samples: drivers: display: distinguish mono pixel format

In exceptional cases, monochrome displays can deviate from the
general interpretation (PIXEL_FORMAT_MONO01) of a logical 1 as
pixel on (white) and 0 as pixel off (black) and instead set the
capability to PIXEL_FORMAT_MONO10. This small but significant
difference has been ignored so far, resulting in an inverse
display for those displays. In order to be technically correct
here, the buffers for a "white" background should be set to 0
instead of 1 and for "black" to 1 instead of 0.

Signed-off-by: Stephan Linz <linz@li-pro.net>

samples/drivers/display/src/main.c

@@ -140,23 +140,36 @@ static void fill_buffer_bgr565(enum corner corner, uint8_t grey, uint8_t *buf,
 	}
 }
 
-static void fill_buffer_mono(enum corner corner, uint8_t grey, uint8_t *buf,
-			     size_t buf_size)
+static void fill_buffer_mono(enum corner corner, uint8_t grey,
+			     uint8_t black, uint8_t white,
+			     uint8_t *buf, size_t buf_size)
 {
 	uint16_t color;
 
 	switch (corner) {
 	case BOTTOM_LEFT:
-		color = (grey & 0x01u) ? 0xFFu : 0x00u;
+		color = (grey & 0x01u) ? white : black;
 		break;
 	default:
-		color = 0;
+		color = black;
 		break;
 	}
 
 	memset(buf, color, buf_size);
 }
 
+static inline void fill_buffer_mono01(enum corner corner, uint8_t grey,
+				      uint8_t *buf, size_t buf_size)
+{
+	fill_buffer_mono(corner, grey, 0x00u, 0xFFu, buf, buf_size);
+}
+
+static inline void fill_buffer_mono10(enum corner corner, uint8_t grey,
+				      uint8_t *buf, size_t buf_size)
+{
+	fill_buffer_mono(corner, grey, 0xFFu, 0x00u, buf, buf_size);
+}
+
 int main(void)
 {
 	size_t x;
@@ -166,6 +179,7 @@ int main(void)
 	size_t h_step;
 	size_t scale;
 	size_t grey_count;
+	uint8_t bg_color;
 	uint8_t *buf;
 	int32_t grey_scale_sleep;
 	const struct device *display_dev;
@@ -216,24 +230,34 @@ int main(void)
 
 	switch (capabilities.current_pixel_format) {
 	case PIXEL_FORMAT_ARGB_8888:
+		bg_color = 0xFFu;
 		fill_buffer_fnc = fill_buffer_argb8888;
 		buf_size *= 4;
 		break;
 	case PIXEL_FORMAT_RGB_888:
+		bg_color = 0xFFu;
 		fill_buffer_fnc = fill_buffer_rgb888;
 		buf_size *= 3;
 		break;
 	case PIXEL_FORMAT_RGB_565:
+		bg_color = 0xFFu;
 		fill_buffer_fnc = fill_buffer_rgb565;
 		buf_size *= 2;
 		break;
 	case PIXEL_FORMAT_BGR_565:
+		bg_color = 0xFFu;
 		fill_buffer_fnc = fill_buffer_bgr565;
 		buf_size *= 2;
 		break;
 	case PIXEL_FORMAT_MONO01:
+		bg_color = 0xFFu;
+		fill_buffer_fnc = fill_buffer_mono01;
+		buf_size = DIV_ROUND_UP(DIV_ROUND_UP(
+			buf_size, NUM_BITS(uint8_t)), sizeof(uint8_t));
+		break;
 	case PIXEL_FORMAT_MONO10:
-		fill_buffer_fnc = fill_buffer_mono;
+		bg_color = 0x00u;
+		fill_buffer_fnc = fill_buffer_mono10;
 		buf_size = DIV_ROUND_UP(DIV_ROUND_UP(
 			buf_size, NUM_BITS(uint8_t)), sizeof(uint8_t));
 		break;
@@ -257,7 +281,7 @@ int main(void)
 #endif
 	}
 
-	(void)memset(buf, 0xFFu, buf_size);
+	(void)memset(buf, bg_color, buf_size);
 
 	buf_desc.buf_size = buf_size;
 	buf_desc.pitch = capabilities.x_resolution;