错误剩余（）<count <在GLSurfaceView.Renderer中需要

Question

I am trying to create a triangle in OpenGL ES. But app is crashing for line gl.glDrawElements(GL10.GL_TRIANGLES, pIndex.length, GL10.GL_UNSIGNED_SHORT, pBuff); in below code inside draw method.

public class GLTriangleEx {

    private float vertices[] = {
        0f, 1f, // point 0
        1f, -1f, // point 1
        -1f, -1f // point 2
    };

    private  FloatBuffer vertBuff;

    private short[] pIndex = {0, 1, 2};

    private ShortBuffer pBuff;

    public GLTriangleEx() {
        ByteBuffer bBuff = ByteBuffer.allocateDirect(vertices.length * 4);
        bBuff.order(ByteOrder.nativeOrder());
        vertBuff = bBuff.asFloatBuffer();
        vertBuff.put(vertices);
        vertBuff.position(0);

        ByteBuffer pbBuff = ByteBuffer.allocateDirect(pIndex.length * 2);
        pbBuff.order(ByteOrder.nativeOrder());
        pBuff = pbBuff.asShortBuffer();
        pBuff.put(pIndex);
        pbBuff.position(0);
    }

    public void draw(GL10 gl){
        gl.glFrontFace(GL10.GL_CW);
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glVertexPointer(2, GL10.GL_FLOAT, 0, vertBuff);

        // app crashes here.
        gl.glDrawElements(GL10.GL_TRIANGLES, pIndex.length, GL10.GL_UNSIGNED_SHORT, pBuff);
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    }

Crash log cat is

            java.lang.ArrayIndexOutOfBoundsException: remaining() < count < needed
            at com.google.android.gles_jni.GLImpl.glDrawElements(Native Method)
            at com.mobility.opengleslearning.GLTriangleEx.draw(GLTriangleEx.java:45)
            at com.mobility.opengleslearning.GLRenderer.onDrawFrame(GLRenderer.java:38)
            at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1522)
            at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1239)

I have checked below links for help but of no use for my case:

1. Android OpenGL error: "remaining() < needed" and Android 4.4

2. Beginning to learn OpenGL ES. Drawing quad

Answer 1

You need to rewind the ShortBuffer you use for the indices. In this code:

ByteBuffer pbBuff = ByteBuffer.allocateDirect(pIndex.length * 2);
pbBuff.order(ByteOrder.nativeOrder());
pBuff = pbBuff.asShortBuffer();
pBuff.put(pIndex);
pbBuff.position(0);

you're rewinding pbBuff , which is the underlying ByteBuffer .

asShortBuffer() returns a view buffer that shares the underlying data with the original buffer. From the documentation (emphasis added by me):

A view buffer is simply another buffer whose content is backed by the byte buffer. Changes to the byte buffer's content will be visible in the view buffer, and vice versa; the two buffers' position , limit, and mark values are independent .

So pBuff , which is your view buffer, has its own position. You need to rewind the view buffer, which is the buffer you use later:

pBuff.position(0);