Now uses grayscalescvs diff -u apps/plugins/mandelbrot.c! Plus some internal changes, like removing TAB chars, and preventing unnecessary redraws etc.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4535 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 705 insertions, 96 deletions

diff --git a/apps/plugins/mandelbrot.c b/apps/plugins/mandelbrot.c
index 3c948e8130..11c51bb556 100644
--- a/apps/plugins/mandelbrot.c
+++ b/apps/plugins/mandelbrot.c
@@ -9,8 +9,6 @@
  *
  * Copyright (C) 2004 Matthias Wientapper
  *
- * Thanks to Jens Arnold and Joerg Hohensohn for the speed tips.
- * Boy, that was a hell of a code review ;-)
  *
  * All files in this archive are subject to the GNU General Public License.
  * See the file COPYING in the source tree root for full license agreement.
@@ -18,11 +16,8 @@
  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  * KIND, either express or implied.
  *
- *
- * further optimization ideas:
- *    - incremental recalculation when moving
- *    
  ****************************************************************************/
+#ifndef SIMULATOR 
 #include "plugin.h"
 
 #ifdef HAVE_LCD_BITMAP // this is not fun on the player
@@ -36,9 +31,603 @@ static int y_min;
 static int y_max;
 static int delta;
 static int max_iter;
+static unsigned char *gbuf;
+static unsigned int gbuf_size = 0;
+
+/**************** Begin grayscale framework ******************/
+
+/* This is a generic framework to use grayscale display within
+ * rockbox plugins. It obviously does not work for the player.
+ *
+ * If you want to use grayscale display within a plugin, copy
+ * this section (up to "End grayscale framework") into your
+ * source and you are able to use it. For detailed documentation
+ * look at the head of each public function.
+ *
+ * It requires a global Rockbox api pointer in "rb" and uses 
+ * timer 4 so you cannot use timer 4 for other purposes while
+ * displaying grayscale.
+ *
+ * The framework consists of 3 sections:
+ *
+ * - internal core functions and definitions
+ * - public core functions
+ * - public optional functions
+ *
+ * Usually you will use functions from the latter two sections
+ * in your code. You can cut out functions from the third section
+ * that you do not need in order to not waste space. Don't forget
+ * to cut the prototype as well.
+ */
+
+/**** internal core functions and definitions ****/
+
+/* You do not want to touch these if you don't know exactly what
+ * you're doing.
+ */
+
+#define IMIA4 (*((volatile unsigned long*)0x09000180)) /* timer 4 */
+
+#define GRAY_RUNNING          0x0001  /* grayscale overlay is running */
+#define GRAY_DEFERRED_UPDATE  0x0002  /* lcd_update() requested */
+
+typedef struct
+{
+    int x;
+    int by;        /* 8-pixel units */
+    int width;
+    int height;
+    int bheight;   /* 8-pixel units */
+    int plane_size;
+    int depth;     /* number_of_bitplanes  = (number_of_grayscales - 1) */
+    int cur_plane; /* for the timer isr */
+    unsigned long randmask; /* mask for random value in graypixel() */
+    unsigned long flags;    /* various flags, see #defines */
+    unsigned char *data;    /* pointer to start of bitplane data */
+    unsigned long *bitpattern; /* pointer to start of pattern table */
+} tGraybuf;
+
+static tGraybuf *graybuf = NULL;
+
+/** prototypes **/
+
+void timer_set(unsigned period);
+void timer4_isr(void) __attribute__((interrupt_handler));
+void graypixel(int x, int y, unsigned long pattern);
+void grayinvertmasked(int x, int yb, unsigned char mask);
+
+/** implementation **/
+
+/* setup ISR and timer registers */
+void timer_set(unsigned period)
+{
+    if (period)
+    {
