在OpenGL中无法在android中创建三角形

Question

我一直在尝试使用开发者网站上的android opengl 2.0教程创建一个基本三角形。但无法创造三角形。只创建了GLSurface，但没有渲染Triangle。我使用Android Studio 1.2.1.1与Target SDK版本22并在Android 4.4.4上运行。任何人都可以指出我的错误吗？

import android.content.Context;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;

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

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


public class MainActivity extends AppCompatActivity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public class MyGLSurfaceView extends GLSurfaceView {

        private final MyGLRenderer mRenderer;
        public MyGLSurfaceView(Context context) {
            super(context);
            setEGLContextClientVersion(2);
            mRenderer = new MyGLRenderer();
            setRenderer(mRenderer);
            setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
        }
    }

    public static class MyGLRenderer implements GLSurfaceView.Renderer {

        private Triangle mTriangle;

        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            mTriangle = new Triangle();
            GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        }

        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            GLES20.glViewport(0, 0, width, height);
        }

        @Override
        public void onDrawFrame(GL10 gl) {
            GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
            mTriangle.draw();
            //mSquare.draw();
        }

        public static int loadShader(int type, String shaderCode) {
            int shader = GLES20.glCreateShader(type);
            GLES20.glShaderSource(shader, shaderCode);
            GLES20.glCompileShader(shader);
            return shader;
        }
    }

    public static class Triangle {
        private FloatBuffer vertexBuffer;
        static final int COORDS_PER_VERTEX = 3;
        float[] triangleCoords =

                {
                        0.0f, 0.622008459f, 0.0f,
                        -0.5f, -0.311004243f, 0.0f,
                        0.5f, -0.311004243f, 0.0f
                };

        float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

        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 int mProgram;
        private int mPositionHandle;
        private int mColorHandle;
        private final int vertexCount = triangleCoords.length/COORDS_PER_VERTEX;
        private final int vertexStride = COORDS_PER_VERTEX*4;
        public Triangle() {
            ByteBuffer bb = ByteBuffer.allocateDirect(triangleCoords.length * 4);
            bb.order(ByteOrder.nativeOrder());
            vertexBuffer = bb.asFloatBuffer();
            vertexBuffer.put(triangleCoords);
            vertexBuffer.position();
            int vertexShader = MyGLRenderer.loadShader(GLES20.GL_VERTEX_SHADER,vertexShaderCode);
            int fragmentShader = MyGLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,fragmentShaderCode);
            mProgram = GLES20.glCreateProgram();
            GLES20.glAttachShader(mProgram,vertexShader);
            GLES20.glAttachShader(mProgram,fragmentShader);
            GLES20.glLinkProgram(mProgram);
        }

        public void draw() {
            GLES20.glUseProgram(mProgram);
            mPositionHandle = GLES20.glGetAttribLocation(mProgram,"vPosition");
            GLES20.glEnableVertexAttribArray(mPositionHandle);
            GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, vertexStride, vertexBuffer);
            mColorHandle=GLES20.glGetUniformLocation(mProgram, "vColor");
            GLES20.glUniform4fv(mColorHandle, 1, color, 0);
            GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);
            GLES20.glEnableVertexAttribArray(mPositionHandle);
        }
    }
}

Answer 1

该问题的解决方案是将Reto Koradi

建议将vertexBuffer.position（）替换为vertexBuffer.position（0）