From ca0b703526151149d060d6d38f307e9e38c3dcd2 Mon Sep 17 00:00:00 2001
From: Lukasz Kasprzak <lukas@labunix.xyz>
Date: Thu, 17 Sep 2026 00:40:46 +0200
Subject: gui: the preview is as big as you drag it, and PDFs render to suit

---
 gui/internal/model/preview.go | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

(limited to 'gui/internal/model/preview.go')

diff --git a/gui/internal/model/preview.go b/gui/internal/model/preview.go
index d2a2830..4ec0569 100644
--- a/gui/internal/model/preview.go
+++ b/gui/internal/model/preview.go
@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"unicode/utf8"
 
@@ -47,9 +48,11 @@ const (
 )
 
 // MakePreview looks at one file. tmp is a directory the caller owns, where
-// a rendered PDF page is written; the caller removes it. Nothing is written
-// anywhere else, and the file itself is only read.
-func MakePreview(ctx context.Context, path, tmp string) Preview {
+// a rendered PDF page is written; the caller removes it. px is how tall the
+// preview will be shown, so a page is rendered to suit it rather than to a
+// fixed size - 0 takes the default. Nothing is written anywhere else, and
+// the file itself is only read.
+func MakePreview(ctx context.Context, path, tmp string, px int) Preview {
 	fi, err := os.Stat(path)
 	if err != nil {
 		return Preview{Note: err.Error()}
@@ -65,7 +68,7 @@ func MakePreview(ctx context.Context, path, tmp string) Preview {
 		}
 		return Preview{Kind: PreviewImage, Image: path, Note: fmt.Sprintf("image, %s", size(fi.Size()))}
 	case ext == "pdf":
-		return pdfPreview(ctx, path, tmp, fi.Size())
+		return pdfPreview(ctx, path, tmp, fi.Size(), px)
 	}
 	text, ok := textHead(path)
 	if !ok {
@@ -82,7 +85,7 @@ func MakePreview(ctx context.Context, path, tmp string) Preview {
 // called page-1.png and the wrong one could be picked up - which is what
 // happened: a preview showed the page of a PDF looked at earlier (his
 // report, 2026-09-17).
-func pdfPreview(ctx context.Context, path, tmp string, sz int64) Preview {
+func pdfPreview(ctx context.Context, path, tmp string, sz int64, px int) Preview {
 	if _, err := exec.LookPath("pdftoppm"); err == nil {
 		dir, err := os.MkdirTemp(tmp, "page-")
 		if err != nil {
@@ -90,7 +93,7 @@ func pdfPreview(ctx context.Context, path, tmp string, sz int64) Preview {
 		}
 		out := filepath.Join(dir, "page")
 		cmd := exec.CommandContext(ctx, "pdftoppm", "-png", "-f", "1", "-l", "1",
-			"-scale-to", "700", "--", path, out)
+			"-scale-to", strconv.Itoa(renderPixels(px)), "--", path, out)
 		if err := cmd.Run(); err == nil {
 			if rendered := firstMatch(out + "*.png"); rendered != "" {
 				return Preview{Kind: PreviewImage, Image: rendered, Dir: dir,
@@ -111,6 +114,20 @@ func pdfPreview(ctx context.Context, path, tmp string, sz int64) Preview {
 		Note: fmt.Sprintf("text of the first pages, %s", size(sz))}
 }
 
+// renderPixels is how large a page is rendered for a preview px tall: twice
+// the size it is shown at, so it stays sharp when the pane is dragged a
+// little wider, within limits that keep the render quick.
+func renderPixels(px int) int {
+	n := px * 2
+	switch {
+	case n < 700:
+		return 700
+	case n > 2400:
+		return 2400
+	}
+	return n
+}
+
 // firstMatch is the first file matching a glob, "" when there is none.
 func firstMatch(glob string) string {
 	names, err := filepath.Glob(glob)
-- 
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