Android入门（4）OpenGL ES编程环境搭建

一、提要

       偶然在Android developers看到这篇教程，遍一步步做了下来，下面是一点记录。

二、在Android中绘制OpenGL es的方法

     为了在Android应用中使用OpenGL绘制图形，我们必须创建一个View容器。一个最直接的方法就是implement GLSurfaceView 和a GLSurfaceView.Renderer。前者就是容器，后者控制View中渲染的内容。

    还有两种方法是SurfaceView和TextureView，但有点小复杂。

    最终效果：










三、必要的声明

在manifest文件中添加下面的代码：

<uses-feature
        android:glEsVersion="0x00020000"
        android:required="true" />

    <supports-gl-texture android:name="GL_OES_compressed_ETC1_RGB8_texture" />
    <supports-gl-texture android:name="GL_OES_compressed_paletted_texture" />

前面是声明OpenGL的版本，后两行是声明贴图的类型。

四、主Activity类

package com.example.opengles;

import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.view.Menu;

public class OpenGLActivity extends Activity {

	private GLSurfaceView mGLView;
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		mGLView = new MyGLSurfaceView(this);
		setContentView(mGLView);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.activity_open_gl, menu);
		return true;
	}
	@Override
	protected void onPause() {
		super.onPause();
		// The following call pauses the rendering thread.
		// If your OpenGL application is memory intensive,
		// you should consider de-allocating objects that
		// consume significant memory here.
		mGLView.onPause();
	}

	@Override
	protected void onResume() {
		super.onResume();
		// The following call resumes a paused rendering thread.
		// If you de-allocated graphic objects for onPause()
		// this is a good place to re-allocate them.
		mGLView.onResume();
	}
}

class MyGLSurfaceView extends GLSurfaceView {

	public MyGLSurfaceView(Context context){
		super(context);



		// Create an OpenGL ES 2.0 context.
		setEGLContextClientVersion(2);

		// Set the Renderer for drawing on the GLSurfaceView
				setRenderer(new MyRender());
		// Render the view only when there is a change in the drawing data
		setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
		
	}


}

四、渲染器类

package com.example.opengles;


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

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLES20;
import android.opengl.GLSurfaceView;

public class MyRender implements GLSurfaceView.Renderer {

	private Triangle mTriangle;
	@Override
	public void onDrawFrame(GL10 gl) {
		// TODO Auto-generated method stub
        // Draw background color
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
        // Draw triangle
       mTriangle.draw();
	}

	@Override
	public void onSurfaceChanged(GL10 gl, int width, int height) {
		// TODO Auto-generated method stub
		  // Adjust the viewport based on geometry changes,
        // such as screen rotation
        GLES20.glViewport(0, 0, width, height);
	}
    public static int loadShader(int type, String shaderCode){

        // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
        // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
        int shader = GLES20.glCreateShader(type);

        // add the source code to the shader and compile it
        GLES20.glShaderSource(shader, shaderCode);
        GLES20.glCompileShader(shader);

        return shader;
    }


	@Override
	public void onSurfaceCreated(GL10 gl, EGLConfig config) {
		// TODO Auto-generated method stub
	    // Set the background frame color
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        mTriangle = new Triangle();
	}
	

}

class Triangle {

    private final String vertexShaderCode =
        "attribute vec4 vPosition;" +
        "void main() {" +
        "  gl_Position = vPosition;" +
        "}";

    private final String fragmentShaderCode =
        "precision mediump float;" +
        "uniform vec4 vColor;" +
        "void main() {" +
        "  gl_FragColor = vColor;" +
        "}";

    private final FloatBuffer vertexBuffer;
    private final int mProgram;
    private int mPositionHandle;
    private int mColorHandle;

    // number of coordinates per vertex in this array
    static final int COORDS_PER_VERTEX = 3;
    static float triangleCoords[] = { // in counterclockwise order:
         0.0f,  0.622008459f, 0.0f,   // top
        -0.5f, -0.311004243f, 0.0f,   // bottom left
         0.5f, -0.311004243f, 0.0f    // bottom right
    };
    private final int vertexCount = triangleCoords.length / COORDS_PER_VERTEX;
    private final int vertexStride = COORDS_PER_VERTEX * 4; // bytes per vertex

    // Set color with red, green, blue and alpha (opacity) values
    float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

    public Triangle() {
        // initialize vertex byte buffer for shape coordinates
        ByteBuffer bb = ByteBuffer.allocateDirect(
                // (number of coordinate values * 4 bytes per float)
                triangleCoords.length * 4);
        // use the device hardware's native byte order
        bb.order(ByteOrder.nativeOrder());

        // create a floating point buffer from the ByteBuffer
        vertexBuffer = bb.asFloatBuffer();
        // add the coordinates to the FloatBuffer
        vertexBuffer.put(triangleCoords);
        // set the buffer to read the first coordinate
        vertexBuffer.position(0);

        // prepare shaders and OpenGL program
        int vertexShader = MyRender.loadShader(GLES20.GL_VERTEX_SHADER,
                                                   vertexShaderCode);
        int fragmentShader = MyRender.loadShader(GLES20.GL_FRAGMENT_SHADER,
                                                     fragmentShaderCode);

        mProgram = GLES20.glCreateProgram();             // create empty OpenGL Program
        GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
        GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
        GLES20.glLinkProgram(mProgram);                  // create OpenGL program executables

    }

    public void draw() {
        // Add program to OpenGL environment
        GLES20.glUseProgram(mProgram);

        // get handle to vertex shader's vPosition member
        mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");

        // Enable a handle to the triangle vertices
        GLES20.glEnableVertexAttribArray(mPositionHandle);

        // Prepare the triangle coordinate data
        GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX,
                                     GLES20.GL_FLOAT, false,
                                     vertexStride, vertexBuffer);

        // get handle to fragment shader's vColor member
        mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

        // Set color for drawing the triangle
        GLES20.glUniform4fv(mColorHandle, 1, color, 0);

        // Draw the triangle
        GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);

        // Disable vertex array
        GLES20.glDisableVertexAttribArray(mPositionHandle);
    }
}

       这个类中最重要的三个函数是

onSurfaceCreated() - 初始化OpenGL环境

onDrawFrame() - 绘制View

onSurfaceChanged() - 当View发生改变的时候掉用是不是很熟悉，就是Qt的OpenGL中的paintGL() ，resizeGL() ，initializeGL() 。

      最后运行的时候会在屏幕上绘制一个三角形，用的是ShaderLanguage，这个就直接copy了，当然也可以用那种比较原始的一个个定义点定义颜色来绘图。

     注意：OpenGL的程序在模拟器中没办法跑起来，需要真机调试。

五、参考资料

android develop：http://developer.android.com/training/graphics/opengl/environment.html