+        and_b(~0x10, &TSTR); /* Stop the timer 4 */
+        and_b(~0x10, &TSNC); /* No synchronization */
+        and_b(~0x10, &TMDR); /* Operate normally */
+
+        IMIA4 = (unsigned long) timer4_isr; /* install ISR */
+
+        and_b(~0x01, &TSR4);
+        TIER4 = 0xF9; /* Enable GRA match interrupt */
+
+        GRA4 = (unsigned short)(period/4 - 1);
+        TCR4 = 0x22; /* clear at GRA match, sysclock/4 */
+        IPRD = (IPRD & 0xFF0F) | 0x0010; /* interrupt priority 1 (lowest) */
+        or_b(0x10, &TSTR); /* start timer 4 */
+    }
+    else
+    {
+        and_b(~0x10, &TSTR);    /* stop the timer 4 */
+        IPRD = (IPRD & 0xFF0F); /* disable interrupt */
+    }
+}
+
+/* timer interrupt handler: display next bitplane */
+void timer4_isr(void) /* IMIA4 */
+{
+    and_b(~0x01, &TSR4); /* clear the interrupt */
+
+    rb->lcd_blit(graybuf->data + (graybuf->plane_size * graybuf->cur_plane),
+                 graybuf->x, graybuf->by, graybuf->width, graybuf->bheight,
+                 graybuf->width);
+
+    if (++graybuf->cur_plane >= graybuf->depth)
+        graybuf->cur_plane = 0;
+
+    if (graybuf->flags & GRAY_DEFERRED_UPDATE)  /* lcd_update() requested? */
+    {
+        int x1 = MAX(graybuf->x, 0);
+        int x2 = MIN(graybuf->x + graybuf->width, LCD_WIDTH);
+        int y1 = MAX(graybuf->by << 3, 0);
+        int y2 = MIN((graybuf->by + graybuf->bheight) << 3, LCD_HEIGHT);
+
+        if(y1 > 0)  /* refresh part above overlay, full width */
+            rb->lcd_update_rect(0, 0, LCD_WIDTH, y1);
+
+        if(y2 < LCD_HEIGHT) /* refresh part below overlay, full width */
+            rb->lcd_update_rect(0, y2, LCD_WIDTH, LCD_HEIGHT - y2);
+
+        if(x1 > 0) /* refresh part to the left of overlay */
+            rb->lcd_update_rect(0, y1, x1, y2 - y1);
+
+        if(x2 < LCD_WIDTH) /* refresh part to the right of overlay */
+            rb->lcd_update_rect(x2, y1, LCD_WIDTH - x2, y2 - y1);
+
+        graybuf->flags &= ~GRAY_DEFERRED_UPDATE; /* clear request */
+    }
+}
+
+/* Set a pixel to a specific bit pattern
+ * This is the fundamental graphics primitive, asm optimized */
+void graypixel(int x, int y, unsigned long pattern)
+{
+    static short random_buffer;
+    register long address, mask, random;
+
+    /* Some (pseudo-)random function must be used here to shift
+     * the bit pattern randomly, otherwise you would get flicker
+     * and/or moire.
+     * Since rand() is relatively slow, I've implemented a simple,
+     * but very fast pseudo-random generator based on linear
+     * congruency in assembler. It delivers 16 pseudo-random bits
+     * in each iteration.
+     */
+
+    /* simple but fast pseudo-random generator */
+    asm(
+        "mov.w   @%1,%0          \n"  /* load last value */
+        "mov     #75,r1          \n"
+        "mulu    %0,r1           \n"  /* multiply by 75 */
+        "sts     macl,%0         \n"  /* get result */
+        "add     #74,%0          \n"  /* add another 74 */
+        "mov.w   %0,@%1          \n"  /* store new value */
+        /* Since the lower bits are not very random: */
+        "shlr8   %0              \n"  /* get bits 8..15 (need max. 5) */
+        "and     %2,%0           \n"  /* mask out unneeded bits */
+        : /* outputs */
+        /* %0 */ "=&r"(random)
+        : /* inputs */
+        /* %1 */ "r"(&random_buffer),
+        /* %2 */ "r"(graybuf->randmask)
+        : /* clobbers */
+        "r1","macl"
+    );
+
+    /* precalculate mask and byte address in first bitplane */
+    asm(
+        "mov     %3,%0           \n"  /* take y as base for address offset */
+        "shlr2   %0              \n"  /* shift right by 3 (= divide by 8) */
