Draw Rectangle (random times, random location)

[Jneiswin]

I am practicing using the drawing commands, and have gotten a grass background and black happy face that moves around the background.
It's a 10x10 grid of 50 pixels.

I want (at the moment, when i press enter) it to generate a random number of trees (15 ~ 25) at random locations on the background. The program doesn't freak out about anything, and the variables seem to be right (using stop commands) but it's not drawing anything. Here is the code for the "GenerateTrees" command I have for when I press enter.

    Private Sub GenerateTrees()

        NumberOfTrees = Int(Rnd() * 10) + 15
        For i = 0 To NumberOfTrees - 1
            bmap.MakeTransparent(Color.Fuchsia)
            TreeX = Int(Rnd() * 10) * 50
            TreeY = Int(Rnd() * 10) * 50
            sRect = New Rectangle(0, 50, 50, 50)
            dRect = New Rectangle(TreeX, TreeY, 50, 50)
            G.DrawImage(bmap, TreeX, TreeY, sRect, GraphicsUnit.Pixel)
        Next

[Jneiswin]

Here is my whole code, as I just thought of something. It MIGHT be drawing the trees under the grass.

Imports System.Drawing

Public Class Form1

    Dim G As Graphics
    Dim BBG As Graphics
    Dim sRect As Rectangle
    Dim dRect As Rectangle
    Dim bmap As Bitmap
    Dim BB As Bitmap
    Dim NumberOfTrees As Integer
    Dim TreeX As Integer
    Dim TreeY As Integer
    Dim GuyY As Integer = 1
    Dim GuyX As Integer = 1

    Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown

        Select Case e.KeyCode
            Case Keys.W
                GuyY = GuyY - 50
            Case Keys.A
                GuyX = GuyX - 50
            Case Keys.S
                GuyY = GuyY + 50
            Case Keys.D
                GuyX = GuyX + 50
            Case Keys.Space
                ChopTree()
            Case Keys.Enter
                GenerateTrees()
        End Select

        DrawAll()

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        bmap = New Bitmap(PictureBox1.Image)
        G = Me.CreateGraphics
        BB = New Bitmap(Me.Width, Me.Height)

        DrawAll()
    End Sub

    Private Sub ChopTree()

        MsgBox("Attempting to chop a tree")

    End Sub

    Private Sub GenerateTrees()

        NumberOfTrees = Int(Rnd() * 10) + 15
        For i = 0 To NumberOfTrees - 1
            bmap.MakeTransparent(Color.Fuchsia)
            TreeX = Int(Rnd() * 10) * 50
            TreeY = Int(Rnd() * 10) * 50
            sRect = New Rectangle(0, 50, 50, 50)
            dRect = New Rectangle(TreeX, TreeY, 50, 50)
            G.DrawImage(bmap, TreeX, TreeY, sRect, GraphicsUnit.Pixel)
        Next
        Label1.Text = NumberOfTrees

    End Sub
    Private Sub DrawAll()

        Dim X, Y As Integer

        For X = 0 To 9
            For Y = 0 To 9
                sRect = New Rectangle(0, 0, 50, 50)
                dRect = New Rectangle(X * 50, Y * 50, 50, 50)
                G.DrawImage(bmap, dRect, sRect, GraphicsUnit.Pixel)
            Next
        Next

        bmap.MakeTransparent(Color.Fuchsia)
        sRect = New Rectangle(50, 50, 50, 50)
        G.DrawImage(bmap, GuyX, GuyY, sRect, GraphicsUnit.Pixel)

        G = (Graphics.FromImage(BB))
        BBG = Me.CreateGraphics
        BBG.DrawImage(BB, 0, 0, Me.Width, Me.Height)

    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint

        DrawAll()

    End Sub
End Class

[Niya]

lol you have to use the graphics object from the Paint event to draw. You do not create a graphics object to draw on. How would you expect the Runtime to know that you want to draw on the form ?

Here is an example of how to draw a rectangle on a form:-

Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
 
        Dim rect As New Rectangle(20, 20, 150, 150)
 
        e.Graphics.DrawRectangle(Pens.Black, rect)
 
    End Sub

[stepdragon]

As Niya mentioned, you need to use a graphics object which pertains to your form for drawing... You can easily do this by passing the graphics object to each of your subroutines and drawing on that.

I would also suggest simplifying your drawing to one routine. For example, if you draw your background every _Paint event, but your trees only when the user hits a button, your trees will be drawn over the moment the form refreshes.

It would be better to have variables for whether trees should be visible, and where, and then setting the variables, and calling me.Refresh(). Then, your form will redraw, your sub will be called, and it will draw trees instead of just a background.

Make sense?

[Jneiswin]

So I when it generates the trees and their locations, i need to store those values somewhere and call on them every time it refreshes?