Is Graphics.DrawImage too slow for bigger images?

Question

I\'m currently working on a game and I wish to have a main menu with background image.

However, I find the method Graphics.DrawImage() really slow. I ha

Answer 1

Although this is an ancient question and WinForms is an ancient Framework, I would like to share what I have just discovered by accident: drawing a Bitmap into a BufferedGraphics and rendering it afterwards to the graphics context provided by OnPaint is way faster than drawing the Bitmap directly to OnPaint's graphics context - at least on my Windows 10 machine.

That's surprising because intuitively I had assumed that it would be slightly slower to copy data twice (and so I thought that this is usually only justified when one wants to do double-buffering manually). But obviously there is something more sophisticated going on with the BufferedGraphics object.

So create a BufferedGraphics in the constructor of the Control that shall host the Bitmap (in my case I wanted to draw a fullscreen bitmap 1920x1080):

        using (Graphics graphics = CreateGraphics())
        {
            graphicsBuffer = BufferedGraphicsManager.Current.Allocate(graphics, new Rectangle(0,0,Screen.PrimaryScreen.Bounds.Width,Screen.PrimaryScreen.Bounds.Height));
        }

and use it in OnPaint (while voiding OnPaintBackground)

    protected override void OnPaintBackground(PaintEventArgs e) {/* just rely on the bitmap to fill the screen */}

    protected override void OnPaint(PaintEventArgs e)
    {   
        Graphics g = graphicsBuffer.Graphics;

        g.DrawImage(someBitmap,0,0,bitmap.Width, bitmap.Height);

        graphicsBuffer.Render(e.Graphics);
    }

instead of naively defining

    protected override void OnPaintBackground(PaintEventArgs e) {/* just rely on the bitmap to fill the screen */}

    protected override void OnPaint(PaintEventArgs e)
    {   
        e.Graphics.DrawImage(someBitmap,0,0,bitmap.Width, bitmap.Height);
    }

See the following screenshots for a comparison of the resulting MouseMove event frequency (I am implementing a very simple bitmap sketching control). At the top is the version where the Bitmap is drawn directly, at the bottom BufferedGraphics is used. I moved the mouse at about the same speed in both cases.