jme3-core: add a CenterQuad class based on the one in jme3-vr (#1704)

* jme3-core:  add a CenterQuad class based on the one in jme3-vr

* CenterQuad:  updateGeometry() invokes setStatic() for the constructor

jme3-core/src/main/java/com/jme3/scene/shape/CenterQuad.java

@@ -0,0 +1,189 @@
+/*
+ * Copyright (c) 2009-2021 jMonkeyEngine
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of 'jMonkeyEngine' nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.jme3.scene.shape;
+
+import com.jme3.export.InputCapsule;
+import com.jme3.export.JmeExporter;
+import com.jme3.export.JmeImporter;
+import com.jme3.export.OutputCapsule;
+import com.jme3.scene.Mesh;
+import com.jme3.scene.VertexBuffer.Type;
+import java.io.IOException;
+
+/**
+ * A static, indexed, Triangles-mode mesh for an axis-aligned rectangle in the
+ * X-Y plane.
+ *
+ * <p>The rectangle extends from (-width/2, -height/2, 0) to
+ * (width/2, height/2, 0) with normals set to (0,0,1).
+ *
+ * <p>This differs from {@link com.jme3.scene.shape.Quad} because it puts
+ * (0,0,0) at the rectangle's center instead of in a corner.
+ *
+ * @author Kirill Vainer
+ */
+public class CenterQuad extends Mesh {
+
+    private float width;
+    private float height;
+
+    /**
+     * For serialization only. Do not use.
+     */
+    protected CenterQuad() {
+    }
+
+    /**
+     * Instantiate an unflipped quad in the X-Y plane with the specified width
+     * and height.
+     *
+     * @param width the desired X extent or width
+     * @param height the desired Y extent or height
+     */
+    public CenterQuad(float width, float height) {
+        updateGeometry(width, height, false);
+    }
+
+    /**
+     * Instantiate a quad in the X-Y plane with the specified width and height.
+     *
+     * @param width the desired X extent or width
+     * @param height the desired Y extent or height
+     * @param flipCoords true to flip the texture coordinates (v=0 when
+     *     y=height/2) or false to leave them unflipped (v=1 when y=height/2)
+     */
+    public CenterQuad(float width, float height, boolean flipCoords) {
+        updateGeometry(width, height, flipCoords);
+    }
+
+    /**
+     * Returns the height (or Y extent).
+     *
+     * @return the height
+     */
+    public float getHeight() {
+        return height;
+    }
+
+    /**
+     * Returns the width (or X extent).
+     *
+     * @return the width
+     */
+    public float getWidth() {
+        return width;
+    }
+
+    /**
+     * De-serializes from the specified importer, for example when loading from
+     * a J3O file.
+     *
+     * @param importer the importer to use (not null)
+     * @throws IOException from the importer
+     */
+    @Override
+    public void read(JmeImporter importer) throws IOException {
+        super.read(importer);
+        InputCapsule capsule = importer.getCapsule(this);
+
+        width = capsule.readFloat("width", 0f);
+        height = capsule.readFloat("height", 0f);
+    }
+
+    /**
+     * Serializes to the specified exporter, for example when saving to a J3O
+     * file. The current instance is unaffected.
+     *
+     * @param exporter the exporter to use (not null)
+     * @throws IOException from the exporter
+     */
+    @Override
+    public void write(JmeExporter exporter) throws IOException {
+        super.write(exporter);
+        OutputCapsule capsule = exporter.getCapsule(this);
+
+        capsule.write(width, "width", 0f);
+        capsule.write(height, "height", 0f);
+    }
+
+    private void updateGeometry(float width, float height, boolean flipCoords) {
+        this.width = width;
+        this.height = height;
+
+        float x = width / 2;
+        float y = height / 2;
+        setBuffer(Type.Position, 3, new float[]{
+            -x, -y, 0f,
+            +x, -y, 0f,
+            +x, +y, 0f,
+            -x, +y, 0f
+        });
+
+        if (flipCoords) {
+            setBuffer(Type.TexCoord, 2, new float[]{
+                0f, 1f,
+                1f, 1f,
+                1f, 0f,
+                0f, 0f
+            });
+        } else {
+            setBuffer(Type.TexCoord, 2, new float[]{
+                0f, 0f,
+                1f, 0f,
+                1f, 1f,
+                0f, 1f
+            });
+        }
+
+        setBuffer(Type.Normal, 3, new float[]{
+            0f, 0f, 1f,
+            0f, 0f, 1f,
+            0f, 0f, 1f,
+            0f, 0f, 1f
+        });
+
+        if (width * height < 0f) {
+            setBuffer(Type.Index, 3, new byte[]{
+                0, 2, 1,
+                0, 3, 2
+            });
+        } else {
+            setBuffer(Type.Index, 3, new byte[]{
+                0, 1, 2,
+                0, 2, 3
+            });
+        }
+
+        updateBound();
+        setStatic();
+    }
+}