text: /* nuklear - v1.05 - public domain */
  #include <stdio.h>
  #include <stdlib.h>
  #include <stdint.h>
  #include <stdarg.h>
  #include <string.h>
  #include <math.h>
  #include <assert.h>
  #include <time.h>
  #include <limits.h>
  
  #include <GL/glew.h>
  #include <GLFW/glfw3.h>
  
  #define NK_PRIVATE
  #define NK_INCLUDE_FIXED_TYPES
  #define NK_INCLUDE_STANDARD_IO
  #define NK_INCLUDE_DEFAULT_ALLOCATOR
  #define NK_INCLUDE_VERTEX_BUFFER_OUTPUT
  #define NK_INCLUDE_FONT_BAKING
  #define NK_INCLUDE_DEFAULT_FONT
  #define NK_IMPLEMENTATION
  #include "../nuklear.h"
  
  #define STB_IMAGE_IMPLEMENTATION
  #include "stb_image.h"
  
  /* macros */
  #define WINDOW_WIDTH 1200
  #define WINDOW_HEIGHT 800
  
  #define MAX_VERTEX_MEMORY 512 * 1024
  #define MAX_ELEMENT_MEMORY 128 * 1024
  
  #define UNUSED(a) (void)a
  #define MIN(a,b) ((a) < (b) ? (a) : (b))
  #define MAX(a,b) ((a) < (b) ? (b) : (a))
  #define LEN(a) (sizeof(a)/sizeof(a)[0])
  
  #define NK_SHADER_VERSION "#version 150\n"
  
  /* ===============================================================
   *
   *                          DEVICE
   *
   * ===============================================================*/
  struct nk_glfw_vertex {
      float position[2];
      float uv[2];
      nk_byte col[4];
  };
  
  struct device {
      struct nk_buffer cmds;
      struct nk_draw_null_texture null;
      GLuint vbo, vao, ebo;
      GLuint prog;
      GLuint vert_shdr;
      GLuint frag_shdr;
      GLint attrib_pos;
      GLint attrib_uv;
      GLint attrib_col;
      GLint uniform_tex;
      GLint uniform_proj;
      GLuint font_tex;
  };
  
  static void
  die(const char *fmt, ...)
  {
      va_list ap;
      va_start(ap, fmt);
      vfprintf(stderr, fmt, ap);
      va_end(ap);
      fputs("\n", stderr);
      exit(EXIT_FAILURE);
  }
  
  /* function icon_load () is not used to build this file but might still be useful :) */
  /*
  static struct nk_image	
  icon_load(const char *filename)	
  {	
      int x,y,n;	
      GLuint tex;	
      unsigned char *data = stbi_load(filename, &x, &y, &n, 0);	
      if (!data) die("[SDL]: failed to load image: %s", filename);	
  
       glGenTextures(1, &tex);	
      glBindTexture(GL_TEXTURE_2D, tex);	
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);	
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_NEAREST);	
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);	
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);	
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, x, y, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);	
      glGenerateMipmap(GL_TEXTURE_2D);	
      stbi_image_free(data);	
      return nk_image_id((int)tex);	
  }
  */
  
  static void
  device_init(struct device *dev)
  {
      GLint status;
      static const GLchar *vertex_shader =
          NK_SHADER_VERSION
          "uniform mat4 ProjMtx;\n"
          "in vec2 Position;\n"
          "in vec2 TexCoord;\n"
          "in vec4 Color;\n"
          "out vec2 Frag_UV;\n"
          "out vec4 Frag_Color;\n"
          "void main() {\n"
          "   Frag_UV = TexCoord;\n"
          "   Frag_Color = Color;\n"
          "   gl_Position = ProjMtx * vec4(Position.xy, 0, 1);\n"
          "}\n";
      static const GLchar *fragment_shader =
          NK_SHADER_VERSION
          "precision mediump float;\n"
          "uniform sampler2D Texture;\n"
          "in vec2 Frag_UV;\n"
          "in vec4 Frag_Color;\n"
          "out vec4 Out_Color;\n"
          "void main(){\n"
          "   Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
          "}\n";
  
