Apply global matrix transform drawing text and shapes.

[tocsoft]

Prerequisites

• [x] I have written a descriptive pull-request title
• [x] I have verified that there are no overlapping pull-requests open
• [x] I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules :cop:.
• [x] I have provided test coverage for my change (where applicable)

Description

Adds a Transform property to both ShapeOptions and TextOptions (which can be registered globally).

This allows for usages using this syntax (for shapes):

var matrix = Matrix3x2.CreateSkew(GeometryUtilities.DegreeToRadian(-15), 0, new Vector2(200, 200));
image.Mutate(c=> c.SetShapeOptions(x => x.Transform = matrix)
                .FillPolygon(Color.White, simplePath));

or for text

var matrix = Matrix3x2.CreateSkew(GeometryUtilities.DegreeToRadian(-15), 0, new Vector2(200, 200));
image.Mutate(c=> c.SetTextOptions(x => x.Transform = matrix)
                .DrawText(text, font, Color.White, new PointF(10, 10)));

Current limitations on this pattern is that it uses 2 separate properties... Ideally we would add the Transform property to GraphicsOptions (which is available for both shapes and text processors) but that class lives in the main ImageSharp repo so would require a change over there.. if we are happy to make the change over there then we should do that first then update this PR to set it centrally.

resolves #125

[codecov[bot]]

Codecov Report

Merging #126 (45c2a26) into master (c29e5de) will decrease coverage by 6.00%. The diff coverage is 82.66%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
- Coverage   71.05%   65.05%   -6.01%     
==========================================
  Files          86       86              
  Lines        5472     5488      +16     
  Branches     1119     1121       +2     
==========================================
- Hits         3888     3570     -318     
- Misses       1359     1695     +336     
+ Partials      225      223       -2     

Flag	Coverage Δ
unittests	65.05% <82.66%> (-6.01%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../Processing/Extensions/ClearRectangleExtensions.cs	100.00% <ø> (ø)
...wing/Processing/Extensions/DrawBezierExtensions.cs	100.00% <ø> (ø)
...rawing/Processing/Extensions/DrawLineExtensions.cs	100.00% <ø> (ø)
...ing/Processing/Extensions/FillPolygonExtensions.cs	100.00% <ø> (ø)
...g/Processing/Extensions/FillRectangleExtensions.cs	100.00% <ø> (ø)
...rocessing/ShapeGraphicOptionsDefaultsExtensions.cs	100.00% <ø> (ø)
src/ImageSharp.Drawing/Processing/ShapeOptions.cs	100.00% <ø> (ø)
src/ImageSharp.Drawing/Processing/TextOptions.cs	100.00% <ø> (ø)
...rawing/Processing/TextOptionsDefaultsExtensions.cs	100.00% <ø> (ø)
...ssing/Processors/Text/DrawTextProcessor{TPixel}.cs	75.35% <57.89%> (-22.65%)	:arrow_down:
... and 42 more

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[JimBobSquarePants]

@tocsoft Are there any issues you see with adding the property upstream? I.E do you think people will try to use it for non related operations?

[antonfirsov]

I would love to see the duplication between TextGraphicsOptions and ShapeGraphicsOptions being removed, but I don't think adding .Transform to the common GraphicsOptions is a good idea unless we want to make all the processors in the core library to support it. Otherwise it would be confusing to users (there is a Transform property but it's not being applied ...).

This would mean that for example .Resize(...) also applies an arbitrary free transform, and .Transform(...) has an additional transform etc. This is not the way our API-s were evolving in the core library so far, and it's just too big change to even consider at this point IMO.

We should rather do an API simplification right within ImageSharp.Drawing.

ShapeGraphicsOptions, TextGraphicsOptions, ShapeOptions, TextOptions ... it's just too confusing.

How about something like this:

- public class ShapeGraphicsOptions { ... }
- public class TextGraphicsOptions { ... }
+public class DrawingOptions
+{
+    public ShapeOptions ShapeOptions { get; set; }
+    public TextOptions ShapeOptions { get; set; }
+    public Matrix3x2 Transform { get; set; }
+    public GraphicsOptions GraphicsOptions { get; set; }
+}

Then instead of doing .SetShapeOptions(x => x.Transform = ...) or .SetShapeOptions(x => x.Transform = ...), we can have a SetTransform(Matrix3x2) extension method.