/* aya5.c - Don Yang (uguu.org)

   10/04/06
                                                                           */

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

double
   PI,
   ColorCurveR[] =
   {
      0.9, 0.98,
      1.0, 0.0,
      -1.0
   },
   ColorCurveGB[] =
   {
      0.32, 0.98,
      0.36, 0.12,
      0.54, 0.12,
      0.58, 0.98,
      0.9, 0.98,
      1.0, 0.0,
      -1.0
   },
   ColorCurveA[] =
   {
      0.56, 0.99,
      0.58, 0.70,
      0.9, 0.0,
      -1.0
   },
   CurrentTime,
   x, y, r, c, ix0, iy0, ix1, iy1;

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

int i, j, k, TextureHandle, SpriteHandle;
unsigned char TextureImage[64 * 64 * 4], *p;

double RandomRange(double u, double v)
{
   return u + (v - u) * (rand() & 0x3fff) / 16383.0;
}

void UpdateClock(void)
{
   struct timeval t;
   gettimeofday(&t, NULL);
   CurrentTime = (double)t.tv_sec + (double)(t.tv_usec / 1000000.0);
}

void Render(void)
{
   UpdateClock();

   glDrawBuffer(GL_BACK);
   glClear(GL_COLOR_BUFFER_BIT);

   i = glutGet(GLUT_WINDOW_WIDTH);
   j = glutGet(GLUT_WINDOW_HEIGHT);
   glViewport(0, 0, i, j);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if( i > j )
      gluOrtho2D(-i / j, i / j, -1.0, 1.0);
   else
      gluOrtho2D(-1.0, 1.0, -j / i, j / i);

   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

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

   for(i = 0; i < 23; i++)
   {
      ix1 = ix0 - (i / 23.0);
      if( ix1 < 0.0 )
         continue;
      r = ix1 * 2.1;
      for(j = 0; j < 32; j++)
      {
         x = GlobalEmitter.r0 + j * PI * 2.0 / 32.0;
         y = GlobalEmitter.r1 + j * PI * 2.0 / 32.0;
         iy1 = ix1 * (y - x) + x;
         if( (i & 1) != 0 )
            iy1 += PI * 2.0 / 64.0;
         x = r * cos(iy1) + GlobalEmitter.x;
         y = r * sin(iy1) + GlobalEmitter.y;

         glPushMatrix();
         glTranslated(x, y, 0.0);
         glCallList(SpriteHandle);
         glPopMatrix();
      }
   }

   if( ix0 > 2.2 )
   {
      GlobalEmitter.t0 = CurrentTime;
      GlobalEmitter.r0 = GlobalEmitter.r1 = RandomRange(0.0, PI * 2.0);
      if( (rand() & 3) == 0 )
         GlobalEmitter.r1 += RandomRange(-PI / 3.0, PI / 3.0);
      GlobalEmitter.x = RandomRange(-0.5, 0.5);
      GlobalEmitter.y = RandomRange(-0.5, 0.5);
   }

   glutSwapBuffers();
   glFlush();
}

void RenderFirstFrame(void)
{
   UpdateClock();
   srand((unsigned int)CurrentTime);

   glGenTextures(1, &TextureHandle);
   glBindTexture(GL_TEXTURE_2D, TextureHandle);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 64, 64, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*)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, 0.0); glVertex2d(-0.07, -0.07);
      glTexCoord2d(1.0, 0.0); glVertex2d( 0.07, -0.07);
      glTexCoord2d(1.0, 1.0); glVertex2d( 0.07,  0.07);
      glTexCoord2d(0.0, 1.0); glVertex2d(-0.07,  0.07);
   glEnd();
   glEndList();

   GlobalEmitter.t0 = CurrentTime;
   GlobalEmitter.x = GlobalEmitter.y =
   GlobalEmitter.r0 = GlobalEmitter.r1 = 0.0;

   glutDisplayFunc(Render);
   Render();
}

void Animate(void)
{
   glutPostRedisplay();
}

void Reshape(int w, int h)
{
   glutPostRedisplay();
}

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

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

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

   PI = atan2(0.0, -1.0);

   p = memset(TextureImage, 0, 64 * 64 * 4);
   for(i = 0; i < 64; i++)
   {
      x = ((double)i - (64 / 2)) / (64 / 2);
      for(j = 0; j < 64; j++)
      {
         y = ((double)j - (64 / 2)) / (64 / 2);
         r = sqrt(x * x + y * y);

         c = StepFunc(r, ColorCurveR);
         k = (int)(255 * c);
         if( k > 255 ) k = 255;
         *(p++) = (unsigned char)k;

         c = StepFunc(r, ColorCurveGB);
         k = (int)(255 * c);
         if( k > 255 ) k = 255;
         *(p++) = (unsigned char)k;
         *(p++) = (unsigned char)k;

         c = StepFunc(r, ColorCurveA);
         k = (int)(255 * c);
         if( k > 255 ) k = 255;
         *(p++) = (unsigned char)k;
      }
   }

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

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

   glutMainLoop();
   return 0;
}