Question

I have a problem with OpenGl ES 2.0. I’ve designed a very simple framework to help me load OBJ files and draw them on my Android phone, but I have 2 bugs that I haven’t been able to fix:

1. My app doesn’t show anything until I change the orientation and the Activity gets scraped and reloaded. Until it reloads only GLES20.glClear() can be seen(I’ve set it to a grayish color).

2. Sometimes when I load an OBJ and do the orientation trick, half of my faces are missing and I see gaps, but the problem might be with the OBJ files I’ve used.

package com.ideas.opengl;

import java.io.IOException;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLES20;
import android.opengl.GLSurfaceView.Renderer;
import android.opengl.Matrix;

public class DemoRenderer implements Renderer {
    public static int mProgramHandle;
    private int mMVPMatrixHandle;
    private float[] mModelMatrix = new float[16];
    private float[] mViewMatrix = new float[16];
    private float[] mProjectionMatrix = new float[16];
    private float[] mMVPMatrix = new float[16];

    public Object banana;

    private OpenGLDemoActivity activity;

    private int angle;

    public DemoRenderer(OpenGLDemoActivity activity) throws IOException {
        this.activity = activity;
    }



    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config){
        GLES20.glClearColor(0.65f, 0.65f, 0.65f, 0.65f);

        //GLES20.glEnable(GLES20.GL_CULL_FACE);

        GLES20.glEnable(GLES20.GL_DEPTH_TEST);

        GLES20.glEnable(GLES20.GL_TEXTURE_2D);

        Shader shader = null;
        try {
            shader = new Shader(activity, "simple");
        } catch (IOException e) {
            e.printStackTrace();
        }
        Vector position = new Vector();
        Vector speed = new Vector();
        Vector accel = new Vector();
        Model model = null;
        try {
            model = new Model("banana", activity);
        } catch (IOException e) {
            e.printStackTrace();
        }

        banana = new Object(position, speed, accel, model);

        mProgramHandle = shader.getProgramHandle();

        final float eyeX = 0.0f;
        final float eyeY = 0.0f;
        final float eyeZ = 3.5f;

        final float lookX = 0.0f;
        final float lookY = 0.0f;
        final float lookZ = -5.0f;

        final float upX = 0.0f;
        final float upY = 1.0f;
        final float upZ = 0.0f;

        Matrix.setLookAtM(mViewMatrix, 0, eyeX, eyeY, eyeZ, lookX, lookY, lookZ, upX, upY, upZ);

        mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgramHandle, "u_MVPMatrix");
    }

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

        final float ratio = (float) width / height;
        final float left = -ratio;
        final float right = ratio;
        final float bottom = -1.0f;
        final float top = 1.0f;
        final float near = 1.0f;
        final float far = 10.0f;

        Matrix.frustumM(mProjectionMatrix, 0, left, right, bottom, top, near, far);

    }


    @Override
    public void onDrawFrame(GL10 gl) {      
        GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);

        angle++;

        Matrix.setIdentityM(mModelMatrix, 0);
        Matrix.rotateM(mModelMatrix, 0, angle, 0.0f, 1.0f, 1.0f);

        Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);

        Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);

        GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

        banana.draw();
    }
}

`

Answer 1

Tried some glGetError() and got to errors, one regarding a variable that had its value unchanged and another was that glGetAttributeLocation() return a -1 if the attribute is not used in the vertex shader. Thaks for the help!