Add on-device OpenGL video filter architecture

server/build_without_gradle.sh

@@ -60,6 +60,7 @@ SRC=( \
     com/genymobile/scrcpy/audio/*.java \
     com/genymobile/scrcpy/control/*.java \
     com/genymobile/scrcpy/device/*.java \
+    com/genymobile/scrcpy/opengl/*.java \
     com/genymobile/scrcpy/util/*.java \
     com/genymobile/scrcpy/video/*.java \
     com/genymobile/scrcpy/wrappers/*.java \

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -14,6 +14,7 @@ import com.genymobile.scrcpy.device.DesktopConnection;
 import com.genymobile.scrcpy.device.Device;
 import com.genymobile.scrcpy.device.NewDisplay;
 import com.genymobile.scrcpy.device.Streamer;
+import com.genymobile.scrcpy.opengl.OpenGLRunner;
 import com.genymobile.scrcpy.util.Ln;
 import com.genymobile.scrcpy.util.LogUtils;
 import com.genymobile.scrcpy.video.CameraCapture;
@@ -191,6 +192,8 @@ public final class Server {
                 asyncProcessor.stop();
             }
 
+            OpenGLRunner.quit(); // quit the OpenGL thread, if any
+
             connection.shutdown();
 
             try {
@@ -200,6 +203,7 @@ public final class Server {
                 for (AsyncProcessor asyncProcessor : asyncProcessors) {
                     asyncProcessor.join();
                 }
+                OpenGLRunner.join();
             } catch (InterruptedException e) {
                 // ignore
             }

