// OpenGL + stb sample. PNG image is in memory
//
// PNGファイルをOpenGLで扱う話
// https://proken.mydns.jp/index.php?plugin=attach&refer=pg_koneta%2FPNGInOpenGL&openfile=PNGInOpenGL.html
//
// 008 PNGテクスチャの読み込み [stepism]
// https://stepism.sakura.ne.jp/wiki/doku.php?id=wiki:opengl:tips:008
//
// nothings/stb: stb single-file public domain libraries for C/C++
// https://github.com/nothings/stb

#include <stdio.h>
#include <stdlib.h>
#include <GL/freeglut.h>

// use stb library
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

// include png image binary
#include "texture.h"

GLuint texture;

/**
 * Load texture from png image on memory
 *
 * @param[in] _pngData png binary on memory
 * @param[in] _pngDataLen png binary size
 * return GLuint OpenGL texture ID. if 0, process fails
 */
GLuint createTextureFromPngInMemory(const unsigned char* _pngData, int _pngLen)
{
  GLuint texture;
  int width = 0, height = 0, bpp = 0;
  unsigned char *data = NULL;

  data = stbi_load_from_memory(_pngData, _pngLen, &width, &height, &bpp, 4);
  
  // create OpenGL texture
  glGenTextures(1, &texture);
  glBindTexture(GL_TEXTURE_2D, texture);
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);

  // Release allocated all memory
  stbi_image_free(data);

  return texture;
}

// draw OpenGL
void display()
{
  glClear(GL_COLOR_BUFFER_BIT);

  glColor4f(1.0f, 1.0f, 1.0f, 1.0f);

  // enable texture
  glEnable(GL_TEXTURE_2D);
  glBindTexture(GL_TEXTURE_2D, texture);

  // draw polygon
  glBegin(GL_QUADS);

  GLfloat v = 0.85f;

  glTexCoord2f(0.0, 0.0); // set texture u, v
  glVertex2f(-v, v);

  glTexCoord2f(0.0, 1.0);
  glVertex2f(-v, -v);

  glTexCoord2f(1.0, 1.0);
  glVertex2f(v, -v);

  glTexCoord2f(1.0, 0.0);
  glVertex2f(v, v);

  glEnd();

  // disable texture
  glDisable(GL_TEXTURE_2D);

  glFlush();
}

// Keyboard callback function
void keyboard(unsigned char key, int x, int y)
{
  switch (key)
    {
      case '\x1B':
      case 'q':
        // Exit on escape or 'q' key press
        glutLeaveMainLoop();
        // exit(EXIT_SUCCESS);
        break;
    }
}

int main(int argc, char **argv)
{
  glutInit(&argc, argv);

  glutInitDisplayMode(GLUT_RGBA);
  glutInitWindowSize(1280, 720);
  glutCreateWindow("OpenGL Texture Example");

  // create OpenGL texture from PNG image
  texture = createTextureFromPngInMemory((void *)&texture_png, texture_png_size);

  if (!texture)
    {
      fprintf(stderr, "Failed create texture\n");
      exit(1);
    }

  glClearColor(0.2f, 0.4f, 0.8f, 1.0f);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);

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

  glutSetOption(GLUT_ACTION_ON_WINDOW_CLOSE, GLUT_ACTION_GLUTMAINLOOP_RETURNS);

  glutMainLoop();

  return EXIT_SUCCESS;
}