+        "shlr    %0              \n"
+        "mulu    %0,%2           \n"  /* multiply with width */
+        "and     #7,%3           \n"  /* get lower 3 bits of y */
+        "sts     macl,%0         \n"  /* get mulu result */
+        "add     %4,%0           \n"  /* add base + x to get final address */
+
+        "mov     %3,%1           \n"  /* move lower 3 bits of y out of r0 */
+        "mova    .pp_table,%3    \n"  /* get address of mask table in r0 */
+        "bra     .pp_end         \n"  /* skip the table */
+        "mov.b   @(%3,%1),%1     \n"  /* get entry from mask table */
+        
+        ".align  2               \n"
+    ".pp_table:                  \n"  /* mask table */
+        ".byte   0x01            \n"
+        ".byte   0x02            \n"
+        ".byte   0x04            \n"
+        ".byte   0x08            \n"
+        ".byte   0x10            \n"
+        ".byte   0x20            \n"
+        ".byte   0x40            \n"
+        ".byte   0x80            \n"
+
+    ".pp_end:                    \n"
+        : /* outputs */
+        /* %0 */ "=&r"(address),
+        /* %1 */ "=&r"(mask)
+        : /* inputs */
+        /* %2 */ "r"(graybuf->width),
+        /* %3 = r0 */ "z"(y),
+        /* %4 */ "r"(graybuf->data + x)
+        : /* clobbers */
+        "macl"
+    );
+
+    /* the hard part: set bits in all bitplanes according to pattern */
+    asm(
+        "cmp/hs  %1,%5           \n"  /* random >= depth ? */
+        "bf      .p_ntrim        \n"
+        "sub     %1,%5           \n"  /* yes: random -= depth */
+        /* it's sufficient to do this once, since the mask guarantees
+         * random < 2 * depth */
+    ".p_ntrim:                   \n"
+    
+        /* calculate some addresses */
+        "mulu    %4,%1           \n"  /* end address offset */
+        "not     %3,r1           \n"  /* get inverse mask (for "and") */
+        "sts     macl,%1         \n"  /* result of mulu */
+        "mulu    %4,%5           \n"  /* address offset of <random>'th plane */
+        "add     %2,%1           \n"  /* end offset -> end address */
+        "sts     macl,%5         \n"  /* result of mulu */
+        "add     %2,%5           \n"  /* address of <random>'th plane */
+        "bra     .p_start1       \n"
+        "mov     %5,r2           \n"  /* copy address */
+
+        /* first loop: set bits from <random>'th bitplane to last */
+    ".p_loop1:                   \n"
+        "mov.b   @r2,r3          \n"  /* get data byte */
+        "shlr    %0              \n"  /* shift bit mask, sets t bit */
+        "and     r1,r3           \n"  /* reset bit (-> "white") */
+        "bf      .p_white1       \n"  /* t=0? -> "white" bit */
+        "or      %3,r3           \n"  /* set bit ("black" bit) */
+    ".p_white1:                  \n"
+        "mov.b   r3,@r2          \n"  /* store data byte */
+        "add     %4,r2           \n"  /* advance address to next bitplane */
+    ".p_start1:                  \n"
+        "cmp/hi  r2,%1           \n"  /* address < end address ? */
+        "bt      .p_loop1        \n"
+        
+        "bra     .p_start2       \n"
+        "nop                     \n"
+
+        /* second loop: set bits from first to <random-1>'th bitplane
+         * Bit setting works the other way round here to equalize average
+         * execution times for bright and dark pixels */
+    ".p_loop2:                   \n"
+        "mov.b   @%2,r3          \n"  /* get data byte */
+        "shlr    %0              \n"  /* shift bit mask, sets t bit */
+        "or      %3,r3           \n"  /* set bit (-> "black") */
+        "bt      .p_black2       \n"  /* t=1? -> "black" bit */