      nk_buffer_init_default(&dev->cmds);
      dev->prog = glCreateProgram();
      dev->vert_shdr = glCreateShader(GL_VERTEX_SHADER);
      dev->frag_shdr = glCreateShader(GL_FRAGMENT_SHADER);
      glShaderSource(dev->vert_shdr, 1, &vertex_shader, 0);
      glShaderSource(dev->frag_shdr, 1, &fragment_shader, 0);
      glCompileShader(dev->vert_shdr);
      glCompileShader(dev->frag_shdr);
      glGetShaderiv(dev->vert_shdr, GL_COMPILE_STATUS, &status);
      assert(status == GL_TRUE);
      glGetShaderiv(dev->frag_shdr, GL_COMPILE_STATUS, &status);
      assert(status == GL_TRUE);
      glAttachShader(dev->prog, dev->vert_shdr);
      glAttachShader(dev->prog, dev->frag_shdr);
      glLinkProgram(dev->prog);
      glGetProgramiv(dev->prog, GL_LINK_STATUS, &status);
      assert(status == GL_TRUE);
  
      dev->uniform_tex = glGetUniformLocation(dev->prog, "Texture");
      dev->uniform_proj = glGetUniformLocation(dev->prog, "ProjMtx");
      dev->attrib_pos = glGetAttribLocation(dev->prog, "Position");
      dev->attrib_uv = glGetAttribLocation(dev->prog, "TexCoord");
      dev->attrib_col = glGetAttribLocation(dev->prog, "Color");
  
      {
          /* buffer setup */
          GLsizei vs = sizeof(struct nk_glfw_vertex);
          size_t vp = offsetof(struct nk_glfw_vertex, position);
          size_t vt = offsetof(struct nk_glfw_vertex, uv);
          size_t vc = offsetof(struct nk_glfw_vertex, col);
  
          glGenBuffers(1, &dev->vbo);
          glGenBuffers(1, &dev->ebo);
          glGenVertexArrays(1, &dev->vao);
  
          glBindVertexArray(dev->vao);
          glBindBuffer(GL_ARRAY_BUFFER, dev->vbo);
          glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, dev->ebo);
  
          glEnableVertexAttribArray((GLuint)dev->attrib_pos);
          glEnableVertexAttribArray((GLuint)dev->attrib_uv);
          glEnableVertexAttribArray((GLuint)dev->attrib_col);
  
          glVertexAttribPointer((GLuint)dev->attrib_pos, 2, GL_FLOAT, GL_FALSE, vs, (void*)vp);
          glVertexAttribPointer((GLuint)dev->attrib_uv, 2, GL_FLOAT, GL_FALSE, vs, (void*)vt);
          glVertexAttribPointer((GLuint)dev->attrib_col, 4, GL_UNSIGNED_BYTE, GL_TRUE, vs, (void*)vc);
      }
  
      glBindTexture(GL_TEXTURE_2D, 0);
      glBindBuffer(GL_ARRAY_BUFFER, 0);
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
      glBindVertexArray(0);
  }
  
  static void
  device_upload_atlas(struct device *dev, const void *image, int width, int height)
  {
      glGenTextures(1, &dev->font_tex);
      glBindTexture(GL_TEXTURE_2D, dev->font_tex);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)width, (GLsizei)height, 0,
                  GL_RGBA, GL_UNSIGNED_BYTE, image);
  }
  
  static void
  device_shutdown(struct device *dev)
  {
      glDetachShader(dev->prog, dev->vert_shdr);
      glDetachShader(dev->prog, dev->frag_shdr);
      glDeleteShader(dev->vert_shdr);
      glDeleteShader(dev->frag_shdr);
      glDeleteProgram(dev->prog);
      glDeleteTextures(1, &dev->font_tex);
      glDeleteBuffers(1, &dev->vbo);
      glDeleteBuffers(1, &dev->ebo);
      nk_buffer_free(&dev->cmds);
  }
  
  static void
  device_draw(struct device *dev, struct nk_context *ctx, int width, int height,
      enum nk_anti_aliasing AA)
  {
      GLfloat ortho[4][4] = {
          {2.0f, 0.0f, 0.0f, 0.0f},
          {0.0f,-2.0f, 0.0f, 0.0f},
          {0.0f, 0.0f,-1.0f, 0.0f},
          {-1.0f,1.0f, 0.0f, 1.0f},
      };
      ortho[0][0] /= (GLfloat)width;
      ortho[1][1] /= (GLfloat)height;
  
      /* setup global state */
      glEnable(GL_BLEND);
      glBlendEquation(GL_FUNC_ADD);
      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
      glDisable(GL_CULL_FACE);
      glDisable(GL_DEPTH_TEST);
      glEnable(GL_SCISSOR_TEST);
      glActiveTexture(GL_TEXTURE0);
  
      /* setup program */
      glUseProgram(dev->prog);
      glUniform1i(dev->uniform_tex, 0);
      glUniformMatrix4fv(dev->uniform_proj, 1, GL_FALSE, &ortho[0][0]);
      {
          /* convert from command queue into draw list and draw to screen */
          const struct nk_draw_command *cmd;
          void *vertices, *elements;
          const nk_draw_index *offset = NULL;
  
