第3章（第24讲） 示例24-- OpenGL绘制功能

分类：C#、Android、百度地图应用； 日期：2016-02-04

一、简介

百度地图SDK为广大开发者开放了OpenGL绘制接口，帮助开发者在地图上实现更灵活的样式绘制，丰富地图使用效果体验。

二、运行截图

简介：介绍如何使用OpenGL在地图上实现自定义绘制。

详述：

（1）利用OpenGL绘制基本折线；

（2）利用OpenGL在地图上进行纹理绘制；

本示例运行截图如下：

三、设计步骤

1、添加demo24_opengl.xml文件

在layout文件夹下添加该文件，然后将代码改为下面的内容：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
  <com.baidu.mapapi.map.TextureMapView
      android:id="@+id/bmapView"
      android:layout_width="match_parent"
      android:layout_height="fill_parent" />
</RelativeLayout>

2、添加Demo24OpenGL.cs文件

在SrcSdkDemos文件夹下添加该文件，然后将代码改为下面的内容：

using Android.App;
using Android.OS;
using Com.Baidu.Mapapi.Map;
using Com.Baidu.Mapapi.Model;
using Android.Graphics;
using Android.Util;
using System.Collections.Generic;
using Javax.Microedition.Khronos.Opengles;
using Java.Nio;
using Android.Opengl;

namespace BdMapV371Demos.SrcSdkDemos
{
    /// <summary>
    /// 此demo用来展示如何在地图绘制的每帧中再额外绘制一些用户自己的内容
    /// </summary>
    [Activity(Label = "@string/demo_name_opengl")]
    public class Demo24OpenGL : Activity, BaiduMap.IOnMapDrawFrameCallback
    {
        // 地图相关
        private TextureMapView mMapView;
        private BaiduMap mBaiduMap;
        private Bitmap bitmap;
        private LatLng latlng1 = new LatLng(39.97923, 116.357428);
        private LatLng latlng2 = new LatLng(39.94923, 116.397428);
        private LatLng latlng3 = new LatLng(39.96923, 116.437428);
        private IList<LatLng> latLngPolygon;
        private float[] vertexs;
        private FloatBuffer vertexBuffer;
        private int textureId = -1;
        private readonly string LTAG = "Demo24OpenGL";

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.demo24_opengl);
            mMapView = FindViewById<TextureMapView>(Resource.Id.bmapView);
            mBaiduMap = mMapView.Map;
            latLngPolygon = new List<LatLng>()
            {
                latlng1,latlng2,latlng3
            };
            mBaiduMap.SetOnMapDrawFrameCallback(this);
            bitmap = BitmapFactory.DecodeResource(Resources,
                Resource.Drawable.ground_overlay);
        }

        protected override void OnPause()
        {
            mMapView.OnPause();
            base.OnPause();
        }
        protected override void OnResume()
        {
            mMapView.OnResume();
            textureId = -1;
            base.OnResume();
        }

        protected override void OnDestroy()
        {
            mMapView.OnDestroy();
            base.OnDestroy();
        }

        public void OnMapDrawFrame(IGL10 gl, MapStatus drawingMapStatus)
        {
            if (mBaiduMap.Projection != null)
            {
                calPolylinePoint(drawingMapStatus);
                drawPolyline(gl, Color.Argb(255, 255, 0, 0), vertexBuffer, 10, 3,
                        drawingMapStatus);
                drawTexture(gl, bitmap, drawingMapStatus);
            }
        }
        public void calPolylinePoint(MapStatus mspStatus)
        {
            PointF[] polyPoints = new PointF[latLngPolygon.Count];
            vertexs = new float[3 * latLngPolygon.Count];
            int i = 0;
            foreach (LatLng xy in latLngPolygon)
            {
                polyPoints[i] = mBaiduMap.Projection.ToOpenGLLocation(xy, mspStatus);
                vertexs[i * 3] = polyPoints[i].X;
                vertexs[i * 3 + 1] = polyPoints[i].Y;
                vertexs[i * 3 + 2] = 0.0f;
                i++;
            }
            for (int j = 0; j < vertexs.Length; j++)
            {
                Log.Debug(LTAG, "vertexs[" + j + "]: " + vertexs[j]);
            }
            vertexBuffer = makeFloatBuffer(vertexs);
        }

        private FloatBuffer makeFloatBuffer(float[] fs)
        {
            ByteBuffer bb = ByteBuffer.AllocateDirect(fs.Length * 4);
            bb.Order(ByteOrder.NativeOrder());
            FloatBuffer fb = bb.AsFloatBuffer();
            fb.Put(fs);
            fb.Position(0);
            return fb;
        }

        private void drawPolyline(IGL10 gl, int color, FloatBuffer lineVertexBuffer,
                float lineWidth, int pointSize, MapStatus drawingMapStatus)
        {

