c++ - Extract cursor image in Java

Question

I was wondering if there is a way to extract an Image object from a Cursor object in Java.

A use for this would be for instance :

Image img = extractCursorImage(Cursor.getDefaultCursor());

Which you then can draw on a toolbar button (that's the purpose I want it for).

Answer 1

The Cursor class is pretty abstract - all the important stuff is delegated to native code, so you can't just draw one onto at graphics context. There isn't an immediately obvious way of getting round the need to either predefine the icons or do it in native code.

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could you help me use that function you mentioned?

Below is some code to draw built-in Windows cursors using the JNA library. If you can use JNA, you can avoid C++ compilers.

I'm probably making too many native calls, but the cost is not significant for one-shot icon generation.

hand cursor drawn in Java http://f.imagehost.org/0709/hand.png

Code to display a cursor as a Java image:

public class LoadCursor {

  public static void draw(BufferedImage image, int cursor,
      int diFlags) {
    int width = image.getWidth();
    int height = image.getHeight();

    User32 user32 = User32.INSTANCE;
    Gdi32 gdi32 = Gdi32.INSTANCE;

    Pointer hIcon = user32
        .LoadCursorW(Pointer.NULL, cursor);
    Pointer hdc = gdi32.CreateCompatibleDC(Pointer.NULL);
    Pointer bitmap = gdi32.CreateCompatibleBitmap(hdc,
        width, height);

    gdi32.SelectObject(hdc, bitmap);
    user32.DrawIconEx(hdc, 0, 0, hIcon, width, height, 0,
        Pointer.NULL, diFlags);

    for (int x = 0; x < width; x++) {
      for (int y = 0; y < width; y++) {
        int rgb = gdi32.GetPixel(hdc, x, y);
        image.setRGB(x, y, rgb);
      }
    }

    gdi32.DeleteObject(bitmap);
    gdi32.DeleteDC(hdc);
  }

  public static void main(String[] args) {
    final int width = 128;
    final int height = 128;

    BufferedImage image = new BufferedImage(width, height,
        BufferedImage.TYPE_INT_ARGB);
    draw(image, User32.IDC_HAND, User32.DI_NORMAL);
    BufferedImage mask = new BufferedImage(width, height,
        BufferedImage.TYPE_INT_RGB);
    draw(mask, User32.IDC_HAND, User32.DI_MASK);
    applyMask(image, mask);

    JLabel icon = new JLabel();
    icon.setIcon(new ImageIcon(image));

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setContentPane(icon);
    frame.pack();
    frame.setVisible(true);
  }

  private static void applyMask(BufferedImage image,
      BufferedImage mask) {
    int width = image.getWidth();
    int height = image.getHeight();
    for (int x = 0; x < width; x++) {
      for (int y = 0; y < height; y++) {
        int masked = mask.getRGB(x, y);
        if ((masked & 0x00FFFFFF) == 0) {
          int rgb = image.getRGB(x, y);
          rgb = 0xFF000000 | rgb;
          image.setRGB(x, y, rgb);
        }
      }
    }
  }

}

User32.dll interface:

public interface User32 extends Library {

  public static User32 INSTANCE = (User32) Native
      .loadLibrary("User32", User32.class);

  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_ARROW = 32512;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_IBEAM = 32513;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_WAIT = 32514;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_CROSS = 32515;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_UPARROW = 32516;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZENWSE = 32642;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZENESW = 32643;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZEWE = 32644;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZENS = 32645;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZEALL = 32646;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_NO = 32648;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_HAND = 32649;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_APPSTARTING = 32650;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_HELP = 32651;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_ICON = 32641;
  /** @see #LoadCursorW(Pointer, int) */
  public static final int IDC_SIZE = 32640;

  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_COMPAT = 4;
  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_DEFAULTSIZE = 8;
  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_IMAGE = 2;
  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_MASK = 1;
  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_NORMAL = 3;
  /** @see #DrawIconEx(Pointer, int, int, Pointer, int, int, int, Pointer, int) */
  public static final int DI_APPBANDING = 1;

  /** http://msdn.microsoft.com/en-us/library/ms648391(VS.85).aspx */
  public Pointer LoadCursorW(Pointer hInstance,
      int lpCursorName);

  /** http://msdn.microsoft.com/en-us/library/ms648065(VS.85).aspx */
  public boolean DrawIconEx(Pointer hdc, int xLeft,
      int yTop, Pointer hIcon, int cxWidth, int cyWidth,
      int istepIfAniCur, Pointer hbrFlickerFreeDraw,
      int diFlags);

}

Gdi32.dll interface:

public interface Gdi32 extends Library {

  public static Gdi32 INSTANCE = (Gdi32) Native
      .loadLibrary("Gdi32", Gdi32.class);

  /** http://msdn.microsoft.com/en-us/library/dd183489(VS.85).aspx */
  public Pointer CreateCompatibleDC(Pointer hdc);

  /** http://msdn.microsoft.com/en-us/library/dd183488(VS.85).aspx */
  public Pointer CreateCompatibleBitmap(Pointer hdc,
      int nWidth, int nHeight);

  /** http://msdn.microsoft.com/en-us/library/dd162957(VS.85).aspx */
  public Pointer SelectObject(Pointer hdc, Pointer hgdiobj);

  /** http://msdn.microsoft.com/en-us/library/dd145078(VS.85).aspx */
  public int SetPixel(Pointer hdc, int X, int Y, int crColor);

  /** http://msdn.microsoft.com/en-us/library/dd144909(VS.85).aspx */
  public int GetPixel(Pointer hdc, int nXPos, int nYPos);

  /** http://msdn.microsoft.com/en-us/library/dd183539(VS.85).aspx */
  public boolean DeleteObject(Pointer hObject);

  /** http://msdn.microsoft.com/en-us/library/dd183533(VS.85).aspx */
  public boolean DeleteDC(Pointer hdc);

}