          /* allocate vertex and element buffer */
          glBindVertexArray(dev->vao);
          glBindBuffer(GL_ARRAY_BUFFER, dev->vbo);
          glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, dev->ebo);
  
          glBufferData(GL_ARRAY_BUFFER, MAX_VERTEX_MEMORY, NULL, GL_STREAM_DRAW);
          glBufferData(GL_ELEMENT_ARRAY_BUFFER, MAX_ELEMENT_MEMORY, NULL, GL_STREAM_DRAW);
  
          /* load draw vertices & elements directly into vertex + element buffer */
          vertices = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
          elements = glMapBuffer(GL_ELEMENT_ARRAY_BUFFER, GL_WRITE_ONLY);
          {
              /* fill convert configuration */
              struct nk_convert_config config;
              static const struct nk_draw_vertex_layout_element vertex_layout[] = {
                  {NK_VERTEX_POSITION, NK_FORMAT_FLOAT, NK_OFFSETOF(struct nk_glfw_vertex, position)},
                  {NK_VERTEX_TEXCOORD, NK_FORMAT_FLOAT, NK_OFFSETOF(struct nk_glfw_vertex, uv)},
                  {NK_VERTEX_COLOR, NK_FORMAT_R8G8B8A8, NK_OFFSETOF(struct nk_glfw_vertex, col)},
                  {NK_VERTEX_LAYOUT_END}
              };
              NK_MEMSET(&config, 0, sizeof(config));
              config.vertex_layout = vertex_layout;
              config.vertex_size = sizeof(struct nk_glfw_vertex);
              config.vertex_alignment = NK_ALIGNOF(struct nk_glfw_vertex);
              config.null = dev->null;
              config.circle_segment_count = 22;
              config.curve_segment_count = 22;
              config.arc_segment_count = 22;
              config.global_alpha = 1.0f;
              config.shape_AA = AA;
              config.line_AA = AA;
  
              /* setup buffers to load vertices and elements */
              {struct nk_buffer vbuf, ebuf;
              nk_buffer_init_fixed(&vbuf, vertices, MAX_VERTEX_MEMORY);
              nk_buffer_init_fixed(&ebuf, elements, MAX_ELEMENT_MEMORY);
              nk_convert(ctx, &dev->cmds, &vbuf, &ebuf, &config);}
          }
          glUnmapBuffer(GL_ARRAY_BUFFER);
          glUnmapBuffer(GL_ELEMENT_ARRAY_BUFFER);
  
        /* iterate over and execute each draw command */
          nk_draw_foreach(cmd, ctx, &dev->cmds)
          {
              if (!cmd->elem_count) continue;
              glBindTexture(GL_TEXTURE_2D, (GLuint)cmd->texture.id);
              glScissor(
                  (GLint)(cmd->clip_rect.x),
                  (GLint)((height - (GLint)(cmd->clip_rect.y + cmd->clip_rect.h))),
                  (GLint)(cmd->clip_rect.w),
                  (GLint)(cmd->clip_rect.h));
              glDrawElements(GL_TRIANGLES, (GLsizei)cmd->elem_count, GL_UNSIGNED_SHORT, offset);
              offset += cmd->elem_count;
          }
          nk_clear(ctx);
          nk_buffer_clear(&dev->cmds);
      }
  
      /* default OpenGL state */
      glUseProgram(0);
      glBindBuffer(GL_ARRAY_BUFFER, 0);
      glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
      glBindVertexArray(0);
      glDisable(GL_BLEND);
      glDisable(GL_SCISSOR_TEST);
  }
  
  /* glfw callbacks (I don't know if there is a easier way to access text and scroll )*/
  static void error_callback(int e, const char *d){printf("Error %d: %s\n", e, d);}
  static void text_input(GLFWwindow *win, unsigned int codepoint)
  {nk_input_unicode((struct nk_context*)glfwGetWindowUserPointer(win), codepoint);}
  static void scroll_input(GLFWwindow *win, double _, double yoff)
  {UNUSED(_);nk_input_scroll((struct nk_context*)glfwGetWindowUserPointer(win), nk_vec2(0, (float)yoff));}
  
  static void
  pump_input(struct nk_context *ctx, GLFWwindow *win)
  {
      double x, y;
      nk_input_begin(ctx);
      glfwPollEvents();
  