server/src/main/java/com/genymobile/scrcpy/opengl/AffineOpenGLFilter.java

@@ -0,0 +1,138 @@
+package com.genymobile.scrcpy.opengl;
+
+import com.genymobile.scrcpy.util.AffineMatrix;
+
+import android.opengl.GLES11Ext;
+import android.opengl.GLES20;
+
+import java.nio.FloatBuffer;
+
+public class AffineOpenGLFilter implements OpenGLFilter {
+
+    private int program;
+    private FloatBuffer vertexBuffer;
+    private FloatBuffer texCoordsBuffer;
+    private final float[] userMatrix;
+
+    private int vertexPosLoc;
+    private int texCoordsInLoc;
+
+    private int texLoc;
+    private int texMatrixLoc;
+    private int userMatrixLoc;
+
+    public AffineOpenGLFilter(AffineMatrix transform) {
+        this.userMatrix = transform.to4x4();
+    }
+
+    @Override
+    public void init() throws OpenGLFilterException {
+        // inputSize and outputSize are not used for an affine filter, but in theory they are necessary if we want to apply filters which operate
+        // on specific pixels
+
+        // @formatter:off
+        String vertexShaderCode = "#version 100\n"
+                + "attribute vec4 vertex_pos;\n"
+                + "attribute vec4 tex_coords_in;\n"
+                + "varying vec2 tex_coords;\n"
+                + "uniform mat4 tex_matrix;\n"
+                + "uniform mat4 user_matrix;\n"
+                + "void main() {\n"
+                + "    gl_Position = vertex_pos;\n"
+                + "    tex_coords = (tex_matrix * user_matrix * tex_coords_in).xy;\n"
+                + "}";
+
+        // @formatter:off
+        String fragmentShaderCode = "#version 100\n"
+                + "#extension GL_OES_EGL_image_external : require\n"
+                + "precision highp float;\n"
+                + "uniform samplerExternalOES tex;\n"
+                + "varying vec2 tex_coords;\n"
+                + "void main() {\n"
+                + "    if (tex_coords.x >= 0.0 && tex_coords.x <= 1.0\n"
+                + "            && tex_coords.y >= 0.0 && tex_coords.y <= 1.0) {\n"
+                + "        gl_FragColor = texture2D(tex, tex_coords);\n"
+                + "    } else {\n"
+                + "        gl_FragColor = vec4(0.0);\n"
+                + "    }\n"
+                + "}";
+
+        program = GLUtils.createProgram(vertexShaderCode, fragmentShaderCode);
+        if (program == 0) {
+            throw new OpenGLFilterException("Cannot create OpenGL program");
+        }
+
+        float[] vertices = {
+                -1, -1, // Bottom-left
+                1, -1, // Bottom-right
+                -1, 1, // Top-left
+                1, 1, // Top-right
+        };
+
+        float[] texCoords = {
+                0, 0, // Bottom-left
+                1, 0, // Bottom-right
+                0, 1, // Top-left
+                1, 1, // Top-right
+        };
+
+        // OpenGL will fill the 3rd and 4th coordinates of the vec4 automatically to 0.0 and 1.0 respectively
+        vertexBuffer = GLUtils.createFloatBuffer(vertices);
+        texCoordsBuffer = GLUtils.createFloatBuffer(texCoords);
+
+        vertexPosLoc = GLES20.glGetAttribLocation(program, "vertex_pos");
+        assert vertexPosLoc != -1;
+
+        texCoordsInLoc = GLES20.glGetAttribLocation(program, "tex_coords_in");
+        assert texCoordsInLoc != -1;
+
+        texLoc = GLES20.glGetUniformLocation(program, "tex");
+        assert texLoc != -1;
+
+        texMatrixLoc = GLES20.glGetUniformLocation(program, "tex_matrix");
+        assert texMatrixLoc != -1;
+
+        userMatrixLoc = GLES20.glGetUniformLocation(program, "user_matrix");
+        assert userMatrixLoc != -1;
+    }
+
+    @Override
+    public void draw(int textureId, float[] texMatrix) {
+        GLES20.glUseProgram(program);
+        GLUtils.checkGlError();
+
+        GLES20.glEnableVertexAttribArray(vertexPosLoc);
+        GLUtils.checkGlError();
+        GLES20.glEnableVertexAttribArray(texCoordsInLoc);
+        GLUtils.checkGlError();
+
+        GLES20.glVertexAttribPointer(vertexPosLoc, 2, GLES20.GL_FLOAT, false, 0, vertexBuffer);
+        GLUtils.checkGlError();
+        GLES20.glVertexAttribPointer(texCoordsInLoc, 2, GLES20.GL_FLOAT, false, 0, texCoordsBuffer);
+        GLUtils.checkGlError();
+
+        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
+        GLUtils.checkGlError();
+        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, textureId);
+        GLUtils.checkGlError();
+        GLES20.glUniform1i(texLoc, 0);
+        GLUtils.checkGlError();
+
+        GLES20.glUniformMatrix4fv(texMatrixLoc, 1, false, texMatrix, 0);
+        GLUtils.checkGlError();
+
+        GLES20.glUniformMatrix4fv(userMatrixLoc, 1, false, userMatrix, 0);
+        GLUtils.checkGlError();
+
+        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
+        GLUtils.checkGlError();
+        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
+        GLUtils.checkGlError();
+    }
+
+    @Override
+    public void release() {
+        GLES20.glDeleteProgram(program);
+        GLUtils.checkGlError();
+    }
+}

