Android OpenGL ES 2.0 Only Limited To 16 Textures In Memory?

Question

Basically while I was working on an app in Android Studio using OpenGL ES 2.0, I ran into a big problem that I can't wrap my head around, and it's been bugging me for about a week.

So, anytime I load more than 16, maybe 17 textures of any size in memory, and attempt to display them in 2D through either my emulator in Genymotion or my ASUS tablet, it either begins to display different images than what I was binding at that particular index, or not display at all. Yet if I run it through my Samsung Galaxy S6, it runs fine. However if I load 16 textures or less, it works all around in all devices I test it on, including the emulator.

This made me attempt a little experiment to see if it will show letter images a-z with each letter being 16x16 png, all within my drawable folder. When each letter get's displayed, it will be 80x80 in size on screen so I can see them. So I tried to have it run "a" through "z". On the emulator, as well as my tablet, it only showed "a" through "o", with a "z" at the end where "p" is suppose to be, and stopped right there. On my Samsung Galaxy, it actually showed "a" through "z" and did what it was suppose to. This didn't make any sense as to why it would not load right on other devices considering that I set the number of textures at 27 or even higher in my constant. I hope I explained my problem ok. And I'm pretty sure they are all capable of loading a lot more than 16 textures so I must be doing something wrong with my code. Rather than show the entire project, I'm gonna show you the relevant areas where the problem may lie. Any help is appreciated and thanks in advance. Here's my code:

Constants:

public class Constants
{
public static final int BYTES_PER_FLOAT = 4;
public static final int POSITION_COMPONENT_COUNT = 4;
public static final int NORMAL_COMPONENT_COUNT = 3;
public static final int COLOR_COMPONENT_COUNT = 4;
public static final int TEXTURE_COORDS_COMPONENT_COUNT = 2;

public static final String A_COLOR = "a_Color";
public static final String A_POSITION = "a_Position";
public static final String A_NORMAL = "a_Normal";
public static final String A_TEXTURECOORDS = "a_TextureCoords";
public static final String U_MVMATRIX = "u_MVMatrix";
public static final String U_MVPMATRIX = "u_MVPMatrix";
public static final String U_TEXTURE_UNIT = "u_Texture_Unit";
public static final String U_LIGHTPOS = "u_LightPos";
public static final String V_COLOR = "v_Color";
public static final String V_POSITION = "v_Position";
public static final String V_NORMAL = "v_Normal";

public static float SCREEN_WIDTH;
public static float SCREEN_HEIGHT;

public static int NUMBER_OF_TEXTURES = 27;
}

Texture.java:

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

import static android.opengl.GLES20.*;

public class Texture
{
public static int[] texture;

public static void Load(Context context, int resourceId, int index)
{
    //glGenTextures(Constants.NUMBER_OF_TEXTURES, texture, starting_index);
    //int n: specifies the number of texture names to be generated
    //int[] textures: specifies an array in which the generated texture names are stored
    //int offset: the starting index of your array!

    Bitmap bitmap;
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inScaled = false;

    // loading texture
    bitmap = BitmapFactory.decodeResource(context.getResources(), resourceId, options);

    // ...and bind it to our array
    glActiveTexture(GL_TEXTURE0 + index);
    glBindTexture(GL_TEXTURE_2D, texture[index]);

    // create nearest filtered texture
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    // Use Android GLUtils to specify a two-dimensional texture image from our bitmap
    GLUtils.texImage2D(GL_TEXTURE_2D, 0, bitmap, 0);

    // Clean up
    bitmap.recycle();
}

public static void Delete(int[] texture, int starting_index)
{
    try
    {
        glDeleteTextures(1, texture, starting_index);
    }
    catch(Exception e)
    {
        return;
    }

}
}

Quad.java

import static android.opengl.GLES20.*;

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

public class Quad
 {
public float vertices[];
public float colors[];
public float texture_coords[];

public FloatBuffer vertexBuffer;
public FloatBuffer textureBuffer;
public FloatBuffer colorBuffer;

public Quad(float x1, float y1, float z1, float w1,
            float x2, float y2, float z2, float w2,
            float x3, float y3, float z3, float w3,
            float x4, float y4, float z4, float w4,
            float red, float green, float blue, float alpha,
            float u1, float v1, float u2, float v2)
{
    vertices = new float[]{x1, y1, z1, w1,
            x2, y2, z2, w2,
            x3, y3, z3, w3,
            x4, y4, z4, w4};

    colors = new float[]{red, green, blue, alpha,
            red, green, blue, alpha,
            red, green, blue, alpha,
            red, green, blue, alpha};

    ByteBuffer vertexByteBuffer = ByteBuffer.allocateDirect(vertices.length * Constants.BYTES_PER_FLOAT);
    vertexByteBuffer.order(ByteOrder.nativeOrder());
    vertexBuffer = vertexByteBuffer.asFloatBuffer();
    vertexBuffer.put(vertices);
    vertexBuffer.position(0);

