From 93d99ce693fed2f6e5051f496561b95e51770622 Mon Sep 17 00:00:00 2001
From: Yonah <contrib@gensokyo.uk>
Date: Sun, 13 Jul 2025 03:04:05 +0900
Subject: [PATCH] line: optional bounds check

This has significant overhead so is made optional.
---
 line.go                                       | 20 +++++++++++++
 caption_sample_test.go => line_sample_test.go |  0
 caption_test.go => line_test.go               | 28 ++++++++++++++++++-
 3 files changed, 47 insertions(+), 1 deletion(-)
 rename caption_sample_test.go => line_sample_test.go (100%)
 rename caption_test.go => line_test.go (81%)

diff --git a/line.go b/line.go
index fb9230b..70d848a 100644
--- a/line.go
+++ b/line.go
@@ -3,6 +3,7 @@ package caption
 import (
 	"image"
 	"image/color"
+	"syscall"
 
 	"github.com/golang/freetype/truetype"
 	"golang.org/x/image/draw"
@@ -20,11 +21,16 @@ type Line struct {
 
 	// contains reference to parsed font, populated once per instance
 	face font.Face
+	// whether to fail if pixels are drawn out-of-bounds
+	bounds bool
 }
 
 // SetFont clears line font cache and sets the new font.
 func (l *Line) SetFont(v []byte, opts *truetype.Options) { l.face = nil; l.Font = v; l.Options = opts }
 
+// SetBoundsCheck changes whether the frame's bounding box is enforced.
+func (l *Line) SetBoundsCheck(v bool) { l.bounds = v }
+
 type Segment struct {
 	Value string      `json:"value"`
 	Color color.Color `json:"color"`
@@ -59,12 +65,26 @@ func (l *Line) Render(ctx *Context, frame draw.Image, x, y int) error {
 		face = ctx.defaultFont
 	}
 
+	outOfBounds := false
+	bounds := frame.Bounds()
+	boundsFixed := fixed.R(bounds.Min.X, bounds.Min.Y, bounds.Max.X, bounds.Max.Y)
+
 	drawer := &font.Drawer{Dst: frame, Src: new(image.Uniform), Face: face, Dot: fixed.Point26_6{X: fixed.I(x), Y: fixed.I(y)}}
 	for _, seg := range l.Data {
 		drawer.Src.(*image.Uniform).C = seg.Color
+
+		// optional bounds check to reduce overhead
+		if l.bounds && !outOfBounds {
+			b, _ := drawer.BoundString(seg.Value)
+			outOfBounds = !b.In(boundsFixed)
+		}
+
 		drawer.DrawString(seg.Value)
 	}
 
+	if outOfBounds {
+		return syscall.EDOM
+	}
 	return nil
 }
 
diff --git a/caption_sample_test.go b/line_sample_test.go
similarity index 100%
rename from caption_sample_test.go
rename to line_sample_test.go
diff --git a/caption_test.go b/line_test.go
similarity index 81%
rename from caption_test.go
rename to line_test.go
index 8387185..71fd852 100644
--- a/caption_test.go
+++ b/line_test.go
@@ -7,6 +7,7 @@ import (
 	"image"
 	"image/color"
 	"image/png"
+	"syscall"
 	"testing"
 
 	"git.gensokyo.uk/yonah/caption"
@@ -33,6 +34,16 @@ func TestRender(t *testing.T) {
 		{"bad fast path font", &caption.Line{}, caption.NewContext([]byte{0xfd}, nil),
 			0, 0, "", truetype.FormatError("TTF data is too short")},
 
+		{"out of bounds top left", &caption.Line{
+			Data: []caption.Segment{{"Beispieltext", color.Black}},
+		}, nil, 0, 0, "", syscall.EDOM},
+		{"out of bounds right", &caption.Line{
+			Data: []caption.Segment{{"Beispieltext", color.Black}},
+		}, nil, 1<<10 - 0x3e, 1 << 8, "", syscall.EDOM},
+		{"right edge", &caption.Line{
+			Data: []caption.Segment{{"Beispieltext", color.Black}},
+		}, nil, 1<<10 - 0x3f, 1 << 8, "8037459938bcaa6c427412be2ec1e8e77f8ff0e4", nil},
+
 		{"custom line options", &caption.Line{
 			Data:    []caption.Segment{{"Beispieltext", color.Black}},
 			Options: &truetype.Options{Size: 24},
@@ -74,12 +85,14 @@ func TestRender(t *testing.T) {
 				ctx = sharedCtx
 			}
 
+			tc.line.SetBoundsCheck(true)
+
 			redraw := ""
 		redraw:
 			got := image.NewRGBA64(image.Rectangle{Max: image.Point{X: 1 << 10, Y: 1 << 9}})
 			err := tc.line.Render(ctx, got, tc.x, tc.y)
 			for _, f := range beforeCheck {
-				f(t, tc.name, redraw == "", got)
+				f(t, tc.name, redraw != "", got)
 			}
 
 			if !errors.Is(err, tc.wantErr) {
@@ -127,6 +140,19 @@ func TestRender(t *testing.T) {
 				err, wantErr)
 		}
 	})
+
+	t.Run("bounds check skip", func(t *testing.T) {
+		err := (&caption.Line{Data: []caption.Segment{{"Beispieltext", color.Black}}}).
+			Render(
+				new(caption.Context),
+				image.NewRGBA64(image.Rectangle{Max: image.Point{X: 1 << 10, Y: 1 << 9}}),
+				0, 0,
+			)
+		if err != nil {
+			t.Errorf("Render: error = %q",
+				err)
+		}
+	})
 }
 
 func c(r, g, b uint8) color.Color { return color.NRGBA{R: r, G: g, B: b, A: 0xff} }