Icons: small images of their own size for pages

Bitmaps that only pages use (backgrounds, images by state) are now icons:
own width and height, stored in /icons, not in the page lists or the Home
Assistant dropdowns. Page backgrounds and image elements use icons or
bitmaps; the renderer gets icons expanded at the top left, so pages look
the same. Web UI: Icons tab with an editor, Make icon / Make bitmap, Save
as icon on the Draw tab, icons in the backup.

A one-time migration in time-boxed steps moves the uploaded bitmaps that
only pages use, after the new firmware is marked good.

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

src/esp32/logic/icon_format.cpp

@@ -0,0 +1,103 @@
+#include "logic/icon_format.h"
+
+#include <string.h>
+
+bool validIconSize(int width, int height)
+{
+	return width >= 1 && height >= 1 && width <= ICON_MAX_WIDTH && height <= ICON_MAX_HEIGHT;
+}
+
+bool iconPixel(const Icon &icon, int x, int y)
+{
+	if (x < 0 || y < 0 || x >= icon.width || y >= icon.height)
+		return false;
+	return icon.data[y * iconRowBytes(icon.width) + x / 8] & (0x80 >> (x & 7));
+}
+
+void setIconPixel(Icon &icon, int x, int y, bool on)
+{
+	if (x < 0 || y < 0 || x >= icon.width || y >= icon.height)
+		return;
+	uint8_t &byte = icon.data[y * iconRowBytes(icon.width) + x / 8];
+	if (on)
+		byte |= 0x80 >> (x & 7);
+	else
+		byte &= ~(0x80 >> (x & 7));
+}
+
+static int hexValue(char c)
+{
+	if (c >= '0' && c <= '9')
+		return c - '0';
+	if (c >= 'a' && c <= 'f')
+		return c - 'a' + 10;
+	if (c >= 'A' && c <= 'F')
+		return c - 'A' + 10;
+	return -1;
+}
+
+bool iconFromHex(int width, int height, const char *hex, Icon &icon)
+{
+	if (!validIconSize(width, height) || hex == nullptr)
+		return false;
+	int bytes = iconBytes(width, height);
+	if (strlen(hex) != (size_t)bytes * 2)
+		return false;
+	Icon result;
+	result.width = width;
+	result.height = height;
+	for (int i = 0; i < bytes; i++)
+	{
+		int high = hexValue(hex[2 * i]);
+		int low = hexValue(hex[2 * i + 1]);
+		if (high < 0 || low < 0)
+			return false;
+		result.data[i] = (high << 4) | low;
+	}
+	// The unused bits at the end of each row stay off
+	for (int y = 0; y < height; y++)
+		for (int x = width; x < iconRowBytes(width) * 8; x++)
+			result.data[y * iconRowBytes(width) + x / 8] &= ~(0x80 >> (x & 7));
+	icon = result;
+	return true;
+}
+
+void iconToHex(const Icon &icon, char *out)
+{
+	static const char digits[] = "0123456789abcdef";
+	int bytes = iconBytes(icon.width, icon.height);
+	for (int i = 0; i < bytes; i++)
+	{
+		out[2 * i] = digits[icon.data[i] >> 4];
+		out[2 * i + 1] = digits[icon.data[i] & 0x0F];
+	}
+	out[bytes * 2] = '\0';
+}
+
+void iconToBitmap(const Icon &icon, uint8_t *bitmap)
+{
+	memset(bitmap, 0, BITMAP_BYTES);
+	for (int y = 0; y < icon.height; y++)
+		for (int x = 0; x < icon.width; x++)
+			if (iconPixel(icon, x, y))
+				setBitmapPixel(bitmap, x, y, true);
+}
+
+void iconFromBitmap(const uint8_t *bitmap, Icon &icon)
+{
+	int right = 0, bottom = 0;
+	for (int y = 0; y < BITMAP_HEIGHT; y++)
+		for (int x = 0; x < BITMAP_WIDTH; x++)
+			if (bitmapPixel(bitmap, x, y))
+			{
+				right = x > right ? x : right;
+				bottom = y > bottom ? y : bottom;
+			}
+	icon = Icon();
+	icon.width = right + 1;
+	icon.height = bottom + 1;
+	for (int y = 0; y < icon.height; y++)
+		for (int x = 0; x < icon.width; x++)
+			if (bitmapPixel(bitmap, x, y))
+				setIconPixel(icon, x, y, true);
+}