    ByteBuffer colorByteBuffer = ByteBuffer.allocateDirect(colors.length * Constants.BYTES_PER_FLOAT);
    colorByteBuffer.order(ByteOrder.nativeOrder());
    colorBuffer = colorByteBuffer.asFloatBuffer();
    colorBuffer.put(colors);
    colorBuffer.position(0);

    texture_coords = new float[]{u1, v1,
            u2, v1,
            u1, v2,
            u2, v2};
    ByteBuffer textureByteBuffer = ByteBuffer.allocateDirect(texture_coords.length * Constants.BYTES_PER_FLOAT);
    textureByteBuffer.order(ByteOrder.nativeOrder());
    textureBuffer = textureByteBuffer.asFloatBuffer();
    textureBuffer.put(texture_coords);
    textureBuffer.position(0);
}

public void Draw_Polygon(int index, int program, float[] modelview_projection_matrix, float[] modelview_matrix)
{
    int aPositionHandle = glGetAttribLocation(program, Constants.A_POSITION);
    glEnableVertexAttribArray(aPositionHandle);
    glVertexAttribPointer(aPositionHandle, Constants.POSITION_COMPONENT_COUNT, GL_FLOAT, false, 0, vertexBuffer);

    int aColorHandle = glGetAttribLocation(program, Constants.A_COLOR);
    glEnableVertexAttribArray(aColorHandle);
    glVertexAttribPointer(aColorHandle, Constants.COLOR_COMPONENT_COUNT, GL_FLOAT, false, 0, colorBuffer);

    int aTextureCoordsHandle = glGetAttribLocation(program, Constants.A_TEXTURECOORDS);
    glEnableVertexAttribArray(aTextureCoordsHandle);
    glVertexAttribPointer(aTextureCoordsHandle, Constants.TEXTURE_COORDS_COMPONENT_COUNT, GL_FLOAT, false, 0, textureBuffer);

    int uModelViewProjectionMatrixHandle = glGetUniformLocation(program, Constants.U_MVPMATRIX);
    glUniformMatrix4fv(uModelViewProjectionMatrixHandle, 1, false, modelview_projection_matrix, 0);

    int uModelViewMatrixHandle = glGetUniformLocation(program, Constants.U_MVMATRIX);
    glUniformMatrix4fv(uModelViewMatrixHandle, 1, false, modelview_matrix, 0);

    int uTextureUnit = glGetUniformLocation(program, Constants.U_TEXTURE_UNIT);
    glUniform1i(uTextureUnit, index);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    glDisableVertexAttribArray(aPositionHandle);
    glDisableVertexAttribArray(aColorHandle);
    glDisableVertexAttribArray(aTextureCoordsHandle);
}
}

Text.java:

import android.opengl.Matrix;

import static android.opengl.GLES20.*;

public class Text
{
public Quad[] poly = new Quad[1];
public String string;
public int char_width;
public int char_height;

void Draw()
{
    int texture_num = 0;
    int x_pos = 0;
    int y_pos = 0;
    for (int i = 0; i < string.length(); i++)
    {
        char character = string.charAt(i);

        switch(character)
        {
            case ' ':
            {
                texture_num = 0;
                break;
            }
            case 'a':
            {
                texture_num = 1;
                break;
            }
            case 'b':
            {
                texture_num = 2;
                break;
            }
            case 'c':
            {
                texture_num = 3;
                break;
            }
            case 'd':
            {
                texture_num = 4;
                break;
            }
            case 'e':
            {
                texture_num = 5;
                break;
            }
            case 'f':
            {
                texture_num = 6;
                break;
            }
            case 'g':
            {
                texture_num = 7;
                break;
            }
            case 'h':
            {
                texture_num = 8;
                break;
            }
            case 'i':
            {
                texture_num = 9;
                break;
            }
            case 'j':
            {
                texture_num = 10;
                break;
            }
            case 'k':
            {
                texture_num = 11;
                break;
            }
            case 'l':
            {
                texture_num = 12;
                break;
            }
            case 'm':
            {
                texture_num = 13;
                break;
            }
            case 'n':
            {
                texture_num = 14;
                break;
            }
            case 'o':
            {
                texture_num = 15;
                break;
            }
            case 'p':
            {
                texture_num = 16;
                break;
            }
            case 'q':
            {
                texture_num = 17;
                break;
            }
            case 'r':
            {
                texture_num = 18;
                break;
            }
            case 's':
            {
                texture_num = 19;
                break;
            }
            case 't':
            {
                texture_num = 20;
                break;
            }
            case 'u':
            {
                texture_num = 21;
                break;
            }
            case 'v':
            {
                texture_num = 22;
                break;
            }
            case 'w':
            {
                texture_num = 23;
                break;
            }
            case 'x':
            {
                texture_num = 24;
                break;
            }
            case 'y':
            {
                texture_num = 25;
                break;
            }
            case 'z':
            {
                texture_num = 26;
                break;
            }
        }

