Android OpenGL ES 2.0 black textures

Question

I'm learning gles2.0 (I'm a new-bite :)) on Android, and I want to draw a textured square, but I can't. I googled a lot, but I can't figure out the answer, i get only a black square.

I set up a GLSurfaceView, then a Renderer:

public class MySurfaceRenderer implements GLSurfaceView.Renderer {

    private Context context;
    private Sprite sprite1;

    @Override
    public void onDrawFrame(GL10 gl) {
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
        sprite1.Draw();
    }

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

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        GLES20.glEnable(GLES20.GL_BLEND);
        GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA,GLES20.GL_ONE_MINUS_SRC_ALPHA);
        GLES20.glClearColor(0.0f, 0.3f, 0.0f, 1.0f);
        sprite1 = new Sprite(context, R.drawable.test);
    }

}

Sprite class:

public class Sprite {

    private static String TAG = "SpriteRender";

    private Context context;

    private FloatBuffer databuffer;
    private FloatBuffer texturebuffer;
    // x, y,
    float data[] =  {-0.5f,  -0.5f,
                     -0.5f, 0.5f,
                     0.5f, 0.5f,
                     0.5f, -0.5f};
    // u,v 
    float texturedata[] =   {0.0f, 0.0f,
                            0.0f, 1.0f,
                            1.0f, 1.0f,
                            1.0f, 0.0f};
    private int mProgram;
    private int vertexShader;
    private int fragmentShader;
    private int texture;
    private int positionHandler;
    private int texCoordHandler;
    private int textureHandler;

    public Sprite(Context context, int textureid){
        this.context = context;

        ByteBuffer bb_data = ByteBuffer.allocateDirect(data.length * 4);
        bb_data.order(ByteOrder.nativeOrder());
        ByteBuffer bb_texture = ByteBuffer.allocateDirect(texturedata.length * 4);
        bb_texture.order(ByteOrder.nativeOrder());

        databuffer = bb_data.asFloatBuffer();
        databuffer.put(data);
        databuffer.position(0);
        texturebuffer = bb_texture.asFloatBuffer();
        texturebuffer.put(texturedata);
        texturebuffer.position(0);

        vertexShader = ShaderLoader.loadShader(GLES20.GL_VERTEX_SHADER, ShaderLoader.readFromAssert(context, R.raw.tvs));
        fragmentShader = ShaderLoader.loadShader(GLES20.GL_FRAGMENT_SHADER, ShaderLoader.readFromAssert(context, R.raw.tfs));

        mProgram = GLES20.glCreateProgram();
        GLES20.glAttachShader(mProgram, fragmentShader);
        GLES20.glAttachShader(mProgram, vertexShader);
        GLES20.glLinkProgram(mProgram);

        int[] linkStatus = new int[1];
        GLES20.glGetProgramiv(mProgram, GLES20.GL_LINK_STATUS, linkStatus, 0);

        if (linkStatus[0] == 0){
            // Displays error message
        }
        positionHandler     = GLES20.glGetAttribLocation(mProgram, "a_Position");
        texCoordHandler     = GLES20.glGetAttribLocation(mProgram, "a_TexCoordinate");
        textureHandler      = GLES20.glGetUniformLocation(mProgram, "u_Texture");

        texture = TextureLoader.loadTexture(context, textureid);
    }

    public void Draw(){
        GLES20.glUseProgram(mProgram);
        databuffer.position(0);
        texturebuffer.position(0);  

        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texture);

        GLES20.glUniform1i(textureHandler, 0);

        GLES20.glEnableVertexAttribArray(texCoordHandler);
        GLES20.glEnableVertexAttribArray(positionHandler);

        GLES20.glVertexAttribPointer(positionHandler, 2, GLES20.GL_FLOAT, false, 8, databuffer);
        GLES20.glVertexAttribPointer(texCoordHandler, 2, GLES20.GL_FLOAT, false, 8, texturebuffer);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 4);
    }

}

ShaderLoader.loadShader loads a shader from a file (in res/raw), TextureLoader.loadTexture loads a texture from a resource:

public static int loadTexture(Context context, int resource){
    int[] texture = new int[1];

    GLES20.glGenTextures(1, texture, 0);

    BitmapFactory.Options bo = new BitmapFactory.Options();
    bo.inScaled = false;
    Bitmap tex = BitmapFactory.decodeResource(context.getResources(), resource, bo);

    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_NEAREST);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);

    GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, tex, 0);
    tex.recycle();

    if(texture[0] == 0){
        // Displays error
    }

    return texture[0];

}

Vertex shader:

attribute vec4 a_Position;
attribute vec2 a_TexCoordinate;
varying vec2 v_TexCoordinate;

void main() {
  v_TexCoordinate = a_TexCoordinate;
  gl_Position = a_Position;
}

Fragment shader:

precision mediump float;
varying vec2 v_TexCoordinate;
uniform sampler2D u_Texture;

void main() {
  gl_FragColor = texture2D(u_Texture, v_TexCoordinate);
}

I looked some stuff:

• Tested with png, jpg, bmp(565), resolution: 32x32 and 64x64
• In draw function after all line glGetError()​ returns 0
• When loading a texture, Sprite.texture is not 0 (its about 70001)
• If I change fragment shader to gl_FragColor = vec4(1.0, 0.0, 0.0, 0.5); it's working.

Thanks for help!

Answer 1

I've figured out the answer:

When I loaded the texture, I didn't pass it to OpenGL correctly.

I added TextureLoader.loadTexture a GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texture[0]); line like this:

...
Bitmap tex = BitmapFactory.decodeResource(context.getResources(), resource, bo);    
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texture[0]); 
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);
...

Now it's working.