server/src/main/java/com/genymobile/scrcpy/opengl/GLUtils.java

@@ -0,0 +1,124 @@
+package com.genymobile.scrcpy.opengl;
+
+import com.genymobile.scrcpy.BuildConfig;
+import com.genymobile.scrcpy.util.Ln;
+
+import android.opengl.GLES20;
+import android.opengl.GLU;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.FloatBuffer;
+
+public final class GLUtils {
+
+    private static final boolean DEBUG = BuildConfig.DEBUG;
+
+    private GLUtils() {
+        // not instantiable
+    }
+
+    public static int createProgram(String vertexSource, String fragmentSource) {
+        int vertexShader = createShader(GLES20.GL_VERTEX_SHADER, vertexSource);
+        if (vertexShader == 0) {
+            return 0;
+        }
+
+        int fragmentShader = createShader(GLES20.GL_FRAGMENT_SHADER, fragmentSource);
+        if (fragmentShader == 0) {
+            GLES20.glDeleteShader(vertexShader);
+            return 0;
+        }
+
+        int program = GLES20.glCreateProgram();
+        if (program == 0) {
+            GLES20.glDeleteShader(fragmentShader);
+            GLES20.glDeleteShader(vertexShader);
+            return 0;
+        }
+
+        GLES20.glAttachShader(program, vertexShader);
+        checkGlError();
+        GLES20.glAttachShader(program, fragmentShader);
+        checkGlError();
+        GLES20.glLinkProgram(program);
+        checkGlError();
+
+        int[] linkStatus = new int[1];
+        GLES20.glGetProgramiv(program, GLES20.GL_LINK_STATUS, linkStatus, 0);
+        if (linkStatus[0] == 0) {
+            Ln.e("Could not link program: " + GLES20.glGetProgramInfoLog(program));
+            GLES20.glDeleteProgram(program);
+            GLES20.glDeleteShader(fragmentShader);
+            GLES20.glDeleteShader(vertexShader);
+            return 0;
+        }
+
+        return program;
+    }
+
+    public static int createShader(int type, String source) {
+        int shader = GLES20.glCreateShader(type);
+        if (shader == 0) {
+            Ln.e(getGlErrorMessage("Could not create shader"));
+            return 0;
+        }
+
+        GLES20.glShaderSource(shader, source);
+        GLES20.glCompileShader(shader);
+
+        int[] compileStatus = new int[1];
+        GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, compileStatus, 0);
+        if (compileStatus[0] == 0) {
+            Ln.e("Could not compile " + getShaderTypeString(type) + ": " + GLES20.glGetShaderInfoLog(shader));
+            GLES20.glDeleteShader(shader);
+            return 0;
+        }
+
+        return shader;
+    }
+
+    private static String getShaderTypeString(int type) {
+        switch (type) {
+            case GLES20.GL_VERTEX_SHADER:
+                return "vertex shader";
+            case GLES20.GL_FRAGMENT_SHADER:
+                return "fragment shader";
+            default:
+                return "shader";
+        }
+    }
+
+    /**
+     * Throws a runtime exception if {@link GLES20#glGetError()} returns an error (useful for debugging).
+     */
+    public static void checkGlError() {
+        if (DEBUG) {
+            int error = GLES20.glGetError();
+            if (error != GLES20.GL_NO_ERROR) {
+                throw new RuntimeException(toErrorString(error));
+            }
+        }
+    }
+
+    public static String getGlErrorMessage(String userError) {
+        int glError = GLES20.glGetError();
+        if (glError == GLES20.GL_NO_ERROR) {
+            return userError;
+        }
+
+        return userError + " (" + toErrorString(glError) + ")";
+    }
+
+    private static String toErrorString(int glError) {
+        String errorString = GLU.gluErrorString(glError);
+        return "glError 0x" + Integer.toHexString(glError) + " " + errorString;
+    }
+
+    public static FloatBuffer createFloatBuffer(float[] values) {
+        FloatBuffer fb = ByteBuffer.allocateDirect(values.length * 4).order(ByteOrder.nativeOrder()).asFloatBuffer();
+        fb.put(values);
+        fb.position(0);
+        return fb;
+    }
+}

server/src/main/java/com/genymobile/scrcpy/opengl/OpenGLException.java

@@ -0,0 +1,13 @@
+package com.genymobile.scrcpy.opengl;
+
+import java.io.IOException;
+
+public class OpenGLException extends IOException {
+    public OpenGLException(String message) {
+        super(message);
+    }
+
+    public OpenGLException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

server/src/main/java/com/genymobile/scrcpy/opengl/OpenGLFilter.java

@@ -0,0 +1,21 @@
+package com.genymobile.scrcpy.opengl;
+
+public interface OpenGLFilter {
+
+    /**
+     * Initialize the OpenGL filter (typically compile the shaders and create the program).
+     *
+     * @throws OpenGLFilterException if an initialization error occurs
+     */
+    void init() throws OpenGLFilterException;
+
+    /**
+     * Render a frame (call for each frame)
+     */
+    void draw(int textureId, float[] texMatrix);
+
+    /**
+     * Release resources
+     */
+    void release();
+}

