Do not work properly ImageFilter and SKMatrix [bug]

[GalaxyVelocity]

Description

When adding to SKPaint filter: ImageFilter SKImageFilter.CreateDropShadow then using the transformation matrix is incomprehensible. It is expected to see that two rectangles turned and shifted to the desired values, but this does not happen. Rotates and moves only one "rectangle"(SKPath ), which is painted paintFill, the other remains untouched and in the same place.

Correct work:
If you remove "ImageFilter = SKImageFilter.CreateDropShadow...." then rotate and move both rectangles.

or

And also if you change the canvas drawing in places. Do this way:

canvas.DrawPath(testPath, paintStroke);
canvas.DrawPath(testPath, paintFill);

then everything is reflected normally. both rectangles moved.

Tell me, is this a bug or am I doing something wrong?

Code

If you run this code, you can see that one rectangle (white with shadow) turned and moved, another rectangle (with a black stroke) stayed in place at 0,0.

SKPaint paintFill = new SKPaint()
{
    Color = SKColors.White,
    Style = SKPaintStyle.Fill,
    ImageFilter = SKImageFilter.CreateDropShadow(5, 5, 15, 15, SKColors.Black, SKDropShadowImageFilterShadowMode.DrawShadowAndForeground)
};

SKPaint paintStroke = new SKPaint()
{
    Color = SKColors.Black,
    Style = SKPaintStyle.Stroke,
    StrokeWidth = 2,
};

SKPath testPath = new SKPath();
testPath.AddRect(SKRect.Create(0, 0, 300, 300));

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeRotationDegrees(-5f, 150, 150));
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeTranslation(500, 500));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

Basic Information

.NET Framework 4.6.1
Windows Forms
SkiaSharp 1.60.3

[GalaxyVelocity]

Conducted several test.

Used code:

SKPaint paintFill = new SKPaint()
{
    Color = SKColors.White,
    Style = SKPaintStyle.Fill,
    ImageFilter = SKImageFilter.CreateDropShadow(5, 5, 15, 15, SKColors.Black, SKDropShadowImageFilterShadowMode.DrawShadowAndForeground)
};

SKPaint paintStroke = new SKPaint()
{
    Color = SKColors.Black,
    Style = SKPaintStyle.Stroke,
    StrokeWidth = 1
};

SKPath testPath = new SKPath();
testPath.AddRect(SKRect.Create(0, 0, 100, 100));

test 1

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeTranslation(200, 200));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

It's OK, the rectangle and stroke have moved to the right place.

test 2

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeScale(5, 5));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

It's OK, the rectangle and stroke have increased.

test 3

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeScale(2, 2));
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeTranslation(200, 200));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

It's OK, the rectangle and stroke have increased in moved.

test 4

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeSkew(2, 2));
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeTranslation(200, 200));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

Not everything is ok, the rectangle with the shadow with skew and moved, the stroke only increased and stayed in place, I consider this a bug.

test 5

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeSkew(2, 2));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

Not everything is ok, the same behavior as in test 4, only without moving.

test 6

SKMatrix matrix = canvas.TotalMatrix;
SKMatrix.PostConcat(ref matrix, SKMatrix.MakeRotationDegrees(-25f, 50, 50));
canvas.SetMatrix(matrix);

canvas.DrawPath(testPath, paintFill);
canvas.DrawPath(testPath, paintStroke);

Not everything is ok, a rectangle with a shadow in turned, the outline remained in place.

Using canvas.DrawRect the same results.

[GalaxyVelocity]

If removed "ImageFilter = SKImageFilter.CreateDropShadow......" from "paintFill" all tests are normal.

[mattleibow]

Thanks for reporting this, I will investigate further.

[GalaxyVelocity]

@mattleibow Thank you for noticing this issue.

Some more simple bug tests.

test 7

  canvas.SetMatrix(SKMatrix.MakeRotationDegrees(-25f, 50, 50));

  canvas.DrawPath(testPath, paintFill);
  canvas.DrawPath(testPath, paintStroke);

Not everything is ok, a rectangle with a shadow in turned, the outline remained in place.

test 8

  canvas.SetMatrix(SKMatrix.MakeSkew(2, 2));

  canvas.DrawPath(testPath, paintFill);
  canvas.DrawPath(testPath, paintStroke);

Not everything is ok, the rectangle with the shadow increased and distorted (stretched out), the stroke has only increased, but not distorted.

Such impression that when using "ImageFilter" where that loses the transformation matrix.

[GalaxyVelocity]

I tried the new version SkiaSharp 1.68.0 in Windows Forms (.NET Framework 4.6.1) All tests from previous messages passed successfully. It's OK. The bug is gone.

[mattleibow]

That is great news! The v1.68 update had many fixes.