      nk_input_key(ctx, NK_KEY_DEL, glfwGetKey(win, GLFW_KEY_DELETE) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_ENTER, glfwGetKey(win, GLFW_KEY_ENTER) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_TAB, glfwGetKey(win, GLFW_KEY_TAB) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_BACKSPACE, glfwGetKey(win, GLFW_KEY_BACKSPACE) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_LEFT, glfwGetKey(win, GLFW_KEY_LEFT) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_RIGHT, glfwGetKey(win, GLFW_KEY_RIGHT) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_UP, glfwGetKey(win, GLFW_KEY_UP) == GLFW_PRESS);
      nk_input_key(ctx, NK_KEY_DOWN, glfwGetKey(win, GLFW_KEY_DOWN) == GLFW_PRESS);
  
      if (glfwGetKey(win, GLFW_KEY_LEFT_CONTROL) == GLFW_PRESS ||
          glfwGetKey(win, GLFW_KEY_RIGHT_CONTROL) == GLFW_PRESS) {
          nk_input_key(ctx, NK_KEY_COPY, glfwGetKey(win, GLFW_KEY_C) == GLFW_PRESS);
          nk_input_key(ctx, NK_KEY_PASTE, glfwGetKey(win, GLFW_KEY_P) == GLFW_PRESS);
          nk_input_key(ctx, NK_KEY_CUT, glfwGetKey(win, GLFW_KEY_X) == GLFW_PRESS);
          nk_input_key(ctx, NK_KEY_CUT, glfwGetKey(win, GLFW_KEY_E) == GLFW_PRESS);
          nk_input_key(ctx, NK_KEY_SHIFT, 1);
      } else {
          nk_input_key(ctx, NK_KEY_COPY, 0);
          nk_input_key(ctx, NK_KEY_PASTE, 0);
          nk_input_key(ctx, NK_KEY_CUT, 0);
          nk_input_key(ctx, NK_KEY_SHIFT, 0);
      }
  
      glfwGetCursorPos(win, &x, &y);
      nk_input_motion(ctx, (int)x, (int)y);
      nk_input_button(ctx, NK_BUTTON_LEFT, (int)x, (int)y, glfwGetMouseButton(win, GLFW_MOUSE_BUTTON_LEFT) == GLFW_PRESS);
      nk_input_button(ctx, NK_BUTTON_MIDDLE, (int)x, (int)y, glfwGetMouseButton(win, GLFW_MOUSE_BUTTON_MIDDLE) == GLFW_PRESS);
      nk_input_button(ctx, NK_BUTTON_RIGHT, (int)x, (int)y, glfwGetMouseButton(win, GLFW_MOUSE_BUTTON_RIGHT) == GLFW_PRESS);
      nk_input_end(ctx);
  }
  
  struct nk_canvas {
      struct nk_command_buffer *painter;
      struct nk_vec2 item_spacing;
      struct nk_vec2 panel_padding;
      struct nk_style_item window_background;
  };
  
  static void
  canvas_begin(struct nk_context *ctx, struct nk_canvas *canvas, nk_flags flags,
      int x, int y, int width, int height, struct nk_color background_color)
  {
      /* save style properties which will be overwritten */
      canvas->panel_padding = ctx->style.window.padding;
      canvas->item_spacing = ctx->style.window.spacing;
      canvas->window_background = ctx->style.window.fixed_background;
  
      /* use the complete window space and set background */
      ctx->style.window.spacing = nk_vec2(0,0);
      ctx->style.window.padding = nk_vec2(0,0);
      ctx->style.window.fixed_background = nk_style_item_color(background_color);
  
      /* create/update window and set position + size */
      flags = flags & ~NK_WINDOW_DYNAMIC;
      nk_window_set_bounds(ctx, "Window", nk_rect(x, y, width, height));
      nk_begin(ctx, "Window", nk_rect(x, y, width, height), NK_WINDOW_NO_SCROLLBAR|flags);
  
      /* allocate the complete window space for drawing */
      {struct nk_rect total_space;
      total_space = nk_window_get_content_region(ctx);
      nk_layout_row_dynamic(ctx, total_space.h, 1);
      nk_widget(&total_space, ctx);
      canvas->painter = nk_window_get_canvas(ctx);}
  }
  
  static void
  canvas_end(struct nk_context *ctx, struct nk_canvas *canvas)
  {
      nk_end(ctx);
      ctx->style.window.spacing = canvas->panel_padding;
      ctx->style.window.padding = canvas->item_spacing;
      ctx->style.window.fixed_background = canvas->window_background;
  }
  
  int main(int argc, char *argv[])
  {
      /* Platform */
      static GLFWwindow *win;
      int width = 0, height = 0;
  
      /* GUI */
      struct device device;
      struct nk_font_atlas atlas;
      struct nk_context ctx;
  