server/src/main/java/com/genymobile/scrcpy/opengl/OpenGLFilterException.java

@@ -0,0 +1,7 @@
+package com.genymobile.scrcpy.opengl;
+
+public class OpenGLFilterException extends OpenGLException {
+    public OpenGLFilterException(String message) {
+        super(message);
+    }
+}

server/src/main/java/com/genymobile/scrcpy/opengl/OpenGLRunner.java

@@ -0,0 +1,244 @@
+package com.genymobile.scrcpy.opengl;
+
+import com.genymobile.scrcpy.device.Size;
+
+import android.graphics.SurfaceTexture;
+import android.opengl.EGL14;
+import android.opengl.EGLConfig;
+import android.opengl.EGLContext;
+import android.opengl.EGLDisplay;
+import android.opengl.EGLExt;
+import android.opengl.EGLSurface;
+import android.opengl.GLES11Ext;
+import android.opengl.GLES20;
+import android.os.Handler;
+import android.os.HandlerThread;
+import android.view.Surface;
+
+import java.util.concurrent.Semaphore;
+
+public final class OpenGLRunner {
+
+    private static HandlerThread handlerThread;
+    private static Handler handler;
+    private static boolean quit;
+
+    private EGLDisplay eglDisplay;
+    private EGLContext eglContext;
+    private EGLSurface eglSurface;
+
+    private final OpenGLFilter filter;
+
+    private SurfaceTexture surfaceTexture;
+    private Surface inputSurface;
+    private int textureId;
+
+    private boolean stopped;
+
+    public OpenGLRunner(OpenGLFilter filter) {
+        this.filter = filter;
+    }
+
+    public static synchronized void initOnce() {
+        if (handlerThread == null) {
+            if (quit) {
+                throw new IllegalStateException("Could not init OpenGLRunner after it is quit");
+            }
+            handlerThread = new HandlerThread("OpenGLRunner");
+            handlerThread.start();
+            handler = new Handler(handlerThread.getLooper());
+        }
+    }
+
+    public static void quit() {
+        HandlerThread thread;
+        synchronized (OpenGLRunner.class) {
+            thread = handlerThread;
+            quit = true;
+        }
+        if (thread != null) {
+            thread.quitSafely();
+        }
+    }
+
+    public static void join() throws InterruptedException {
+        HandlerThread thread;
+        synchronized (OpenGLRunner.class) {
+            thread = handlerThread;
+        }
+        if (thread != null) {
+            thread.join();
+        }
+    }
+
+    public Surface start(Size inputSize, Size outputSize, Surface outputSurface) throws OpenGLException {
+        initOnce();
+
+        // Simulate CompletableFuture, but working for all Android versions
+        final Semaphore sem = new Semaphore(0);
+        Throwable[] throwableRef = new Throwable[1];
+
+        // The whole OpenGL execution must be performed on a Handler, so that SurfaceTexture.setOnFrameAvailableListener() works correctly.
+        // See <https://github.com/Genymobile/scrcpy/issues/5444>
+        handler.post(() -> {
+            try {
+                run(inputSize, outputSize, outputSurface);
+            } catch (Throwable throwable) {
+                throwableRef[0] = throwable;
+            } finally {
+                sem.release();
+            }
+        });
+
+        try {
+            sem.acquire();
+        } catch (InterruptedException e) {
+            // Behave as if this method call was synchronous
+            Thread.currentThread().interrupt();
+        }
+
+        Throwable throwable = throwableRef[0];
+        if (throwable != null) {
+            if (throwable instanceof OpenGLException) {
+                throw (OpenGLException) throwable;
+            }
+            throw new OpenGLException("Asynchronous OpenGL runner init failed", throwable);
+        }
+
+        // No need for synchronization, if it is called after start() (synchronized with the semaphore) and before release()
+        return inputSurface;
+    }
+
+    private void run(Size inputSize, Size outputSize, Surface outputSurface) throws OpenGLException {
+        eglDisplay = EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);
+        if (eglDisplay == EGL14.EGL_NO_DISPLAY) {
+            throw new OpenGLException("Unable to get EGL14 display");
+        }
+
+        int[] version = new int[2];
+        if (!EGL14.eglInitialize(eglDisplay, version, 0, version, 1)) {
+            throw new OpenGLException("Unable to initialize EGL14");
+        }
+
+        // @formatter:off
+        int[] attribList = {