+        "and     r1,r3           \n"  /* reset bit ("white" bit) */
+    ".p_black2:                  \n"
+        "mov.b   r3,@%2          \n"  /* store data byte */
+        "add     %4,%2           \n"  /* advance address to next bitplane */
+    ".p_start2:                  \n"
+        "cmp/hi  %2,%5           \n"  /* address < <random>'th address ? */
+        "bt      .p_loop2        \n"
+        : /* outputs */
+        : /* inputs */
+        /* %0 */ "r"(pattern),
+        /* %1 */ "r"(graybuf->depth),
+        /* %2 */ "r"(address),
+        /* %3 */ "r"(mask),
+        /* %4 */ "r"(graybuf->plane_size),
+        /* %5 */ "r"(random)
+        : /* clobbers */
+        "r1", "r2", "r3", "macl"
+    );
+}
+
+/* Invert the bits for 1-8 pixels within the buffer */
+void grayinvertmasked(int x, int yb, unsigned char mask)
+{
+    asm(
+        "mulu    %4,%5           \n"  /* width * by (offset of row) */
+        "mov     #0,r1           \n"  /* current_plane = 0 */
+        "sts     macl,r2         \n"  /* get mulu result */
+        "add     r2,%1           \n"  /* -> address in 1st bitplane */
+        
+    ".i_loop:                    \n"
+        "mov.b   @%1,r2          \n"  /* get data byte */
+        "add     #1,r1           \n"  /* current_plane++; */
+        "xor     %2,r2           \n"  /* invert bits */
+        "mov.b   r2,@%1          \n"  /* store data byte */
+        "add     %3,%1           \n"  /* advance address to next bitplane */
+        "cmp/hi  r1,%0           \n"  /* current_plane < depth ? */
+        "bt      .i_loop         \n"
+        : /* outputs */
+        : /* inputs */
+        /* %0 */ "r"(graybuf->depth),
+        /* %1 */ "r"(graybuf->data + x),
+        /* %2 */ "r"(mask),
+        /* %3 */ "r"(graybuf->plane_size),
+        /* %4 */ "r"(graybuf->width),
+        /* %5 */ "r"(yb)
+        : /* clobbers */
+        "r1", "r2", "macl"
+    );
+}
+
+/*** public core functions ***/
+
+/** prototypes **/
+
+int gray_init_buffer(unsigned char *gbuf, int gbuf_size, int width,
+                     int bheight, int depth);
+void gray_release_buffer(void);
+void gray_position_display(int x, int by);
+void gray_show_display(bool enable);
+
+/** implementation **/
+
+/* Prepare the grayscale display buffer
+ *
+ * arguments:
+ *   gbuf      = pointer to the memory area to use (e.g. plugin buffer)
+ *   gbuf_size = max usable size of the buffer
+ *   width     = width in pixels  (1..112)
+ *   bheight   = height in 8-pixel units  (1..8)
+ *   depth     = desired number of grayscales - 1  (1..32)
+ *
+ * result:
+ *   = depth  if there was enough memory
+ *   < depth  if there wasn't enough memory. The number of displayable
+ *            grayscales is smaller than desired, but it still works
+ *   = 0      if there wasn't even enough memory for 1 bitplane (black & white)
+ *
+ * You can request any depth from 1 to 32, not just powers of 2. The routine
+ * performs "graceful degradation" if the memory is not sufficient for the
+ * desired depth. As long as there is at least enough memory for 1 bitplane,
+ * it creates as many bitplanes as fit into memory, although 1 bitplane will
+ * only deliver black & white display.
+ *
+ * The total memory needed can be calculated as follows:
+ *   total_mem =
+ *     sizeof(tGraymap)      (= 48 bytes currently)
+ *   + sizeof(long)          (=  4 bytes)
+ *   + (width * bheight + sizeof(long)) * depth
+ */
+int gray_init_buffer(unsigned char *gbuf, int gbuf_size, int width,
+                     int bheight, int depth)
+{
+    int plane_size;
+    int possible_depth;
+    int i, j;
+
