From f0040edff20df5faffe25ac17af4f1bc295e6a98 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 7 Oct 2025 13:30:28 +0530
Subject: [PATCH] More work on image previews

---
 kittens/choose_files/image_preview.go | 81 +++++++++++++++++++++++++--
 kittens/choose_files/preview.go       |  7 ++-
 2 files changed, 79 insertions(+), 9 deletions(-)

diff --git a/kittens/choose_files/image_preview.go b/kittens/choose_files/image_preview.go
index 821461b02..32ce021bd 100644
--- a/kittens/choose_files/image_preview.go
+++ b/kittens/choose_files/image_preview.go
@@ -21,21 +21,89 @@ var preview_cache = sync.OnceValues(func() (*disk_cache.DiskCache, error) {
 	return disk_cache.NewDiskCache(cdir, dc_size.Load())
 })
 
+type PreviewRenderer interface {
+	Render(string) (map[string][]byte, error)
+	Show(h *Handler, abspath string, metadata fs.FileInfo, x, y, width, height int, cached_data map[string]string)
+}
+
+type render_data struct {
+	cached_data map[string]string
+	err         error
+}
+
 type ImagePreview struct {
-	abspath, cache_key string
-	disk_cache         *disk_cache.DiskCache
+	abspath, cache_key    string
+	metadata              fs.FileInfo
+	disk_cache            *disk_cache.DiskCache
+	cached_data           map[string]string
+	render_err            Preview
+	render_channel        chan render_data
+	renderer              PreviewRenderer
+	file_metadata_preview Preview
+	WakeupMainThread      func() bool
 }
 
 func (p ImagePreview) IsValidForColorScheme(bool) bool { return true }
 
 func (p ImagePreview) Render(h *Handler, x, y, width, height int) {
-	offset := 0
-	offset += h.render_wrapped_text_in_region("Rendering image, please wait...", x, y, width, height, true)
+	if p.render_channel == nil {
+		if p.render_err == nil {
+			p.renderer.Show(h, p.abspath, p.metadata, x, y, width, height, p.cached_data)
+		} else {
+			p.render_err.Render(h, x, y, width, height)
+		}
+		return
+	}
+	select {
+	case hd := <-p.render_channel:
+		p.render_channel = nil
+		p.cached_data = hd.cached_data
+		p.render_err = NewErrorPreview(fmt.Errorf("Failed to render the preview with error: %w", hd.err))
+		p.Render(h, x, y, width, height)
+		return
+	default:
+	}
+	if p.file_metadata_preview == nil {
+		p.file_metadata_preview = NewFileMetadataPreview(p.abspath, p.metadata)
+	}
+	p.file_metadata_preview.Render(h, x, y, width, height)
 }
 
-func NewImagePreview(abspath string, metadata fs.FileInfo, opts Settings) (Preview, error) {
+func (p *ImagePreview) start_rendering() {
+	defer func() {
+		p.WakeupMainThread()
+	}()
+	ans := p.disk_cache.Get(p.cache_key)
+	if len(ans) > 0 {
+		p.render_channel <- render_data{ans, nil}
+		return
+	}
+	rdata, err := p.renderer.Render(p.abspath)
+	if err != nil {
+		p.render_channel <- render_data{nil, err}
+	} else {
+		ans, err = p.disk_cache.Add(p.cache_key, rdata)
+		p.render_channel <- render_data{utils.IfElse(err == nil, ans, nil), err}
+	}
+}
+
+type ImagePreviewRenderer uint
+
+func (p ImagePreviewRenderer) Render(abspath string) (ans map[string][]byte, err error) {
+	return
+}
+
+func (p ImagePreviewRenderer) Show(h *Handler, abspath string, metadata fs.FileInfo, x, y, width, height int, cached_data map[string]string) {
+}
+
+func NewImagePreview(
+	abspath string, metadata fs.FileInfo, opts Settings, WakeupMainThread func() bool, r PreviewRenderer,
+) (Preview, error) {
 	dc_size.Store(opts.DiskCacheSize())
-	ans := &ImagePreview{abspath: abspath}
+	ans := &ImagePreview{
+		abspath: abspath, metadata: metadata, render_channel: make(chan render_data),
+		WakeupMainThread: WakeupMainThread, renderer: r,
+	}
 	if dc, err := preview_cache(); err != nil {
 		return nil, err
 	} else {
@@ -46,5 +114,6 @@ func NewImagePreview(abspath string, metadata fs.FileInfo, opts Settings) (Previ
 	} else {
 		ans.cache_key = key
 	}
+	go ans.start_rendering()
 	return ans, nil
 }
diff --git a/kittens/choose_files/preview.go b/kittens/choose_files/preview.go
index a42a43708..a569b342f 100644
--- a/kittens/choose_files/preview.go
+++ b/kittens/choose_files/preview.go
@@ -298,11 +298,12 @@ func (pm *PreviewManager) preview_for(abspath string, ftype fs.FileMode) (ans Pr
 		return NewTextFilePreview(abspath, s, ch, pm.highlighter.Sanitize)
 	}
 	if strings.HasPrefix(mt, "image/") {
-		ans, err := NewImagePreview(abspath, s, pm.settings)
-		if err != nil {
+		var r ImagePreviewRenderer
+		if ans, err := NewImagePreview(abspath, s, pm.settings, pm.WakeupMainThread, r); err == nil {
+			return ans
+		} else {
 			return NewErrorPreview(err)
 		}
-		return ans
 	}
 	return NewFileMetadataPreview(abspath, s)
 }