feat: 格式扩展 — 支持 BMP/JPEG/WebP 输出

- png.rs 重命名为 image.rs，新增 OutputFormat 枚举
- QrCode::to_image_bytes 支持 PNG/BMP/JPEG/WebP
- CLI 新增 -f/--format 参数（png/bmp/jpeg/webp）
- Web API fmt 参数扩展至全部 4 种图像格式
- core/Cargo.toml: image crate 新增 bmp feature

core/src/render/image.rs

@@ -1,6 +1,62 @@
+//! QR 码图像渲染（支持 PNG/BMP/JPEG/WebP）
+//!
+//! 使用 `image` crate 将 QR 模块矩阵渲染为像素缓冲区，可选叠加 Logo。
+
 use crate::qr::QrCode;
 use image::{imageops, ImageBuffer, Rgba, RgbaImage};
 
+/// 输出图像格式
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum OutputFormat {
+    Png,
+    Bmp,
+    Jpeg,
+    WebP,
+}
+
+impl OutputFormat {
+    /// 转为 `image` crate 的格式枚举
+    fn to_image_format(self) -> image::ImageFormat {
+        match self {
+            Self::Png => image::ImageFormat::Png,
+            Self::Bmp => image::ImageFormat::Bmp,
+            Self::Jpeg => image::ImageFormat::Jpeg,
+            Self::WebP => image::ImageFormat::WebP,
+        }
+    }
+
+    /// 文件扩展名（不含点）
+    pub fn extension(self) -> &'static str {
+        match self {
+            Self::Png => "png",
+            Self::Bmp => "bmp",
+            Self::Jpeg => "jpeg",
+            Self::WebP => "webp",
+        }
+    }
+
+    /// MIME 类型
+    pub fn mime(self) -> &'static str {
+        match self {
+            Self::Png => "image/png",
+            Self::Bmp => "image/bmp",
+            Self::Jpeg => "image/jpeg",
+            Self::WebP => "image/webp",
+        }
+    }
+
+    /// 从扩展名解析
+    pub fn from_ext(ext: &str) -> Option<Self> {
+        match ext.to_lowercase().as_str() {
+            "png" => Some(Self::Png),
+            "bmp" => Some(Self::Bmp),
+            "jpeg" | "jpg" => Some(Self::Jpeg),
+            "webp" => Some(Self::WebP),
+            _ => None,
+        }
+    }
+}
+
 fn fill_module(
     img: &mut RgbaImage,
     x: u32,
@@ -24,32 +80,27 @@ fn fill_module(
     }
 }
 
-/// 在 QR 码 PNG 缓冲区中央叠加 logo
 fn overlay_logo(img: &mut RgbaImage, logo_bytes: &[u8], logo_size_pct: f32) -> Result<(), String> {
     let logo = image::load_from_memory(logo_bytes).map_err(|e| format!("Logo 加载失败: {e}"))?;
     let logo = logo.to_rgba8();
-
     let img_w = img.width();
     let img_h = img.height();
-
-    // Logo 边长 = min(图像边长 * pct, 实际 QR 区域 * pct)
     let logo_size = (img_w.min(img_h) as f32 * logo_size_pct) as u32;
     if logo_size < 4 {
-        return Ok(()); // 太小，跳过
+        return Ok(());
     }
-
     let resized = imageops::resize(&logo, logo_size, logo_size, imageops::FilterType::Lanczos3);
-
     let x = (img_w - logo_size) / 2;
     let y = (img_h - logo_size) / 2;
     imageops::overlay(img, &resized, x as i64, y as i64);
-
     Ok(())
 }
 
-pub fn render_png(
+/// 渲染 QR 码到图像字节（支持 PNG/BMP/JPEG/WebP）
+pub fn render_image(
     qr: &QrCode,
     module_size: u8,
+    format: OutputFormat,
     logo: Option<&[u8]>,
 ) -> Result<Vec<u8>, image::ImageError> {
     let matrix_size = qr.size() as u32;
@@ -72,7 +123,6 @@ pub fn render_png(
             } else {
                 false
             };
-
             fill_module(
                 &mut img,
                 x,
@@ -85,13 +135,14 @@ pub fn render_png(
         }
     }
 
-    // Logo 叠加
     if let Some(logo_data) = logo {
-        // 忽略 logo 叠加错误（logo 有损不影响 QR 主体）
         let _ = overlay_logo(&mut img, logo_data, 0.25);
     }
 
     let mut buf = Vec::new();
-    img.write_to(&mut std::io::Cursor::new(&mut buf), image::ImageFormat::Png)?;
+    img.write_to(
+        &mut std::io::Cursor::new(&mut buf),
+        format.to_image_format(),
+    )?;
     Ok(buf)
 }

core/src/render/mod.rs

@@ -1,3 +1,3 @@
 pub mod ascii;
-pub mod png;
+pub mod image;
 pub mod svg;