Memory expensive rubber band selection?

[Luc Pattyn]

Graphics objects are expensive, and you should dispose them. Why not use a using statement, just like you did for the region Bitmap? And why would you need two Graphics instances, and a DrawImage()? Couldn't you just use the Bitmap(Image) constructor, and have its Graphics, just the one? :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

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[Chesnokov Yuriy]

I was looking for a way to darken non ROI region in the image. You optimizations would be welcomed. Why the picture box update is very slow if I keep drawing on every mouse move event?

Чесноков

[Lost User]

Mouse-move events are fired continuesly, and the drawing routine looks expensive. You might want to check whether the mouse has moved in the meantime, not redrawing if there's no movement detected.

Bastard Programmer from Hell :suss:

[BobJanova]

I recommend overlaying the semitransparent mask over the base image (either in OnPaint on the picture box or by placing another object over the top). Then all you have to redraw is the mask. Creating graphics objects is slow, which is why you should typically do it in OnPaint. In fact, in this case, you should do that, and your mouse move handler should only call Invalidate.

[Pete OHanlon]

One other thing to bear in mind. The managed version of GDI+ is slow in comparison to the unmanaged version. You pay a price for the simplicity, and that price is speed.

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[Luc Pattyn]

Chesnokov Yuriy wrote:

Why the picture box update is very slow if I keep drawing on every mouse move event?

Because the MouseMove events fire at high frequency (allowing you to track well assuming your handler is fast), possibly 50Hz or higher (which is too high for the human eye to notice), because Graphics objects are expensive, and finally because PictureBoxes are stupid (I wouldn't be surprised if the fact you change the image just causes another mouse move event). You want to run such things continuously? I would experiment with keeping the two Graphics and the Bitmap around as class members, i.e. not create new objects at all, just keep using them over and over. :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

The quality and detail of your question reflects on the effectiveness of the help you are likely to get.
Please use <PRE> tags for code snippets, they improve readability.
CP Vanity has been updated to V2.3

[Chesnokov Yuriy]

I need to implement rubber band like ROI selection in the image as in paint editor

Чесноков

[_Erik_]

What I understand is that you are trying to darken a rectangle within a image, and that rectangle must be refreshed as long as the mouse is moving. Am I right? If this is what you want to do, the problem is that you are creating too many new Graphics and Bitmap objects in a very short time (and these are expensive objects), and updating the Image property a lot of times as well. The best way to do it is to subscribe to the Paint event of the control and code everything in this event handler, so you will receive a Graphics object as a parameter. In the next example there is only a PictureBox in the Form, called pct:

public partial class Form1 : Form
{
bool drawRect = false;
Rectangle r = new Rectangle();
Brush br = new SolidBrush(Color.FromArgb(50, Color.Red));

public Form1()
{
    InitializeComponent();
}

private void pct\_Paint(object sender, PaintEventArgs e)
{
    if (drawRect)
        e.Graphics.FillRectangle(br, r);
}

private void pct\_MouseDown(object sender, MouseEventArgs e)
{
    drawRect = true;
    r.X = e.X;
    r.Y = e.Y;
}

private void pct\_MouseMove(object sender, MouseEventArgs e)
{
    r.Width = e.X - r.X;
    r.Height = e.Y - r.Y;

    Refresh();
}

private void pct\_MouseUp(object sender, MouseEventArgs e)
{
    drawRect = false;
    Refresh();
}

}

I've made it quick. You would have to modify it in order to draw the rectangle if the mouse moves to a lower X and/or lower Y coordinate.

[Chesnokov Yuriy]

No, I need to darken the area outside rectangle. Consider ROI region. ROI remains clear and the area outside it is darked. I tried preinitialization of graphics and bitmaps and found that the problem part taking much of the time is:

...
roi_g.FillRectangle(new SolidBrush(Color.FromArgb(64, 0, 0, 0)), new Rectangle(0, 0, FrameWithRoi.Width, FrameWithRoi.Height));
roi_g.FillRectangle(new SolidBrush(Color.Red), rect);
region.MakeTransparent(Color.Red);
g.DrawImage(region, 0, 0);
...

Despite prinitialization it takes about 150ms

Чесноков

[_Erik_]

Well, then, draw four rectangles around the area you want to keep clear. Just change the Paint event handler I posted before this way:

private void pct_Paint(object sender, PaintEventArgs e)
{
if (drawRect)
{
e.Graphics.FillRectangle(br, 0, 0, pct.Width, r.Y);
e.Graphics.FillRectangle(br, 0, r.Y, r.X, pct.Height);
e.Graphics.FillRectangle(br, r.X, r.Y + r.Height, pct.Width, pct.Height);
e.Graphics.FillRectangle(br, r.X + r.Width, r.Y, pct.Width, r.Height);
}
}

This will work pretty well. Do you also want to save the image after you have darkened the area?