Hello all

I'm working on my second project; a layered image displayer.
It works like this:
- The user adds a new "image layer"
- The user can set the texture, image, size, rotation and color
- This all can be done using a selection square and some dialogs

It all works fine, but I found that there is one thing still unclear to me:
- Can you render layers without totally starting over (refresh) on every change?

As example, I have 200 image layers. I change one image layer somewhere in between them, and the program has to refresh all those images. (1 - 200)
This takes awfully long.

Now I found a small solution; I gave all layers a "finalimage" so it can render a single layer. Next I used, in the program, a back, active and fore layer.

This way the program only has to render 3 images when chaging the "active" layer. When you select another layer, all 3 layers will refresh. (with all those 200 layers).

here is the code to get an idea:
Code:
    Dim OLDINDEX As Integer = -1
    Dim BackLayer As New Bitmap(800, 600)
    Dim ActiveLayer As New Bitmap(800, 600)
    Dim FrontLayer As New Bitmap(800, 600)
    Public CurrentIndex As Integer = -1
    Public PerformGlobalUpdate As Boolean = False
    Public Sub Render(ByRef g As Graphics)
        'Get the layer modified types
        Dim UpdateActiveLayer As Boolean = False
        Dim UpdateBackLayer As Boolean = False
        Dim UpdateFrontLayer As Boolean = False
        If OLDINDEX = CurrentIndex And PerformGlobalUpdate = False Then
            For i As Integer = 0 To Layers.Count - 1
                If Layers(i).Changed = True And i < CurrentIndex Then UpdateBackLayer = True
                If Layers(i).Changed = True And i > CurrentIndex Then UpdateFrontLayer = True
                If Layers(i).Changed = True And i = CurrentIndex Then UpdateActiveLayer = True
            Next
        Else
            PerformGlobalUpdate = False
            UpdateBackLayer = True
            UpdateActiveLayer = True
            UpdateFrontLayer = True
        End If
        If UpdateActiveLayer = True Then ActiveLayer = New Bitmap(800, 600)
        If UpdateFrontLayer = True Then FrontLayer = New Bitmap(800, 600)
        If UpdateBackLayer = True Then BackLayer = New Bitmap(800, 600)
        If UpdateBackLayer = True Or UpdateFrontLayer = True Or UpdateActiveLayer = True Then
            Dim e As Integer = Layers.Count - 1
            Dim s As Integer = 1
            If UpdateBackLayer = False Then s = CurrentIndex
            If UpdateFrontLayer = False Then e = CurrentIndex
            For i As Integer = s To e
                If i < Layers.Count And i > 0 And ((UpdateBackLayer = True And i < CurrentIndex) Or (UpdateFrontLayer = True And i > CurrentIndex) Or (UpdateActiveLayer = True And i = CurrentIndex)) Then
                    If i < CurrentIndex Then Layers(i).ApplyToImage(BackLayer)
                    If i > CurrentIndex Then Layers(i).ApplyToImage(FrontLayer)
                    If i = CurrentIndex Then Layers(i).ApplyToImage(ActiveLayer)
                End If
            Next
        End If
        'Render all 3 the layers
        If CurrentIndex <> 0 Then g.DrawImage(BackLayer, New Point(0, 0))
        If CurrentIndex <> -1 Then g.DrawImage(ActiveLayer, New Point(0, 0))
        If CurrentIndex <> Layers.Count - 1 Then g.DrawImage(FrontLayer, New Point(0, 0))
        OLDINDEX = CurrentIndex
    End Sub
It all works fine, but the only problem now is that it takes ages to select a different layer.

Anyone knows of an alternative solution to render different layers?