OpenCV Java Highgui Class

The objective is to:

    *Reduce greatly the number of lines of code in the Java codes;
    *Make it easy for Java users to add a trackbar and show the results;
    *Get the code more similar between C++, Java and Python, making the tutorials more uniform.

modules/highgui/CMakeLists.txt

@@ -1,5 +1,9 @@
 set(the_description "High-level GUI")
-ocv_add_module(highgui opencv_imgproc opencv_imgcodecs OPTIONAL opencv_videoio WRAP python)
+if(ANDROID)
+  ocv_add_module(highgui opencv_imgproc opencv_imgcodecs OPTIONAL opencv_videoio WRAP python)
+else()
+  ocv_add_module(highgui opencv_imgproc opencv_imgcodecs OPTIONAL opencv_videoio WRAP python java)
+endif()
 
 # ----------------------------------------------------------------------------
 #  CMake file for highgui. See root CMakeLists.txt

modules/highgui/misc/java/src/java/highgui+HighGui.java

@@ -0,0 +1,193 @@
+package org.opencv.highgui;
+
+import org.opencv.core.Mat;
+
+import javax.swing.*;
+import java.awt.*;
+import java.awt.event.KeyEvent;
+import java.awt.event.KeyListener;
+import java.awt.image.BufferedImage;
+import java.awt.image.DataBufferByte;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * This class was designed for use in Java applications
+ * to recreate the OpenCV HighGui functionalities.
+ */
+public final class HighGui {
+
+    // Constants for namedWindow
+    public final static int WINDOW_NORMAL = ImageWindow.WINDOW_NORMAL;
+    public final static int WINDOW_AUTOSIZE = ImageWindow.WINDOW_AUTOSIZE;
+
+    // Control Variables
+    public static int n_closed_windows = 0;
+    public static int pressedKey = -1;
+    public static CountDownLatch latch = new CountDownLatch(1);
+
+    // Windows Map
+    public static Map<String, ImageWindow> windows = new HashMap<String, ImageWindow>();
+
+    public static void namedWindow(String winname) {
+        namedWindow(winname, HighGui.WINDOW_AUTOSIZE);
+    }
+
+    public static void namedWindow(String winname, int flag) {
+        ImageWindow newWin = new ImageWindow(winname, flag);
+        if (windows.get(winname) == null) windows.put(winname, newWin);
+    }
+
+    public static void imshow(String winname, Mat img) {
+        if (img.empty()) {
+            System.err.println("Error: Empty image in imshow");
+            System.exit(-1);
+        } else {
+            ImageWindow tmpWindow = windows.get(winname);
+            if (tmpWindow == null) {
+                ImageWindow newWin = new ImageWindow(winname, img);
+                windows.put(winname, newWin);
+            } else {
+                tmpWindow.setMat(img);
+            }
+        }
+    }
+
+    public static Image toBufferedImage(Mat m) {
+        int type = BufferedImage.TYPE_BYTE_GRAY;
+
+        if (m.channels() > 1) {
+            type = BufferedImage.TYPE_3BYTE_BGR;
+        }
+
+        int bufferSize = m.channels() * m.cols() * m.rows();
+        byte[] b = new byte[bufferSize];
+        m.get(0, 0, b); // get all the pixels
+        BufferedImage image = new BufferedImage(m.cols(), m.rows(), type);
+
+        final byte[] targetPixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
+        System.arraycopy(b, 0, targetPixels, 0, b.length);
+
+        return image;
+    }
+
+    public static JFrame createJFrame(String title, int flag) {
+        JFrame frame = new JFrame(title);
+
+        frame.addWindowListener(new java.awt.event.WindowAdapter() {
+            @Override
+            public void windowClosing(java.awt.event.WindowEvent windowEvent) {
+                n_closed_windows++;
+                if (n_closed_windows == windows.size()) latch.countDown();
+            }
+        });
+
+        frame.addKeyListener(new KeyListener() {
+            @Override
+            public void keyTyped(KeyEvent e) {
+            }
+
+            @Override
+            public void keyReleased(KeyEvent e) {
+            }
+
+            @Override
+            public void keyPressed(KeyEvent e) {
+                pressedKey = e.getKeyCode();
+                latch.countDown();
+            }
+        });
+
+        if (flag == WINDOW_AUTOSIZE) frame.setResizable(false);
+
+        return frame;
+    }
+
+    public static void waitKey(){
+        waitKey(0);
+    }
+
+    public static int waitKey(int delay) {
+        // Reset control values
+        latch = new CountDownLatch(1);
+        n_closed_windows = 0;
+        pressedKey = -1;
+
+        // If there are no windows to be shown return
+        if (windows.isEmpty()) {
+            System.err.println("Error: waitKey must be used after an imshow");
+            System.exit(-1);
+        }
+
+        // Remove the unused windows
+        Iterator<Map.Entry<String,
+                ImageWindow>> iter = windows.entrySet().iterator();
+        while (iter.hasNext()) {
+            Map.Entry<String,
+                    ImageWindow> entry = iter.next();
+            ImageWindow win = entry.getValue();
+            if (win.alreadyUsed) {
+                iter.remove();
+                win.frame.dispose();
+            }
+        }
+
+        // (if) Create (else) Update frame
+        for (ImageWindow win : windows.values()) {
+
+            if (win.img != null) {
+
+                ImageIcon icon = new ImageIcon(toBufferedImage(win.img));
+
+                if (win.lbl == null) {
+                    JFrame frame = createJFrame(win.name, win.flag);
+                    JLabel lbl = new JLabel(icon);
+                    win.setFrameLabelVisible(frame, lbl);
+                } else {
+                    win.lbl.setIcon(icon);
+                }
+            } else {
+                System.err.println("Error: no imshow associated with" + " namedWindow: \"" + win.name + "\"");
+                System.exit(-1);
+            }
+        }
+
+        try {
+            if (delay == 0) {
+                latch.await();
+            } else {
+                latch.await(delay, TimeUnit.MILLISECONDS);
+            }
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+        // Set all windows as already used
+        for (ImageWindow win : windows.values())
+            win.alreadyUsed = true;
+
+        return pressedKey;
+    }
+
+    public static void destroyWindow(String winname) {
+        ImageWindow tmpWin = windows.get(winname);
+        if (tmpWin != null) windows.remove(winname);
+    }
+
+    public static void destroyAllWindows() {
+        windows.clear();
+    }
+
+    public static void resizeWindow(String winname, int width, int height) {
+        ImageWindow tmpWin = windows.get(winname);
+        if (tmpWin != null) tmpWin.setNewDimension(width, height);
+    }
+
+    public static void moveWindow(String winname, int x, int y) {
+        ImageWindow tmpWin = windows.get(winname);
+        if (tmpWin != null) tmpWin.setNewPosition(x, y);
+    }
+}

