Add grayscale EInk support

Author: tannewt

shared-bindings/displayio/EPaperDisplay.c

@@ -49,7 +49,19 @@
 //|     Most people should not use this class directly. Use a specific display driver instead that will
 //|     contain the startup and shutdown sequences at minimum."""
 //|
-//|     def __init__(self, display_bus: _DisplayBus, start_sequence: ReadableBuffer, stop_sequence: ReadableBuffer, *, width: int, height: int, ram_width: int, ram_height: int, colstart: int = 0, rowstart: int = 0, rotation: int = 0, set_column_window_command: Optional[int] = None, set_row_window_command: Optional[int] = None, single_byte_bounds: bool = False, write_black_ram_command: int, black_bits_inverted: bool = False, write_color_ram_command: Optional[int] = None, color_bits_inverted: bool = False, highlight_color: int = 0x000000, refresh_display_command: int, refresh_time: float = 40, busy_pin: Optional[microcontroller.Pin] = None, busy_state: bool = True, seconds_per_frame: float = 180, always_toggle_chip_select: bool = False) -> None:
+//|     def __init__(self, display_bus: _DisplayBus,
+//|                  start_sequence: ReadableBuffer, stop_sequence: ReadableBuffer, *,
+//|                  width: int, height: int, ram_width: int, ram_height: int,
+//|                  colstart: int = 0, rowstart: int = 0, rotation: int = 0,
+//|                  set_column_window_command: Optional[int] = None,
+//|                  set_row_window_command: Optional[int] = None, single_byte_bounds: bool = False,
+//|                  write_black_ram_command: int, black_bits_inverted: bool = False,
+//|                  write_color_ram_command: Optional[int] = None,
+//|                  color_bits_inverted: bool = False, highlight_color: int = 0x000000,
+//|                  refresh_display_command: int, refresh_time: float = 40,
+//|                  busy_pin: Optional[microcontroller.Pin] = None, busy_state: bool = True,
+//|                  seconds_per_frame: float = 180, always_toggle_chip_select: bool = False,
+//|                  grayscale: bool = False) -> None:
 //|         """Create a EPaperDisplay object on the given display bus (`displayio.FourWire` or `displayio.ParallelBus`).
 //|
 //|         The ``start_sequence`` and ``stop_sequence`` are bitpacked to minimize the ram impact. Every
@@ -84,11 +96,18 @@
 //|         :param microcontroller.Pin busy_pin: Pin used to signify the display is busy
 //|         :param bool busy_state: State of the busy pin when the display is busy
 //|         :param float seconds_per_frame: Minimum number of seconds between screen refreshes
-//|         :param bool always_toggle_chip_select: When True, chip select is toggled every byte"""
+//|         :param bool always_toggle_chip_select: When True, chip select is toggled every byte
+//|         :param bool grayscale: When true, the color ram is the low bit of 2-bit grayscale"""
 //|         ...
 //|
 STATIC mp_obj_t displayio_epaperdisplay_make_new(const mp_obj_type_t *type, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
-    enum { ARG_display_bus, ARG_start_sequence, ARG_stop_sequence, ARG_width, ARG_height, ARG_ram_width, ARG_ram_height, ARG_colstart, ARG_rowstart, ARG_rotation, ARG_set_column_window_command, ARG_set_row_window_command, ARG_set_current_column_command, ARG_set_current_row_command, ARG_write_black_ram_command, ARG_black_bits_inverted, ARG_write_color_ram_command, ARG_color_bits_inverted, ARG_highlight_color, ARG_refresh_display_command,  ARG_refresh_time, ARG_busy_pin, ARG_busy_state, ARG_seconds_per_frame, ARG_always_toggle_chip_select };
+    enum { ARG_display_bus, ARG_start_sequence, ARG_stop_sequence, ARG_width, ARG_height,
+           ARG_ram_width, ARG_ram_height, ARG_colstart, ARG_rowstart, ARG_rotation,
+           ARG_set_column_window_command, ARG_set_row_window_command, ARG_set_current_column_command,
+           ARG_set_current_row_command, ARG_write_black_ram_command, ARG_black_bits_inverted,
+           ARG_write_color_ram_command, ARG_color_bits_inverted, ARG_highlight_color,
+           ARG_refresh_display_command,  ARG_refresh_time, ARG_busy_pin, ARG_busy_state,
+           ARG_seconds_per_frame, ARG_always_toggle_chip_select, ARG_grayscale };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_display_bus, MP_ARG_REQUIRED | MP_ARG_OBJ },
         { MP_QSTR_start_sequence, MP_ARG_REQUIRED | MP_ARG_OBJ },
@@ -115,6 +134,7 @@ STATIC mp_obj_t displayio_epaperdisplay_make_new(const mp_obj_type_t *type, size
         { MP_QSTR_busy_state, MP_ARG_BOOL | MP_ARG_KW_ONLY, {.u_bool = true} },
         { MP_QSTR_seconds_per_frame, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_obj = MP_OBJ_NEW_SMALL_INT(180)} },
         { MP_QSTR_always_toggle_chip_select, MP_ARG_BOOL | MP_ARG_KW_ONLY, {.u_bool = false} },
+        { MP_QSTR_grayscale, MP_ARG_BOOL | MP_ARG_KW_ONLY, {.u_bool = false} },
     };
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
@@ -151,11 +171,14 @@ STATIC mp_obj_t displayio_epaperdisplay_make_new(const mp_obj_type_t *type, size
         self,
         display_bus,
         start_bufinfo.buf, start_bufinfo.len, stop_bufinfo.buf, stop_bufinfo.len,
-        args[ARG_width].u_int, args[ARG_height].u_int, args[ARG_ram_width].u_int, args[ARG_ram_height].u_int, args[ARG_colstart].u_int, args[ARG_rowstart].u_int, rotation,
+        args[ARG_width].u_int, args[ARG_height].u_int, args[ARG_ram_width].u_int, args[ARG_ram_height].u_int,
+        args[ARG_colstart].u_int, args[ARG_rowstart].u_int, rotation,
         args[ARG_set_column_window_command].u_int, args[ARG_set_row_window_command].u_int,
         args[ARG_set_current_column_command].u_int, args[ARG_set_current_row_command].u_int,
-        args[ARG_write_black_ram_command].u_int, args[ARG_black_bits_inverted].u_bool, write_color_ram_command, args[ARG_color_bits_inverted].u_bool, highlight_color, args[ARG_refresh_display_command].u_int, refresh_time,
-        busy_pin, args[ARG_busy_state].u_bool, seconds_per_frame, args[ARG_always_toggle_chip_select].u_bool
+        args[ARG_write_black_ram_command].u_int, args[ARG_black_bits_inverted].u_bool, write_color_ram_command,
+        args[ARG_color_bits_inverted].u_bool, highlight_color, args[ARG_refresh_display_command].u_int, refresh_time,
+        busy_pin, args[ARG_busy_state].u_bool, seconds_per_frame,
+        args[ARG_always_toggle_chip_select].u_bool, args[ARG_grayscale].u_bool
         );
 
