feat: add device-side subtitle overlay using FreeType for rendering Chinese text

- Updated Cargo.toml to include freetype-rs for font rendering.
- Modified message.rs to introduce a new Message variant for subtitles.
- Enhanced HttpPlugin to send subtitle messages to the live2d plugin.
- Implemented text rendering in the live2d plugin using FreeType for Chinese characters.
- Added OpenGL shaders for rendering text overlays.
- Created a new text.rs module for handling text rasterization and texture rendering.
- Updated renderer.rs to integrate subtitle rendering logic.

src/plugins/live2d/text.rs

@@ -0,0 +1,239 @@
+//! 基于 FreeType 的中文文字光栅化 + OpenGL 纹理渲染（设备端 Live2D 字幕 overlay）。
+//!
+//! 设计：每个字符首次出现时用 FreeType 渲染为灰度位图（经 `render_glyph` 拿到位图），转成
+//! 白色字形（alpha=灰度）的 RGBA 纹理并缓存；绘制时按 pen 位置贴纹理即可。纹理创建需要
+//! `Gl` 函数指针（与渲染器共用同一 EGL 上下文）。
+
+use super::gl::gl as gl_const;
+use super::gl::Gl;
+use freetype::face::LoadFlag;
+use freetype::Face;
+use freetype::Library;
+use freetype::RenderMode;
+use std::collections::HashMap;
+use std::path::Path;
+
+use anyhow::Result;
+
+/// 单个字符的缓存字形
+#[derive(Clone)]
+pub struct CachedGlyph {
+    /// 字形纹理（0 表示该字符无可见像素，仅用于步进）
+    pub tex: gl_const::GLuint,
+    pub w: i32,
+    pub h: i32,
+    /// 字形位图相对 pen 原点的偏移
+    pub left: i32,
+    pub top: i32,
+    /// 26.6 定点像素步进（渲染端需 >> 6 转为像素）
+    pub advance: i32,
+}
+
+pub struct TextRenderer {
+    face: Face<'static>,
+    font_px: u32,
+    glyphs: HashMap<char, CachedGlyph>,
+    white_tex: Option<gl_const::GLuint>,
+}
+
+// FreeType 的 Face 包裹裸指针，仅在本插件单一渲染线程使用。
+unsafe impl Send for TextRenderer {}
+
+/// FT_LOAD_RENDER 标志位（0x4）：加载字符的同时渲染为位图
+const FT_LOAD_RENDER: i32 = 0x4;
+
+impl TextRenderer {
+    pub fn new(font_path: &Path, font_px: u32) -> Result<Self> {
+        let library = Library::init()?;
+        // 让 Library 成为 'static（程序级单例），从而 Face<'static> 可长期持有而不会悬垂
+        let library: &'static Library = Box::leak(Box::new(library));
+        let face = library.new_face(font_path, 0)?;
+        let tr = Self {
+            face,
+            font_px,
+            glyphs: HashMap::new(),
+            white_tex: None,
+        };
+        tr.face.set_pixel_sizes(0, font_px)?;
+        println!("[Live2D] 字幕字体就绪: {:?} ({}px)", font_path, font_px);
+        Ok(tr)
+    }
+
+    /// 当前字号（像素）
+    pub fn font_size(&self) -> u32 {
+        self.font_px
+    }
+
+    /// 1x1 白色纹理（用于纯色背景框，alpha 恒为 1）。
+    fn white_tex(&mut self, gl: &Gl) -> gl_const::GLuint {
+        if let Some(t) = self.white_tex {
+            return t;
+        }
+        let mut tex = 0u32;
+        unsafe {
+            (gl.gl_gen_textures)(1, &mut tex);
+            (gl.gl_bind_texture)(gl_const::GL_TEXTURE_2D, tex);
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_MIN_FILTER,
+                gl_const::GL_LINEAR as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_MAG_FILTER,
+                gl_const::GL_LINEAR as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_WRAP_S,
+                gl_const::GL_CLAMP_TO_EDGE as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_WRAP_T,
+                gl_const::GL_CLAMP_TO_EDGE as i32,
+            );
+            let px: [u8; 4] = [255, 255, 255, 255];
+            (gl.gl_tex_image_2d)(
+                gl_const::GL_TEXTURE_2D,
+                0,
+                gl_const::GL_RGBA as i32,
+                1,
+                1,
+                0,
+                gl_const::GL_RGBA,
+                gl_const::GL_UNSIGNED_BYTE,
+                px.as_ptr() as *const std::ffi::c_void,
+            );
+        }
+        self.white_tex = Some(tex);
+        tex
+    }
+
+    /// 取 1x1 白纹理（供外部画背景框）。
