MonoTouch, drawing a cropping region layer over a UIImageView - ios

Question

In our app we'd like to be able to crop, scale and pan an image, and I just can't seem to figure out how I am supposed to draw a cropping region on top of my UIImageView.
I tried messing with coregraphics, I could render a region with a black stroke on my image, but the image would flip. Not only that, but since I had drawn ON the image, I'm afraid that if I were to move and scale it using gestures, the region would be affected too!
A push in the right direction would be much appreciated!
Heres my code that doesen't really do what I want, to show some research effort.
// Aspect ration - Currently 1:1
const int arWidth = 1;
const int arHeight = 1;
UIGraphics.BeginImageContext(ImgToCrop.Frame.Size);
var context = UIGraphics.GetCurrentContext();
// Set the line width
context.SetLineWidth(4);
UIColor.Black.SetStroke();
// Our starting points.
float x = 0, y = 0;
// The sizes
float width = ImgToCrop.Frame.Width, height = ImgToCrop.Frame.Height;
// Calculate the geometry
if(arWidth == arHeight){
// The aspect ration is 1:1
width = ImgToCrop.Frame.Width;
height = width;
x = 0;
y = ImgToCrop.Frame.GetMidY()-height/2;
}
// The rect
var drawRect = new RectangleF(x,y,width,height);
context.DrawImage(new RectangleF(
ImgToCrop.Frame.X,
ImgToCrop.Frame.Y,
ImgToCrop.Frame.Width,
ImgToCrop.Frame.Height),ImgToCrop.Image.CGImage);
// Draw it
context.StrokeRect(drawRect);
ImgToCrop.Image = UIGraphics.GetImageFromCurrentImageContext();

Answer 1

Maybe this will help you:
public static UIImage ScaleToSize (UIImage image, int width, int height)
{
UIGraphics.BeginImageContext (new SizeF (width, height));
CGContext ctx = UIGraphics.GetCurrentContext ();
float ratio = (float) width / (float) height;
ctx.AddRect (new RectangleF (0.0f, 0.0f, width, height));
ctx.Clip ();
var cg = image.CGImage;
float h = cg.Height;
float w = cg.Width;
float ar = w / h;
if (ar != ratio) {
// Image's aspect ratio is wrong so we'll need to crop
float scaleY = height / h;
float scaleX = width / w;
PointF offset;
SizeF crop;
float size;
if (scaleX >= scaleY) {
size = h * (w / width);
offset = new PointF (0.0f, h / 2.0f - size / 2.0f);
crop = new SizeF (w, size);
} else {
size = w * (h / height);
offset = new PointF (w / 2.0f - size / 2.0f, 0.0f);
crop = new SizeF (size, h);
}
// Crop the image and flip it to the correct orientation (otherwise it will be upside down)
ctx.ScaleCTM (1.0f, -1.0f);
using (var copy = cg.WithImageInRect (new RectangleF (offset, crop))) {
ctx.DrawImage (new RectangleF (0.0f, 0.0f, width, -height), copy);
}
} else {
image.Draw (new RectangleF (0.0f, 0.0f, width, height));
}
UIImage scaled = UIGraphics.GetImageFromCurrentImageContext ();
UIGraphics.EndImageContext ();
return scaled;
}