Take text alignment for LinkLabels into account (#12643)

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## Problem
`LinkLabels` ignore the text alignment for rendering the "hitbox" and the text color (= the `LinkArea`), and the focus rectangle. Also every text behind the end of this LinkArea/focus rectangle region is not painted at all.
This becomes visible if `AutoSize = false` and the `Size` is bigger than the text would need,
and if the text alignment is anything different than `TopLeft`.

## Cause
I think this is because the `piece.regions` are only translated regarding the padding, but neglecting the text alignment.

## Solution
Calculate the offset due to alignment and add it to the translation in `LinkLabel.CreateLinkPieces ()`

Fixes #12402 

## One more problem:
~Right now, a very tiny bit at the end of the label is still cut off (see my zipped and attached comparison pictures). Maybe `GetBounds ()` returns a value little bit smaller than it should be.
Can someone help?~

Also, maybe I took the wrong approach to this issue, but I don't know the inner mechanisms of mono.
So feel free to either advise me to change something, or change it yourself(s) :)

1 files changed, 65 insertions, 1 deletions

diff --git a/mcs/class/System.Windows.Forms/System.Windows.Forms/LinkLabel.cs b/mcs/class/System.Windows.Forms/System.Windows.Forms/LinkLabel.cs
index 5bb0e05abd1..17d50d15f55 100644
--- a/mcs/class/System.Windows.Forms/System.Windows.Forms/LinkLabel.cs
+++ b/mcs/class/System.Windows.Forms/System.Windows.Forms/LinkLabel.cs
@@ -668,9 +668,73 @@ namespace System.Windows.Forms
 										 PaddingClientRectangle,
 										 string_format);
 
+			// Get offset for different text alignments
+			float align_offset_x = 0F;
+			float align_offset_y = 0F;
+
+			if (TextAlign != ContentAlignment.TopLeft) {
+				Region all_regions = new Region (new Rectangle ());
+
+				foreach (Region region in regions) {
+					all_regions.Union (region);
+				}
+
+				Graphics graphics = CreateGraphics ();
+
+				if (TextAlign == ContentAlignment.TopCenter) {
+					float text_width = all_regions.GetBounds(graphics).Width;
+
+					align_offset_x = (ClientRectangle.Width / 2 - text_width  / 2);
+				}
+				if (TextAlign == ContentAlignment.TopRight) {
+					float text_width = all_regions.GetBounds(graphics).Width;
+
+					align_offset_x = (ClientRectangle.Width - text_width);
+				}
+				if (TextAlign == ContentAlignment.MiddleLeft) {
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_y = (ClientRectangle.Height / 2 - text_height / 2);
+				}
+				if (TextAlign == ContentAlignment.MiddleCenter) {
+					float text_width  = all_regions.GetBounds(graphics).Width;
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_x = (ClientRectangle.Width  / 2 - text_width  / 2);
+					align_offset_y = (ClientRectangle.Height / 2 - text_height / 2);
+				}
+				if (TextAlign == ContentAlignment.MiddleRight) {
+					float text_width  = all_regions.GetBounds(graphics).Width;
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_x = (ClientRectangle.Width      - text_width);
+					align_offset_y = (ClientRectangle.Height / 2 - text_height / 2);
+				}
+				if (TextAlign == ContentAlignment.BottomLeft) {
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_y = (ClientRectangle.Height - text_height);
+				}
+				if (TextAlign == ContentAlignment.BottomCenter) {
+					float text_width  = all_regions.GetBounds(graphics).Width;
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_x = (ClientRectangle.Width / 2 - text_width / 2);
+					align_offset_y = (ClientRectangle.Height    - text_height);
+				}
+				if (TextAlign == ContentAlignment.BottomRight) {
+					float text_width  = all_regions.GetBounds(graphics).Width;
+					float text_height = all_regions.GetBounds(graphics).Height;
+
+					align_offset_x = (ClientRectangle.Width  - text_width);
+					align_offset_y = (ClientRectangle.Height - text_height);
+				}
+			}
+
+
 			for (int i = 0; i < pieces.Length; i ++) {
 				pieces[i].region = regions[i];
-				pieces[i].region.Translate (Padding.Left, Padding.Top);
+				pieces[i].region.Translate (Padding.Left + align_offset_x, Padding.Top + align_offset_y);
 			}
 
 			Invalidate ();