        Matrix.setIdentityM(OpenGL.model_matrix, 0);
        Matrix.translateM(OpenGL.model_matrix, 0, OpenGL.model_matrix, 0, 0.0f, 0.0f, 0.0f);
        Matrix.multiplyMM(OpenGL.matrix_ortho_projection_and_view, 0, OpenGL.matrix_ortho_projection, 0, OpenGL.model_matrix, 0);

        glUseProgram(Shader.textured_colored_shader_program);

        poly[0] = new Quad(x_pos + 0.0f, y_pos + 0.0f, 0.0f, 1.0f,
                x_pos + char_width, y_pos + 0.0f, 0.0f, 1.0f,
                x_pos + 0.0f, y_pos + char_height, 0.0f, 1.0f,
                x_pos + char_width, y_pos + char_height, 0.0f, 1.0f,
                1.0f, 1.0f, 1.0f, 1.0f,
                0.0f, 0.0f, 1.0f, 1.0f);

        poly[0].Draw_Polygon(texture_num, Shader.textured_colored_shader_program, OpenGL.matrix_ortho_projection_and_view, OpenGL.model_matrix);

        x_pos += char_width;

        if (x_pos >= Constants.SCREEN_WIDTH)
        {
            x_pos = 0;
            y_pos += char_height;
        }
    }
}
}

OpenGL.java:

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

import android.content.Context;
import android.opengl.GLSurfaceView.Renderer;
import static android.opengl.GLES20.*;

import android.util.Log;
import android.opengl.Matrix;

public class OpenGL implements Renderer
{
public static Context context;

public static final float[] matrix_ortho_projection = new float[16];
public static float[] model_matrix = new float[16];
private final float[] matrix_view = new float[16];
public static final float[] matrix_ortho_projection_and_view = new float[16];
public int get_width, get_height;
public static boolean texture_loading_enabled = true;
Text text = new Text();

public OpenGL(Context context)
{
    this.context = context;
}

public static void Load_Textures()
{
    switch(State.game_state)
    {
        case State.LOGO:
        {
            Texture.Delete(Texture.texture, 0);

            glFlush();

            Texture.texture = new int[Constants.NUMBER_OF_TEXTURES];

            glGenTextures(Constants.NUMBER_OF_TEXTURES, Texture.texture, 0);

            Texture.Load(context, R.drawable.c64_space, 0);
            Texture.Load(context, R.drawable.c64_a, 1);
            Texture.Load(context, R.drawable.c64_b, 2);
            Texture.Load(context, R.drawable.c64_c, 3);
            Texture.Load(context, R.drawable.c64_d, 4);
            Texture.Load(context, R.drawable.c64_e, 5);
            Texture.Load(context, R.drawable.c64_f, 6);
            Texture.Load(context, R.drawable.c64_g, 7);
            Texture.Load(context, R.drawable.c64_h, 8);
            Texture.Load(context, R.drawable.c64_i, 9);
            Texture.Load(context, R.drawable.c64_j, 10);
            Texture.Load(context, R.drawable.c64_k, 11);
            Texture.Load(context, R.drawable.c64_l, 12);
            Texture.Load(context, R.drawable.c64_m, 13);
            Texture.Load(context, R.drawable.c64_n, 14);
            Texture.Load(context, R.drawable.c64_o, 15);
            Texture.Load(context, R.drawable.c64_p, 16);
            Texture.Load(context, R.drawable.c64_q, 17);
            Texture.Load(context, R.drawable.c64_r, 18);
            Texture.Load(context, R.drawable.c64_s, 19);
            Texture.Load(context, R.drawable.c64_t, 20);
            Texture.Load(context, R.drawable.c64_u, 21);
            Texture.Load(context, R.drawable.c64_v, 22);
            Texture.Load(context, R.drawable.c64_w, 23);
            Texture.Load(context, R.drawable.c64_x, 24);
            Texture.Load(context, R.drawable.c64_y, 25);
            Texture.Load(context, R.drawable.c64_z, 26);

            break;
        }

        case State.TITLE:
        {
            break;
        }

        case State.GAME:
        {
            break;
        }
    }

    texture_loading_enabled = false;
}

private void Controls()
{

    switch(State.game_state)
    {
        case State.LOGO:
        {
            break;
        }

        case State.TITLE:
        {
            break;
        }

        case State.GAME:
        {
            break;
        }
    }

}

@Override
public void onDrawFrame(GL10 glUnused)
{
    Controls();

