/* aya7.c - Don Yang (uguu.org)

   10/07/06
                                                                           */

#include<sys/time.h>
#include<math.h>
#include<stdio.h>
#include<stdlib.h>
#include<GL/glut.h>

double
   PI,
   ColorCurveR[] =
   {
      .9, .98,
      1, 0,
      -1
   },
   ColorCurveGB[] =
   {
      .32, .98,
      .36, .12,
      .54, .12,
      .58, .98,
      .9, .98,
      1, 0,
      -1
   },
   ColorCurveA[] =
   {
      .56, .99,
      .58, .7,
      .9, 0,
      -1
   },
   CurrentTime,
   x, r, ix0, iy0, ix1, iy1;

struct
{
   double t0, x, y, r0, r1;
} GlobalEmitter;

int i, j, k, TextureHandle, SpriteHandle;
unsigned char TextureImage[16384], *p;

double RandomRange(double u)
{
   return u * (rand() & 0x3fff) / 8191. - u;
}

UpdateClock()
{
   struct timeval t;
   gettimeofday(&t, NULL);
   CurrentTime = t.tv_sec + t.tv_usec / 1e6;
}

Render()
{
   UpdateClock();
   srand(CurrentTime);

   glDrawBuffer(GL_BACK);
   glClear(GL_COLOR_BUFFER_BIT);

   glViewport(0, 0,
              i = glutGet(GLUT_WINDOW_WIDTH), j = glutGet(GLUT_WINDOW_HEIGHT));
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if( i > j )
      gluOrtho2D(-i / (double)j, i / (double)j, -1, 1);
   else
      gluOrtho2D(-1, 1, -j / (double)i, j / (double)i);

   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   ix0 = (CurrentTime - GlobalEmitter.t0) / 1.5;

   for(i = 0; i < 23; i++)
   {
      if( (ix1 = ix0 - i / 23.) >= 0 )
      {
         r = ix1 * 2.1;
         for(j = 0; j < 32; j++)
         {
            x = GlobalEmitter.r0 + j * PI / 16.;
            iy1 = ix1 * ((GlobalEmitter.r1 + j * PI / 16.) - x) + x;
            if( i & 1 )
               iy1 += PI / 32;
            glPushMatrix();
            glTranslated(r * cos(iy1) + GlobalEmitter.x,
                         r * sin(iy1) + GlobalEmitter.y, 0);
            glCallList(SpriteHandle);
            glPopMatrix();
         }
      }
   }

   if( ix0 > 2.2 )
   {
      GlobalEmitter.t0 = CurrentTime;
      GlobalEmitter.r0 = GlobalEmitter.r1 = RandomRange(PI);
      if( !(rand() & 3) )
         GlobalEmitter.r1 += RandomRange(PI / 3);
      GlobalEmitter.x = RandomRange(.5);
      GlobalEmitter.y = RandomRange(.5);
   }

   glutSwapBuffers();
   glFlush();
}

RenderFirstFrame()
{
   UpdateClock();

   glGenTextures(1, &TextureHandle);
   glBindTexture(GL_TEXTURE_2D, TextureHandle);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 64, 64, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, TextureImage);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

   glEnable(GL_BLEND);
   glEnable(GL_TEXTURE_2D);
   glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

   glNewList(SpriteHandle = glGenLists(1), GL_COMPILE);
   glBegin(GL_TRIANGLE_FAN);
      glTexCoord2d(0, 0); glVertex2d(-.07, -.07);
      glTexCoord2d(1, 0); glVertex2d( .07, -.07);
      glTexCoord2d(1, 1); glVertex2d( .07,  .07);
      glTexCoord2d(0, 1); glVertex2d(-.07,  .07);
   glEnd();
   glEndList();

   GlobalEmitter.t0 = CurrentTime;
   GlobalEmitter.x = GlobalEmitter.y =
   GlobalEmitter.r0 = GlobalEmitter.r1 = 0;

   glutDisplayFunc(Render);
   Render();
}

Animate()
{
   glutPostRedisplay();
}

Reshape(int w, int h)
{
   Animate();
}

Quit(unsigned char c, int u, int v)
{
   glFlush();
   glDeleteLists(SpriteHandle, 1);
   glDeleteTextures(1, &TextureHandle);
   exit(0);
}

double StepFunc(double *curve)
{
   ix0 = *curve++;
   iy0 = *curve++;
   if( r > ix0 )
   {
      for(; (ix1 = *curve++) > ix0;)
      {
         iy1 = *curve++;
         if( r < ix1 )
         {
            iy0 = (iy1 - iy0) * (r - ix0) / (ix1 - ix0) + iy0;
            break;
         }
         ix0 = ix1;
         iy0 = iy1;
      }
   }
   return 255 * iy0;
}

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

   PI = atan2(0, -1);

   for(i = 0; i < 16384; TextureImage[i++] = 0);
   p = TextureImage;
   for(i = 0; i < 64; i++)
   {
      x = i / 32. - 1;
      for(j = 0; j < 64; j++)
      {
         r = j / 32. - 1;
         r = sqrt(x * x + r * r);

         if( (k = StepFunc(ColorCurveR)) > 255 ) k = 255;
         *p++ = k;

         if( (k = StepFunc(ColorCurveGB)) > 255 ) k = 255;
         *p++ = k;
         *p++ = k;

         if( (k = StepFunc(ColorCurveA)) > 255 ) k = 255;
         *p++ = k;
      }
   }

   glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
   glutSetWindow(glutCreateWindow("Aya"));

   glutDisplayFunc(RenderFirstFrame);
   glutIdleFunc(Animate);
   glutReshapeFunc(Reshape);
   glutKeyboardFunc(Quit);

   glutMainLoop();
}