+    if (width > LCD_WIDTH || bheight > (LCD_HEIGHT >> 3) || depth < 1)
+        return 0;
+
+    plane_size = width * bheight;
+    possible_depth = (gbuf_size - sizeof(tGraybuf) - sizeof(unsigned long))
+                     / (plane_size + sizeof(unsigned long));
+
+    if (possible_depth < 1)
+        return 0;
+
+    depth = MIN(depth, 32);
+    depth = MIN(depth, possible_depth);
+
+    graybuf = (tGraybuf *) gbuf; /* global pointer to buffer structure */
+
+    graybuf->x = 0;
+    graybuf->by = 0;
+    graybuf->width = width;
+    graybuf->height = bheight << 3;
+    graybuf->bheight = bheight;
+    graybuf->plane_size = plane_size;
+    graybuf->depth = depth;
+    graybuf->cur_plane = 0;
+    graybuf->flags = 0;
+    graybuf->data = gbuf + sizeof(tGraybuf);
+    graybuf->bitpattern = (unsigned long *) (graybuf->data 
+                           + depth * plane_size);
+    
+    i = depth;
+    j = 8;
+    while (i != 0)
+    {
+        i >>= 1;
+        j--;
+    }
+    graybuf->randmask = 0xFF >> j;
+
+    /* initial state is all white */
+    rb->memset(graybuf->data, 0, depth * plane_size);
+    
+    /* Precalculate the bit patterns for all possible pixel values */
+    for (i = 0; i <= depth; i++)
+    {
+        unsigned long pattern = 0;
+        int value = 0;
+
+        for (j = 0; j < depth; j++)
+        {
+            pattern <<= 1;
+            value += i;
+
+            if (value >= depth)
+                value -= depth;   /* "white" bit */
+            else
+                pattern |= 1;     /* "black" bit */
+        }  
+        /* now the lower <depth> bits contain the pattern */
+
+        graybuf->bitpattern[i] = pattern;
+    }
+    
+    return depth;
+}
+
+/* Release the grayscale display buffer
+ *
+ * Switches the grayscale overlay off at first if it is still running,
+ * then sets the pointer to NULL.
+ * DO CALL either this function or at least gray_show_display(false)
+ * before you exit, otherwise nasty things may happen.
+ */
+void gray_release_buffer(void)
+{
+    gray_show_display(false);
+    graybuf = NULL;
+}
+
+/* Set position of the top left corner of the grayscale overlay
+ *
+ * arguments:
+ *   x  = left margin in pixels
+ *   by = top margin in 8-pixel units
+ *
+ * You may set this in a way that the overlay spills across the right or
+ * bottom display border. In this case it will simply be clipped by the 
+ * LCD controller. You can even set negative values, this will clip at the
+ * left or top border. I did not test it, but the limits may be +127 / -128
+ *
+ * If you use this while the grayscale overlay is running, the now-freed area
+ * will be restored.
+ */
+void gray_position_display(int x, int by)
+{
+    if (graybuf == NULL)
+        return;
+
+    graybuf->x = x;
+    graybuf->by = by;
+    
+    if (graybuf->flags & GRAY_RUNNING)
+        graybuf->flags |= GRAY_DEFERRED_UPDATE;
+}
+
+/* Switch the grayscale overlay on or off
+ *
+ * arguments:
+ *   enable = true:  the grayscale overlay is switched on if initialized
+ *          = false: the grayscale overlay is switched off and the regular lcd
+ *                   content is restored
+ *
+ * DO NOT call lcd_update() or any other api function that directly accesses
+ * the lcd while the grayscale overlay is running! If you need to do
+ * lcd_update() to update something outside the grayscale overlay area, use 
+ * gray_deferred_update() instead.
+ *
+ * Other functions to avoid are:
+ *   lcd_blit() (obviously), lcd_update_rect(), lcd_set_contrast(),
+ *   lcd_set_invert_display(), lcd_set_flip(), lcd_roll()
+ *
+ * The grayscale display consumes ~50 % CPU power (for a full screen overlay,
