From 52346d972efc9db35df6ad80876e05664f55e8ce Mon Sep 17 00:00:00 2001
From: Loren Burkholder <computersemiexpert@outlook.com>
Date: Sat, 23 Dec 2023 16:27:07 -0500
Subject: [PATCH] Make the image overlay behave better

Previously, the image would not try to stay centered; furthermore,
on mobile devices, it was impossible to zoom images without dropping
them at a slightly off rotation. This bothered me enough that I've
clamped images to the center of the screen (as long as they aren't
zoomed larger than the screen) and snapped rotations to 45-degree
increments (with a nice animation to boot).
---
 resources/qml/dialogs/ImageOverlay.qml | 47 ++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/resources/qml/dialogs/ImageOverlay.qml b/resources/qml/dialogs/ImageOverlay.qml
index fb68fc12..e12777bf 100644
--- a/resources/qml/dialogs/ImageOverlay.qml
+++ b/resources/qml/dialogs/ImageOverlay.qml
@@ -48,8 +48,10 @@ Window {
     Item {
         id: imgContainer
 
-        property int imgSrcWidth: (imageOverlay.originalWidth && imageOverlay.originalWidth > 100) ? imageOverlay.originalWidth : Screen.width
-        property int imgSrcHeight: imageOverlay.proportionalHeight ? imgSrcWidth * imageOverlay.proportionalHeight : Screen.height
+        property int imgSrcWidth: (imageOverlay.originalWidth && imageOverlay.originalWidth > 100) ? imageOverlay.originalWidth : imageOverlay.width
+        property int imgSrcHeight: imageOverlay.proportionalHeight ? imgSrcWidth * imageOverlay.proportionalHeight : imageOverlay.height
+        readonly property int physicalWidth: width * scale
+        readonly property int physicalHeight: height * scale
 
         property double initialScale: Math.min(Window.height/imgSrcHeight, Window.width/imgSrcWidth, 1.0)
 
@@ -59,6 +61,22 @@ Window {
         x: (parent.width - width) / 2
         y: (parent.height - height) / 2
 
+        onXChanged: {
+            if (physicalWidth < imageOverlay.width)
+                x = (parent.width - width) / 2;
+        }
+        onYChanged: {
+            if (physicalHeight < imageOverlay.height)
+                y = (parent.height - height) / 2;
+        }
+
+        Behavior on rotation {
+            NumberAnimation {
+                duration: 100
+                easing.type: Easing.InOutQuad
+            }
+        }
+
         Image {
             id: img
 
@@ -89,13 +107,30 @@ Window {
     }
 
     Item {
-        anchors.fill: parent
+        id: handlerContainer
 
+        function snapImageRotation()
+        {
+            // snap to 15-degree angles
+            let rotationOffset = imgContainer.rotation % 15;
+            if (rotationOffset != 0)
+            {
+                if (rotationOffset < 7.5)
+                    imgContainer.rotation -= rotationOffset;
+                else
+                    imgContainer.rotation += rotationOffset;
+
+            }
+        }
+
+        anchors.fill: parent
 
         PinchHandler {
             target: imgContainer
             maximumScale: 10
             minimumScale: 0.1
+
+            onGrabChanged: handlerContainer.snapImageRotation()
         }
 
         WheelHandler {
@@ -105,10 +140,16 @@ Window {
             // and we don't yet distinguish mice and trackpads on Wayland either
             acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad
             target: imgContainer
+
+            onWheel: handlerContainer.snapImageRotation()
         }
 
         DragHandler {
             target: imgContainer
+            xAxis.enabled: imgContainer.physicalWidth > imageOverlay.width
+            yAxis.enabled: imgContainer.physicalHeight > imageOverlay.height
+
+            onGrabChanged: handlerContainer.snapImageRotation()
         }
 
         HoverHandler {