      /* GLFW */
      glfwSetErrorCallback(error_callback);
      if (!glfwInit()) {
          fprintf(stdout, "[GFLW] failed to init!\n");
          exit(1);
      }
      glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
      glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
      glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
      glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
      win = glfwCreateWindow(WINDOW_WIDTH, WINDOW_HEIGHT, "Demo", NULL, NULL);
      glfwMakeContextCurrent(win);
      glfwSetWindowUserPointer(win, &ctx);
      glfwSetCharCallback(win, text_input);
      glfwSetScrollCallback(win, scroll_input);
      glfwGetWindowSize(win, &width, &height);
  
      /* OpenGL */
      glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
      glewExperimental = 1;
      if (glewInit() != GLEW_OK) {
          fprintf(stderr, "Failed to setup GLEW\n");
          exit(1);
      }
  
      /* GUI */
      {device_init(&device);
      {const void *image; int w, h;
      struct nk_font *font;
      nk_font_atlas_init_default(&atlas);
      nk_font_atlas_begin(&atlas);
      font = nk_font_atlas_add_default(&atlas, 13, 0);
      image = nk_font_atlas_bake(&atlas, &w, &h, NK_FONT_ATLAS_RGBA32, 1.0f);
      device_upload_atlas(&device, image, w, h);
      nk_font_atlas_end(&atlas, nk_handle_id((int)device.font_tex), &device.null);
      nk_init_default(&ctx, &font->handle);
  
      glEnable(GL_TEXTURE_2D);
      while (!glfwWindowShouldClose(win))
      {
          /* input */
          pump_input(&ctx, win);
  
          /* draw */
          {struct nk_canvas canvas;
          canvas_begin(&ctx, &canvas, 0, 0, 0, width, height, nk_rgb(250,250,250));
          {
              nk_fill_rect(canvas.painter, nk_rect(15,15,210,210), 5, nk_rgb(247, 230, 154));
              nk_fill_rect(canvas.painter, nk_rect(20,20,200,200), 5, nk_rgb(188, 174, 118));
              nk_draw_text(canvas.painter, nk_rect(30, 30, 150, 20), "Text to draw", 12, &font->handle, nk_rgb(188,174,118), nk_rgb(0,0,0));
              nk_fill_rect(canvas.painter, nk_rect(250,20,100,100), 0, nk_rgb(0,0,255));
              nk_fill_circle(canvas.painter, nk_rect(20,250,100,100), nk_rgb(255,0,0));
              nk_fill_triangle(canvas.painter, 250, 250, 350, 250, 300, 350, nk_rgb(0,255,0));
              nk_fill_arc(canvas.painter, 300, 180, 50, 0, 3.141592654f * 3.0f / 4.0f, nk_rgb(255,255,0));
  
              {float points[12];
              points[0] = 200; points[1] = 250;
              points[2] = 250; points[3] = 350;
              points[4] = 225; points[5] = 350;
              points[6] = 200; points[7] = 300;
              points[8] = 175; points[9] = 350;
              points[10] = 150; points[11] = 350;
              nk_fill_polygon(canvas.painter, points, 6, nk_rgb(0,0,0));}
  
              nk_stroke_line(canvas.painter, 15, 10, 200, 10, 2.0f, nk_rgb(189,45,75));
              nk_stroke_rect(canvas.painter, nk_rect(370, 20, 100, 100), 10, 3, nk_rgb(0,0,255));
              nk_stroke_curve(canvas.painter, 380, 200, 405, 270, 455, 120, 480, 200, 2, nk_rgb(0,150,220));
              nk_stroke_circle(canvas.painter, nk_rect(20, 370, 100, 100), 5, nk_rgb(0,255,120));
              nk_stroke_triangle(canvas.painter, 370, 250, 470, 250, 420, 350, 6, nk_rgb(255,0,143));
          }
          canvas_end(&ctx, &canvas);}
  
          /* Draw */
          /* Framebuffer size is used instead of window size because the window size is in screen coordinates instead of pixels.
           * See https://www.glfw.org/docs/latest/window_guide.html#window_size for more info
           */
          glfwGetFramebufferSize(win, &width, &height);
          glViewport(0, 0, width, height);
          glClear(GL_COLOR_BUFFER_BIT);
          glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
          device_draw(&device, &ctx, width, height, NK_ANTI_ALIASING_ON);
          glfwSwapBuffers(win);
      }}}
      nk_font_atlas_clear(&atlas);
      nk_free(&ctx);
      device_shutdown(&device);
      glfwTerminate();
      return 0;
  }
  
  