Setting alpha in Custom Shader not working in cocos2dx

Question

I want to fill the sprite with white and make it transparent but it doesn't work. What's wrong with this code?

#include "HelloWorldScene.h"
#include "SimpleAudioEngine.h"

USING_NS_CC;

constexpr const GLchar* fragmentCode = R"(
#ifdef GL_ES
precision mediump float;
#endif

// v_texCoord is the texture coord position, u_texture is our original texture
varying vec2 v_texCoord;
uniform sampler2D u_texture;
uniform float u_opacity;

void main()
{
  vec4 originalColor = texture2D(u_texture, v_texCoord);

  if (originalColor.a == 0.0)
  {
    gl_FragColor = vec4(originalColor.r, originalColor.g, originalColor.b, 0);;
  }
  else
  {
    gl_FragColor = vec4(1, 1, 1, u_opacity);
  }
}
)";

Scene* HelloWorld::createScene()
{
    return HelloWorld::create();
}

// Print useful error message instead of segfaulting when files are not there.
static void problemLoading(const char* filename)
{
    printf("Error while loading: %s\n", filename);
    printf("Depending on how you compiled you might have to add 'Resources/' in front of filenames in HelloWorldScene.cpp\n");
}

// on "init" you need to initialize your instance
bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !Scene::init() )
    {
        return false;
    }

    auto visibleSize = Director::getInstance()->getVisibleSize();
    Vec2 origin = Director::getInstance()->getVisibleOrigin();

    /////////////////////////////
    // 2. add a menu item with "X" image, which is clicked to quit the program
    //    you may modify it.

    // add a "close" icon to exit the progress. it's an autorelease object
    auto closeItem = MenuItemImage::create(
                                           "CloseNormal.png",
                                           "CloseSelected.png",
                                           CC_CALLBACK_1(HelloWorld::menuCloseCallback, this));

    if (closeItem == nullptr ||
        closeItem->getContentSize().width <= 0 ||
        closeItem->getContentSize().height <= 0)
    {
        problemLoading("'CloseNormal.png' and 'CloseSelected.png'");
    }
    else
    {
        float x = origin.x + visibleSize.width - closeItem->getContentSize().width/2;
        float y = origin.y + closeItem->getContentSize().height/2;
        closeItem->setPosition(Vec2(x,y));
    }

    // create menu, it's an autorelease object
    auto menu = Menu::create(closeItem, NULL);
    menu->setPosition(Vec2::ZERO);
    this->addChild(menu, 1);

    /////////////////////////////
    // 3. add your codes below...

    // add a label shows "Hello World"
    // create and initialize a label

    auto label = Label::createWithTTF("Hello World", "fonts/Marker Felt.ttf", 24);
    if (label == nullptr)
    {
        problemLoading("'fonts/Marker Felt.ttf'");
    }
    else
    {
        // position the label on the center of the screen
        label->setPosition(Vec2(origin.x + visibleSize.width/2,
                                origin.y + visibleSize.height - label->getContentSize().height));

        // add the label as a child to this layer
        this->addChild(label, 1);
    }

    // add "HelloWorld" splash screen"
    auto sprite = Sprite::create("HelloWorld.png");
    if (sprite == nullptr)
    {
        problemLoading("'HelloWorld.png'");
    }
    else
    {
        // position the sprite on the center of the screen
        sprite->setPosition(Vec2(visibleSize.width/2 + origin.x, visibleSize.height/2 + origin.y));

        // add the sprite as a child to this layer
        this->addChild(sprite, 0);
    }
  
  auto bush = Sprite::create("bush01.png");
  bush->setPosition(Vec2(visibleSize.width/2 + origin.x, visibleSize.height/2 + origin.y));
  this->addChild(bush, 1);
  
  auto flashShader = GLProgram::createWithByteArrays(ccPositionTextureColor_noMVP_vert, fragmentCode);
  flashShader->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_POSITION, GLProgram::VERTEX_ATTRIB_POSITION);
  flashShader->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_TEX_COORD, GLProgram::VERTEX_ATTRIB_TEX_COORD);
  flashShader->link();
  CHECK_GL_ERROR_DEBUG();
  flashShader->updateUniforms();
  CHECK_GL_ERROR_DEBUG();
  flashShader->retain();
  
  bush->setBlendFunc(BlendFunc::ALPHA_PREMULTIPLIED);
  
  // Here we set up which textures are associated with which shader variables
  auto glProgramState = GLProgramState::getOrCreateWithGLProgram(flashShader);
  bush->setGLProgramState(glProgramState);
  glProgramState->setUniformFloat("u_opacity", 0.1f);
  glProgramState->setUniformTexture("u_texture", bush->getTexture());
  bush->setGLProgram(flashShader);
  
    return true;
}


void HelloWorld::menuCloseCallback(Ref* pSender)
{
    //Close the cocos2d-x game scene and quit the application
    Director::getInstance()->end();

    /*To navigate back to native iOS screen(if present) without quitting the application  ,do not use Director::getInstance()->end() as given above,instead trigger a custom event created in RootViewController.mm as below*/

    //EventCustom customEndEvent("game_scene_close_event");
    //_eventDispatcher->dispatchEvent(&customEndEvent);


}