    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

    switch(State.game_state)
    {
        case State.LOGO:
        {
            text.Draw();
            break;
        }

        case State.TITLE:
        {
            break;
        }

        case State.GAME:
        {
            break;
        }
    }
}

@Override
public void onSurfaceChanged(GL10 glUnused, int width, int height)
{
    // Set the OpenGL viewport to the same size as the surface.
    Log.d("TAG", "onSurfaceChanged()");

    get_width = width;
    get_height = height;

    glViewport(0, 0, width, height);

    for(int i = 0; i < 16; i++)
    {
        matrix_ortho_projection[i] = 0.0f;
        matrix_view[i] = 0.0f;
        model_matrix[i] = 0.0f;
        matrix_ortho_projection_and_view[i] = 0.0f;
    }

    Matrix.orthoM(matrix_ortho_projection, 0, 0.0f, (float) get_width, (float) get_height, 0.0f, 0.0f, 1.0f);
}

@Override
public void onSurfaceCreated(GL10 glUnused, EGLConfig config)
{
    Log.d("TAG", "onSurfaceCreated()");

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    glEnable(GL_BLEND);
    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

    Shader.Create_Texture_Colored_Shader(context);
    Shader.Create_Colored_Shader(context);

    text.char_width = 80;
    text.char_height = 80;
    text.string = "abcdefghijklmnopqrstuvwxyz";

    switch(State.game_state)
    {
        case State.LOGO:
        {
            if (texture_loading_enabled == true)
                Load_Textures();
            break;
        }

        case State.TITLE:
        {
            break;
        }

        case State.GAME:
        {
            break;
        }
    }
}
}

Shader.java:

import android.content.Context;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import static android.opengl.GLES20.*;

public class Shader
{
public static int textured_colored_shader_program;
public static int colored_shader_program;

public static String readTextFileFromRawResource(final Context context, final int resourceId)
{
    final InputStream inputStream = context.getResources().openRawResource(resourceId);
    final InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
    final BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

    String nextLine;
    final StringBuilder body = new StringBuilder();

    try
    {
        while ((nextLine = bufferedReader.readLine()) != null)
        {
            body.append(nextLine);
            body.append('\n');
        }
    }
    catch (IOException e)
    {
        return null;
    }

    return body.toString();
}

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

public static void Create_Texture_Colored_Shader(Context context)
{
    int vertexShader = loadShader(GL_VERTEX_SHADER, readTextFileFromRawResource(context, R.raw.vertex_shader));
    int fragmentShader = loadShader(GL_FRAGMENT_SHADER, readTextFileFromRawResource(context, R.raw.fragment_shader));
    textured_colored_shader_program = glCreateProgram();
    glAttachShader(textured_colored_shader_program, vertexShader);
    glAttachShader(textured_colored_shader_program, fragmentShader);
    glLinkProgram(textured_colored_shader_program);
}

public static void Create_Colored_Shader(Context context)
{
    int vertexShader = loadShader(GL_VERTEX_SHADER, readTextFileFromRawResource(context, R.raw.vertex_shader_no_texture));
    int fragmentShader = loadShader(GL_FRAGMENT_SHADER, readTextFileFromRawResource(context, R.raw.fragment_shader_no_texture));
    colored_shader_program = glCreateProgram();
    glAttachShader(colored_shader_program, vertexShader);
    glAttachShader(colored_shader_program, fragmentShader);
    glLinkProgram(colored_shader_program);
}
}

Answer 1

The total number of texture objects is not normally limited. At least not within any reasonably range, theoretically you will run of ids that can be represented by a GLuint at some point. But you will run out of memory long before that happens. So the only practical limit is normally given by the amount of memory used for the texture data.

However, the number of texture units is very much limited. And from a quick look at your code, that's what you run into. From your texture loading code:

glActiveTexture(GL_TEXTURE0 + index);
glBindTexture(GL_TEXTURE_2D, texture[index]);

What you're trying to do is keep all textures bound, using a different texture unit for each. Then when you draw, you select which texture unit the shader samples from:

glUniform1i(uTextureUnit, index);

This is a perfectly valid approach... until you run out of texture units. Which is exactly what happens.

The maximum number of texture units is implementation dependent, and can be queried with:

GLint maxUnits = 0;
glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &maxUnits);

The minimum for this value is 8. So unless you check the value, and find more, you can only rely on having 8 texture units.

If you need more than 8 textures, and want your code to run reliably across devices, your somewhat unconventional approach of keeping all textures bound will not work.

The easiest approach is that you do what most people do: Bind the texture you want to use before drawing. For this, you can always use texture unit 0. So you can remove all calls to glActiveTexture(), and simply place a bind call in the Draw_Polygon() method, instead of the glUniform1i() call:

glBindTexture(GL_TEXTURE_2D, texture[index]);