Fix dense images on the Nano and the off image in slow mode

- Nano: B data is drawn fast enough for the serial line. A hex digit arrives
  every 87 us; with a division and four drawPixel() calls per digit a lit
  digit took about 105 us, so dense frames (all yellow, the panda bitmap)
  overflowed the 64 byte receive buffer: frames not shown or wrong, "Line
  too long", frame check repairs that failed the same way. Now the parser
  counts columns and rows and BROSE9323::drawDots() sets the 4 dots
  (about 20 us).
- ESP32: Power off and the start of the night draw the off image also when
  slow mode had the power off already (it powers on for it, once)
- Tests: drawDots() against drawPixel(), off image in slow mode
- Version 2.19.3

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/mocks/BROSE9323.h

@@ -27,6 +27,14 @@ public:
 	void begin() { log("begin"); }
 	void display(bool force = false, bool instant = false) { log("display", force, instant); }
 	void drawPixel(int16_t x, int16_t y, uint16_t color) { log(direct ? "directPixel" : "pixel", x, y, color); }
+	// Recorded as the pixel calls it stands for (the real one is tested in test_driver)
+	void drawDots(int16_t x, int16_t y, uint8_t bits, bool color)
+	{
+		log("dots", x, y, bits);
+		for (int i = 0; i < 4; i++)
+			if (bits & (8 >> i))
+				drawPixel(x + i, y, color);
+	}
 	void fillScreen(uint16_t color) { log("fill", color); }
 	void setDirect(bool d) { direct = d; }
 	void setTiming(uint16_t t) { log("timing", t); }

test/test_driver/test_main.cpp

@@ -226,6 +226,38 @@ void test_crc_of_equal_images_is_equal()
 	delete b;
 }
 
+// The fast path for B data must give the same image as drawPixel(), also at the right edge
+// (B widths are rounded up to 4, so x + 3 can be past it) and below the last row
+void test_draw_dots_is_like_draw_pixel()
+{
+	BROSE9323 *a = make(), *b = make();
+	a->fillScreen(1);
+	b->fillScreen(1);
+	for (int y = 0; y <= H; y++)
+		for (int x = 0; x < W; x += 4)
+		{
+			uint8_t bits = (x * 5 + y * 3) & 0xF;
+			bool color = (x / 4 + y) % 3 == 0;
+			a->drawDots(x + 2, y, bits, color);
+			for (int i = 0; i < 4; i++)
+				if (bits & (8 >> i))
+					b->drawPixel(x + 2 + i, y, color);
+		}
+	TEST_ASSERT_EQUAL_HEX16(b->crc(), a->crc());
+	for (int x = 0; x < W; x++)
+		for (int y = 0; y < H; y++)
+		{
+			a->drawPixel(x, y, 0);
+			b->drawPixel(x, y, 0);
+		}
+	a->drawDots(-2, 0, 0xF, 1); // dots 0 and 1 of the first row
+	b->drawPixel(0, 0, 1);
+	b->drawPixel(1, 0, 1);
+	TEST_ASSERT_EQUAL_HEX16(b->crc(), a->crc());
+	delete a;
+	delete b;
+}
+
 int main()
 {
 	UNITY_BEGIN();
@@ -237,5 +269,6 @@ int main()
 	RUN_TEST(test_refresh_waits_for_a_running_effect);
 	RUN_TEST(test_interrupted_first_frame_still_reaches_every_dot);
 	RUN_TEST(test_crc_of_equal_images_is_equal);
+	RUN_TEST(test_draw_dots_is_like_draw_pixel);
 	return UNITY_END();
 }

test/test_esp32/test_main.cpp

@@ -583,6 +583,38 @@ void test_power_switch_off_keeps_display_off_during_the_day()
 	TEST_ASSERT_EQUAL(0, power.on_count);
 }
 
+// Slow mode had the power off already: the dots still show the clock, so the power goes on
+// for the off image, once
+void test_power_switch_off_in_slow_mode_draws_the_off_image()
+{
+	slowMode(true);
+	run(12, 0, POWER_OFF_DELAY + 200);
+	TEST_ASSERT_FALSE(power.is_on);
+	controller->setPowerEnabled(false);
+	run(12, 1);
+	TEST_ASSERT_TRUE(power.is_on);
+	TEST_ASSERT_EQUAL_STRING("off", frames.last().c_str());
+	run(12, 1, CLEAR_BEFORE_OFF_TIME + 200);
+	TEST_ASSERT_FALSE(power.is_on);
+	run(12, 2, 60000);
+	TEST_ASSERT_EQUAL(2, power.on_count);
+	TEST_ASSERT_EQUAL(2, (int)frames.shown.size());
+}
+
+void test_night_in_slow_mode_draws_the_off_image()
+{
+	slowMode(true);
+	run(23, 15, POWER_OFF_DELAY + 200);
+	TEST_ASSERT_FALSE(power.is_on);
+	run(23, 31);
+	TEST_ASSERT_TRUE(power.is_on);
+	TEST_ASSERT_EQUAL_STRING("off", frames.last().c_str());
+	run(23, 31, POWER_OFF_DELAY + 200);
+	TEST_ASSERT_FALSE(power.is_on);
+	run(3, 0, 60000);
+	TEST_ASSERT_EQUAL(2, power.on_count);
+}
+
 void test_power_switch_on_again_shows_clock()
 {
 	run(12, 0);
@@ -3270,6 +3302,8 @@ int main()
 	RUN_TEST(test_power_switch_off_clears_and_powers_off_quickly);
 	RUN_TEST(test_power_switch_off_waits_for_the_refresh_effect);
 	RUN_TEST(test_power_switch_off_keeps_display_off_during_the_day);
+	RUN_TEST(test_power_switch_off_in_slow_mode_draws_the_off_image);
+	RUN_TEST(test_night_in_slow_mode_draws_the_off_image);
 	RUN_TEST(test_power_switch_on_again_shows_clock);
 	RUN_TEST(test_redraws_after_power_was_switched_off_elsewhere);
 	RUN_TEST(test_no_wifi_is_shown_after_a_minute_without_wifi);