Add Chinese text rendering support

Extend the bitmap font pipeline with the Chinese Joker glyph subset and encode supported UTF-8 text for Tonc TTE. Move the affine map clear of the expanded font, add a compile-time VRAM overlap guard, and cover every custom glyph with host tests.

source/chinese_text.c

@@ -0,0 +1,113 @@
+#include "chinese_text.h"
+
+#include <stdint.h>
+
+#define CHINESE_GLYPH_FIRST 128
+
+static const uint32_t s_chinese_codepoints[] = {
+#define CHINESE_GLYPH(codepoint) codepoint,
+#include "def_chinese_glyph_table.h"
+#undef CHINESE_GLYPH
+};
+
+_Static_assert(
+    sizeof(s_chinese_codepoints) / sizeof(s_chinese_codepoints[0]) <= 256 - CHINESE_GLYPH_FIRST,
+    "Chinese glyph table exceeds the single-byte encoding range"
+);
+
+static uint32_t decode_utf8_codepoint(const unsigned char** cursor)
+{
+    const unsigned char* text = *cursor;
+
+    if (text[0] < 0x80)
+    {
+        *cursor += 1;
+        return text[0];
+    }
+
+    if ((text[0] & 0xE0) == 0xC0 && (text[1] & 0xC0) == 0x80)
+    {
+        *cursor += 2;
+        return ((uint32_t)(text[0] & 0x1F) << 6) | (text[1] & 0x3F);
+    }
+
+    if ((text[0] & 0xF0) == 0xE0 && (text[1] & 0xC0) == 0x80 && (text[2] & 0xC0) == 0x80)
+    {
+        *cursor += 3;
+        return ((uint32_t)(text[0] & 0x0F) << 12) | ((uint32_t)(text[1] & 0x3F) << 6) |
+               (text[2] & 0x3F);
+    }
+
+    *cursor += 1;
+    return '?';
+}
+
+static uint32_t codepoint_to_glyph(uint32_t codepoint)
+{
+    for (size_t i = 0; i < sizeof(s_chinese_codepoints) / sizeof(s_chinese_codepoints[0]); i++)
+    {
+        if (s_chinese_codepoints[i] == codepoint)
+        {
+            return CHINESE_GLYPH_FIRST + i;
+        }
+    }
+
+    return '?';
+}
+
+static size_t encode_tte_codepoint(uint32_t codepoint, char* output, size_t output_size)
+{
+    if (codepoint < 0x80)
+    {
+        if (output_size < 1)
+        {
+            return 0;
+        }
+
+        output[0] = (char)codepoint;
+        return 1;
+    }
+
+    if (codepoint <= 0x7FF)
+    {
+        if (output_size < 2)
+        {
+            return 0;
+        }
+
+        output[0] = (char)(0xC0 | (codepoint >> 6));
+        output[1] = (char)(0x80 | (codepoint & 0x3F));
+        return 2;
+    }
+
+    return 0;
+}
+
+size_t chinese_text_encode(const char* utf8, char* output, size_t output_size)
+{
+    if (utf8 == NULL || output == NULL || output_size == 0)
+    {
+        return 0;
+    }
+
+    const unsigned char* cursor = (const unsigned char*)utf8;
+    size_t output_len = 0;
+
+    while (*cursor != '\0')
+    {
+        uint32_t codepoint = decode_utf8_codepoint(&cursor);
+        uint32_t tte_codepoint = codepoint < 0x80 ? codepoint : codepoint_to_glyph(codepoint);
+        size_t encoded_size =
+            encode_tte_codepoint(tte_codepoint, output + output_len, output_size - output_len - 1);
+
+        if (encoded_size == 0)
+        {
+            break;
+        }
+
+        output_len += encoded_size;
+    }
+
+    output[output_len] = '\0';
+    return output_len;
+}