src/esp32/logic/icon_format.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "logic/bitmap_format.h"
+
+// Icons: small bitmaps of their own size (1 x 1 up to 84 x 19) that pages place as images
+// or backgrounds; they are never shown on their own. Rows from top to bottom, each
+// (width + 7) / 8 bytes, the most significant bit is the leftmost dot (like the full
+// screen bitmaps of logic/bitmap_format.h). Icons share the names of bitmaps and pages.
+// Pure logic, tested in test/test_esp32.
+
+const int ICON_MAX_WIDTH = BITMAP_WIDTH;
+const int ICON_MAX_HEIGHT = BITMAP_HEIGHT;
+
+struct Icon
+{
+	uint8_t width = 0;
+	uint8_t height = 0;
+	uint8_t data[BITMAP_BYTES] = {}; // iconBytes(width, height) are used
+};
+
+inline int iconRowBytes(int width)
+{
+	return (width + 7) / 8;
+}
+inline int iconBytes(int width, int height)
+{
+	return iconRowBytes(width) * height;
+}
+bool validIconSize(int width, int height);
+
+bool iconPixel(const Icon &icon, int x, int y);
+void setIconPixel(Icon &icon, int x, int y, bool on);
+
+// Exactly iconBytes(width, height) * 2 hex digits. Returns false on anything else.
+bool iconFromHex(int width, int height, const char *hex, Icon &icon);
+// out must hold BITMAP_HEX_LENGTH + 1 characters
+void iconToHex(const Icon &icon, char *out);
+
+// The icon in a full screen bitmap, with its top left corner at 0, 0
+void iconToBitmap(const Icon &icon, uint8_t *bitmap);
+// A full screen bitmap as an icon that reaches from 0, 0 to its last dot on the right and
+// at the bottom, so it is drawn on the same dots (1 x 1 when it has no dots)
+void iconFromBitmap(const uint8_t *bitmap, Icon &icon);

src/esp32/logic/page.cpp

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 
 static const uint16_t MINUTES_PER_DAY = 24 * 60;
 static const uint32_t MAX_TARGET = 36525UL * MINUTES_PER_DAY; // 2100-01-01
@@ -70,6 +71,31 @@ bool elementUsesHa(const PageElement &element)
 	}
 }
 
+bool pageUsesImage(const DynamicPage &page, const char *name, bool by_state)
+{
+	for (int i = 0; i < page.slot_count; i++)
+		if (sameName(page.slots[i].bitmap, name))
+			return true;
+	for (int i = 0; i < page.element_count; i++)
+	{
+		const PageElement &e = page.elements[i];
+		if (e.type != ElementType::Image)
+			continue;
+		if (!e.entity[0])
+		{
+			if (sameName(e.text, name))
+				return true;
+			continue;
+		}
+		size_t start = strlen(e.text);
+		if (strncasecmp(name, e.text, start) != 0)
+			continue;
+		if (by_state ? name[start] != '\0' : strcasecmp(name + start, "default") == 0)
+			return true;
+	}
+	return false;
+}
+
 bool validEntityId(const char *entity)
 {
 	if (entity == nullptr)

src/esp32/logic/page.h

@@ -223,6 +223,11 @@ void plexUserSlug(const char *name, char *out, size_t out_size);
 // The element shows a Home Assistant value (HaValue; Image, Bar with an entity)
 bool elementUsesHa(const PageElement &element);
 
+// Whether the page uses this bitmap or icon (compared without case): as a background, as
+// a fixed image, or as the "default" image of an image with an entity. by_state: also the
+// names an image with an entity may show (its name start + any state).
+bool pageUsesImage(const DynamicPage &page, const char *name, bool by_state = false);
+
 // Entity ids look like "sensor.outside_temperature" (lower case, digits, '_', one '.');
 // {plex_user} may be in them
 bool validEntityId(const char *entity);