How to setup the fragment shader for multiple textures on multiple objects in OpenGLES? - opengl-es

Question

I try to bind a texture to one object and another texture to a next object. I asked here in stackoverflow almost the same question, but the difference in that time was, that I had just one texture and multiple objects.
How to bind texture just to one object in OpenGLES?
It worked for one texture and multiple objects, but now I have multiple textures and multiple objects. I followed the advice in the answers, but I strongly believe that this time the problem is about the fragment shader.
#Override
public void onDrawFrame(GL10 gl) {
GLES20.glClear(GL10.GL_COLOR_BUFFER_BIT);
synchronized (mediaPlayerObject) {
surfaceTextureMediaPlayer.updateTexImage();
mediaPlayeUpdate = false;
}
vertexBuffer.position(0);
GLES20.glVertexAttribPointer(aPositionLocation, POSITION_COMPONENT_COUNT, GLES20.GL_FLOAT, false, STRIDETEXTURE, vertexBuffer);
vertexBuffer.position(TEXTURE_COMPONENT_COUNT);
GLES20.glVertexAttribPointer(aTextureCoordinatesLocation, TEXTURE_COMPONENT_COUNT, GLES20.GL_FLOAT, false, STRIDETEXTURE, vertexBuffer);
GLES20.glEnableVertexAttribArray(aPositionLocation);
GLES20.glEnableVertexAttribArray(aTextureCoordinatesLocation);
GLES20.glUniform1i(textureUnitLocation2, 1);
GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, textures[1]);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 6);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, 0);
GLES20.glDisableVertexAttribArray(aPositionLocation);
GLES20.glDisableVertexAttribArray(aTextureCoordinatesLocation);
synchronized (camerObject) {
surfaceTextureCamera.updateTexImage();
cameraUpdate = false;
}
vertexBuffer2.position(0);
GLES20.glVertexAttribPointer(aPositionLocation, POSITION_COMPONENT_COUNT, GLES20.GL_FLOAT, false, STRIDETEXTURE, vertexBuffer2);
vertexBuffer2.position(TEXTURE_COMPONENT_COUNT);
GLES20.glVertexAttribPointer(aTextureCoordinatesLocation, TEXTURE_COMPONENT_COUNT, GLES20.GL_FLOAT, false, STRIDETEXTURE, vertexBuffer2);
GLES20.glEnableVertexAttribArray(aPositionLocation);
GLES20.glEnableVertexAttribArray(aTextureCoordinatesLocation);
GLES20.glUniform1i(textureUnitLocation, 0);
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, textures[0]);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 6);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, 0);
GLES20.glDisableVertexAttribArray(aPositionLocation);
GLES20.glDisableVertexAttribArray(aTextureCoordinatesLocation);
Here the fragment shader:
#extension GL_OES_EGL_image_external : require
precision mediump float;
uniform samplerExternalOES u_Texture;
uniform samplerExternalOES b_Texture;
varying vec2 v_TextureCoordinates;
void main() {
gl_FragColor = texture2D(u_Texture, v_TextureCoordinates) * texture2D(b_Texture, v_TextureCoordinates);
}

Answer 1

There is no need for a second texture sampler in the fragment shader, so delete b_Texture. It is sufficient to bind the texture object to the texture unit and to set the index of the texture unit to the texture sampler uniform:
#extension GL_OES_EGL_image_external : require
precision mediump float;
uniform samplerExternalOES u_Texture;
varying vec2 v_TextureCoordinates;
void main() {
gl_FragColor = texture2D(u_Texture, v_TextureCoordinates);
}
Draw 1st object:
GLES20.glUniform1i(textureUnitLocation, 1);
GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, textures[1]);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 6);
Draw 2nd object:
GLES20.glUniform1i(textureUnitLocation, 0);
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, textures[0]);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 6);
Note, it is not necessary to use 2 different texture units. You can use GL_TEXTURE0 in both cases.