+    pub fn white_texture(&mut self, gl: &Gl) -> gl_const::GLuint {
+        self.white_tex(gl)
+    }
+
+    /// 估算字符像素宽度（用于换行布局，不创建纹理）。返回像素值。
+    pub fn measure_advance(&mut self, ch: char) -> i32 {
+        if self
+            .face
+            .load_char(ch as usize, LoadFlag::from_bits_truncate(FT_LOAD_RENDER))
+            .is_ok()
+        {
+            (self.face.glyph().advance().x >> 6) as i32
+        } else {
+            (self.font_px as f32 * 0.5) as i32
+        }
+    }
+
+    fn rasterize(&mut self, gl: &Gl, ch: char) -> Option<CachedGlyph> {
+        let half_advance_26_6 = (self.font_px as i32) << 5; // 半字宽，26.6 定点
+        if self
+            .face
+            .load_char(ch as usize, LoadFlag::from_bits_truncate(FT_LOAD_RENDER))
+            .is_err()
+        {
+            return Some(CachedGlyph {
+                tex: 0,
+                w: 0,
+                h: 0,
+                left: 0,
+                top: 0,
+                advance: half_advance_26_6,
+            });
+        }
+        let glyph = self.face.glyph();
+        if glyph.render_glyph(RenderMode::Normal).is_err() {
+            let adv = glyph.advance().x as i32; // 26.6 定点
+            return Some(CachedGlyph {
+                tex: 0,
+                w: 0,
+                h: 0,
+                left: 0,
+                top: 0,
+                advance: adv,
+            });
+        }
+        let bitmap = glyph.bitmap();
+        let w = bitmap.width();
+        let h = bitmap.rows();
+        let left = glyph.bitmap_left();
+        let top = glyph.bitmap_top();
+        let advance = glyph.advance().x as i32; // 26.6 定点
+        if w == 0 || h == 0 {
+            return Some(CachedGlyph {
+                tex: 0,
+                w: 0,
+                h: 0,
+                left,
+                top,
+                advance,
+            });
+        }
+        // 灰度 -> RGBA：白色字形，alpha=灰度
+        let buf = bitmap.buffer();
+        let mut rgba: Vec<u8> = Vec::with_capacity((w * h * 4) as usize);
+        for &g in buf {
+            rgba.push(255);
+            rgba.push(255);
+            rgba.push(255);
+            rgba.push(g);
+        }
+        let mut tex = 0u32;
+        unsafe {
+            (gl.gl_gen_textures)(1, &mut tex);
+            (gl.gl_bind_texture)(gl_const::GL_TEXTURE_2D, tex);
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_MIN_FILTER,
+                gl_const::GL_LINEAR as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_MAG_FILTER,
+                gl_const::GL_LINEAR as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_WRAP_S,
+                gl_const::GL_CLAMP_TO_EDGE as i32,
+            );
+            (gl.gl_tex_parameteri)(
+                gl_const::GL_TEXTURE_2D,
+                gl_const::GL_TEXTURE_WRAP_T,
+                gl_const::GL_CLAMP_TO_EDGE as i32,
+            );
+            (gl.gl_tex_image_2d)(
+                gl_const::GL_TEXTURE_2D,
+                0,
+                gl_const::GL_RGBA as i32,
+                w,
+                h,
+                0,
+                gl_const::GL_RGBA,
+                gl_const::GL_UNSIGNED_BYTE,
+                rgba.as_ptr() as *const std::ffi::c_void,
+            );
+        }
+        Some(CachedGlyph {
+            tex,
+            w,
+            h,
+            left,
+            top,
+            advance,
+        })
+    }
+
+    /// 获取（必要时光栅化并缓存）字符字形。
+    pub fn glyph(&mut self, gl: &Gl, ch: char) -> Option<CachedGlyph> {
+        if !self.glyphs.contains_key(&ch) {
+            if let Some(g) = self.rasterize(gl, ch) {
+                self.glyphs.insert(ch, g);
+            }
+        }
+        self.glyphs.get(&ch).cloned()
+    }
+}