Improve compression targeting and UI hint

.gitignore

@@ -6,6 +6,7 @@
 
 /uploads
 /static
+/logs
 
 /frontend/node_modules
 /frontend/dist

frontend/src/pages/HomePage.vue

@@ -382,7 +382,7 @@ async function resendVerification() {
                 step="1"
                 class="w-full"
               />
-              <div class="text-xs text-slate-500">数值越大压缩越强，输出保持原格式。</div>
+              <div class="text-xs text-slate-500">数值越大压缩越强，系统尽量接近目标节省比例。</div>
             </label>
 
             <div class="grid grid-cols-2 gap-3">

src/services/compress.rs

@@ -187,6 +187,7 @@ pub async fn compress_image_bytes(
     max_height: Option<u32>,
     preserve_metadata: bool,
 ) -> Result<Vec<u8>, AppError> {
+    let original_size = input.len() as u64;
     if format_in == ImageFmt::Gif {
         if is_animated_gif(input)? {
             return Err(AppError::new(
@@ -197,6 +198,7 @@ pub async fn compress_image_bytes(
     }
 
     let rate = effective_rate(compression_rate, level);
+    let target_size = compression_rate.map(|value| target_size_from_rate(original_size, value));
     let (icc_profile, exif) = if preserve_metadata {
         extract_metadata(input)
     } else {
@@ -227,9 +229,18 @@ pub async fn compress_image_bytes(
 
         match format_out {
             ImageFmt::Png => encode_png(image, rate, preserve_metadata)?,
-            ImageFmt::Jpeg => encode_jpeg(image, rate)?,
-            ImageFmt::Webp => encode_webp(image, rate)?,
-            ImageFmt::Avif => encode_avif(image, rate)?,
+            ImageFmt::Jpeg => match target_size {
+                Some(target) => encode_jpeg_target(image, target)?,
+                None => encode_jpeg(image, rate)?,
+            },
+            ImageFmt::Webp => match target_size {
+                Some(target) => encode_webp_target(image, target)?,
+                None => encode_webp(image, rate)?,
+            },
+            ImageFmt::Avif => match target_size {
+                Some(target) => encode_avif_target(image, target)?,
+                None => encode_avif(image, rate)?,
+            },
             ImageFmt::Gif => encode_gif(image, rate)?,
             ImageFmt::Bmp => encode_bmp(image)?,
             ImageFmt::Tiff => encode_tiff(image)?,
@@ -329,17 +340,22 @@ fn encode_png(
 }
 
 fn encode_jpeg(image: DynamicImage, rate: u8) -> Result<Vec<u8>, AppError> {
+    let quality = jpeg_quality_from_rate(rate);
+    encode_jpeg_with_quality(image, quality)
+}
+
+fn encode_jpeg_with_quality(image: DynamicImage, quality: u8) -> Result<Vec<u8>, AppError> {
     let rgb = image.to_rgb8();
     let (w, h) = rgb.dimensions();
+    encode_jpeg_raw(rgb.as_raw(), w, h, quality)
+}
+
+fn encode_jpeg_raw(raw: &[u8], w: u32, h: u32, quality: u8) -> Result<Vec<u8>, AppError> {
     let mut out = Vec::new();
-
-    let quality = jpeg_quality_from_rate(rate);
-
     let mut encoder = JpegEncoder::new_with_quality(&mut out, quality);
     encoder
-        .encode(rgb.as_raw(), w, h, ExtendedColorType::Rgb8)
+        .encode(raw, w, h, ExtendedColorType::Rgb8)
         .map_err(|err| AppError::new(ErrorCode::CompressionFailed, "JPEG 编码失败").with_source(err))?;
-
     Ok(out)
 }
 
@@ -357,6 +373,17 @@ fn encode_webp(image: DynamicImage, rate: u8) -> Result<Vec<u8>, AppError> {
     Ok(bytes.to_vec())
 }
 
+fn encode_webp_with_quality(image: DynamicImage, quality: u8) -> Result<Vec<u8>, AppError> {
+    let rgba = image.to_rgba8();
+    let (w, h) = rgba.dimensions();
+    encode_webp_raw(rgba.as_raw(), w, h, quality)
+}
+
+fn encode_webp_raw(raw: &[u8], w: u32, h: u32, quality: u8) -> Result<Vec<u8>, AppError> {
+    let encoder = webp::Encoder::from_rgba(raw, w, h);
+    Ok(encoder.encode(quality as f32).to_vec())
+}
+
 fn encode_avif(image: DynamicImage, rate: u8) -> Result<Vec<u8>, AppError> {
     let rgba = image.to_rgba8();
     let (w, h) = rgba.dimensions();
@@ -375,6 +402,93 @@ fn encode_avif(image: DynamicImage, rate: u8) -> Result<Vec<u8>, AppError> {
     Ok(encoded.avif_file)
 }
 