+                EGL14.EGL_RED_SIZE, 8,
+                EGL14.EGL_GREEN_SIZE, 8,
+                EGL14.EGL_BLUE_SIZE, 8,
+                EGL14.EGL_ALPHA_SIZE, 8,
+                EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,
+                EGL14.EGL_NONE
+        };
+        EGLConfig[] configs = new EGLConfig[1];
+        int[] numConfigs = new int[1];
+        EGL14.eglChooseConfig(eglDisplay, attribList, 0, configs, 0, configs.length, numConfigs, 0);
+        if (numConfigs[0] <= 0) {
+            EGL14.eglTerminate(eglDisplay);
+            throw new OpenGLException("Unable to find ES2 EGL config");
+        }
+        EGLConfig eglConfig = configs[0];
+
+        // @formatter:off
+        int[] contextAttribList = {
+                EGL14.EGL_CONTEXT_CLIENT_VERSION, 2,
+                EGL14.EGL_NONE
+        };
+        eglContext = EGL14.eglCreateContext(eglDisplay, eglConfig, EGL14.EGL_NO_CONTEXT, contextAttribList, 0);
+        if (eglContext == null) {
+            throw new OpenGLException("Failed to create EGL context");
+        }
+
+        int[] surfaceAttribList = {
+                EGL14.EGL_NONE
+        };
+        eglSurface = EGL14.eglCreateWindowSurface(eglDisplay, eglConfig, outputSurface, surfaceAttribList, 0);
+        if (eglSurface == null) {
+            EGL14.eglDestroyContext(eglDisplay, eglContext);
+            EGL14.eglTerminate(eglDisplay);
+            throw new OpenGLException("Failed to create EGL window surface");
+        }
+
+        if (!EGL14.eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext)) {
+            EGL14.eglDestroySurface(eglDisplay, eglSurface);
+            EGL14.eglDestroyContext(eglDisplay, eglContext);
+            EGL14.eglTerminate(eglDisplay);
+            throw new OpenGLException("Failed to make EGL context current");
+        }
+
+        int[] textures = new int[1];
+        GLES20.glGenTextures(1, textures, 0);
+        GLUtils.checkGlError();
+        textureId = textures[0];
+
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
+        GLUtils.checkGlError();
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
+        GLUtils.checkGlError();
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
+        GLUtils.checkGlError();
+        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
+        GLUtils.checkGlError();
+
+        surfaceTexture = new SurfaceTexture(textureId);
+        surfaceTexture.setDefaultBufferSize(inputSize.getWidth(), inputSize.getHeight());
+        inputSurface = new Surface(surfaceTexture);
+
+        filter.init();
+
+        surfaceTexture.setOnFrameAvailableListener(surfaceTexture -> {
+            if (stopped) {
+                // Make sure to never render after resources have been released
+                return;
+            }
+
+            render(outputSize);
+        }, handler);
+    }
+
+    private void render(Size outputSize) {
+        GLES20.glViewport(0, 0, outputSize.getWidth(), outputSize.getHeight());
+        GLUtils.checkGlError();
+
+        surfaceTexture.updateTexImage();
+        float[] matrix = new float[16];
+        surfaceTexture.getTransformMatrix(matrix);
+
+        filter.draw(textureId, matrix);
+
+        EGLExt.eglPresentationTimeANDROID(eglDisplay, eglSurface, surfaceTexture.getTimestamp());
+        EGL14.eglSwapBuffers(eglDisplay, eglSurface);
+    }
+
+    public void stopAndRelease() {
+        final Semaphore sem = new Semaphore(0);
+
+        handler.post(() -> {
+            stopped = true;
+            surfaceTexture.setOnFrameAvailableListener(null, handler);
+
+            filter.release();
+
+            int[] textures = {textureId};
+            GLES20.glDeleteTextures(1, textures, 0);
+            GLUtils.checkGlError();
+
+            EGL14.eglDestroySurface(eglDisplay, eglSurface);
+            EGL14.eglDestroyContext(eglDisplay, eglContext);
+            EGL14.eglTerminate(eglDisplay);
+            eglDisplay = EGL14.EGL_NO_DISPLAY;
+            eglContext = EGL14.EGL_NO_CONTEXT;
+            eglSurface = EGL14.EGL_NO_SURFACE;
+            surfaceTexture.release();
+            inputSurface.release();
+
+            sem.release();
+        });
+
+        try {
+            sem.acquire();
+        } catch (InterruptedException e) {
+            // Behave as if this method call was synchronous
+            Thread.currentThread().interrupt();
+        }
+    }
+}

