Can I draw to a PictBox outside of a paint event?

[Swisskid]

Guys,

I finally realized pros/cons of CreateGraphics Method vs. Paint event (with some help from members here) for a Picture box.

I want program code that is doing calculations to to update several different PictureBoxes but it seems weird to have calculation code have to be inside a Paint event to paint the "data"...

Structurally I am asking if I can have a program that calculates something and then updates multiple different Pictureboxes (mostly just drawing points or showing displaying data in a plot format)...

Is there a method to call DrawRectangle() function from code running OUTSIDE of the PaintEvent and update a drawing in a specific PictureBox by passing the right parameters?

Ideally I would have the main program running its calcs and when it gets a result to be displayed I can draw to pictBox a, b, c and so forth form the main program event (not from a Paint Event for each Picture Box).

Right now the program runs the specific code within the Paint event itself...this becomes problematic when I do different calculations and want to print them to different PictureBoxes.
Seems like I need to split up the calculations so that each calculation occurs in a different PictureBox Paint event...

Appreciate any hints as to how to do this, assuming it is possible.

[.paul.]

To create persistent graphics outside of a paint event…

Dim img As Nee Bitmap(width, height)
Dim gr As Graphics = Graphics.FromImage(img)

gr.Draw… “etc

PictureBox1.Image = img

[jmcilhinney]

it seems weird to have calculation code have to be inside a Paint event to paint the "data"...

So don't. Store the data in one or more fields and have the drawing code in the Paint event handler use that data. The code to calculate the data and set the fields can be elsewhere. That way, you don't have to do the same calculations over and over in order to do the same drawing. Any time you need to change the drawing, run the code to do the calculation and set the fields and then call Invalidate on the control to force a Paint event, which will erase the old drawing and redraw with the new data. Here's one I prepared earlier:

https://www.vbforums.com/showthread....rawing-Program

That stores the data for the lines to be drawn in a List at the class level. The Paint event handler simply draws whatever is in that List. If a new line needs to be added, the List is modified and a Paint event is triggered.

[Swisskid]

Thank you Paul - so drawing to a bitmap and then loading thru img. I had some trouble with that approach but will try again. Thank you!

[Swisskid]

Thank you jmcilhinney...I think you and Paul may have commented on my questions regarding graphics previously. bmp handling is the last thing I need to master after PaintEvent and CreateGraphics & I think I will be able to do just about anything with the pictbox. Thanks for the help & the example!

[jmcilhinney]

For the record, I would tend to use a Bitmap assigned to the Image property (or setting the ImageLocation for a file) if the image doesn't change at all or not very much. If the image changes relatively frequently especially to make modifications to an existing image, then I'd consider using the Paint event.

[Swisskid]

OK - great advice from you both - got it working in no time.

My only remaining issue is that I would like to clear the screen prior to the next calculation results being displayed on the picture box. Right now every time I push the button new results are simply added to the existing results.

Right now the code is event driven (button push "start calculation") and all the drawing code is where I want it and the image is persistent. My remaining issue is that I would like to clear the screen to the background color each time the button is pushed to make room for a second calculation => drawing result. Look back at past posts and tried "Pictbox.Image = nothing" and it did nothing (drawn image persists). I tried a combination of the previous with "Pictbox.image.dispose()" and this just removes the entire picture box - even tried drawing a black colored box over the entire previosly drawn image and this did not work either. Any suggestions?

[Swisskid]

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

'gr.DrawRectangle(myPenCLS, 0, 0, 800, 800)<=== this is where I would like code that will clear teh screen but not get ride of the picture box
'PictureBox1.Image = Nothing

While LoopIndex < 100000
radius = CryptoRadius() : psi = CryptoPsi() : psiradians = psi * Math.PI / 180
rx = CInt(radius * Math.Cos(psiradians)) : ry = CInt(radius * Math.Sin(psiradians))
gr.DrawRectangle(myPen2, Math.Round(400 + rx, 0), Math.Round(400 + ry, 0), 1, 1)
LoopIndex = LoopIndex + 1
End While

LoopIndex = 0

PictureBox1.Image = img
PictureBox1.Refresh()

End Sub

[.paul.]

gr.Clear(a color)

[.paul.]

If you just want to clear a rectangular part of the image, you can use gr.FillRectangle( ' etc

[jmcilhinney]

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

'gr.DrawRectangle(myPenCLS, 0, 0, 800, 800)<=== this is where I would like code that will clear teh screen but not get ride of the picture box
'PictureBox1.Image = Nothing

While LoopIndex < 100000
radius = CryptoRadius() : psi = CryptoPsi() : psiradians = psi * Math.PI / 180
rx = CInt(radius * Math.Cos(psiradians)) : ry = CInt(radius * Math.Sin(psiradians))
gr.DrawRectangle(myPen2, Math.Round(400 + rx, 0), Math.Round(400 + ry, 0), 1, 1)
LoopIndex = LoopIndex + 1
End While

LoopIndex = 0

PictureBox1.Image = img
PictureBox1.Refresh()

End Sub

It's hard to say for sure but, based on that code, it looks like you may be creating one Graphics object and kjeeping it around. Don't do that. Create a Grpahics object when you need one and then destroy it when you're done with it. Create another one later if you need to draw again later. The same goes for a Pen or Brush object, if you're not using the standard, system-suplied ones.

Using g = Graphics.FromImage(myImage),
      p As New Pen(someColor)
    'Use g and p here.
End Using

[Swisskid]

Hi Paul,

Thank you! BTW I tried just filling with a color but stupidly used DrawRect vs. FillRect.
Perfect.

Thank you!

[Swisskid]

Thank you jmcilhinney. Yes I understand that - that was the next step ...

[.paul.]

This will help you understand PictureBoxes...

https://www.vbforums.com/showthread....86#post5655986