Give a page a time budget, and take the fixes from underneath

go.mod

@@ -3,9 +3,11 @@ module github.com/go-pdfkit/app
 go 1.26.4
 
 require (
-	github.com/go-pdfkit/ops v0.5.0
-	github.com/go-pdfkit/reader v0.4.1
-	github.com/go-pdfkit/render v0.7.0
+	github.com/go-gfx/gfx v0.10.0
+	github.com/go-pdfkit/forms v0.2.1
+	github.com/go-pdfkit/ops v0.7.0
+	github.com/go-pdfkit/reader v0.5.0
+	github.com/go-pdfkit/render v0.10.0
 	github.com/go-widgets/painter v0.11.0
 	github.com/go-widgets/toolkit v0.250.0
 	github.com/go-widgets/webcanvas v0.1.0
@@ -16,14 +18,12 @@ require (
 	github.com/coder/websocket v1.8.15 // indirect
 	github.com/go-crdt/collab v0.25.0 // indirect
 	github.com/go-crdt/crdt v0.31.0 // indirect
-	github.com/go-gfx/gfx v0.10.0 // indirect
 	github.com/go-iconoir/iconoir v0.2.0 // indirect
 	github.com/go-images/images v0.0.0-20260811115337-bc5d586f8e38 // indirect
 	github.com/go-opentype/fonts v0.9.0 // indirect
-	github.com/go-opentype/opentype v0.9.0 // indirect
+	github.com/go-opentype/opentype v0.10.0 // indirect
 	github.com/go-opentype/shape v0.5.0 // indirect
-	github.com/go-pdfkit/forms v0.2.1 // indirect
-	github.com/go-pdfkit/pdffont v0.2.0 // indirect
+	github.com/go-pdfkit/pdffont v0.3.0 // indirect
 	github.com/go-richdoc/richdoc v0.2.0 // indirect
 	github.com/go-typeset/bidi v0.3.0 // indirect
 	github.com/go-widgets/mvvm v0.5.0 // indirect