server/src/main/java/com/genymobile/scrcpy/util/AffineMatrix.java

@@ -0,0 +1,367 @@
+package com.genymobile.scrcpy.util;
+
+import com.genymobile.scrcpy.device.Point;
+import com.genymobile.scrcpy.device.Size;
+
+/**
+ * Represents a 2D affine transform (a 3x3 matrix):
+ *
+ * <pre>
+ *     / a c e \
+ *     | b d f |
+ *     \ 0 0 1 /
+ * </pre>
+ * <p>
+ * Or, a 4x4 matrix if we add a z axis:
+ *
+ * <pre>
+ *     / a c 0 e \
+ *     | b d 0 f |
+ *     | 0 0 1 0 |
+ *     \ 0 0 0 1 /
+ * </pre>
+ */
+public class AffineMatrix {
+
+    private final double a, b, c, d, e, f;
+
+    /**
+     * The identity matrix.
+     */
+    public static final AffineMatrix IDENTITY = new AffineMatrix(1, 0, 0, 1, 0, 0);
+
+    /**
+     * Create a new matrix:
+     *
+     * <pre>
+     *     / a c e \
+     *     | b d f |
+     *     \ 0 0 1 /
+     * </pre>
+     */
+    public AffineMatrix(double a, double b, double c, double d, double e, double f) {
+        this.a = a;
+        this.b = b;
+        this.c = c;
+        this.d = d;
+        this.e = e;
+        this.f = f;
+    }
+
+    @Override
+    public String toString() {
+        return "[" + a + ", " + c + ", " + e + "; " + b + ", " + d + ", " + f + "]";
+    }
+
+    /**
+     * Return a matrix which converts from Normalized Device Coordinates to pixels.
+     *
+     * @param size the target size
+     * @return the transform matrix
+     */
+    public static AffineMatrix ndcFromPixels(Size size) {
+        double w = size.getWidth();
+        double h = size.getHeight();
+        return new AffineMatrix(1 / w, 0, 0, -1 / h, 0, 1);
+    }
+
+    /**
+     * Return a matrix which converts from pixels to Normalized Device Coordinates.
+     *
+     * @param size the source size
+     * @return the transform matrix
+     */
+    public static AffineMatrix ndcToPixels(Size size) {
+        double w = size.getWidth();
+        double h = size.getHeight();
+        return new AffineMatrix(w, 0, 0, -h, 0, h);
+    }
+
+    /**
+     * Apply the transform to a point ({@code this} should be a matrix converted to pixels coordinates via {@link #ndcToPixels(Size)}).
+     *
+     * @param point the source point
+     * @return the converted point
+     */
+    public Point apply(Point point) {
+        int x = point.getX();
+        int y = point.getY();
+        int xx = (int) (a * x + c * y + e);
+        int yy = (int) (b * x + d * y + f);
+        return new Point(xx, yy);
+    }
+
+    /**
+     * Compute <code>this * rhs</code>.
+     *
+     * @param rhs the matrix to multiply
+     * @return the product
+     */
+    public AffineMatrix multiply(AffineMatrix rhs) {
+        if (rhs == null) {
+            // For convenience
+            return this;
+        }
+
+        double aa = this.a * rhs.a + this.c * rhs.b;
+        double bb = this.b * rhs.a + this.d * rhs.b;
+        double cc = this.a * rhs.c + this.c * rhs.d;
+        double dd = this.b * rhs.c + this.d * rhs.d;
+        double ee = this.a * rhs.e + this.c * rhs.f + this.e;
+        double ff = this.b * rhs.e + this.d * rhs.f + this.f;
+        return new AffineMatrix(aa, bb, cc, dd, ee, ff);
+    }
+
+    /**
+     * Multiply all matrices from left to right, ignoring any {@code null} matrix (for convenience).
+     *
+     * @param matrices the matrices
+     * @return the product
+     */
+    public static AffineMatrix multiplyAll(AffineMatrix... matrices) {
+        AffineMatrix result = null;
+        for (AffineMatrix matrix : matrices) {
+            if (result == null) {
+                result = matrix;
