samples/ApiDemos/src/com/example/android/apis/graphics/spritetext/Grid.java

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.graphics.spritetext;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.CharBuffer;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

/**
 * A 2D rectangular mesh. Can be drawn textured or untextured.
 *
 */
class Grid {

    public Grid(int w, int h) {
        if (w < 0 || w >= 65536) {
            throw new IllegalArgumentException("w");
        }
        if (h < 0 || h >= 65536) {
            throw new IllegalArgumentException("h");
        }
        if (w * h >= 65536) {
            throw new IllegalArgumentException("w * h >= 65536");
        }

        mW = w;
        mH = h;
        int size = w * h;
        final int FLOAT_SIZE = 4;
        final int CHAR_SIZE = 2;
        mVertexBuffer = ByteBuffer.allocateDirect(FLOAT_SIZE * size * 3)
            .order(ByteOrder.nativeOrder()).asFloatBuffer();
        mTexCoordBuffer = ByteBuffer.allocateDirect(FLOAT_SIZE * size * 2)
            .order(ByteOrder.nativeOrder()).asFloatBuffer();

        int quadW = mW - 1;
        int quadH = mH - 1;
        int quadCount = quadW * quadH;
        int indexCount = quadCount * 6;
        mIndexCount = indexCount;
        mIndexBuffer = ByteBuffer.allocateDirect(CHAR_SIZE * indexCount)
            .order(ByteOrder.nativeOrder()).asCharBuffer();

        /*
         * Initialize triangle list mesh.
         *
         *     [0]-----[  1] ...
         *      |    /   |
         *      |   /    |
         *      |  /     |
         *     [w]-----[w+1] ...
         *      |       |
         *
         */

        {
            int i = 0;
            for (int y = 0; y < quadH; y++) {
                for (int x = 0; x < quadW; x++) {
                    char a = (char) (y * mW + x);
                    char b = (char) (y * mW + x + 1);
                    char c = (char) ((y + 1) * mW + x);
                    char d = (char) ((y + 1) * mW + x + 1);

                    mIndexBuffer.put(i++, a);
                    mIndexBuffer.put(i++, b);
                    mIndexBuffer.put(i++, c);

                    mIndexBuffer.put(i++, b);
                    mIndexBuffer.put(i++, c);
                    mIndexBuffer.put(i++, d);
                }
            }
        }

    }

    void set(int i, int j, float x, float y, float z, float u, float v) {
        if (i < 0 || i >= mW) {
            throw new IllegalArgumentException("i");
        }
        if (j < 0 || j >= mH) {
            throw new IllegalArgumentException("j");
        }

        int index = mW * j + i;

        int posIndex = index * 3;
        mVertexBuffer.put(posIndex, x);
        mVertexBuffer.put(posIndex + 1, y);
        mVertexBuffer.put(posIndex + 2, z);

        int texIndex = index * 2;
        mTexCoordBuffer.put(texIndex, u);
        mTexCoordBuffer.put(texIndex + 1, v);
    }

    public void draw(GL10 gl, boolean useTexture) {
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mVertexBuffer);

        if (useTexture) {
            gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
            gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, mTexCoordBuffer);
            gl.glEnable(GL10.GL_TEXTURE_2D);
        } else {
            gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
            gl.glDisable(GL10.GL_TEXTURE_2D);
        }

        gl.glDrawElements(GL10.GL_TRIANGLES, mIndexCount,
                GL10.GL_UNSIGNED_SHORT, mIndexBuffer);
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    }

    private FloatBuffer mVertexBuffer;
    private FloatBuffer mTexCoordBuffer;
    private CharBuffer mIndexBuffer;

    private int mW;
    private int mH;
    private int mIndexCount;
}