            gl.GlEnable(GL10.GlBlend);
            gl.GlEnableClientState(GL10.GlVertexArray);

            gl.GlBlendFunc(GL10.GlSrcAlpha, GL10.GlOneMinusSrcAlpha);

            float colorA = Color.GetAlphaComponent(color) / 255f;
            float colorR = Color.GetRedComponent(color) / 255f;
            float colorG = Color.GetGreenComponent(color) / 255f;
            float colorB = Color.GetBlueComponent(color) / 255f;

            gl.GlVertexPointer(3, GL10.GlFloat, 0, lineVertexBuffer);
            gl.GlColor4f(colorR, colorG, colorB, colorA);
            gl.GlLineWidth(lineWidth);
            gl.GlDrawArrays(GL10.GlLineStrip, 0, pointSize);

            gl.GlDisable(GL10.GlBlend);
            gl.GlDisableClientState(GL10.GlVertexArray);
        }

        /// <summary>
        /// 使用opengl坐标绘制
        /// </summary>
        /// <param name="gl"></param>
        /// <param name="bitmap"></param>
        /// <param name="drawingMapStatus"></param>
        public void drawTexture(IGL10 gl, Bitmap bitmap, MapStatus drawingMapStatus)
        {
            PointF p1 = mBaiduMap.Projection.ToOpenGLLocation(latlng2,
                    drawingMapStatus);
            PointF p2 = mBaiduMap.Projection.ToOpenGLLocation(latlng3,
                    drawingMapStatus);
            ByteBuffer byteBuffer = ByteBuffer.AllocateDirect(4 * 3 * 4);
            byteBuffer.Order(ByteOrder.NativeOrder());
            FloatBuffer vertices = byteBuffer.AsFloatBuffer();
            vertices.Put(new float[] { p1.X, p1.Y, 0.0f, p2.X, p1.Y, 0.0f, p1.X,
                p2.Y, 0.0f, p2.X, p2.Y, 0.0f });

            ByteBuffer indicesBuffer = ByteBuffer.AllocateDirect(6 * 2);
            indicesBuffer.Order(ByteOrder.NativeOrder());
            ShortBuffer indices = indicesBuffer.AsShortBuffer();
            indices.Put(new short[] { 0, 1, 2, 1, 2, 3 });

            ByteBuffer textureBuffer = ByteBuffer.AllocateDirect(4 * 2 * 4);
            textureBuffer.Order(ByteOrder.NativeOrder());
            FloatBuffer texture = textureBuffer.AsFloatBuffer();
            texture.Put(new float[] { 0, 1f, 1f, 1f, 0f, 0f, 1f, 0f });

            indices.Position(0);
            vertices.Position(0);
            texture.Position(0);

            // 生成纹理
            if (textureId == -1)
            {
                int[] textureIds = new int[1];
                gl.GlGenTextures(1, textureIds, 0);
                textureId = textureIds[0];
                Log.Debug(LTAG, "textureId: " + textureId);
                gl.GlBindTexture(GL10.GlTexture2d, textureId);
                GLUtils.TexImage2D(GL10.GlTexture2d, 0, bitmap, 0);
                gl.GlTexParameterf(GL10.GlTexture2d, GL10.GlTextureMinFilter, GL10.GlNearest);
                gl.GlTexParameterf(GL10.GlTexture2d, GL10.GlTextureMagFilter, GL10.GlNearest);
                gl.GlBindTexture(GL10.GlTexture2d, 0);
            }

            gl.GlEnable(GL10.GlTexture2d);
            gl.GlEnableClientState(GL10.GlVertexArray);
            gl.GlEnableClientState(GL10.GlTextureCoordArray);
            gl.GlEnable(GL10.GlBlend);
            gl.GlBlendFunc(GL10.GlSrcAlpha, GL10.GlOneMinusSrcAlpha);
            gl.GlColor4f(1.0f, 1.0f, 1.0f, 1.0f);

            // 绑定纹理ID
            gl.GlBindTexture(GL10.GlTexture2d, textureId);
            gl.GlVertexPointer(3, GL10.GlFloat, 0, vertices);
            gl.GlTexCoordPointer(2, GL10.GlFloat, 0, texture);
            gl.GlDrawElements(GL10.GlTriangleStrip, 6, GL10.GlUnsignedShort, indices);
            gl.GlDisable(GL10.GlTexture2d);
            gl.GlDisableClientState(GL10.GlVertexArray);
            gl.GlDisableClientState(GL10.GlTextureCoordArray);
            gl.GlDisable(GL10.GlBlend);
        }
    }
}

3、修改MainActivity.cs文件

在MainActivity.cs文件的demos字段定义中，去掉【示例24】下面的注释。

运行观察效果。