Skaisharp Bind CroppedBitmap - xamarin.forms

Question

I followed this tutorial to create an Image cropping page https://learn.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/graphics/skiasharp/bitmaps/cropping. However i now bound two views of the PhotoCropperCanvasView to an carousel view an wanted to Bind the CroppedBitMap so that i can access this property directl in the viewmodel. I just cannot figure ouit how i would achieve that. I f i just make this a Bindable Property the property does not change when i make a new rectangle. So i think i kind of have to exclude the Code of the property but i am very confused.
The whole ocde:
public class PhotoCropperCanvasView : SKCanvasView, INotifyPropertyChanged
{
const int CORNER = 50; // pixel length of cropper corner
const int RADIUS = 100; // pixel radius of touch hit-test
//SKBitmap bitmap;
//CroppingRectangle croppingRect;
SKMatrix inverseBitmapMatrix;
public SKBitmap testmap;
//public SKBitmap bitmap { get; set; }
public Image testImage { get; set; }
public static readonly BindableProperty mapProperty =
BindableProperty.Create(nameof(map), typeof(SKBitmap), typeof(PhotoCropperCanvasView), null);
public SKBitmap map
{
get
{
return (SKBitmap)GetValue(mapProperty);
}
set
{
SetValue(mapProperty, value);
}
}
public CroppingRectangle croppingRect { get; set; }
//public SKMatrix inverseBitmapMatrix { get; set; }
public static readonly BindableProperty bitmapProperty =
BindableProperty.Create(nameof(bitmap), typeof(SKBitmap), typeof(Image),null,propertyChanged: OnbitmapChanged);
static void OnbitmapChanged(BindableObject bindable, object oldValue, object newValue)
{
Console.WriteLine("test");
}
public SKBitmap bitmap
{
get
{
return (SKBitmap)GetValue(bitmapProperty);
}
set
{
SetValue(bitmapProperty, value);
}
}
public SKBitmap CroppedBitmap
{
get
{
SKRect cropRect = new SKRect(croppingRect.Rect.Left,croppingRect.Rect.Top,croppingRect.Rect.Right,croppingRect.Rect.Bottom);
SKBitmap croppedBitmap = new SKBitmap((int)cropRect.Width,
(int)cropRect.Height);
SKRect dest = new SKRect(0, 0, cropRect.Width, cropRect.Height);
SKRect source = new SKRect(cropRect.Left, cropRect.Top,
cropRect.Right, cropRect.Bottom);
using (SKCanvas canvas = new SKCanvas(croppedBitmap))
{
canvas.DrawBitmap(bitmap, source, dest);
}
return croppedBitmap;
}
}
// Touch tracking
TouchEffect touchEffect = new TouchEffect();
struct TouchPoint
{
public int CornerIndex { set; get; }
public SKPoint Offset { set; get; }
}
Dictionary<long, TouchPoint> touchPoints = new Dictionary<long, TouchPoint>();
// Drawing objects
SKPaint cornerStroke = new SKPaint
{
Style = SKPaintStyle.Stroke,
Color = SKColors.White,
StrokeWidth = 10
};
SKPaint edgeStroke = new SKPaint
{
Style = SKPaintStyle.Stroke,
Color = SKColors.White,
StrokeWidth = 2
};
// this constructor for profile image
public PhotoCropperCanvasView(SKBitmap bitmap, float? aspectRatio = null)
{
this.bitmap = bitmap;
SKRect bitmapRect = new SKRect(0, 0, bitmap.Width, bitmap.Height);
croppingRect = new CroppingRectangle(bitmapRect, aspectRatio);
touchEffect.TouchAction += OnTouchEffectTouchAction;
}
// this constructor for post images
public PhotoCropperCanvasView()
{
}
protected override void OnPropertyChanged([CallerMemberName] string propertyName = nameof(bitmap))
{
base.OnPropertyChanged(propertyName);
if (bitmap != null)
{
SKRect bitmapRect = new SKRect(0, 0, bitmap.Width, bitmap.Width);
croppingRect = new CroppingRectangle(bitmapRect, 1);
touchEffect.TouchAction += OnTouchEffectTouchAction;
}
}
protected override void OnParentSet()
{
base.OnParentSet();
// Attach TouchEffect to parent view
Parent.Effects.Add(touchEffect);
}
protected override void OnPaintSurface(SKPaintSurfaceEventArgs args)
{
base.OnPaintSurface(args);
SKImageInfo info = args.Info;
SKSurface surface = args.Surface;
SKCanvas canvas = surface.Canvas;
canvas.Clear(SKColors.Gray);
// Calculate rectangle for displaying bitmap
float scale = Math.Min((float)info.Width / bitmap.Width, (float)info.Height / bitmap.Height);
float x = (info.Width - scale * bitmap.Width) / 2;
float y = (info.Height - scale * bitmap.Height) / 2;
SKRect bitmapRect = new SKRect(x, y, x + scale * bitmap.Width, y + scale * bitmap.Height);
canvas.DrawBitmap(bitmap, bitmapRect);
// Calculate a matrix transform for displaying the cropping rectangle
SKMatrix bitmapScaleMatrix = SKMatrix.MakeIdentity();
bitmapScaleMatrix.SetScaleTranslate(scale, scale, x, y);
// Display rectangle
SKRect scaledCropRect = bitmapScaleMatrix.MapRect(croppingRect.Rect);