+ * less if the overlay is smaller) when switched on. You can switch the overlay
+ * on and off as many times as you want.
+ */
+void gray_show_display(bool enable)
+{
+    if (graybuf == NULL)
+        return;
+
+    if (enable)
+    {
+        graybuf->flags |= GRAY_RUNNING;
+        timer_set(FREQ / 67);
+    }
+    else
+    {
+        timer_set(0);
+        graybuf->flags &= ~GRAY_RUNNING;
+        rb->lcd_update(); /* restore whatever there was before */
+    }
+}
+
+/*** public optional functions ***/
+
+/* Here are the various graphics primitives. Cut out functions you do not
+ * need in order to keep plugin code size down.
+ */
+
+/** prototypes **/
+
+/* functions affecting the whole display */
+void gray_clear_display(void);
+//void gray_black_display(void);
+//void gray_deferred_update(void);
+
+/* scrolling functions */
+//void gray_scroll_left(int count, bool black_border);
+//void gray_scroll_right(int count, bool black_border);
+//void gray_scroll_up8(bool black_border);
+//void gray_scroll_down8(bool black_border);
+//void gray_scroll_up1(bool black_border);
+//void gray_scroll_down1(bool black_border);
+//
+/* pixel functions */
+void gray_drawpixel(int x, int y, int brightness);
+//void gray_invertpixel(int x, int y);
+
+/* line functions */
+//void gray_drawline(int x1, int y1, int x2, int y2, int brightness);
+//void gray_invertline(int x1, int y1, int x2, int y2);
+
+/* rectangle functions */
+//void gray_drawrect(int x1, int y1, int x2, int y2, int brightness);
+//void gray_fillrect(int x1, int y1, int x2, int y2, int brightness);
+//void gray_invertrect(int x1, int y1, int x2, int y2);
+
+/* bitmap functions */
+//void gray_drawgraymap(unsigned char *src, int x, int y, int nx, int ny);
+//void gray_drawbitmap(unsigned char *src, int x, int y, int nx, int ny,
+//                     bool draw_bg, int fg_brightness, int bg_brightness);
+
+/** implementation **/
+
+/* Clear the grayscale display (sets all pixels to white)
+ */
+void gray_clear_display(void)
+{
+    if (graybuf == NULL)
+        return;
+
+    rb->memset(graybuf->data, 0, graybuf->depth * graybuf->plane_size);
+}
+
+/* Set the grayscale display to all black
+ */
+void gray_black_display(void)
+{
+    if (graybuf == NULL)
+        return;
+
+    rb->memset(graybuf->data, 0xFF, graybuf->depth * graybuf->plane_size);
+}
+
+/* Do a lcd_update() to show changes done by rb->lcd_xxx() functions (in areas
+ * of the screen not covered by the grayscale overlay). If the grayscale 
+ * overlay is running, the update will be done in the next call of the
+ * interrupt routine, otherwise it will be performed right away. See also
+ * comment for the gray_show_display() function.
+ */
+void gray_deferred_update(void)
+{
+    if (graybuf != NULL && (graybuf->flags & GRAY_RUNNING))
+        graybuf->flags |= GRAY_DEFERRED_UPDATE;
+    else
+        rb->lcd_update();
+}
+
+
+/* Set a pixel to a specific gray value
+ *
+ * brightness is 0..255 (black to white) regardless of real bit depth
+ */
+void gray_drawpixel(int x, int y, int brightness)
+{
+    if (graybuf == NULL || x >= graybuf->width || y >= graybuf->height
+        || brightness > 255)
+        return;
+
+    graypixel(x, y, graybuf->bitpattern[(brightness
+                    * (graybuf->depth + 1)) >> 8]);
+}
+
+/* Invert a pixel
+ *
+ * The bit pattern for that pixel in the buffer is inverted, so white
+ * becomes black, light gray becomes dark gray etc.
+ */
+void gray_invertpixel(int x, int y)
+{
+    if (graybuf == NULL || x >= graybuf->width || y >= graybuf->height)
+        return;
+
+    grayinvertmasked(x, (y >> 3), 1 << (y & 7));
+}
+
+
+
+
+
+/**************** end grayscale framework ********************/
+
+
 
