Drawing simultaneously on two controls in two windows without delay

Question

In my application, there are 2 windows and both contain a PictureBox. The first (pb1) allows interaction and the image can be changed through click- and mouseMove-events. These events call pb1.Invalidate(); which works fine.

I want the second PictureBox (pb2) to redraw as well so I call pb2.Invalidate() from the paint-event of pb1. [Just for context, the second PictureBox shows nearly the same Image but on a bigger scale and some parts of the drawing will be left out in the future so I use the same Method in both paint events which decides what to draw and what not]

It works but it's "laggy" and I want it to be as smooth as the paint on the first PictureBox. I reduced the paint event just to a grid for test purposes.

• Both windows are double buffered.
• I tried replacing the picture boxes with SKGLControls from SkiaSharp (which should have better performance). The example code still uses the SkiaEvents so don't be confused if the problem occurs with both controls.
• I tried to use .Update() or .Refresh() instead of .Invalidate() but i guess its to much to handle, the application just crashes..

Here is the method that is called by both OnPaint events

public void Update(SKPaintGLSurfaceEventArgs e, bool bigscreen)
    {
        SKCanvas canvas = e.Surface.Canvas;
        canvas.Clear(SKColors.Beige);
        //Zoom to specified area
        SKMatrix matrix = SKMatrix.Identity;
        if (!bigscreen)
        {
            matrix = matrix.PostConcat(SKMatrix.CreateScale(canvasSize / (float)zoomArea.Width, canvasSize / (float)zoomArea.Height));
        }
        else
        {
            matrix = matrix.PostConcat(SKMatrix.CreateScale(bigCanvasSize / (float)zoomArea.Width, bigCanvasSize / (float)zoomArea.Height));
        }
        matrix = matrix.PreConcat(SKMatrix.CreateTranslation(-zoomArea.X, -zoomArea.Y));
        canvas.SetMatrix(matrix);
        DrawGrid(canvas);
    }

and the grid-draw method

private void DrawGrid(SKCanvas canvas)
    {
        using (SKPaint paint = new SKPaint() { IsAntialias = true,Color=SKColors.LightGray,StrokeWidth = 1})
        {
            canvas.DrawLine(0, 0, 0, gridCanvas.Height, paint); //Size gridCanvas is always the same at the moment and defines the space where the grid is drawn
            canvas.DrawLine(0, 0, gridCanvas.Width, 0, paint);

            for (int i = 0; i <= (gridCanvas.Width - gridoffsetX) / pxPerSquare; i++)
            {
                canvas.DrawLine(i * pxPerSquare + gridoffsetX, 0, i * pxPerSquare + gridoffsetX, gridCanvas.Height, paint);
            }
            for (int i = 0; i <= (gridCanvas.Height - gridoffsetY) / pxPerSquare; i++)
            {
                canvas.DrawLine(0, i * pxPerSquare + gridoffsetY, gridCanvas.Width, i * pxPerSquare + gridoffsetY, paint);
            }
        }


    }

and finally the original Paint Event

private void Pb1_PaintSurface(object sender, SKPaintGLSurfaceEventArgs e)
    {
        win2.UpdateDrawing(); //Just calls .Invalidate() on pb2
        painter.Update(e, false);
    }

examplePicture

So my question is: Is there a way to make both controls draw at nearly the same time without delay, although I don't understand why the first PictureBox draws in real time and the second doesn't... Thanks!

Answer 1

after searching for day i found this page right after posting, which helped me: Onpaint events (invalidated) changing execution order after a period normal operation (runtime)