canvas.DrawRect(scaledCropRect, edgeStroke);
// Display heavier corners
using (SKPath path = new SKPath())
{
path.MoveTo(scaledCropRect.Left, scaledCropRect.Top + CORNER);
path.LineTo(scaledCropRect.Left, scaledCropRect.Top);
path.LineTo(scaledCropRect.Left + CORNER, scaledCropRect.Top);
path.MoveTo(scaledCropRect.Right - CORNER, scaledCropRect.Top);
path.LineTo(scaledCropRect.Right, scaledCropRect.Top);
path.LineTo(scaledCropRect.Right, scaledCropRect.Top + CORNER);
path.MoveTo(scaledCropRect.Right, scaledCropRect.Bottom - CORNER);
path.LineTo(scaledCropRect.Right, scaledCropRect.Bottom);
path.LineTo(scaledCropRect.Right - CORNER, scaledCropRect.Bottom);
path.MoveTo(scaledCropRect.Left + CORNER, scaledCropRect.Bottom);
path.LineTo(scaledCropRect.Left, scaledCropRect.Bottom);
path.LineTo(scaledCropRect.Left, scaledCropRect.Bottom - CORNER);
canvas.DrawPath(path, cornerStroke);
}
// Invert the transform for touch tracking
bitmapScaleMatrix.TryInvert(out inverseBitmapMatrix);
}
void OnTouchEffectTouchAction(object sender, TouchActionEventArgs args)
{
int i = 0;
SKPoint pixelLocation = ConvertToPixel(args.Location);
SKPoint bitmapLocation = inverseBitmapMatrix.MapPoint(pixelLocation);
switch (args.Type)
{
case TouchActionType.Pressed:
// Convert radius to bitmap/cropping scale
float radius = inverseBitmapMatrix.ScaleX * RADIUS;
// Find corner that the finger is touching
int cornerIndex = croppingRect.HitTest(bitmapLocation, radius);
if (cornerIndex != -1 && !touchPoints.ContainsKey(args.Id))
{
TouchPoint touchPoint = new TouchPoint
{
CornerIndex = cornerIndex,
Offset = bitmapLocation - croppingRect.Corners[cornerIndex]
};
touchPoints.Add(args.Id, touchPoint);
}
break;
case TouchActionType.Moved:
if (touchPoints.ContainsKey(args.Id))
{
TouchPoint touchPoint = touchPoints[args.Id];
croppingRect.MoveCorner(touchPoint.CornerIndex,
bitmapLocation - touchPoint.Offset);
InvalidateSurface();
}
break;
case TouchActionType.Released:
case TouchActionType.Cancelled:
if (touchPoints.ContainsKey(args.Id))
{
touchPoints.Remove(args.Id);
//map = CroppedBitmap;
}
break;
}
}
SKPoint ConvertToPixel(Xamarin.Forms.Point pt)
{
return new SKPoint((float)(CanvasSize.Width * pt.X / Width),
(float)(CanvasSize.Height * pt.Y / Height));
}
}
}
Since the case TouchActionType.Cancelled gets only triggerd once everytime the rectangel was moved, i thought i would set thew bindable Proeprty map to the Cropped bitmap property so that i can get the Cropped Image from the view obver a Binding to the viewmodel. This part works, however, when i activate the line map = CroppedBitmap the cropping rectangle can only be moved by opposite corners. So if i start moving it with the bottom right corner i con only use the top left or bottom right. If i leave the line map = CroppedBitman(249) deactivated i can move the rectangle on all corners at every times. I do not understand this behaviour.
the view:
<CarouselView Grid.Row="0"
IsSwipeEnabled="False"
x:Name="carousel"
Margin="0,-40,0,0"
CurrentItem="{Binding CurrentCutImage, Mode=TwoWay}"
CurrentItemChanged="CarouselView_CurrentItemChanged"
HorizontalScrollBarVisibility="Always"
IsScrollAnimated="True"
ItemsSource="{Binding ImageObjects}"
VerticalScrollBarVisibility="Always"
>
<CarouselView.ItemTemplate>
<DataTemplate x:DataType="viewmodel:CutImages">
<Grid>
<bitmaps:PhotoCropperCanvasView bitmap="{Binding ImageSource }" map="{Binding MapSource, Mode=TwoWay}" >
</bitmaps:PhotoCropperCanvasView>
</Grid>
</DataTemplate>
</CarouselView.ItemTemplate>
</CarouselView>
and the VM:
public partial class CutImagesViewModel : ObservableObject
{
// == observable properties ==
[ObservableProperty]
public Collection<CutImages> imageObjects = new Collection<CutImages>();
[ObservableProperty]
CutImages currentCutImage;
[ObservableProperty]
public SKBitmap maps;
public CutImagesViewModel(Collection<SKBitmapImageSource> images)
{
foreach(var image in images)
{
ImageObjects.Add(new CutImages(image));
}
this.CurrentCutImage = this.ImageObjects.FirstOrDefault();
}
}
public partial class CutImages : ObservableObject
{
[ObservableProperty]
public SKBitmap imageSource;
[ObservableProperty]
public SKBitmap mapSource;
partial void OnMapSourceChanged(SKBitmap value)
{
if(!images.Contains(value))
{
images.Add(value);
}
}
[ObservableProperty]
Collection<SKBitmap> images = new Collection<SKBitmap>();
public CutImages(ImageSource imageSource)
{
SKBitmapImageSource sourceImage = (SKBitmapImageSource)imageSource;
SKBitmap image = sourceImage;
ImageSource = image;
}
}