 void init_mandelbrot_set(void){
-    x_min = -5<<25;  // -2.5<<26
+    x_min = -5<<25;  // -2.0<<26
     x_max =  1<<26;  //  1.0<<26
     y_min = -1<<26;  // -1.0<<26
     y_max =  1<<26;  //  1.0<<26
@@ -53,11 +642,14 @@ void calc_mandelbrot_set(void){
     int x_pixel, y_pixel;
     int x, x2, y, y2, a, b;
     int x_fact, y_fact;
+    int brightness;
     
     start_tick = *rb->current_tick;  
     
-    rb->lcd_clear_display();
-    rb->lcd_update();
+//    rb->lcd_clear_display();
+//    rb->lcd_update();
+
+    gray_clear_display();
 
     x_fact = (x_max - x_min) / LCD_WIDTH;
     y_fact = (y_max - y_min) / LCD_HEIGHT;
@@ -81,115 +673,132 @@ void calc_mandelbrot_set(void){
                 y = 2 * x * y + b;
                 x = x2 - y2 + a;
             }
-            
+            
             // "coloring"
-            if ( (n_iter > max_iter) ||
-                (n_iter == (max_iter >> 1)) ||
-                (n_iter == (max_iter >> 2)) ||
-                (n_iter == (max_iter >> 3)) 
-                ){
-                rb->lcd_drawpixel(x_pixel,y_pixel);
-            }
-        }
-        
-        /* update block of 8 lines */
-        if ((y_pixel & 0x7) == 0)
-            rb->lcd_update_rect(0, y_pixel, LCD_WIDTH, 8);
+            brightness = 0;
+            if  (n_iter > max_iter){
+                brightness = 0; // black
+            } else {
+                brightness = 255 - (31 * (n_iter & 7));
+            }
+        
+            gray_drawpixel( x_pixel, y_pixel, brightness);
+        }
     }
-    
-    /* we want to know how long we had to wait */
-    rb->lcd_setfont(FONT_SYSFIXED);
-    rb->snprintf(buff, sizeof(buff), "%d", (*rb->current_tick - start_tick));
-    rb->lcd_puts(0,0,buff);
-    rb->snprintf(buff, sizeof(buff), "%d",  max_iter);
-    rb->lcd_puts(0,1,buff);
-    rb->lcd_update_rect(0,0,24,16);
 }
 
