allow to use different blur placeholder modes (#49070)

### What?

allows to change blur mode for structured images

also improve performance for static metadata images in app dir by avoiding computing blur placeholder

### Why?

we might want to change the blur mode (in dicussion)

### How?

adds an enum to control the mode

packages/next-swc/crates/next-core/src/app_source.rs

@@ -92,7 +92,7 @@ use crate::{
         context::{get_edge_compile_time_info, get_edge_resolve_options_context},
         transition::NextEdgeTransition,
     },
-    next_image::module::StructuredImageModuleType,
+    next_image::module::{BlurPlaceholderMode, StructuredImageModuleType},
     next_route_matcher::NextParamsMatcherVc,
     next_server::context::{
         get_server_compile_time_info, get_server_module_options_context,
@@ -783,6 +783,7 @@ import {}, {{ chunks as {} }} from "COMPONENT_{}";
                         inner_module_id,
                         StructuredImageModuleType::create_module(
                             SourceAssetVc::new(*path).into(),
+                            BlurPlaceholderMode::None,
                             state.context,
                         )
                         .into(),

packages/next-swc/crates/next-core/src/next_image/module.rs

@@ -19,19 +19,43 @@ use turbo_binding::{
 
 use super::source_asset::StructuredImageSourceAsset;
 
+#[turbo_tasks::value(serialization = "auto_for_input")]
+#[derive(Clone, Copy, Debug, PartialOrd, Ord, Hash)]
+pub enum BlurPlaceholderMode {
+    /// Do not generate a blur placeholder at all.
+    None,
+    /// Generate a blur placeholder as data url and embed it directly into the
+    /// JavaScript code. This needs to compute the blur placeholder eagerly and
+    /// has a higher computation overhead.
+    DataUrl,
+    /// Avoid generating a blur placeholder eagerly and uses `/_next/image`
+    /// instead to compute one on demand. This changes the UX slightly (blur
+    /// placeholder is shown later than it should be) and should
+    /// only be used for development.
+    NextImageUrl,
+}
+
 /// Module type that analyzes images and offers some meta information like
 /// width, height and blur placeholder as export from the module.
 #[turbo_tasks::value]
-pub struct StructuredImageModuleType {}
+pub struct StructuredImageModuleType {
+    pub blur_placeholder_mode: BlurPlaceholderMode,
+}
 
 impl StructuredImageModuleType {
     pub(crate) fn create_module(
         source: AssetVc,
+        blur_placeholder_mode: BlurPlaceholderMode,
         context: AssetContextVc,
     ) -> EcmascriptModuleAssetVc {
         let static_asset = StaticModuleAssetVc::new(source, context);
         EcmascriptModuleAssetVc::new_with_inner_assets(
-            StructuredImageSourceAsset { image: source }.cell().into(),
+            StructuredImageSourceAsset {
+                image: source,
+                blur_placeholder_mode,
+            }
+            .cell()
+            .into(),
             context,
             Value::new(EcmascriptModuleAssetType::Ecmascript),
             EcmascriptInputTransformsVc::empty(),
@@ -49,8 +73,10 @@ impl StructuredImageModuleType {
 #[turbo_tasks::value_impl]
 impl StructuredImageModuleTypeVc {
     #[turbo_tasks::function]
-    pub fn new() -> Self {
-        StructuredImageModuleTypeVc::cell(StructuredImageModuleType {})
+    pub fn new(blur_placeholder_mode: Value<BlurPlaceholderMode>) -> Self {
+        StructuredImageModuleTypeVc::cell(StructuredImageModuleType {
+            blur_placeholder_mode: blur_placeholder_mode.into_value(),
+        })
     }
 }
 
@@ -63,6 +89,6 @@ impl CustomModuleType for StructuredImageModuleType {
         context: AssetContextVc,
         _part: Option<ModulePartVc>,
     ) -> AssetVc {
-        StructuredImageModuleType::create_module(source, context).into()
+        StructuredImageModuleType::create_module(source, self.blur_placeholder_mode, context).into()
     }
 }

packages/next-swc/crates/next-core/src/next_image/source_asset.rs

@@ -1,7 +1,6 @@
 use std::io::Write;
 
 use anyhow::{bail, Result};
-use serde::Serialize;
 use turbo_binding::{
     turbo::{
         tasks::primitives::StringVc,
@@ -17,6 +16,8 @@ use turbo_binding::{
     },
 };
 
+use super::module::BlurPlaceholderMode;
+
 fn modifier() -> StringVc {
     StringVc::cell("structured image object".to_string())
 }
@@ -30,22 +31,12 @@ fn blur_options() -> BlurPlaceholderOptionsVc {
     .cell()
 }
 
