The Hilbert Curve, named from the german mathmatician Hilbert, is a well known fractal curve.

希爾伯特曲線，以德國數(shù)學(xué)家希爾伯特命名，是一個(gè)很有名的分形曲線。

下面將以“山寨機(jī)”版本的MediaTek的MT6225版本號(hào)為W0812F1為例來演示曲線的生成過程。算法來源于ACM Graphics Gems，右圖為模擬生成的圖像，請(qǐng)注意盡量減少迭代的次數(shù)，在嵌入式當(dāng)中玩迭代，純粹是搞怪，慎用。

/* Hibert Curve */

#define STEP_SIZE 4    /* # of pixels in each step */

long orgin[2];
long coord[2];         /* X,Y for graphics calls */

static void step(long angle)
{
   while (angle > 270) angle -= 360;    /* Fold ANGLE to be 0, 90, 180, 270 */
   while (angle <   0) angle += 360;
   if      (angle == 0)   {orgin[0] = coord[0]; coord[0] += STEP_SIZE;}  /* +X */
   else if (angle == 90)  {orgin[1] = coord[1]; coord[1] += STEP_SIZE;}  /* +Y */
   else if (angle == 180) {orgin[0] = coord[0]; coord[0] -= STEP_SIZE;}  /* -X */
   else if (angle == 270) {orgin[1] = coord[1]; coord[1] -= STEP_SIZE;}  /* -Y */
  
   gdi_draw_line(orgin[0], orgin[1], coord[0], coord[1], GDI_COLOR_TRANSPARENT);
   gdi_layer_blt_previous(0, 0, UI_DEVICE_WIDTH - 1, UI_DEVICE_HEIGHT - 1);
}

/* Recursive Hilbert-curve generation algorithm                    */
/* ORIENT is either +1 or -1...it swaps left turns and right turns */
/* ANGLE is some multiple of 90 degrees...positive or negative     */
/* LEVEL is the recursion level                                    */
/* 2^LEVEL by 2^LEVEL points will be visited in total              */

void hilbert (long orient,long *angle, long level)
{
   if (level-- <= 0) return;
   *angle += orient * 90;
   hilbert(-orient,angle,level);
   step(*angle);
   *angle -= orient * 90;
   hilbert(orient,angle,level);
   step(*angle);
   hilbert(orient,angle,level);
   *angle -= orient * 90;
   step(*angle);
   hilbert(-orient,angle,level);
   *angle += orient * 90;
}

/* Recursive Peano-curve generation  */
/* Same parameters as Hilbert above  */
/* 3^LEVEL by 3^LEVEL points visited */

void peano (long orient, long *angle, long level)
{
   if (level-- <= 0) return;
   peano(orient,angle,level);
   step(*angle);
   peano(-orient,angle,level);
   step(*angle);
   peano(orient,angle,level);
   *angle -= orient * 90;
   step(*angle);
   *angle -= orient * 90;
   peano(-orient,angle,level);
   step(*angle);
   peano(orient,angle,level);
   step(*angle);
   peano(-orient,angle,level);
   *angle += orient * 90;
   step(*angle);
   *angle += orient * 90;
   peano(orient,angle,level);
   step(*angle);
   peano(-orient,angle,level);
   step(*angle);
   peano(orient,angle,level);
}

void HilbertCurve(void)
{
 long initial_angle;
 
 orgin[0] = 0; orgin[1] = 0;
 coord[0] = 0; coord[1] = 0;

 gdi_layer_push_and_set_active(effect_layer_1);
 gdi_layer_set_source_key(TRUE, GDI_COLOR_TRANSPARENT);
 gdi_layer_clear(GDI_COLOR_BLACK);
 gdi_layer_pop_and_restore_active();

 gdi_layer_set_blt_layer(effect_layer_1, 0, 0, 0);
 gdi_layer_blt_previous(0, 0, UI_DEVICE_WIDTH - 1, UI_DEVICE_HEIGHT - 1);

 gdi_layer_push_and_set_active(effect_layer_1);
 gdi_layer_set_blt_layer(effect_layer_2, effect_layer_1, 0, 0);
 
 /* Visit 128x128 points along Hilbert curve using STEP_SIZE steps, */
 /* so pattern will fill 512x512 area on screen since STEP_SIZE = 4 */
    initial_angle = 0;
    hilbert(1,&initial_angle,7);

 /* Visit 81x81 points along Peano curve using STEP_SIZE steps,     */
 /* so pattern will fill 324x324 area on screen since STEP_SIZE = 4 */
    initial_angle = 0;
    peano(-1,&initial_angle,4);

 gdi_layer_pop_and_restore_active();
 
}