     return self;

shared-bindings/displayio/EPaperDisplay.h

@@ -44,7 +44,7 @@ void common_hal_displayio_epaperdisplay_construct(displayio_epaperdisplay_obj_t*
         uint16_t set_column_window_command, uint16_t set_row_window_command,
         uint16_t set_current_column_command, uint16_t set_current_row_command,
         uint16_t write_black_ram_command, bool black_bits_inverted, uint16_t write_color_ram_command, bool color_bits_inverted, uint32_t highlight_color, uint16_t refresh_display_command, mp_float_t refresh_time,
-        const mcu_pin_obj_t* busy_pin, bool busy_state, mp_float_t seconds_per_frame, bool always_toggle_chip_select);
+        const mcu_pin_obj_t* busy_pin, bool busy_state, mp_float_t seconds_per_frame, bool always_toggle_chip_select, bool grayscale);
 
 bool common_hal_displayio_epaperdisplay_refresh(displayio_epaperdisplay_obj_t* self);
 

shared-module/displayio/ColorConverter.c

@@ -165,9 +165,9 @@ void displayio_colorconverter_convert(displayio_colorconverter_t *self, const _d
             g8 = MIN(255,g8 + (randg&0x03));
         } else {
             int bitmask = 0xFF >> colorspace->depth;
-            b8 = MIN(255,b8 + (randb&bitmask));
-            r8 = MIN(255,r8 + (randr&bitmask));
-            g8 = MIN(255,g8 + (randg&bitmask));
+            b8 = MIN(255,b8 + (randb & bitmask));
+            r8 = MIN(255,r8 + (randr & bitmask));
+            g8 = MIN(255,g8 + (randg & bitmask));
         }
         pixel = r8 << 16 | g8 << 8 | b8;
     }
@@ -196,7 +196,8 @@ void displayio_colorconverter_convert(displayio_colorconverter_t *self, const _d
         return;
     }  else if (colorspace->grayscale && colorspace->depth <= 8) {
         uint8_t luma = displayio_colorconverter_compute_luma(pixel);
-        output_color->pixel = luma >> (8 - colorspace->depth);
+        size_t bitmask = (1 << colorspace->depth) - 1;
+        output_color->pixel = (luma >> colorspace->grayscale_bit) & bitmask;
         output_color->opaque = true;
         return;
     }

