Fix how the toggle switch draws itself

[Skorinn]

Three faults in how ToggleButton draws itself, all found by giving the switch a colour other than the black
it defaults to. The first two had been there since the original implementation and were invisible while the
switch was black; the third was introduced fixing the first, in this same branch.

Black corners

OnPaint cleared the control with this.Parent.BackColor. That was wrong three ways: it ignored the
control's own BackColor, which is the property a consumer sets to say what the switch is sitting on, so
setting it did nothing; it required a parent to exist at paint time, so rendering an unparented instance
threw; and it turned the corners the rounded switch does not reach black whenever the parent's
BackColor was Color.Transparent, because clearing with a transparent colour writes it into the double
buffer rather than letting anything through.

The clear now comes from the control's own BackColor. SupportsTransparentBackColor is added alongside, so
a consumer can set BackColor = Color.Transparent and have whatever the control sits on show through
properly.

A notch off the corner, and a toggle that looked to have escaped

The background stopped two pixels short of the control's right edge, leaving a sliver of the control
uncovered beside the rounded end, which showed as a notch hanging off the corner.

Separately, the toggle's size and its position came from expressions that did not agree: it was inset two
pixels from the top and the left, but its diameter left it four pixels short of the right end of the
background, and the checked position put it two pixels from that end instead. The gap on the side the toggle
had travelled to came out narrower than the others, and a gap of a pixel or two, once antialiasing has taken
its share, reads as the toggle breaking out of the background rather than sitting in it.

Both the diameter and the two positions now come from one inset, so the gap is the same on every side and
the two states are mirror images of each other.

A fringe of the previous frame

Removing the clear in the first commit went one step too far. The reasoning was that AllPaintingInWmPaint
has the background painted before OnPaint runs — true of Control, but not of ButtonBase, which paints
its own background from OnPaint, by way of the renderer it runs there. This control's override replaces
that, so nothing was left clearing the surface.

The previous frame therefore stayed underneath, and every repaint blended the new switch's antialiased edge
over the old one. Switching the toggle on left a grey fringe of the off state's track hanging outside the
blue, one pixel clear of it, following the curve of the rounded end.

Verification

There are no tests in this repository, so this was verified by driving the consumer that uncovered it. Read
straight out of the bitmap, along the middle row of a 71-pixel-wide control:

State	Track before	Toggle	Track after
Off	4 px	17 px	50 px
On	50 px	17 px	4 px

Exact mirror images, and no neutral-grey pixel anywhere in the switch — the switch's own antialiased edges
blend toward the colour behind them, so on a white surface anything neutral had come from somewhere else.

The disabled state was checked separately for any blue left over from the previous frame: none.

Version

AssemblyVersion and AssemblyFileVersion are bumped to 1.0.1.0. The release workflow requires the tag to
be reachable from master, so a release can be cut once this lands.

🤖 Generated with Claude Code

https://claude.ai/code/session_0153VVkWg7DQmdaNLcvtY37w

[Copilot]

🟡 Changes recommended

AssemblyInformationalVersion remains at 1.0.0, leaving the user-visible/release-tag version inconsistent with the bumped 1.0.1.0 version.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes rendering issues in ToggleButton when using non-default colors by properly clearing/painting the background surface (including transparent scenarios) and by making the track/toggle geometry consistent so the toggle sits evenly inside the background in both states.

Changes:

• Paint/clear the control surface using the control’s own BackColor, enabling proper transparent-corner behavior via SupportsTransparentBackColor.
• Adjust background path geometry to reach the right edge and unify toggle sizing/positioning via a single inset.
• Bump assembly version/file version to 1.0.1.0.

File summaries

File	Description
ToggleButton.cs	Fixes background clearing behavior and corrects track/toggle geometry so drawing is consistent with non-black colors and transparent backgrounds.
Properties/AssemblyInfo.cs	Updates assembly versioning for the 1.0.1.0 release.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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