[OpenGL ES] VBO 頂點緩沖物件

VBO： Vertex Buffer object 頂點緩沖物件

為什么要用VBO?

不使用VBO時，每次繪制（ glDrawArrays ）圖形時都是從本地記憶體處獲取頂點資料然后傳輸給OpenGL來繪制，這樣就會頻繁的操作CPU->GPU增大開銷，從而降低效率，使用VBO，可以把頂點資料快取到GPU開辟的一段記憶體中，然后使用時不必再從本地獲取，而是直接從顯存中獲取，這樣就能提升繪制的效率，

創建VBO

1、創建VBO
GLES20.glGenBuffers(1, vbos, 0);

2、系結VBO
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vbos[0]);

3、分配VBO需要的快取大小
GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, vertex.length * 4,null, GLES20. GL_STATIC_DRAW);

4、為VBO設定頂點資料的值
GLES20.glBufferSubData(GLES20.GL_ARRAY_BUFFER, 0, vertexData.length * 4, vertexBuffer);

5、解綁VBO
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);

使用VBO

1、系結VBO
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vbos[0]);

2、設定頂點資料
GLES20.glVertexAttribPointer(vPosition, 2, GLES20.GL_FLOAT, false, 8, 0);

3、解綁VBO
GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);

GGLTextureRender    VBO的使用

package com.example.opengldemo;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES20;
import android.opengl.GLUtils;

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

public class GGLTextureRender implements MyGLSurfaceView.MyGLRender {

    private Context context;
    //頂點坐標
    private final float[] vertexData = {
            -1f, -1f,
            1f, -1f,
            -1f, 1f,
            1f, 1f
    };

    //紋理坐標
    private final float[] fragmentData = {
            0f, 1f,
            1f, 1f,
            0f, 0f,
            1f, 0f
    };

    private FloatBuffer vertexBuffer;
    private FloatBuffer fragmentBuffer;

    public GGLTextureRender(Context context) {
        this.context = context;

        vertexBuffer = ByteBuffer.allocateDirect(vertexData.length * 4)
                .order(ByteOrder.nativeOrder())
                .asFloatBuffer()
                .put(vertexData);
        vertexBuffer.position(0);

        fragmentBuffer = ByteBuffer.allocateDirect(fragmentData.length * 4)
                .order(ByteOrder.nativeOrder())
                .asFloatBuffer()
                .put(fragmentData);
        fragmentBuffer.position(0);
    }

    private int program;

    private int vPosition;
    private int fPosition;

    private int textureid;
    private int sampler;

    private int vboId;

    @Override
    public void onSufaceCreated() {
        String vertexSource = GShaderUtil.getRawResource(context, R.raw.vertex_shader);
        String fragmentSource = GShaderUtil.getRawResource(context, R.raw.fragment_shader);
        program = GShaderUtil.createProgram(vertexSource, fragmentSource);

        if (program > 0) {
            //頂點坐標
            vPosition = GLES20.glGetAttribLocation(program, "v_Position");
            //紋理坐標
            fPosition = GLES20.glGetAttribLocation(program, "f_Position");

            sampler = GLES20.glGetUniformLocation(program,"sTexture");

            /**********************創建VBO-START************************************************/
            int [] vbos = new int[1];
            GLES20.glGenBuffers(1, vbos, 0);
            vboId = vbos[0];
            //系結
            GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vboId);
            //分配記憶體
            GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, vertexData.length*4 + fragmentData.length*4,
                    null,GLES20. GL_STATIC_DRAW);
            //快取到顯存
            GLES20.glBufferSubData(GLES20.GL_ARRAY_BUFFER, 0, vertexData.length * 4, vertexBuffer);
            GLES20.glBufferSubData(GLES20.GL_ARRAY_BUFFER, vertexData.length * 4, fragmentData.length*4,
                    fragmentBuffer);
            //解綁
            GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
           /******************************VBO-END***********************************************/

            int[] textureIds = new int[1];
            GLES20.glGenTextures(1, textureIds, 0);
            textureid = textureIds[0];


            GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureid);
            GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
            GLES20.glUniform1i(sampler, 0);

            //設定環繞過濾方法
            GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_REPEAT);
            GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_REPEAT);

            GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
            GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);

            Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.androids);
            if (bitmap == null) {
                return;
            }
            GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);
            //回收
            bitmap.recycle();
            bitmap = null;

            //解綁
            GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
        }
    }

    @Override
    public void onSufaceChanged(int width, int height) {
        GLES20.glViewport(0,0,width,height);
    }

    @Override
    public void onDrawFrame() {
        //清屏
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
        //使用顏色清屏
        GLES20.glClearColor(1.0f, 0.0f, 0.0f, 1.0f);

        //使用program
        GLES20.glUseProgram(program);

        //系結
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureid);

        /**********************VBO-START************************************************/
        //系結VBO
        GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, vboId);
        /**********************VBO-END************************************************/

        //使用頂點坐標
        GLES20.glEnableVertexAttribArray(vPosition);
        /**********************VBO-START************************************************/
        //傳0 從VBO中取值
        GLES20.glVertexAttribPointer(vPosition, 2, GLES20.GL_FLOAT, false, 8, 0);
        /**********************VBO-END************************************************/

        GLES20.glEnableVertexAttribArray(fPosition);

        /**********************VBO-START************************************************/
        //VBO
        GLES20.glVertexAttribPointer(fPosition, 2, GLES20.GL_FLOAT, false, 8,
                vertexData.length * 4);
        /**********************VBO-END************************************************/

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
        //解綁
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);

        /**********************VBO-START************************************************/
        //解綁VBO
        GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
        /**********************VBO-END************************************************/
    }
}