altos/st7565: Diff image during update

This minimizes the amount of data sent to the device. Mostly this is
useful to skip updates that don't change the display at all.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/drivers/ao_st7565.c b/src/drivers/ao_st7565.c
index 261ed857b16d840ce7fcd7acc46178845cc5bcbb..7540297cb3f686b6147048c3f493d1e36f90c85c 100644 (file)
--- a/src/drivers/ao_st7565.c
+++ b/src/drivers/ao_st7565.c
@@ -133,42 +133,87 @@ ao_st7565_setup(void)
 
 static uint8_t rotbuf[AO_ST7565_WIDTH];
 
+#define WIDTH  AO_ST7565_WIDTH
+#define HEIGHT AO_ST7565_HEIGHT
+#define STRIDE AO_BITMAP_STRIDE(WIDTH)
+
+static uint32_t        previous_image[STRIDE * HEIGHT];
+
 void
 ao_st7565_update(struct ao_bitmap *bitmap)
 {
-       uint8_t         col, c, page;
-       int             row;
-       uint32_t        *line;
+       int16_t         col, c, page;
+       int16_t         row;
+       uint32_t        *line, *prev, *l;
+       uint32_t        bits;
        uint8_t         *r;
+       int16_t         min_col, min_row, max_col, max_row;
+       int16_t         min_page, max_page;
 
        ao_st7565_setup();
 
+       min_col = STRIDE - 1;
+       max_col = 0;
+       min_row = HEIGHT - 1;
+       max_row = 0;
        line = bitmap->base;
-       for (page = 0; page < 8; page++) {
+       prev = previous_image;
+       for (row = 0; row < HEIGHT; row++) {
+               for (col = 0; col < STRIDE; col++) {
+                       bits = *line++;
+                       if (bits != *prev) {
+                               *prev = bits;
+                               if (row < min_row)
+                                       min_row = row;
+                               if (row > max_row)
+                                       max_row = row;
+                               if (col < min_col)
+                                       min_col = col;
+                               if (col > max_col)
+                                       max_col = col;
+                       }
+                       prev++;
+               }
+       }
+
+       if (min_col > max_col || min_row > max_row)
+               return;
+
+       min_page = min_row >> 3;
+       max_page = max_row >> 3;
+       line = bitmap->base + min_page * 8 * STRIDE + min_col;
+
+       uint8_t first_col = (uint8_t) (min_col * 32);
+       uint8_t num_col = (uint8_t) (max_col + 1 - min_col) * 32;
+
+       for (page = min_page; page <= max_page; page++) {
                uint8_t         i[4] = {
-                       ST7565_PAGE_ADDRESS_SET(7-page),
-                       ST7565_COLUMN_ADDRESS_SET_MSN(0 >> 4),
-                       ST7565_COLUMN_ADDRESS_SET_MSN(0 & 0xf),
+                       ST7565_PAGE_ADDRESS_SET(7-(uint8_t) page),
+                       ST7565_COLUMN_ADDRESS_SET_MSN(first_col >> 4),
+                       ST7565_COLUMN_ADDRESS_SET_LSN(first_col & 0xf),
                        ST7565_RMW
                };
-               memset(rotbuf, 0, sizeof(rotbuf));
+               memset(rotbuf, 0, num_col);
                for (row = 7; row >= 0; row--) {
                        r = rotbuf;
-                       for (col = 0; col < AO_BITMAP_STRIDE(AO_ST7565_WIDTH); col++) {
-                               uint32_t        bits = ~*line++;
+                       l = line;
+                       line += STRIDE;
+                       for (col = min_col; col <= max_col; col++) {
+                               bits = ~*l++;
                                for (c = 0; c < 32; c++) {
                                        *r++ |= ((bits >> c) & 1) << row;
                                }
                        }
                }
                ao_st7565_instructions(i, 4);
-               ao_st7565_data(rotbuf, AO_ST7565_WIDTH);
+               ao_st7565_data(rotbuf, num_col);
        }
 }
 
 void
 ao_st7565_init(void)
 {
+       memset(previous_image, 0xff, sizeof(previous_image));
        ao_enable_output(AO_ST7565_RESET_PORT, AO_ST7565_RESET_PIN, 1);
        ao_enable_output(AO_ST7565_A0_PORT, AO_ST7565_A0_PIN, 1);