Since Robot.createScreenCaputure() method is slow, I decided to use native library. I searched and found this forum and find a specific code snipplet which uses JNA Library. It's an old version so that I rewrote the code:
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();
}
And a test code to see how much it faster faster than Robot Class:
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);
}
}
And the result is
With JNA Library: 77
With Robot Class 37
Guys, please someone explain why is that and how can I fasten it?
JNA calls take much time, instead JNI uses c++ directly.
Don't try to optimise too early. Create a sensible interface to get the data you want (A screenshot) then create the implementation you want based on either Robot, JNA or JNI.
I would guess that the different implementations give completely different results based on the environment that it is running.
Rule One of Programming: First make it work. Then profile, find a bottleneck and remove or mitigate the effect of the bottleneck.
First, check if the native library is actually faster than your code. It might not be the case.
Assuming you already did check that, I would say the problem here is that calls with JNA are really slow. To skip the one call per cycle problem I would suggest writing a C function like this:
void callWithJNAfunction(int rectPosX, int rectPosY, rectSideX, rectSideY,int numberOfCycles) {
for (int i = 0; i < numberOfCycles; i++) {
//code in C that calls the library
}
Now compile this code and call the callWithJNAfunction(...) with JNA.
If the problem is the slowness of the JNA calls, it will get faster.
来源：https://stackoverflow.com/questions/6998438/jna-library-slower-screenshot-than-robot-class