From 6faed7e7245c2622b00852ce3e7e7e8cf98b6134 Mon Sep 17 00:00:00 2001
From: Chris Waldon <christopher.waldon.dev@gmail.com>
Date: Sat, 27 Feb 2021 22:18:09 -0500
Subject: [PATCH] widget: fix image scaling

Commit 94d242d broke the widget.Image's Scale field so
that it no longer had any effect on the actual size of
the displayed image. This commit fixes that, as well as
adding tests to confirm that the widget.Image type
scales appropriately with DPI changes and its own Scale
field.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>
---
 widget/image.go      |  7 ++++-
 widget/image_test.go | 66 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 widget/image_test.go

diff --git a/widget/image.go b/widget/image.go
index 77062651..54ab62f2 100644
--- a/widget/image.go
+++ b/widget/image.go
@@ -5,6 +5,7 @@ package widget
 import (
 	"image"
 
+	"gioui.org/f32"
 	"gioui.org/layout"
 	"gioui.org/op"
 	"gioui.org/op/clip"
@@ -22,10 +23,12 @@ type Image struct {
 	Scale float32
 }
 
+const defaultScale = float32(160.0 / 72.0)
+
 func (im Image) Layout(gtx layout.Context) layout.Dimensions {
 	scale := im.Scale
 	if scale == 0 {
-		scale = 160.0 / 72.0
+		scale = defaultScale
 	}
 	size := im.Src.Size()
 	wf, hf := float32(size.X), float32(size.Y)
@@ -33,6 +36,8 @@ func (im Image) Layout(gtx layout.Context) layout.Dimensions {
 	cs := gtx.Constraints
 	d := cs.Constrain(image.Pt(w, h))
 	stack := op.Save(gtx.Ops)
+	pixelScale := scale * gtx.Metric.PxPerDp
+	op.Affine(f32.Affine2D{}.Scale(f32.Point{}, f32.Pt(pixelScale, pixelScale))).Add(gtx.Ops)
 	clip.Rect(image.Rectangle{Max: d}).Add(gtx.Ops)
 	im.Src.Add(gtx.Ops)
 	paint.PaintOp{}.Add(gtx.Ops)
diff --git a/widget/image_test.go b/widget/image_test.go
new file mode 100644
index 00000000..edc183ca
--- /dev/null
+++ b/widget/image_test.go
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget
+
+import (
+	"image"
+	"testing"
+
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/paint"
+)
+
+func TestImageScale(t *testing.T) {
+	var ops op.Ops
+	gtx := layout.Context{
+		Ops: &ops,
+		Constraints: layout.Constraints{
+			Max: image.Pt(50, 50),
+		},
+	}
+	imgSize := image.Pt(10, 10)
+	img := image.NewNRGBA(image.Rectangle{Max: imgSize})
+	imgOp := paint.NewImageOp(img)
+
+	// Ensure the default scales correctly.
+	dims := Image{Src: imgOp}.Layout(gtx)
+	expectedSize := imgSize
+	expectedSize.X = int(float32(expectedSize.X) * defaultScale)
+	expectedSize.Y = int(float32(expectedSize.Y) * defaultScale)
+	if dims.Size != expectedSize {
+		t.Fatalf("non-scaled image is wrong size, expected %v, got %v", expectedSize, dims.Size)
+	}
+
+	// Ensure scaling the image via the Scale field works.
+	currentScale := float32(0.5)
+	dims = Image{Src: imgOp, Scale: float32(currentScale)}.Layout(gtx)
+	expectedSize = imgSize
+	expectedSize.X = int(float32(expectedSize.X) * currentScale)
+	expectedSize.Y = int(float32(expectedSize.Y) * currentScale)
+	if dims.Size != expectedSize {
+		t.Fatalf(".5 scale image is wrong size, expected %v, got %v", expectedSize, dims.Size)
+	}
+
+	// Ensure the image responds to changes in DPI.
+	currentScale = float32(1)
+	gtx.Metric.PxPerDp = 2
+	dims = Image{Src: imgOp, Scale: float32(currentScale)}.Layout(gtx)
+	expectedSize = imgSize
+	expectedSize.X = int(float32(expectedSize.X) * currentScale * gtx.Metric.PxPerDp)
+	expectedSize.Y = int(float32(expectedSize.Y) * currentScale * gtx.Metric.PxPerDp)
+	if dims.Size != expectedSize {
+		t.Fatalf("HiDPI non-scaled image is wrong size, expected %v, got %v", expectedSize, dims.Size)
+	}
+
+	// Ensure scaling the image responds to changes in DPI.
+	currentScale = float32(.5)
+	gtx.Metric.PxPerDp = 2
+	dims = Image{Src: imgOp, Scale: float32(currentScale)}.Layout(gtx)
+	expectedSize = imgSize
+	expectedSize.X = int(float32(expectedSize.X) * currentScale * gtx.Metric.PxPerDp)
+	expectedSize.Y = int(float32(expectedSize.Y) * currentScale * gtx.Metric.PxPerDp)
+	if dims.Size != expectedSize {
+		t.Fatalf("HiDPI .5 scale image is wrong size, expected %v, got %v", expectedSize, dims.Size)
+	}
+}