Switching between textures in OpenGL ES 2

Question

I'm trying to figure out how to put different textures into different texture units and choose which texture to draw with. I have the following code in my onDrawFrame() method

    int[] texture = new int[7];
    texture[0] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture1);
    texture[1] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture2);
    texture[2] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture3);
    texture[3] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture4);
    texture[4] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture5);
    texture[5] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture6);
    texture[6] =TextureHelper.loadTexture(mActivityContext,R.drawable.texture7);

    for (int i = 0; i < 7; i ++) {
        GLES20.glActiveTexture(GLES20.GL_TEXTURE0 + i);
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texture[i]);
        GLES20.glUniform1i(mTextureUniformHandle, i);
        Matrix.setIdentityM(mModelMatrix, 0);
        Matrix.translateM(mModelMatrix, 0, -0.60f + 0.2f * i, 0.0f, 0.0f);
        draw();
    }

What this is supposed to do is load seven different textures into separate texture units and draw cubes, each cube with a different texture. However, what ends up happening is that all of the cubes end up being drawn with the first texture.

It works correctly if I change GLES20.glActiveTexture(GLES20.GL_TEXTURE0 + i) to GLES20.glActiveTexture(GLES20.GL_TEXTURE0) and GLES20.glUniform1i(mTextureUniformHandle, i) to GLES20.glUniform1i(mTextureUniformHandle, 0), but that just uses a single texture unit and replaces the texture in that unit every time, which is not what I want to do.

What am I doing wrong? Thanks in advance.

EDIT:

Vertex shader:

            "uniform mat4 u_MVPMatrix;" + // A constant representing the
                                            // combined
                                            // model/view/projection matrix.
            "uniform mat4 u_MVMatrix;" + // A constant representing the
                                            // combined model/view matrix.

            "attribute vec4 a_Position;" + // Per-vertex position
                                            // information we will pass in.
            "attribute vec4 a_Color;" + // Per-vertex color information we
                                        // will pass in.
            "attribute vec2 a_TexCoordinate;" + // Per-vertex texture
                                                // coordinate information we
                                                // will pass in.

            "varying vec3 v_Position;" + // This will be passed into the
                                            // fragment shader.
            "varying vec4 v_Color;" + // This will be passed into the
                                        // fragment shader.
            "varying vec2 v_TexCoordinate;" + // This will be passed into
                                                // the fragment shader.

            // The entry point for our vertex shader.
            "void main()" + "{" +
            // Transform the vertex into eye space.
            "v_Position = vec3(u_MVMatrix * a_Position);" +

            // Pass through the color.
            "v_Color = a_Color;" +

            // Pass through the texture coordinate.
            "v_TexCoordinate = a_TexCoordinate;" +

            // gl_Position is a special variable used to store the final
            // position.
            // Multiply the vertex by the matrix to get the final point in
            // normalized screen coordinates.
            "gl_Position = u_MVPMatrix * a_Position;" + "} ";

Fragment shader:

            "precision mediump float;" + // Set the default precision to medium. We don't need as high of a
            // precision in the fragment shader.
            "uniform sampler2D u_Texture;" + // The input texture.

            "varying vec3 v_Position;" + // Interpolated position for this fragment.
            "varying vec4 v_Color;" + // This is the color from the vertex shader interpolated across the
            // triangle per fragment.
            "varying vec2 v_TexCoordinate;" + // Interpolated texture coordinate per fragment.

            // The entry point for our fragment shader.
            "void main()" +
            "{" +
                // Multiply the color by the diffuse illumination level and texture value to get final output color.
                "gl_FragColor = (v_Color * texture2D(u_Texture, v_TexCoordinate));" +
            "}";

draw() method:

public void draw() {
// Pass in the position information
    mCubePositions.position(0);
    GLES20.glVertexAttribPointer(mPositionHandle, mPositionDataSize, GLES20.GL_FLOAT, false, 0, mCubePositions);
    GLES20.glEnableVertexAttribArray(mPositionHandle);

    // Pass in the color information
    mCubeColors.position(0);
    GLES20.glVertexAttribPointer(mColorHandle, mColorDataSize, GLES20.GL_FLOAT, false, 0, mCubeColors);
    GLES20.glEnableVertexAttribArray(mColorHandle);

    // Pass in the texture coordinate information
    mCubeTextureCoordinates.position(0);
    GLES20.glVertexAttribPointer(mTextureCoordinateHandle, mTextureCoordinateDataSize, GLES20.GL_FLOAT, false, 0, mCubeTextureCoordinates);
    GLES20.glEnableVertexAttribArray(mTextureCoordinateHandle);

    // This multiplies the view matrix by the model matrix, and stores the
    // result in the MVP matrix
    // (which currently contains model * view).
    Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);

    // Pass in the modelview matrix.
    GLES20.glUniformMatrix4fv(mMVMatrixHandle, 1, false, mMVPMatrix, 0);

    // This multiplies the modelview matrix by the projection matrix, and
    // stores the result in the MVP matrix
    // (which now contains model * view * projection).
    Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);

    // Pass in the combined matrix.
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

    // Draw the cube.
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 6);
}

Assigning mTextureUniformHandle :

mTextureUniformHandle = GLES20.glGetUniformLocation(mProgramHandle, "u_Texture");

Answer 1

Lately I've been searching for multiple textures in fragment shader and came across this Binding textures to samplers

from which I got the following to work:

In onSurfaceCreated or onSurfaceChanged:

• Load shaders (attach and link) and get uniform locations for sampler2D (and other variables):

normalMapLoc = GLES20.glGetUniformLocation(shaderProgram, "normalMap"); shadowMapLoc = GLES20.glGetUniformLocation(shaderProgram, "shadowMap");

• Load textures:

GLES20.glGenTextures(2, textures, 0); GLES20.glActiveTexture(GLES20.GL_TEXTURE0); GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]); 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); GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0); bitmap.recycle(); GLES20.glActiveTexture(GLES20.GL_TEXTURE1); GLES20.glBindTexture(GL10.GL_TEXTURE_COORD_ARRAY, textures[1]); 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.glTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, width, height, 0, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, mColorBuffer); GLES20.glUniform1i(normalMapLoc, 0); // Texture unit 0 is for normal images. GLES20.glUniform1i(shadowMapLoc, 1); // Texture unit 1 is for shadow maps.

In onDrawFrame:

GLES20.glClearColor(0f, 0f, 0f, 0f); GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT); // pass variables to the fragment shader ... // get handle to vertex shader's Position member, etcetera int mPositionHandle = GLES20.glGetAttribLocation(shaderProgram, "vPosition"); GLES20.glEnableVertexAttribArray(mPositionHandle); GLES20.glVertexAttribPointer(mPositionHandle, 3, GLES20.GL_FLOAT, false, 0, mVertexBuffer); GLES20.glDrawElements(GLES20.GL_TRIANGLE_STRIP, 4, GLES20.GL_UNSIGNED_SHORT, mIndexBuffer);

and finally the fragment shader looks like this (only relevant portion of code):

    uniform sampler2D normalMap, shadowMap;
    varying vec2 pos;

    void main() {
      vec4 color = texture2D(normalMap, pos);
      vec4 shadow = texture2D(shadowMap, pos);
      // do stuff with the colors
      ...
      gl_FragColor = ...;
    }

This way i was finally able to access both textures !

Hope this helps.