/*
 * ** blendxor.c - Demonstrates the use of the blend_logic_op
 * **    extension to draw hilights.  Using XOR to draw the same
 * **    image twice restores the background to its original value.
 */

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include "gltk.h"

GLenum doubleBuffer, directRender;
int dithering = 0;
GLint windW, windH;

static void Init(void)
{
  glDisable(GL_DITHER);
  glShadeModel(GL_FLAT);
}

static void Reshape(int width, int height)
{

  windW = (GLint) width;
  windH = (GLint) height;

  glViewport(0, 0, (GLint) width, (GLint) height);

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0, 400, 0, 400);
  glMatrixMode(GL_MODELVIEW);
}

static GLenum Key(int key, GLenum mask)
{

  switch (key) {
    case TK_ESCAPE:
      tkQuit();
    case TK_d:
      dithering = !dithering;
      break;
    default:
      return GL_FALSE;
  }
  return GL_TRUE;
}

static void Draw(void)
{
  int i;

  glDisable(GL_BLEND);

  (dithering) ? glEnable(GL_DITHER) : glDisable(GL_DITHER);

  glClearColor(0.5, 0.6, 0.1, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);

  /*
   * Draw background prims 
   */
  glColor3f(0.1, 0.1, 1.0);
  glBegin(GL_TRIANGLES);
  glVertex2i(5, 5);
  glVertex2i(130, 50);
  glVertex2i(100, 300);
  glEnd();
  glColor3f(0.5, 0.2, 0.9);
  glBegin(GL_TRIANGLES);
  glVertex2i(200, 100);
  glVertex2i(330, 50);
  glVertex2i(340, 400);
  glEnd();

  glEnable(GL_BLEND);
  glBlendEquationEXT(GL_LOGIC_OP);
  glLogicOp(GL_XOR);

  /*
   * Draw a set of rectangles across the window 
   */
  glColor3f(0.9, 0.2, 0.8);
  for (i = 0; i < 400; i += 60) {
    glBegin(GL_POLYGON);
    glVertex2i(i, 100);
    glVertex2i(i + 50, 100);
    glVertex2i(i + 50, 200);
    glVertex2i(i, 200);
    glEnd();
  }
  glFlush();								       /*
									        * Added by Brian Paul 
									        */
  sleep(2);

  /*
   * Redraw  the rectangles, which should erase them 
   */
  for (i = 0; i < 400; i += 60) {
    glBegin(GL_POLYGON);
    glVertex2i(i, 100);
    glVertex2i(i + 50, 100);
    glVertex2i(i + 50, 200);
    glVertex2i(i, 200);
    glEnd();
  }
  glFlush();

  if (doubleBuffer) {
    tkSwapBuffers();
  }
}

static GLenum Args(int argc, char **argv)
{
  GLint i;

  doubleBuffer = GL_FALSE;
  directRender = GL_TRUE;

  for (i = 1; i < argc; i++) {
    if (strcmp(argv[i], "-sb") == 0) {
      doubleBuffer = GL_FALSE;
    }
    else if (strcmp(argv[i], "-db") == 0) {
      doubleBuffer = GL_TRUE;
    }
    else if (strcmp(argv[i], "-dr") == 0) {
      directRender = GL_TRUE;
    }
    else if (strcmp(argv[i], "-ir") == 0) {
      directRender = GL_FALSE;
    }
    else {
      printf("%s (Bad option).\n", argv[i]);
      return GL_FALSE;
    }
  }
  return GL_TRUE;
}

void main(int argc, char **argv)
{
  GLenum type;
  char *s;
  char *extName = "GL_EXT_blend_logic_op";

  if (Args(argc, argv) == GL_FALSE) {
    tkQuit();
  }

  tkInitPosition(0, 0, 400, 400);

  type = TK_RGB;
  type |= (doubleBuffer) ? TK_DOUBLE : TK_SINGLE;
  type |= (directRender) ? TK_DIRECT : TK_INDIRECT;
  tkInitDisplayMode(type);

  if (tkInitWindow("Blend XOR") == GL_FALSE) {
    tkQuit();
  }

  /*
   * Make sure blend_logic_op extension is there. 
   */
  s = (char *)glGetString(GL_EXTENSIONS);
  if (!s)
    tkQuit();
  if (strstr(s, extName) == 0) {
    printf("Blend_logic_op extension is not present.\n");
    tkQuit();
  }

  Init();

  tkExposeFunc(Reshape);
  tkReshapeFunc(Reshape);
  tkKeyDownFunc(Key);
  tkDisplayFunc(Draw);
  tkExec();
}