modules/highgui/misc/java/src/java/highgui+ImageWindow.java

@@ -0,0 +1,132 @@
+package org.opencv.highgui;
+
+import org.opencv.core.Mat;
+import org.opencv.core.Size;
+import org.opencv.imgproc.Imgproc;
+
+import javax.swing.*;
+import java.awt.*;
+
+/**
+ * This class was designed to create and manipulate
+ * the Windows to be used by the HighGui class.
+ */
+public final class ImageWindow {
+
+    public final static int WINDOW_NORMAL = 0;
+    public final static int WINDOW_AUTOSIZE = 1;
+
+    public String name;
+    public Mat img = null;
+    public Boolean alreadyUsed = false;
+    public Boolean imgToBeResized = false;
+    public Boolean windowToBeResized = false;
+    public Boolean positionToBeChanged = false;
+    public JFrame frame = null;
+    public JLabel lbl = null;
+    public int flag;
+    public int x = -1;
+    public int y = -1;
+    public int width = -1;
+    public int height = -1;
+
+    public ImageWindow(String name, Mat img) {
+        this.name = name;
+        this.img = img;
+        this.flag = WINDOW_NORMAL;
+    }
+
+    public ImageWindow(String name, int flag) {
+        this.name = name;
+        this.flag = flag;
+    }
+
+    public static Size keepAspectRatioSize(int original_width, int original_height, int bound_width, int bound_height) {
+
+        int new_width = original_width;
+        int new_height = original_height;
+
+        if (original_width > bound_width) {
+            new_width = bound_width;
+            new_height = (new_width * original_height) / original_width;
+        }
+
+        if (new_height > bound_height) {
+            new_height = bound_height;
+            new_width = (new_height * original_width) / original_height;
+        }
+
+        return new Size(new_width, new_height);
+    }
+
+    public void setMat(Mat img) {
+
+        this.img = img;
+        this.alreadyUsed = false;
+
+        if (imgToBeResized) {
+            resizeImage();
+            imgToBeResized = false;
+        }
+
+    }
+
+    public void setFrameLabelVisible(JFrame frame, JLabel lbl) {
+        this.frame = frame;
+        this.lbl = lbl;
+
+        if (windowToBeResized) {
+            lbl.setPreferredSize(new Dimension(width, height));
+            windowToBeResized = false;
+        }
+
+        if (positionToBeChanged) {
+            frame.setLocation(x, y);
+            positionToBeChanged = false;
+        }
+
+        frame.add(lbl);
+        frame.pack();
+        frame.setVisible(true);
+    }
+
+    public void setNewDimension(int width, int height) {
+
+        if (this.width != width || this.height != height) {
+            this.width = width;
+            this.height = height;
+
+            if (img != null) {
+                resizeImage();
+            } else {
+                imgToBeResized = true;
+            }
+
+            if (lbl != null) {
+                lbl.setPreferredSize(new Dimension(width, height));
+            } else {
+                windowToBeResized = true;
+            }
+        }
+    }
+
+    public void setNewPosition(int x, int y) {
+        if (this.x != x || this.y != y) {
+            this.x = x;
+            this.y = y;
+
+            if (frame != null) {
+                frame.setLocation(x, y);
+            } else {
+                positionToBeChanged = true;
+            }
+        }
+    }
+
+    private void resizeImage() {
+        if (flag == WINDOW_NORMAL) {
+            Size tmpSize = keepAspectRatioSize(img.width(), img.height(), width, height);
+            Imgproc.resize(img, img, tmpSize);
+        }
+    }
+}