WorkerThreadExeption: Object is currently in use elsewhere

[midora]

I'm fighting with this issue, maybe someone can provide a hint.

 

In an effect plugin I created a class and four instances of the class.

The class contains as a member an array of matrices.

 

OnSetRenderInfo() calls a member function of the instances to setup these arrays of matrices.

OnRender() uses the instances and the matrices to transform points.

 

Now quite often I'm getting the above exception. OnRender() does not modify the matrices. They are just used to do the transformation job. So I would say the matrices are used read only. But for sure it may happen that two WorkerThreads are accessing the same matrix at the same time.

 

It just happens with the matrix member not with other member variables of the instances.

 

 

[midora]

BTW: I'm using the following code snippet to avoid the exeption. But for sure it slows down the rendering.

So I'm still looking for a better solution.

 

Matrix m;
lock (model.matrices[iFace])
{
    m = model.matrices[iFace].Clone();
}

[Rick Brewster]

If you're using GDI+ classes like Matrix, you can't use them on multiple threads at the same time. Locking or cloning are the two solutions. Or, don't use GDI+.

 

There are some better ways to do what you need, but the ones I'm thinking of all requires .NET 4.0. Since Paint.NET v3.5.10 operates on .NET 3.5 SP1, you'd have to hand-roll an object pool instead of using System.Collections.Concurrent.ConcurrentBag. It wouldn't be too hard though ... a Dictionary<TKey, Stack<TValue>> with locking around all accesses to it would probably work.

 

(GDI+ == System.Drawing)

[midora]

Even cloning failed in OnRender() and this should be a readonly action. And it is not possible to clone in SetRenderInfo because the number of WorkerThreads is unknown ;-)

 

In the meantime I started to replace the Matrix class with my own one. Not because of this issue but Matrix.TransformPoints is really slow. Just replacing this function call improved the rendering speed of the animation in kaleidocycles from 10s to 1.1s...

 

I'm still dreaming that 4.0 would provide a warping methode for polygons on source and dest surface so that I can get rid of this:

 

 

        /*---------------------------------------------------------------------------*\
        Function    GetBilinearPolygonSamples
        Purpose     Copies an polygonal area from <src> to <dst> respecting a matrix
                    transformation and a clipping rectangle.
        Remarks     The final method of src should not use g and src as parameters.
        \*---------------------------------------------------------------------------*/

        private void GetBilinearPolygonSamples(Graphics g, Surface src, Surface dst, PointF[] polygonDst, Rectangle clipRectDst, Matrix mDstToSrc)
        {
            GraphicsPath gpDst = new GraphicsPath();
            gpDst.AddPolygon(polygonDst);

            // Now get for all points in the dst triangle the bilinear samples of src
            Region region = new Region(gpDst);
            region.Intersect(clipRectDst);
            if (region.IsEmpty(g)) return;

            float[] m = mDstToSrc.Elements;
                //! mDstToSrc.TransformPoints(point) is more than 10 times slower than to get the elements and do the multiplication yourself

            RectangleF[] rects = region.GetRegionScans(new Matrix());
            for (int ri = 0; ri < rects.Length; ri++)
            {
                RectangleF rect = rects[ri];
                for (int y = (int)rect.Top; y < rect.Bottom; y++)
                {
                    for (int x = (int)rect.Left; x < rect.Right; x++)
                    {
                        float pointX = x * m[0] + y * m[2] + m[4];
                        float pointY = x * m[1] + y * m[3] + m[5];

                        dst[(int)x, (int)y] = src.GetBilinearSample(pointX, pointY);
                    }
                }
            }
        } /* GetBilinearPolygonSamples */

 

Any idea for an improvement in the moment?

[Rick Brewster]

What? Paint.NET 4.0 won't be providing anything of the sort ... I have no idea where you got that idea from.

 

If you want speed, don't use the GDI+ classes. Whether that's Matrix, Region, GraphicsPath, etc. Don't use them. They're slow.

[midora]

I'm not talking about any gdi extension. I'm just using GDI in the moment to get the region scans.

 

I'm looking for a transformation function from a source to a destination surface which works on a polygon (or maybe just a triangle). You are providing GetBilinearPixel() already to make it easier for a plugin to get an interpolated pixel. A simular funtion for an area would allow plugins to profit from any speed enhancement in Paint.NET. I would expect that there is already such a funtion used in the layer rotate/zoom function.

[Rick Brewster]

GetBilinearPixel() is there because it's used by built-in effects and of obvious utility to many plugins.

 

Rotate/Zoom doesn't work the way you are thinking it does.

 

Like I said, I'm not going to be implementing a bitmap perspective/polygon transformation gizmo for you. That's your job! I don't know why you'd expect it to already be provided for you.