B4J Question Canvas.DrawImage works slowly

[red30]

I use two canvases that show a signal.
When I use one - it runs smoothly, when both - with breaks. Why?
One:

CanvasNCH.DrawImage(CanvasNCH.Snapshot,-1,0,CanvasNCH.Width,CanvasNCH.Height) 
CanvasNCH.DrawLine(t-2,OldSig1,(t-1),Sig1,fx.Colors.Blue,2)
OldSig1=Sig1
CanvasVCH.DrawLine(t-2,OldSig2,(t-1),Sig2,fx.Colors.Green,2)
OldSig2=Sig2

Both:

CanvasNCH.DrawImage(CanvasNCH.Snapshot,-1,0,CanvasNCH.Width,CanvasNCH.Height)
CanvasVCH.DrawImage(CanvasVCH.Snapshot,-1,0,CanvasVCH.Width,CanvasVCH.Height)
CanvasNCH.DrawLine(t-2,OldSig1,(t-1),Sig1,fx.Colors.Blue,2)
OldSig1=Sig1
CanvasVCH.DrawLine(t-2,OldSig2,(t-1),Sig2,fx.Colors.Green,2)
OldSig2=Sig2

 

[Erel]

What is the purpose of this line:

CanvasNCH.DrawImage(CanvasNCH.Snapshot,-1,0,CanvasNCH.Width,CanvasNCH.Height)

 

[red30]

In oder not to stop the graph: so the line keeps up moving right when the graph transfers to left.

 

[red30]

I wanted to do the same as on an oscilloscope screen.

 

[Erel]

Attached is an example that uses BitmapCreator to create a similar graph.

Note that BitmapCreator will be included as an internal library in the next version of B4J to make it easier to use.
You will need to replace it with the class.

 

[Erel]

Same code also works in B4A and B4i:

B4A example is attached.

 

[red30]

Erel, thank you very much, it is exactly what I needed, but still I have some questions.
Is it possible to put numbers on a scale (for ex. voltage on y-axis and time on y-axis)?
How can I change the grid itself? ( ex. 10x10 20x20)
Can it show the coordinate when hovering a cursor over the graph?
Can I change the scale of the graph on axises while it is building?

 

[Erel]

Example with text is attached.

In this implementation it only draws the text when there is enough room for the complete label. It can be further improved to make it appear immediately.

How can I change the grid itself? ( ex. 10x10 20x20)

You need to go over the code and see how it works.

You will need to wait for the next version of B4J (to be released next week) in order to run it.

 

[red30]

In the last program produces an error:

B4J Version: 6.01
Parsing code.    (0.03s)
Compiling code.    Error
Error compiling program.
Error description: Unknown member: measuretext
Error occurred on line: 117
Dim r As B4XRect = cvs.MeasureText(Text, fnt)
Word: measuretext

 

[Erel]

You will need to wait for the next version of B4J (to be released next week) in order to run it.

 

[red30]

A new version of B4J has been released. But I can not figure out how to work with the schedule. Could you explain to me?

 

[Erel]

But I can not figure out how to work with the schedule

What do you mean with schedule?

 

[red30]

I mean graph.

 

[Erel]

Are you able to run the example I posted? Do you see how it adds the values?