IOS Xamarin - Realtime plot draw lines - ios

Question

I'm working in a cross test project for display ecg graph in realtime. it's work fine on windows and android using Xamarin, BUT in IOS i have slow and slow performarces.
I think the problem is due to my lack of expertise in ios..
I've done two tests both failed, someone have a solutions to speed up ?
TEST A
I call Plot and then assign the UIImage wBitmap as MyView Backgroud every < 10ms
public void Plot(PointF pPrec, PointF pNext)
{
SizeF bitmapSize = new SizeF(wBitmap.Size);
using (CGBitmapContext context2 = new CGBitmapContext(IntPtr.Zero, (int)bitmapSize.Width, (int)bitmapSize.Height, 8, (int)(4 * bitmapSize.Width), CGColorSpace.CreateDeviceRGB(), CGImageAlphaInfo.PremultipliedFirst))
{
context2.DrawImage(new RectangleF(0, 0, wBitmap.Size.Width, wBitmap.Size.Height), wBitmap.CGImage);
context2.SetLineWidth(1);
context2.AddLineToPoint(pNext.X, pNext.Y);
context2.DrawPath(CGPathDrawingMode.Stroke);
// output the drawing to the view
wBitmap = UIImage.FromImage(context2.ToImage());
}
}
TEST B
I call Plot and then assign the UIImage wBitmap as MyView Backgroud every < 10ms
public void Plot2(PointF pPrec, PointF pNext) { UIGraphics.BeginImageContext(wBitmap.Size); context = UIGraphics.GetCurrentContext();
using (context)
{
if (wBitmap != null)
{
context.TranslateCTM(0f, wBitmap.Size.Height);
context.ScaleCTM(1.0f, -1.0f);
context.DrawImage(new RectangleF(0f, 0f, wBitmap.Size.Width, wBitmap.Size.Height), wBitmap.CGImage);
context.ScaleCTM(1.0f, -1.0f);
context.TranslateCTM(0f, -wBitmap.Size.Height);
}
context.SetLineWidth(1);
context.MoveTo(pPrec.X, pPrec.Y);
context.AddLineToPoint(pNext.X, pNext.Y);
context.DrawPath(CGPathDrawingMode.Stroke);
wBitmap = UIGraphics.GetImageFromCurrentImageContext();
}//end using cont
UIGraphics.EndImageContext();
}

Answer 1

You don't need to draw into a bitmap first and then use that bitmap in a view. The correct approach to this is to subclass UIView and then override the Draw() method and paint your stuff in there.
You can then call SetNeedsDisplay() on the view to schedule a redraw.
The example below draw an arrow shaped background:
class YourView: UIView
{
public override void Draw(RectangleF rect)
{
const float inset = 15f;
UIColor.Blue.SetFill();
var path = new UIBezierPath();
path.MoveTo(new PointF(0, 0));
path.AddLineTo(new PointF(rect.Width - inset, 0));
path.AddLineTo(new PointF(rect.Width, rect.Height * 0.5f));
path.AddLineTo(new PointF(rect.Width - inset, rect.Bottom));
path.AddLineTo(new PointF(0, rect.Bottom));
path.AddLineTo(new PointF(0, 0));
path.Fill();
}
}
}
Alternatively you might want to look at existing components, like CorePlot or TeeChart available in the Xamarin Components store. TeeChart would even be cross platform, so you wouldn't have to worry about Android vs. iOS.