1 files changed, 176 insertions, 0 deletions
diff --git a/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/CanvasMatrixUtil.java b/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/CanvasMatrixUtil.java
new file mode 100644
index 0000000000..bfab93e375
--- /dev/null
+++ b/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/CanvasMatrixUtil.java
@@ -0,0 +1,176 @@
+package com.google.skar;
+
+import android.graphics.Matrix;
+
+/**
+ * Provides static methods for matrix manipulation needed to draw in ARCore with Canvas.
+ * Input matrices are assumed to be 4x4 android.opengl.Matrix types (16-float arrays in column-major
+ * order).
+ * Output matrices are 3x3 android.graphics.Matrix types.
+ */
+
+public class CanvasMatrixUtil {
+
+    /******************* PUBLIC FUNCTIONS ***********************/
+
+    /**
+     * Returns an android.graphics.Matrix that can be used on a Canvas to draw a 2D object in
+     * perspective. Object will be rotated towards the XZ plane and will appear to stick on Planes.
+     * Undefined behavior when any of the matrices are not of size 16, or are null.
+     *
+     * @param model          4x4 model matrix of the object to be drawn (global/world)
+     * @param view           4x4 camera view matrix (brings objects to camera origin and
+     *                       orientation)
+     * @param projection     4x4 projection matrix
+     * @param viewPortWidth  width of viewport of GLSurfaceView
+     * @param viewPortHeight height of viewport of GLSurfaceView
+     * @return 3x3 matrix that puts a 2D objects in perspective on a Canvas
+     */
+
+    public static Matrix createPerspectiveMatrix(float[] model, float[] view, float[] projection,
+                                                 float viewPortWidth, float viewPortHeight) {
+        float[] viewPort = createViewportMatrix(viewPortWidth, viewPortHeight);
+        float[] planeStickRotation = createXYtoXZRotationMatrix();
+        float[][] matrices = {planeStickRotation, model, view, projection, viewPort};
+        return createMatrixFrom4x4Array(matrices);
+    }
+
+    /**
+     * Returns a 16-float matrix in column-major order that represents a viewport matrix given
+     * the width and height of the viewport.
+     *
+     * @param width  width of viewport
+     * @param height height of viewport
+     */
+
+    public static float[] createViewportMatrix(float width, float height) {
+        float[] viewPort = new float[16];
+        android.opengl.Matrix.setIdentityM(viewPort, 0);
+        android.opengl.Matrix.translateM(viewPort, 0, width / 2, height / 2, 0);
+        android.opengl.Matrix.scaleM(viewPort, 0, width / 2, -height / 2, 0);
+        return viewPort;
+    }
+
+    /**
+     * Returns a 16-float matrix in column-major order that is used to rotate objects from the
+     * XY plane to the XZ plane. This is useful given that objects drawn on the Canvas are on the
+     * XY plane.
+     * In order to get objects to appear as if they are sticking on planes/ceilings/walls, we need
+     * to rotate them from the XY plane to the XZ plane.
+     */
+
+    public static float[] createXYtoXZRotationMatrix() {
+        float[] rotation = new float[16];
+        android.opengl.Matrix.setIdentityM(rotation, 0);
+        android.opengl.Matrix.rotateM(rotation, 0, 90, 1, 0, 0);
+        return rotation;
+    }
+
+
+    /**
+     * Returns an android.graphics.Matrix resulting from a 16-float matrix array in column-major
+     * order.
+     * Undefined behavior when the array is not of size 16 or is null.
+     *
+     * @param m4 16-float matrix in column-major order
+     */
+
+    public static Matrix createMatrixFrom4x4(float[] m4) {
+        float[] m3 = matrix4x4ToMatrix3x3(m4);
+        return createMatrixFrom3x3(m3);
+    }
+
+    /**
+     * Returns an android.graphics.Matrix resulting from the concatenation of 16-float matrices
+     * in column-major order from left to right.
+     * e.g: m4Array = {m1, m2, m3} --> returns m = m3 * m2 * m1
+     * Undefined behavior when the array is empty, null, or contains arrays not of size 9 (or null)
+     *
+     * @param m4Array array of 16-float matrices in column-major order
+     */
+
+    public static Matrix createMatrixFrom4x4Array(float[][] m4Array) {
+        float[] result = multiplyMatrices4x4(m4Array);
+        return createMatrixFrom4x4(result);
+    }
+
+    /**
+     * Returns 4-float array resulting from the multiplication of a Vector of 4 floats
+     * with a 4x4 float Matrix. The return is essentially m4 * v4, with perspective-divide applied
+     * if perspectiveDivide is true
+     * @param m4                16-float matrix in column-major order
+     * @param v4                4-float vector
+     * @param perspectiveDivide if true, divide return value by the w-coordinate
+     * @return                  4-float array resulting from the multiplication
+     */
+
+    public static float[] multiplyMatrixVector(float[] m4, float[] v4, boolean perspectiveDivide) {
+        float[] result = new float[4];
+        android.opengl.Matrix.multiplyMV(result, 0, m4, 0, v4, 0);
+        if (perspectiveDivide) {
+            return new float[] {result[0] / result[3], result[1] / result[3],
+                                result[2] / result[3], 1};
+        }
+
+        return new float[] {result[0], result[1], result[2], result[3]};
+    }
+
+    /**
+     * Returns a 16-float matrix in column-major order resulting from the multiplication of matrices
+     * e.g: m4Array = {m1, m2, m3} --> returns m = m3 * m2 * m1
+     * Undefined behavior when the array is empty, null, or contains arrays not of size 9 (or null)
+     *
+     * @param m4Array array of 16-float matrices in column-major order
+     */
+
+    public static float[] multiplyMatrices4x4(float[][] m4Array) {
+        float[] result = new float[16];
+        android.opengl.Matrix.setIdentityM(result, 0);
+        float[] rhs = result;
+        for (int i = 0; i < m4Array.length; i++) {
+            float[] lhs = m4Array[i];
+            android.opengl.Matrix.multiplyMM(result, 0, lhs, 0, rhs, 0);
+            rhs = result;
+        }
+        return result;
+    }
+
+    /******************* PRIVATE FUNCTIONS ***********************/
+
+    /**
+     * Returns an android.graphics.Matrix resulting from a 9-float matrix array in row-major order.
+     * Undefined behavior when the array is not of size 9 or is null.
+     *
+     * @param m3 9-float matrix array in row-major order
+     */
+
+    private static Matrix createMatrixFrom3x3(float[] m3) {
+        Matrix m = new Matrix();
+        m.setValues(m3);
+        return m;
+    }
+
+    /**
+     * Returns a 9-float matrix in row-major order given a 16-float matrix in column-major order.
+     * This will drop the Z column and row.
+     * Undefined behavior when the array is not of size 9 or is null.
+     *
+     * @param m4 16-float matrix in column-major order
+     */
+
+    private static float[] matrix4x4ToMatrix3x3(float[] m4) {
+        float[] m3 = new float[9];
+
+        int j = 0;
+        for (int i = 0; i < 7; i = i + 3) {
+            if (j == 2) {
+                j++; //skip row #3
+            }
+            m3[i] = m4[j];
+            m3[i + 1] = m4[j + 4];
+            m3[i + 2] = m4[j + 12];
+            j++;
+        }
+        return m3;
+    }
+}