-#[derive(Serialize)]
-#[serde(rename_all = "camelCase")]
-pub struct ImageExport<'a> {
-    width: u32,
-    height: u32,
-    #[serde(rename = "blurDataURL")]
-    blur_data_url: Option<&'a str>,
-    blur_width: u32,
-    blur_height: u32,
-}
-
 /// An source asset that transforms an image into javascript code which exports
 /// an object with meta information like width, height and a blur placeholder.
 #[turbo_tasks::value(shared)]
 pub struct StructuredImageSourceAsset {
     pub image: AssetVc,
+    pub blur_placeholder_mode: BlurPlaceholderMode,
 }
 
 #[turbo_tasks::value_impl]
@@ -62,20 +53,63 @@ impl Asset for StructuredImageSourceAsset {
             bail!("Input source is not a file and can't be transformed into image information");
         };
         let mut result = RopeBuilder::from("");
-        let info = get_meta_data(self.image.ident(), content, Some(blur_options())).await?;
-        let info = ImageExport {
-            width: info.width,
-            height: info.height,
-            blur_width: info.blur_placeholder.as_ref().map_or(0, |p| p.width),
-            blur_height: info.blur_placeholder.as_ref().map_or(0, |p| p.height),
-            blur_data_url: info.blur_placeholder.as_ref().map(|p| p.data_url.as_str()),
-        };
         writeln!(result, "import src from \"IMAGE\";",)?;
-        writeln!(
-            result,
-            "export default {{ src, ...{} }}",
-            StringifyJs(&info)
-        )?;
+        let blur_options = blur_options();
+        match self.blur_placeholder_mode {
+            BlurPlaceholderMode::NextImageUrl => {
+                let info = get_meta_data(self.image.ident(), content, None).await?;
+                let width = info.width;
+                let height = info.height;
+                let blur_options = blur_options.await?;
+                let (blur_width, blur_height) = if width > height {
+                    (
+                        blur_options.size,
+                        (blur_options.size as f32 * height as f32 / width as f32).ceil() as u32,
+                    )
+                } else {
+                    (
+                        (blur_options.size as f32 * width as f32 / height as f32).ceil() as u32,
+                        blur_options.size,
+                    )
+                };
+                writeln!(
+                    result,
+                    "export default {{ src, width: {width}, height: {height}, blurDataURL: \
+                     `/_next/image?w={blur_width}&q={quality}&url=${{encodeURIComponent(src)}}`, \
+                     blurWidth: {blur_width}, blurHeight: {blur_height} }}",
+                    width = StringifyJs(&info.width),
+                    height = StringifyJs(&info.height),
+                    quality = StringifyJs(&blur_options.quality),
+                    blur_width = StringifyJs(&blur_width),
+                    blur_height = StringifyJs(&blur_height),
+                )?;
+            }
+            BlurPlaceholderMode::DataUrl => {
+                let info = get_meta_data(self.image.ident(), content, Some(blur_options)).await?;
+                writeln!(
+                    result,
+                    "export default {{ src, width: {width}, height: {height}, blurDataURL: \
+                     {blur_data_url}, blurWidth: {blur_width}, blurHeight: {blur_height} }}",
+                    width = StringifyJs(&info.width),
+                    height = StringifyJs(&info.height),
+                    blur_data_url =
+                        StringifyJs(&info.blur_placeholder.as_ref().map(|p| p.data_url.as_str())),
+                    blur_width =
+                        StringifyJs(&info.blur_placeholder.as_ref().map_or(0, |p| p.width)),
+                    blur_height =
+                        StringifyJs(&info.blur_placeholder.as_ref().map_or(0, |p| p.height),),
+                )?;
+            }
+            BlurPlaceholderMode::None => {
+                let info = get_meta_data(self.image.ident(), content, None).await?;
+                writeln!(
+                    result,
+                    "export default {{ src, width: {width}, height: {height} }}",
+                    width = StringifyJs(&info.width),
+                    height = StringifyJs(&info.height),
+                )?;
+            }
+        };
         Ok(AssetContent::File(FileContent::Content(result.build().into()).cell()).cell())
     }
 }

packages/next-swc/crates/next-core/src/next_shared/transforms.rs

@@ -27,9 +27,9 @@ use turbo_binding::{
         },
     },
 };
-use turbo_tasks::trace::TraceRawVcs;
+use turbo_tasks::{trace::TraceRawVcs, Value};
 
-use crate::next_image::StructuredImageModuleTypeVc;
+use crate::next_image::{module::BlurPlaceholderMode, StructuredImageModuleTypeVc};
 
 /// Returns a rule which applies the Next.js page export stripping transform.
 pub async fn get_next_pages_transforms_rule(
@@ -98,7 +98,7 @@ pub fn get_next_image_rule() -> ModuleRule {
             ModuleRuleCondition::ResourcePathEndsWith(".svg".to_string()),
         ]),
         vec![ModuleRuleEffect::ModuleType(ModuleType::Custom(
-            StructuredImageModuleTypeVc::new().into(),
+            StructuredImageModuleTypeVc::new(Value::new(BlurPlaceholderMode::DataUrl)).into(),
         ))],
     )
 }