go.sum

@@ -20,24 +20,20 @@ github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/go-opentype/fonts v0.9.0 h1:slB6OB3riLyUPrOxqXe0s6/AzdenF1TDvCN8N87hhQk=
 github.com/go-opentype/fonts v0.9.0/go.mod h1:C6yQL2apHItfEZ5hztpsHF0S5mlX/hklLlq/Z5fRG/g=
-github.com/go-opentype/opentype v0.9.0 h1:GFgcJ3nwTDp4NJr5O+Paw7lhZx5Jv/R+noZwvhYDlkM=
-github.com/go-opentype/opentype v0.9.0/go.mod h1:AOixevJf7XQaH7+WG+OMIOZEbYPXfMqklVk26Y6YTUU=
+github.com/go-opentype/opentype v0.10.0 h1:cZVMZ3RVkcijXmxlmpqyVkjlNc33aSB2ugKVWYvoLUg=
+github.com/go-opentype/opentype v0.10.0/go.mod h1:AOixevJf7XQaH7+WG+OMIOZEbYPXfMqklVk26Y6YTUU=
 github.com/go-opentype/shape v0.5.0 h1:jHNaOMHNBdDj5EixOevlrrsi92svMxvVMKN7GYaPfxo=
 github.com/go-opentype/shape v0.5.0/go.mod h1:3ImRYNIj6zpwWQ/DV3BWhgMFfmzDITH6XpZw2auQHTo=
 github.com/go-pdfkit/forms v0.2.1 h1:INa2GwAadxEhcXvBe7zJYgapYwaGn9WIaLxUJU/lm6A=
 github.com/go-pdfkit/forms v0.2.1/go.mod h1:LORxkdP4FVULFk0/PA0CdPZc1dZF9zTSaHrtfM7IYaw=
-github.com/go-pdfkit/ops v0.4.0 h1:2WeYwDhN2OyoYtjYCdgm7gWGVNmiu+8OwOKEhyb3Cp0=
-github.com/go-pdfkit/ops v0.4.0/go.mod h1:X89phxHICCYl6+zn3L6YXH3mRLBlsLdPYuDCryGLXzI=
-github.com/go-pdfkit/ops v0.5.0 h1:b1LF7hF9QsqtF2AC0G7HjwulNCXJ0AOE7zaUSzswXrg=
-github.com/go-pdfkit/ops v0.5.0/go.mod h1:Is3FBR2NcCUEzNt4eowdsVa+P0SBtGtcxK8lDlOeyrk=
-github.com/go-pdfkit/pdffont v0.2.0 h1:yAp/oR5Z2kkqs4r0GWMalZMC7rc7XSCZXgwIypbpMWM=
-github.com/go-pdfkit/pdffont v0.2.0/go.mod h1:y4vo5DgT95e57C3XxIWfA/xss+x6RwZwyj6KWdJc86s=
-github.com/go-pdfkit/reader v0.4.0 h1:qPbNZSO+Xl+4NBvQoV1PYt7HlqHaEAQ1tUc6/IL8JAU=
-github.com/go-pdfkit/reader v0.4.0/go.mod h1:fQFOVfCMUui1AdvD4qhimdyvvNr9KvvJ1S7IuKZjyV8=
-github.com/go-pdfkit/reader v0.4.1 h1:pRxFqRjsn7H/VsGfWb9nYWyFuDgTU2Pjmoq/f5mgVq4=
-github.com/go-pdfkit/reader v0.4.1/go.mod h1:fQFOVfCMUui1AdvD4qhimdyvvNr9KvvJ1S7IuKZjyV8=
-github.com/go-pdfkit/render v0.7.0 h1:wTEvYxcJkYFYCXJMzrGcMUo0gVgp4A+VqAsTS/hyFq8=
-github.com/go-pdfkit/render v0.7.0/go.mod h1:RCleIv5QnEDbh9kILa7J8pNUNDUyhsx5p8hv06lpcLk=
+github.com/go-pdfkit/ops v0.7.0 h1:W8sK//0nfs/OACvjzvw/GK5ywtd90eDoYcdv74GxW8M=
+github.com/go-pdfkit/ops v0.7.0/go.mod h1:Is3FBR2NcCUEzNt4eowdsVa+P0SBtGtcxK8lDlOeyrk=
+github.com/go-pdfkit/pdffont v0.3.0 h1:G5DKcAmsZJ0e17QhSrcUaL7PKEXKjUx4P/iGMl7bAbI=
+github.com/go-pdfkit/pdffont v0.3.0/go.mod h1:bfmNLna1l1CljNX/Utg55YzFylovfmI7sJnvgA3bzKI=
+github.com/go-pdfkit/reader v0.5.0 h1:DaJ5C6eKXPRG9Cdu+olA/0KLmsQgyHEC1coteQQuBxU=
+github.com/go-pdfkit/reader v0.5.0/go.mod h1:fQFOVfCMUui1AdvD4qhimdyvvNr9KvvJ1S7IuKZjyV8=
+github.com/go-pdfkit/render v0.10.0 h1:2NXlxhb7bDWFfgWpMe1bfZXbefhEkLSeH99xWI8B1uk=
+github.com/go-pdfkit/render v0.10.0/go.mod h1:ZNuGzwPk1m3kmJIg9X0bepSGrAmmCb5nTMbDEbHuFFA=
 github.com/go-richdoc/richdoc v0.2.0 h1:z9cLox9MoInZL6fIlweMzgDT/VqgnB2ZucSIEaRFglY=
 github.com/go-richdoc/richdoc v0.2.0/go.mod h1:aCX8ulqg5CoKqSWgWeEWul1Oj0d2VxQeaQNI0+jsm7c=
 github.com/go-typeset/bidi v0.3.0 h1:4fjGjejvjE2LzLNzY4si8PkVO321NcsKIiANhWT3jF4=

scene.go

@@ -6,7 +6,9 @@
 package main
 
 import (
+	"errors"
 	"fmt"
+	"time"
 
