nanogui texture mapping

#include <mutex>
#include <stb_image.h>
#include <nanogui/nanogui.h>

class VideoView: public nanogui::GLCanvas {

  public:
    nanogui::GLShader shader;
    GLuint textureId;
    unsigned char* pixelBuffer;
    bool needUpdate;
    unsigned int videoWidth, videoHeight;

    // constructor
    VideoView(Widget *parent, std::string videoPath): nanogui::GLCanvas(parent) {
      needUpdate = false;
      textureId = 0;
      videoWidth = 480;
      videoHeight = 320;

      setupGL();
      pixelBuffer = new unsigned char[videoWidth*videoHeight*3];
      int w = videoWidth;
      int h = videoHeight;
      //GLubyte map[*100*4];
      int i,j;
      for(i=0; i<h; i++) {
          for(j=0; j<w; j++) { 
              if(j % 2 == 0) {
                  pixelBuffer[w*i*3 + j*3+0] = 0x00;
                  pixelBuffer[w*i*3 + j*3+1] = 0x00;
                  pixelBuffer[w*i*3 + j*3+2] = 0xFF;
              }
              else {
                  pixelBuffer[w*i*3 + j*3+0] = 0xFF;
                  pixelBuffer[w*i*3 + j*3+1] = 0x00;
                  pixelBuffer[w*i*3 + j*3+2] = 0x00;
              }
          }
      } 
    }

    ~VideoView() {
        shader.free();
    }

    void setupGL() {
      // Setup shader
      shader.init(
          /* registered name */
            "video_shader",

            /* vertex shader */
            "#version 330\n"
            "// inputs: should just be the vertices and uv's for a rectangle\n"
            "in vec2 position;\n"
            "in vec2 texcoord;\n"
            "// outputs: interpolated texture coordinates for fragment shader\n"
            "out vec2 pass_texcoord;\n"
            "void main() {\n"
            "    pass_texcoord = texcoord;\n"
            "    gl_Position   = vec4(position.xy, 0.0f, 1.0f);\n"
            "}\n",

            /* fragment shader */
            "#version 330\n"
            "in vec2 pass_texcoord;// interpolated texture coordinate\n"
            "out vec4 outColor;    // output color sampled from texture\n"
            "uniform sampler2D passTex;// sampler to read the texture\n"
            "void main() {\n"
            "    outColor = texture(passTex, pass_texcoord);\n"
            "}\n"
          );

      // Setup geometry. Two triangles.
      nanogui::MatrixXu indices(3, 2);
      indices.col(0) << 0, 1, 2;
      indices.col(1) << 2, 3, 1;

      nanogui::MatrixXf positions(2, 4);
      positions.col(0) << -1.0f,  1.0f;
      positions.col(1) <<  1.0f,  1.0f;
      positions.col(2) << -1.0f, -1.0f;
      positions.col(3) <<  1.0f, -1.0f;

      nanogui::MatrixXf texcoords(2, 4);
      texcoords.col(0) << 0.0f, 0.0f;
      texcoords.col(1) << 1.0f, 0.0f;
      texcoords.col(2) << 0.0f, 1.0f;
      texcoords.col(3) << 1.0f, 1.0f;

      shader.bind();
      shader.uploadIndices(indices);

      shader.uploadAttrib("position", positions);
      shader.uploadAttrib("texcoord", texcoords);
      //shader.uploadAttrib("texcoord", texcoords);




      // Setup texture
      glGenTextures(1, &textureId);
      glBindTexture(GL_TEXTURE_2D, textureId);
      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_REPEAT);
      //glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
      //glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    }

    void tearDownGL() {
      shader.free();
      // TODO destroy texture, etc.
    }

    virtual void drawGL() override {
      using namespace nanogui;

      glActiveTexture(1);
      glUniform1i(shader.uniform("passTex", true), 1 - GL_TEXTURE0);


      glBindTexture(GL_TEXTURE_2D, textureId);
      glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
      //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, videoWidth, videoHeight, 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, pixelBuffer);
      float pixels[] = {
          0.0f, 0.0f, 0.0f,   1.0f, 1.0f, 1.0f,
          1.0f, 1.0f, 1.0f,   0.0f, 0.0f, 0.0f
      };
      //glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0, GL_RGB, GL_FLOAT, pixels);
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, videoWidth, videoHeight, 0, GL_RGB, GL_UNSIGNED_BYTE,pixelBuffer);

      //if(needUpdate) {
          //needUpdate = false;
      //}

      shader.bind();
      shader.drawIndexed(GL_TRIANGLES, 0, 2);
    }

};


class GUI: public nanogui::Screen {
  public:
    GUI(): Screen(Eigen::Vector2i(800, 600), "Video View Test", false) {
      using namespace nanogui;

      Window *window = new Window(this, "Video");
      window->setPosition(Vector2i(15,15));
      window->setLayout(new GroupLayout());

      VideoView *video = new VideoView(window, "/home/rvg/Projects/Explora/1.m4v");
      video->setSize({480, 320});

      performLayout();
    }

    ~GUI() { }
};


int main(int argc, char *argv[]) {
  nanogui::init();
  GUI *app = new GUI();
  app->drawAll();
  app->setVisible(true);

  nanogui::mainloop();
  nanogui::shutdown();

  return 0;
}