shared-module/displayio/EPaperDisplay.c

@@ -49,7 +49,7 @@ void common_hal_displayio_epaperdisplay_construct(displayio_epaperdisplay_obj_t*
         uint16_t set_column_window_command, uint16_t set_row_window_command,
         uint16_t set_current_column_command, uint16_t set_current_row_command,
         uint16_t write_black_ram_command, bool black_bits_inverted, uint16_t write_color_ram_command, bool color_bits_inverted, uint32_t highlight_color, uint16_t refresh_display_command, mp_float_t refresh_time,
-        const mcu_pin_obj_t* busy_pin, bool busy_state, mp_float_t seconds_per_frame, bool chip_select) {
+        const mcu_pin_obj_t* busy_pin, bool busy_state, mp_float_t seconds_per_frame, bool chip_select, bool grayscale) {
     if (highlight_color != 0x000000) {
         self->core.colorspace.tricolor = true;
         self->core.colorspace.tricolor_hue = displayio_colorconverter_compute_hue(highlight_color);
@@ -72,6 +72,7 @@ void common_hal_displayio_epaperdisplay_construct(displayio_epaperdisplay_obj_t*
     self->refreshing = false;
     self->milliseconds_per_frame = seconds_per_frame * 1000;
     self->chip_select = chip_select ? CHIP_SELECT_TOGGLE_EVERY_BYTE : CHIP_SELECT_UNTOUCHED;
+    self->grayscale = grayscale;
 
     self->start_sequence = start_sequence;
     self->start_sequence_len = start_sequence_len;
@@ -230,17 +231,16 @@ bool displayio_epaperdisplay_refresh_area(displayio_epaperdisplay_obj_t* self, c
     uint32_t mask[mask_length];
 
     uint8_t passes = 1;
-    if (self->core.colorspace.tricolor) {
+    if (self->core.colorspace.tricolor || self->grayscale) {
         passes = 2;
     }
     for (uint8_t pass = 0; pass < passes; pass++) {
         uint16_t remaining_rows = displayio_area_height(&clipped);
 
-        // added false parameter at end for SH1107_addressing quirk
         if (self->set_row_window_command != NO_COMMAND) {
             displayio_display_core_set_region_to_update(&self->core, self->set_column_window_command,
             self->set_row_window_command, self->set_current_column_command, self->set_current_row_command,
-            false, self->chip_select, &clipped, false);
+            false, self->chip_select, &clipped, false /* SH1107_addressing */);
         }
 
         uint8_t write_command = self->write_black_ram_command;
@@ -270,8 +270,13 @@ bool displayio_epaperdisplay_refresh_area(displayio_epaperdisplay_obj_t* self, c
             memset(buffer, 0, buffer_size * sizeof(buffer[0]));
 
             self->core.colorspace.grayscale = true;
+            self->core.colorspace.grayscale_bit = 7;
             if (pass == 1) {
-                self->core.colorspace.grayscale = false;
+                if (self->grayscale) { // 4-color grayscale
+                    self->core.colorspace.grayscale_bit = 6;
+                } else { // Tri-color
+                    self->core.colorspace.grayscale = false;
+                }
             }
             displayio_display_core_fill_area(&self->core, &subrectangle, mask, buffer);
 

shared-module/displayio/EPaperDisplay.h

@@ -55,6 +55,7 @@ typedef struct {
     bool black_bits_inverted;
     bool color_bits_inverted;
     bool refreshing;
+    bool grayscale;
     display_chip_select_behavior_t chip_select;
 } displayio_epaperdisplay_obj_t;
 

shared-module/displayio/Palette.h

@@ -37,6 +37,7 @@ typedef struct {
     uint8_t bytes_per_cell;
     uint8_t tricolor_hue;
     uint8_t tricolor_luma;
+    uint8_t grayscale_bit; // The lowest grayscale bit. Normally 8 - depth.
     bool grayscale;
     bool tricolor;
     bool pixels_in_byte_share_row;

shared-module/displayio/display_core.c

@@ -48,6 +48,7 @@ void displayio_display_core_construct(displayio_display_core_t* self,
         uint16_t color_depth, bool grayscale, bool pixels_in_byte_share_row, uint8_t bytes_per_cell, bool reverse_pixels_in_byte, bool reverse_bytes_in_word) {
     self->colorspace.depth = color_depth;
     self->colorspace.grayscale = grayscale;
+    self->colorspace.grayscale_bit = 8 - color_depth;
     self->colorspace.pixels_in_byte_share_row = pixels_in_byte_share_row;
     self->colorspace.bytes_per_cell = bytes_per_cell;
     self->colorspace.reverse_pixels_in_byte = reverse_pixels_in_byte;