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using System;
using System.Diagnostics;
using Xamarin.Forms.Internals;
namespace Xamarin.Forms.Controls
{
public class PinchToZoomContainer : ContentView
{
public PinchToZoomContainer ()
{
}
public void AddPinch ()
{
var pinch = new PinchGestureRecognizer ();
double xOffset = 0;
double yOffset = 0;
double startScale = 1;
pinch.PinchUpdated += (sender, e) => {
if (e.Status == GestureStatus.Started) {
startScale = Content.Scale;
Content.AnchorX = Content.AnchorY = 0;
}
if (e.Status == GestureStatus.Running) {
_currentScale += (e.Scale - 1) * startScale;
_currentScale = Math.Max (1, _currentScale);
var renderedX = Content.X + xOffset;
var deltaX = renderedX / Width;
var deltaWidth = Width / (Content.Width * startScale);
var originX = (e.ScaleOrigin.X - deltaX) * deltaWidth;
var renderedY = Content.Y + yOffset;
var deltaY = renderedY / Height;
var deltaHeight = Height / (Content.Height * startScale);
var originY = (e.ScaleOrigin.Y - deltaY) * deltaHeight;
double targetX = xOffset - (originX * Content.Width) * (_currentScale - startScale);
double targetY = yOffset - (originY * Content.Height) * (_currentScale - startScale);
Content.TranslationX = targetX.Clamp (-Content.Width * (_currentScale - 1), 0);
Content.TranslationY = targetY.Clamp (-Content.Height * (_currentScale - 1), 0);
Content.Scale = _currentScale;
}
if (e.Status == GestureStatus.Completed) {
xOffset = Content.TranslationX;
yOffset = Content.TranslationY;
}
};
GestureRecognizers.Add (pinch);
}
public bool AlwaysZoomCenter { get; set; }
double _currentScale = 1;
}
public class PinchGestureTestPage : ContentPage
{
public PinchGestureTestPage ()
{
var stack = new StackLayout { VerticalOptions = LayoutOptions.Start, HorizontalOptions = LayoutOptions.Center };
var textBoxScale = new Label { VerticalOptions = LayoutOptions.Start, HorizontalOptions = LayoutOptions.Center };
var textBox = new Label { VerticalOptions = LayoutOptions.Start, HorizontalOptions = LayoutOptions.Center };
var textBoxPoint = new Label { VerticalOptions = LayoutOptions.Start, HorizontalOptions = LayoutOptions.Center };
stack.Children.Add (textBox);
stack.Children.Add (textBoxScale);
stack.Children.Add (textBoxPoint);
var box = new Image { Source = "crimson.jpg", BackgroundColor = Color.Red, WidthRequest = 200, HeightRequest = 200, VerticalOptions = LayoutOptions.Center, HorizontalOptions = LayoutOptions.Center };
var zoomContainer = new PinchToZoomContainer ();
zoomContainer.Content = box;
var btn = new Button { Text = "add pinch gesture", Command = new Command (() => zoomContainer.AddPinch ()) };
var btnRemove = new Button { Text = "remove pinch gesture", Command = new Command (() => zoomContainer.GestureRecognizers.Clear ()) };
Content = new StackLayout { Children = { btn, btnRemove, new Grid { Children = { zoomContainer }, Padding = new Thickness (20) } } };
}
double _currentScale = 1;
}
}
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