 	"github.com/go-pdfkit/ops"
 	"github.com/go-pdfkit/reader"
@@ -346,15 +348,37 @@ func (s *state) renderPage() {
 	if s.at < 1 {
 		s.at = 1
 	}
-	img, err := drawPage(src, s.at, render.Options{Scale: s.fitScale(src)})
-	if err != nil {
+	img, err := drawPage(src, s.at, render.Options{
+		Scale:       s.fitScale(src),
+		MaxDuration: pageBudget,
+	})
+	// A page that ran out of time comes back as far as it got, which is worth
+	// showing: somebody scrolling would rather see most of a figure than a
+	// sentence saying there was one. Anything else, and there is no picture.
+	partial := errors.Is(err, render.ErrTimedOut) && img != nil
+	if err != nil && !partial {
 		s.view = toolkit.NewFrame(toolkit.NewLabel("this page cannot be drawn: " + err.Error()))
 		return
 	}
+	if partial {
+		// Showing half a page without saying so would be the one thing worse
+		// than showing nothing, so the status line says which it is. This is
+		// the only place renderPage writes the note, and it overwrites
+		// whatever was there, because what is on the screen right now matters
+		// more than what happened before it.
+		s.note = fmt.Sprintf("this page was still being drawn after %s; this is as far as it got", pageBudget)
+	}
 	s.page = toolkit.NewImageFit(img.Pix, img.W, img.H)
 	s.view = toolkit.NewFrame(s.page)
 }
 
+// pageBudget is how long one page may be drawn for before what has been drawn
+// so far is shown instead. A handful of pages take minutes — of the 59 432
+// pages the renderer was measured against, 1 131 were still going after twenty
+// seconds and one took two hundred and seventy-three — and a window that stops
+// answering for that long reads as broken rather than as busy.
+const pageBudget = 5 * time.Second
+
 // fitScale is how much to magnify the page so that it fills the view without
 // spilling out of it.
 func (s *state) fitScale(src *reader.Document) float64 {

scene_test.go

@@ -4,9 +4,12 @@ import (
 	"errors"
 	"strings"
 	"testing"
+	"time"
 
+	"github.com/go-gfx/gfx/raster"
 	"github.com/go-pdfkit/ops"
 	"github.com/go-pdfkit/reader"
+	"github.com/go-pdfkit/render"
 	"github.com/go-widgets/toolkit"
 )
 
@@ -588,3 +591,59 @@ func TestAControlIsWideEnoughForItsName(t *testing.T) {
 		t.Errorf("the strip is %d wide and the surface is %d", total, surfaceW-2*margin)
 	}
 }
+
+func TestAPageThatRanOutOfTimeIsShownAsFarAsItGot(t *testing.T) {
+	// The renderer is given a budget, and a page that overruns it comes back
+	// half drawn together with render.ErrTimedOut. Half a page is worth more
+	// to somebody scrolling than a sentence saying there was one, so the
+	// workbench shows it rather than the error.
+	s, _ := opened(t, 1)
+	was := drawPage
+	t.Cleanup(func() { drawPage = was })
+	var budget time.Duration
+	drawPage = func(_ *reader.Document, _ int, opt render.Options) (*raster.Image, error) {
+		budget = opt.MaxDuration
+		return raster.New(4, 4), render.ErrTimedOut
+	}
+
+	s.refresh()
+	if budget <= 0 {
+		t.Error("the renderer was given no budget at all")
+	}
+	if s.page == nil {
+		t.Fatal("the part of the page that was drawn was thrown away")
+	}
+	if !strings.Contains(s.note, "as far as it got") {
+		t.Errorf("half a page was shown without saying so; the status line said %q", s.note)
+	}
+	if got := s.statusLine(); !strings.Contains(strings.Join(got, "|"), "as far as it got") {
+		t.Errorf("the status line does not carry it: %q", got)
+	}
+	buf := buffer()
+	s.draw(buf)
+	if inked(buf, s.theme.Background) == 0 {
+		t.Error("nothing reached the screen")
+	}
+}
+
+func TestAPageThatRanOutOfTimeWithNothingDrawnSaysSo(t *testing.T) {
+	// Coming back timed out and empty is not something the renderer does,
+	// but if it did there is no picture to show, so the view has to fall
+	// back on saying why rather than dereferencing nothing.
+	s, _ := opened(t, 1)
+	was := drawPage
+	t.Cleanup(func() { drawPage = was })
+	drawPage = func(*reader.Document, int, render.Options) (*raster.Image, error) {
+		return nil, render.ErrTimedOut
+	}
+
+	s.refresh()
+	if s.page != nil {
+		t.Error("a page was drawn from nothing")
+	}
+	buf := buffer()
+	s.draw(buf)
+	if inked(buf, s.theme.Background) == 0 {
+		t.Error("the reason was not drawn")
+	}
+}