+            } else {
+                result = result.multiply(matrix);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Invert the matrix
+     *
+     * @return the inverse matrix (or {@code null} if not invertible).
+     */
+    public AffineMatrix invert() {
+        // The 3x3 matrix M can be decomposed into M = M1 * M2:
+        //         M1          M2
+        //      / 1 0 e \   / a c 0 \
+        //      | 0 1 f | * | b d 0 |
+        //      \ 0 0 1 /   \ 0 0 1 /
+        //
+        // The inverse of an invertible 2x2 matrix is given by this formula:
+        //
+        //      / A B \⁻¹     1   /  D -B \
+        //      \ C D /   = ----- \ -C  A /
+        //                  AD-BC
+        //
+        // Let B=c and C=b (to apply the general formula with the same letters).
+        //
+        //     M⁻¹ = (M1 * M2)⁻¹ = M2⁻¹ * M1⁻¹
+        //
+        //                  M2⁻¹              M1⁻¹
+        //           /----------------\
+        //             1   /  d -B  0 \   / 1  0 -e \
+        //         = ----- | -C  a  0 | * | 0  1 -f |
+        //           ad-BC \  0  0  1 /   \ 0  0  1 /
+        //
+        // With the original letters:
+        //
+        //             1   /  d -c  0 \   / 1  0 -e \
+        //     M⁻¹ = ----- | -b  a  0 | * | 0  1 -f |
+        //           ad-cb \  0  0  1 /   \ 0  0  1 /
+        //
+        //             1   /  d -c  cf-de \
+        //         = ----- | -b  a  be-af |
+        //           ad-cb \  0  0    1   /
+        double det = a * d - c * b;
+        if (det == 0) {
+            // Not invertible
+            return null;
+        }
+
+        double aa = d / det;
+        double bb = -b / det;
+        double cc = -c / det;
+        double dd = a / det;
+        double ee = (c * f - d * e) / det;
+        double ff = (b * e - a * f) / det;
+
+        return new AffineMatrix(aa, bb, cc, dd, ee, ff);
+    }
+
+    /**
+     * Return this transform apply from the center (0.5, 0.5).
+     *
+     * @return the resulting matrix
+     */
+    public AffineMatrix fromCenter() {
+        return translate(0.5, 0.5).multiply(this).multiply(translate(-0.5, -0.5));
+    }
+
+    /**
+     * Return this transform with the specified aspect ratio.
+     *
+     * @param ar the aspect ratio
+     * @return the resulting matrix
+     */
+    public AffineMatrix withAspectRatio(double ar) {
+        return scale(1 / ar, 1).multiply(this).multiply(scale(ar, 1));
+    }
+
+    /**
+     * Return this transform with the specified aspect ratio.
+     *
+     * @param size the size describing the aspect ratio
+     * @return the transform
+     */
+    public AffineMatrix withAspectRatio(Size size) {
+        double ar = (double) size.getWidth() / size.getHeight();
+        return withAspectRatio(ar);
+    }
+
+    /**
+     * Return a translation matrix.
+     *
+     * @param x the horizontal translation
+     * @param y the vertical translation
+     * @return the matrix
+     */
+    public static AffineMatrix translate(double x, double y) {
+        return new AffineMatrix(1, 0, 0, 1, x, y);
+    }
+
+    /**
+     * Return a scaling matrix.
+     *
+     * @param x the horizontal scaling
+     * @param y the vertical scaling
+     * @return the matrix
+     */
+    public static AffineMatrix scale(double x, double y) {
+        return new AffineMatrix(x, 0, 0, y, 0, 0);
+    }
+
+    /**
+     * Return a scaling matrix.
+     *
+     * @param from the source size
+     * @param to   the destination size
+     * @return the matrix
+     */
