bmp file reading faster after first time ?

[zhaDe]

hey guys, im making a program to "test darwinism" in C++ and im showing the results in a VB 2010 express app, the results consist of .800x800 bmp files displaying creatures eating , reproducing and evolving. the VB app only has a picture box and it changes the .image param in a timer so that it looks like a video : for example it reads : frame0.bmp then frame1.bmp etc. I get about 30frames seconds with this method (and alot of GB of .bmp files..)

I've got a problem tho.. the .bmp files are read slower if they never have been read.. for example I get about 5frames/sec when im using new .bmp files while I get 30fps if the files have been read once.. only opening and closing the files doesnt make them load faster, I have to load the bitmap image. I noticed that opening the directory where the .bmp files are and letting windows make preview icons make them load faster too.. that looks weird to me.. something with indexing ?

also , my c++ program which creates the .bmp files goes really fast for the 500first but then it becomes slower (even if It just writes black .bmp files in a closed loop). could it be that the hard disc gets overwhelmed by all the writing ?

[HanneSThEGreaT]

Do you load these files from disk?

I'd add some logic into the program loading all the images first, before displaying them. this will reduce the time taking to show the pics quite a lot.

I would load all the associated images into an array of images, then just load each indexed array item as needed.

Does that make sense?

[zhaDe]

yes im loading them from the hard disc
I get about 4GB of .bmps for 5minute of video so loading it all in memory would take way too much RAM

I found a way to overcome the loading time problem for my VB prog, I just reduced the image size so now in 400x400 the images load almost as fast as if they were preloaded. I just split the 800x800 image into 4 400x400, it looked better with 800x800 but you can still select which part you want to see.

[DataMiser]

I would say the speed issue would be related to the way windows handles memory. Once you have loaded the bitmap it will stay in memory or in the page file for a while so a reload will be much faster than the initial load. The same thing happens with many programs. Initially when you load a program it may take a few seconds but if you close that program and open it again it may be almost instant.

[dglienna]

I put a deck of cards in as Images in the Resource File. Loads instantly

[Cimperiali]

4GB of .bmps...Time to switch to a lighter format. How about png ? It is till good even if heavier of jpeg or gif (they both lose too much quality)

[dglienna]

Used .PNG's

[sotoasty]

I would say that the time difference is due to the Hard Drive cache. Once you load a file, your hard drive will cache that information in memory for faster access later. This is why if you open the folder with explorer, and explorer builds the thumbnails, that they load fast from then on. Explorer has already opened and read the entire file from disk to build the thumbnail. So the hard drive has cached it and now you application gets the benefit of the file being cached.

It is the same thing for writing, the cache on the hard drive takes everything into the cache, then does the physical write to disk. So your first 500, fills up the cache, and new ones will get accepted as old ones are written out.

[Craig Gemmill]

There are a few tricks you can use to speed this up. I would start with the drawing. You can obviously gain much greater performance by using DirectX and/or WPF/WinRT, but you can also speed things up in the GDI+ world too. See below:

Public Class Form1
    Friend Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        SetStyle(ControlStyles.OptimizedDoubleBuffer, True)
        SetStyle(ControlStyles.UserPaint, True)
        SetStyle(ControlStyles.AllPaintingInWmPaint, True)
        Me.UpdateStyles()

    End Sub

    Private WithEvents _timer As New Timer()


    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        _timer.Interval = 2000
        _timer.Start()
    End Sub

    Private Sub _timer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles _timer.Tick
        Me.Invalidate(New Rectangle(0, 0, 400, 400))
    End Sub

    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)

        'You would progress through frames here
        e.Graphics.DrawImage(YourImageHere, 0, 0, 400, 400)

    End Sub


End Class

Next, as previously mentioned, you should be working on some type of pre-load cache solution. Kind of like how your video player loads ahead (buffers) while you watch.

Alternatively/Additionally, you could look at using WeakReferences as a poor man’s cache solution, and just load them all up front.