+fn encode_avif_with_quality(image: DynamicImage, quality: u8) -> Result<Vec<u8>, AppError> {
+    let rgba = image.to_rgba8();
+    let (w, h) = rgba.dimensions();
+    encode_avif_raw(rgba.as_raw(), w, h, quality)
+}
+
+fn encode_avif_raw(raw: &[u8], w: u32, h: u32, quality: u8) -> Result<Vec<u8>, AppError> {
+    let pixels = raw.as_rgba();
+    let img = ravif::Img::new(pixels, w as usize, h as usize);
+    let encoder = ravif::Encoder::new().with_quality(quality as f32);
+    let encoded = encoder
+        .encode_rgba(img)
+        .map_err(|err| AppError::new(ErrorCode::CompressionFailed, "AVIF 编码失败").with_source(err))?;
+    Ok(encoded.avif_file)
+}
+
+fn encode_jpeg_target(image: DynamicImage, target_size: u64) -> Result<Vec<u8>, AppError> {
+    let rgb = image.to_rgb8();
+    let (w, h) = rgb.dimensions();
+    let raw = rgb.into_raw();
+    encode_target_quality(35, 95, target_size, |q| encode_jpeg_raw(&raw, w, h, q))
+}
+
+fn encode_webp_target(image: DynamicImage, target_size: u64) -> Result<Vec<u8>, AppError> {
+    let rgba = image.to_rgba8();
+    let (w, h) = rgba.dimensions();
+    let raw = rgba.into_raw();
+    encode_target_quality(30, 95, target_size, |q| encode_webp_raw(&raw, w, h, q))
+}
+
+fn encode_avif_target(image: DynamicImage, target_size: u64) -> Result<Vec<u8>, AppError> {
+    let rgba = image.to_rgba8();
+    let (w, h) = rgba.dimensions();
+    let raw = rgba.into_raw();
+    encode_target_quality(35, 90, target_size, |q| encode_avif_raw(&raw, w, h, q))
+}
+
+fn encode_target_quality<F>(
+    min_q: u8,
+    max_q: u8,
+    target_size: u64,
+    mut encode: F,
+) -> Result<Vec<u8>, AppError>
+where
+    F: FnMut(u8) -> Result<Vec<u8>, AppError>,
+{
+    let mut best: Option<Vec<u8>> = None;
+    let mut best_diff = u64::MAX;
+
+    let mut consider = |bytes: Vec<u8>| {
+        let size = bytes.len() as u64;
+        let diff = if size > target_size {
+            size - target_size
+        } else {
+            target_size - size
+        };
+        if diff < best_diff {
+            best_diff = diff;
+            best = Some(bytes);
+        }
+    };
+
+    consider(encode(min_q)?);
+    if min_q != max_q {
+        consider(encode(max_q)?);
+    }
+
+    let mut low = min_q;
+    let mut high = max_q;
+    for _ in 0..7 {
+        if low > high {
+            break;
+        }
+        let mid = (low + high) / 2;
+        let bytes = encode(mid)?;
+        let size = bytes.len() as u64;
+        consider(bytes);
+        if size > target_size {
+            high = mid.saturating_sub(1);
+        } else {
+            low = mid.saturating_add(1);
+        }
+    }
+
+    best.ok_or_else(|| AppError::new(ErrorCode::CompressionFailed, "压缩失败"))
+}
+
 fn encode_gif(image: DynamicImage, rate: u8) -> Result<Vec<u8>, AppError> {
     let rgba = image.to_rgba8();
     let (w, h) = rgba.dimensions();
@@ -488,6 +602,13 @@ fn effective_rate(rate: Option<u8>, level: CompressionLevel) -> u8 {
     }
 }
 
+fn target_size_from_rate(original_size: u64, rate: u8) -> u64 {
+    let rate = rate.clamp(1, 100) as u64;
+    let remaining = 100_u64.saturating_sub(rate);
+    let target = original_size.saturating_mul(remaining) / 100;
+    target.max(1)
+}
+
 fn png_preset_from_rate(rate: u8) -> u8 {
     (((rate.saturating_sub(1)) as f32 / 99.0) * 6.0).round() as u8
 }