+    public static AffineMatrix scale(Size from, Size to) {
+        double scaleX = (double) to.getWidth() / from.getWidth();
+        double scaleY = (double) to.getHeight() / from.getHeight();
+        return scale(scaleX, scaleY);
+    }
+
+    /**
+     * Return a matrix applying a "reframing" ("cropping" a rectangle).
+     * <p/>
+     * <code>(x, y)</code> is the bottom-left corner, <code>(w, h)</code> is the size of the rectangle.
+     *
+     * @param x horizontal coordinate (increasing to the right)
+     * @param y vertical coordinate (increasing upwards)
+     * @param w width
+     * @param h height
+     * @return the matrix
+     */
+    public static AffineMatrix reframe(double x, double y, double w, double h) {
+        if (w == 0 || h == 0) {
+            throw new IllegalArgumentException("Cannot reframe to an empty area: " + w + "x" + h);
+        }
+        return scale(1 / w, 1 / h).multiply(translate(-x, -y));
+    }
+
+    /**
+     * Return an orthogonal rotation matrix.
+     *
+     * @param ccwRotation the counter-clockwise rotation
+     * @return the matrix
+     */
+    public static AffineMatrix rotateOrtho(int ccwRotation) {
+        switch (ccwRotation) {
+            case 0:
+                return IDENTITY;
+            case 1:
+                // 90° counter-clockwise
+                return new AffineMatrix(0, 1, -1, 0, 1, 0);
+            case 2:
+                // 180°
+                return new AffineMatrix(-1, 0, 0, -1, 1, 1);
+            case 3:
+                // 90° clockwise
+                return new AffineMatrix(0, -1, 1, 0, 0, 1);
+            default:
+                throw new IllegalArgumentException("Invalid rotation: " + ccwRotation);
+        }
+    }
+
+    /**
+     * Return an horizontal flip matrix.
+     *
+     * @return the matrix
+     */
+    public static AffineMatrix hflip() {
+        return new AffineMatrix(-1, 0, 0, 1, 1, 0);
+    }
+
+    /**
+     * Return a vertical flip matrix;
+     *
+     * @return the matrix
+     */
+    public static AffineMatrix vflip() {
+        return new AffineMatrix(1, 0, 0, -1, 0, 1);
+    }
+
+    /**
+     * Return a rotation matrix
+     *
+     * @param ccwDegrees the angle, in degrees (counter-clockwise)
+     * @return the matrix
+     */
+    public static AffineMatrix rotate(double ccwDegrees) {
+        double radians = Math.toRadians(ccwDegrees);
+        double cos = Math.cos(radians);
+        double sin = Math.sin(radians);
+        return new AffineMatrix(cos, sin, -sin, cos, 0, 0);
+    }
+
+    /**
+     * Export this affine transform to a 4x4 column-major order matrix.
+     *
+     * @param matrix output 4x4 matrix
+     */
+    public void to4x4(float[] matrix) {
+        // matrix is a 4x4 matrix in column-major order
+
+        // Column 0
+        matrix[0] = (float) a;
+        matrix[1] = (float) b;
+        matrix[2] = 0;
+        matrix[3] = 0;
+
+        // Column 1
+        matrix[4] = (float) c;
+        matrix[5] = (float) d;
+        matrix[6] = 0;
+        matrix[7] = 0;
+
+        // Column 2
+        matrix[8] = 0;
+        matrix[9] = 0;
+        matrix[10] = 1;
+        matrix[11] = 0;
+
+        // Column 3
+        matrix[12] = (float) e;
+        matrix[13] = (float) f;
+        matrix[14] = 0;
+        matrix[15] = 1;
+    }
+
+    /**
+     * Export this affine transform to a 4x4 column-major order matrix.
+     *
+     * @return 4x4 matrix
+     */
+    public float[] to4x4() {
+        float[] matrix = new float[16];
+        to4x4(matrix);
+        return matrix;
+    }
+}