
                            0, 0, bounds.width, bounds.height,
                            windowDC,
                            bounds.x, bounds.y,
                            GDI32.SRCCOPY);
                } finally {
                    GDI.SelectObject(blitDC, oldBitmap);
                }
                WinGDI.BITMAPINFO bi = new WinGDI.BITMAPINFO(40);
                bi.bmiHeader.biSize = 40;
                boolean ok =
                        GDI.GetDIBits(blitDC, outputBitmap, 0, bounds.height,
                        (byte[]) null, bi, WinGDI.DIB_RGB_COLORS);
                if (ok) {
                    WinGDI.BITMAPINFOHEADER bih = bi.bmiHeader;
                    bih.biHeight = -Math.abs(bih.biHeight);
                    bi.bmiHeader.biCompression = 0;
                    return bufferedImageFromBitmap(blitDC, outputBitmap, bi);
                } else {
                    return null;
                }
            } finally {
                GDI.DeleteObject(blitDC);
            }
        } finally {
            GDI.DeleteObject(outputBitmap);
        }
    }

    private static BufferedImage bufferedImageFromBitmap(WinDef.HDC blitDC,
            WinDef.HBITMAP outputBitmap,
            WinGDI.BITMAPINFO bi) {
        WinGDI.BITMAPINFOHEADER bih = bi.bmiHeader;
        int height = Math.abs(bih.biHeight);
        final ColorModel cm;
        final DataBuffer buffer;
        final WritableRaster raster;
        int strideBits =
                (bih.biWidth * bih.biBitCount);
        int strideBytesAligned =
                (((strideBits - 1) | 0x1F) + 1) >> 3;
        final int strideElementsAligned;
        switch (bih.biBitCount) {
            case 16:
                strideElementsAligned = strideBytesAligned / 2;
                cm = new DirectColorModel(16, 0x7C00, 0x3E0, 0x1F);
                buffer =
                        new DataBufferUShort(strideElementsAligned * height);
                raster =
                        Raster.createPackedRaster(buffer,
                        bih.biWidth, height,
                        strideElementsAligned,
                        ((DirectColorModel) cm).getMasks(),
                        null);
                break;
            case 32:
                strideElementsAligned = strideBytesAligned / 4;
                cm = new DirectColorModel(32, 0xFF0000, 0xFF00, 0xFF);
                buffer =
                        new DataBufferInt(strideElementsAligned * height);
                raster =
                        Raster.createPackedRaster(buffer,
                        bih.biWidth, height,
                        strideElementsAligned,
                        ((DirectColorModel) cm).getMasks(),
                        null);
                break;
            default:
                throw new IllegalArgumentException("Unsupported bit count: " + bih.biBitCount);
        }
        final boolean ok;
        switch (buffer.getDataType()) {
            case DataBuffer.TYPE_INT: {
                int[] pixels = ((DataBufferInt) buffer).getData();
                ok = GDI.GetDIBits(blitDC, outputBitmap, 0, raster.getHeight(), pixels, bi, 0);
            }
            break;
            case DataBuffer.TYPE_USHORT: {
                short[] pixels = ((DataBufferUShort) buffer).getData();
                ok = GDI.GetDIBits(blitDC, outputBitmap, 0, raster.getHeight(), pixels, bi, 0);
            }
            break;
            default:
                throw new AssertionError("Unexpected buffer element type: " + buffer.getDataType());
        }
        if (ok) {
            return new BufferedImage(cm, raster, false, null);
        } else {
            return null;
        }
    }
    private static final User32 USER = User32.INSTANCE;
    private static final GDI32 GDI = GDI32.INSTANCE;
}

interface GDI32 extends com.sun.jna.platform.win32.GDI32,
        com.sun.jna.platform.win32.WinGDI,
        com.sun.jna.platform.win32.WinDef {

    GDI32 INSTANCE =
            (GDI32) Native.loadLibrary(GDI32.class);

    boolean BitBlt(HDC hdcDest, int nXDest, int nYDest,
            int nWidth, int nHeight, HDC hdcSrc,
            int nXSrc, int nYSrc, int dwRop);

    HDC GetDC(HWND hWnd);

    boolean GetDIBits(HDC dc, HBITMAP bmp, int startScan, int scanLines,
            byte[] pixels, BITMAPINFO bi, int usage);

    boolean GetDIBits(HDC dc, HBITMAP bmp, int startScan, int scanLines,
            short[] pixels, BITMAPINFO bi, int usage);

    boolean GetDIBits(HDC dc, HBITMAP bmp, int startScan, int scanLines,
            int[] pixels, BITMAPINFO bi, int usage);
    int SRCCOPY = 0xCC0020;
}

interface User32 extends com.sun.jna.platform.win32.User32 {

    User32 INSTANCE = (User32) Native.loadLibrary(User32.class, W32APIOptions.UNICODE_OPTIONS);

    com.sun.jna.platform.win32.WinDef.HWND GetDesktopWindow();
}

还有一个测试代码，看看它比机器人类快多少：

import java.awt.AWTException;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.image.BufferedImage;

public class testClass {

    public static void main(String[] args) {

        BufferedImage bi = null, bj = null;
        Rectangle rect = new Rectangle(0, 0, 810, 384);
        long startTime, finishTime;

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 10; i++) {
            bi = JNAScreenShot.getScreenshot(rect);
        }
        finishTime = System.currentTimeMillis();

        System.out.println("With JNA Library: " + (finishTime - startTime)/10);

        Robot robo = null;

        startTime = System.currentTimeMillis();
        try {
            robo = new Robot();
        } catch (AWTException a) {
        }
        for (int i = 0; i < 10; i++) {
            bj = robo.createScreenCapture(rect);
        }
        finishTime = System.currentTimeMillis();
        System.out.println("With Robot Class " + (finishTime - startTime)/10);
    }
}

结果是

JNA 图书馆：77
与37级机器人

Guys，请有人解释一下为什么是这样以及如何我可以固定它？

Answer 1

不要过早尝试优化。创建一个合理的接口来获取您想要的数据（屏幕截图），然后基于 Robot、JNA 或 JNI 创建您想要的实现。

我猜想不同的实现会根据其运行的环境给出完全不同的结果。

编程规则一：首先让它工作。然后进行分析，找到瓶颈并消除或减轻瓶颈的影响。

Answer 2

JNA调用需要很多时间，而JNI直接使用c++。

Answer 3

首先，检查本机库是否实际上比您的代码更快。情况可能并非如此。

假设您已经检查过这一点，我想说这里的问题是使用 JNA 的调用非常慢。
要跳过每个周期一次调用问题，我建议编写一个如下所示的 C 函数：

    void callWithJNAfunction(int rectPosX, int rectPosY, rectSideX, rectSideY,int numberOfCycles) {
    for (int i = 0; i < numberOfCycles; i++) {
        //code in C that calls the library
    }

现在编译此代码并使用 JNA 调用 callWithJNAfunction(...)。

如果问题是 JNA 调用缓慢，它会变得更快。