+
 enum plugin_status plugin_start(struct plugin_api* api, void* parameter)
 {
+    int grayscales;
+    bool redraw = true;
 
     TEST_PLUGIN_API(api);
-    (void)parameter;
     rb = api;
+    (void)parameter;
+
+    /* get the remainder of the plugin buffer */
+    gbuf = (unsigned char *) rb->plugin_get_buffer(&gbuf_size);
+
+    /* initialize the grayscale buffer:
+     * 112 pixels wide, 8 rows (64 pixels) high, (try to) reserve
+     * 16 bitplanes for 17 shades of gray.*/
+    grayscales = gray_init_buffer(gbuf, gbuf_size, 112, 8, 16) + 1;
+    if (grayscales != 17){
+        rb->snprintf(buff, sizeof(buff), "%d", grayscales);
+        rb->lcd_puts(0, 1, buff);
+        rb->lcd_update();
+        rb->sleep(HZ*2);
+        return(0);
+    }
+
+    gray_show_display(true); /* switch on grayscale overlay */
 
     init_mandelbrot_set();
     lcd_aspect_ratio = ((LCD_WIDTH<<13) / LCD_HEIGHT)<<13;
 
     /* main loop */
     while (true){
+        if(redraw)
+            calc_mandelbrot_set();
 
-            calc_mandelbrot_set();
+        redraw = false;
+        
+        switch (rb->button_get(true)) {
+        case BUTTON_OFF:
+            gray_release_buffer();
+            return PLUGIN_OK;
 
-            /* FIXME: is this the right way to empty the key-queue? 
-               (Otherwise we have to process things twice :-/ ?! */
-            
-            rb->button_get(true);
+        case BUTTON_ON:
+            x_min -= ((delta>>13)*(lcd_aspect_ratio>>13));
+            x_max += ((delta>>13)*(lcd_aspect_ratio>>13));
+            y_min -= delta;
+            y_max += delta;
+            delta = (x_max - x_min) >> 3;
+            redraw = true;
+            break;
+                
 
+        case BUTTON_PLAY:
+            x_min += ((delta>>13)*(lcd_aspect_ratio>>13));
+            x_max -= ((delta>>13)*(lcd_aspect_ratio>>13));
+            y_min += delta;
+            y_max -= delta;
+            delta = (x_max - x_min) >> 3;
+            redraw = true;
+            break;
+      
+        case BUTTON_UP:
+            y_min -= delta;
+            y_max -= delta;
+            redraw = true;
+            break;
 
-            switch (rb->button_get(true)) {
-            case BUTTON_OFF:
-                return PLUGIN_OK;
+        case BUTTON_DOWN:
+            y_min += delta;
+            y_max += delta;
+            redraw = true;
+            break;
 
-            case BUTTON_ON:
-                x_min -= ((delta>>13)*(lcd_aspect_ratio>>13));
-                x_max += ((delta>>13)*(lcd_aspect_ratio>>13));
-                y_min -= delta;
-                y_max += delta;
-                delta = (x_max - x_min) >> 3;
-                break;
-                
+        case BUTTON_LEFT:
+            x_min -= delta;
+            x_max -= delta;
+            redraw = true;
+            break;
 
-            case BUTTON_PLAY:
-                x_min += ((delta>>13)*(lcd_aspect_ratio>>13));
-                x_max -= ((delta>>13)*(lcd_aspect_ratio>>13));
-                y_min += delta;
-                y_max -= delta;
-                delta = (x_max - x_min) >> 3;
-                break;
-      
-            case BUTTON_UP:
-                y_min -= delta;
-                y_max -= delta;
-                break;
-
-            case BUTTON_DOWN:
-                y_min += delta;
-                y_max += delta;
-                break;
-
-            case BUTTON_LEFT:
-                x_min -= delta;
-                x_max -= delta;
-                break;
-
-            case BUTTON_RIGHT:
-                x_min += delta;
-                x_max += delta;
-                break;
-
-            case BUTTON_F1:
-                if (max_iter>5){
-                    max_iter -= 5;
-                }
-                break;
-
-            case BUTTON_F2:
-                if (max_iter < 195){
-                    max_iter += 5;
-                }
-                break;
-
-            case BUTTON_F3:
-                init_mandelbrot_set();
-                break;
-
-                
-            case SYS_USB_CONNECTED:
-                rb->usb_screen();
-                return PLUGIN_USB_CONNECTED;
-            }
+        case BUTTON_RIGHT:
+            x_min += delta;
+            x_max += delta;
+            redraw = true;
+            break;
+
+        case BUTTON_F1:
+            if (max_iter>5){
+                max_iter -= 5;
+                redraw = true;
+            }
+            break;
+
+        case BUTTON_F2:
+            if (max_iter < 195){
+                max_iter += 5;
+                redraw = true;
+            }
+            break;
+
+        case BUTTON_F3:
+            init_mandelbrot_set();
+            redraw = true;
+            break;
+
+        case SYS_USB_CONNECTED:
+            gray_release_buffer();
+            rb->usb_screen();
+            return PLUGIN_USB_CONNECTED;
+        }
     }
+    gray_release_buffer();
     return false;
 }
 #endif
+#endif