PsOptionButton

An owner-drawn option button (radio button) for FreeBASIC + Win32, built on AfxNova and PsBufferPaint.

A circle and an optional caption, side by side, with a focus ring around the pair. Unchecked draws a thin outlined ring; checked draws an accent-filled disc with a contrasting dot on it. No chrome, no animation, no group box.

The control owns mutual exclusion. Option buttons that share a parent window and a group id form a group, and checking one unchecks the rest. You do not write that logic, and you do not call anything after a click to keep the group consistent.

It also implements the keyboard behaviour a Windows radio group actually has, which is the part most hand-rolled radio buttons get wrong: the whole group is a single tab stop, and the arrow keys move the selection within it. Tab moves past the group, not through it.

Repository: https://github.com/PaulSquires/PsOptionButton

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What it looks like

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Requirements

Copy these files into your project:

File	Purpose
PsOptionButton.bi	public surface — types, enums, callbacks, declarations
PsOptionButton.inc	implementation
PsBufferPaint.bi	flicker-free drawing surface
PsBufferPaint.inc

There is no icon font to ship. The circle is drawn as geometry through GDI+, so nothing here depends on Segoe Fluent Icons being installed.

You also need AfxNova on the include path (-i "C:\dev" if your tree matches this one).

Include order

PsBufferPaint.inc must be included before PsOptionButton.inc, and both after AfxNova:

#include once "windows.bi"
#include once "AfxNova\CWindow.inc"
#include once "AfxNova\AfxStr.inc"
#include once "AfxNova\AfxGdiplus.inc"
using AfxNova

#include once "PsBufferPaint.inc"
#include once "PsOptionButton.inc"

PsOptionButton.bi includes PsBufferPaint.bi itself, so the header is self-sufficient. It does not include windows.bi or AfxNova — the host must already have done so, and must already have said using AfxNova.

GDI+ must be running

Every repaint draws through GDI+. Initialise it before the first paint and shut it down after every window is destroyed:

CoInitialize( null )
dim as ULONG_PTR gdipToken = AfxGdipInit()

' ... create windows, run the message loop ...

AfxGdipShutdown( gdipToken )
CoUninitialize

Without the bracket the control draws nothing at all — no error, just an empty rectangle.

Do not name anything ok

GDI+ defines Ok = 0 as a Status enum value in namespace AfxNova. Every host says using AfxNova, so any host identifier called ok becomes a duplicate definition the moment you adopt this file. Use bOK.

Message pump

This control adds no pump obligation. There is no PsOptionButton_FilterMessage and none is needed. If you are coming from a control that has one, there is nothing to look for here.

It is focusable, though, so the two ordinary rules for a focusable control in a plain CWindow host both apply:

do while GetMessage( @uMsg, null, 0, 0 )
    if uMsg.message = WM_QUIT then exit do
    ' IsDialogMessage is what makes Tab work at all.
    if IsDialogMessage( pWindow->hWindow, @uMsg ) = 0 then
        TranslateMessage @uMsg
        DispatchMessage @uMsg
    end if
loop

and, before the loop starts:

SetFocus( hFirstControl )

Without IsDialogMessage, Tab does nothing and the arrow keys still work. Without the startup SetFocus, the first Tab does nothing: IsDialogMessage only acts when the focused window is a descendant of the window passed to it, and at startup focus is on the form itself — a window is not its own child.

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Quick start

' Three options in one group. The group id is the third Create argument.
dim as HWND hHigh = PsOptionButton_Create( hParent, 1001, 1 )
dim as HWND hMed  = PsOptionButton_Create( hParent, 1002, 1 )
dim as HWND hLow  = PsOptionButton_Create( hParent, 1003, 1 )

dim as HWND opts(0 to 2) = { hHigh, hMed, hLow }
dim as DWSTRING caps(0 to 2) = { "Highest", "Balanced", "Smallest file" }

for i as long = 0 to 2
    PsOptionButton_SetFont( opts(i), hFont )
    PsOptionButton_SetText( opts(i), caps(i) )
    PsOptionButton_SetCheckChangedCallback( opts(i), @OnQualityChanged )

    ' The control is created 0x0 and hidden. Ask it how big it wants to be.
    dim as long iw, ih
    PsOptionButton_GetIdealSize( opts(i), iw, ih )
    SetWindowPos( opts(i), 0, 20, 20 + (i * 30), iw, ih, SWP_NOZORDER or SWP_NOACTIVATE )
    ShowWindow( opts(i), SW_SHOW )
next

' Silent: no callback fires. This also moves the group's tab stop here.
PsOptionButton_SetChecked( hMed, true )

The callback it references:

sub OnQualityChanged( byval hOpt as HWND, byval isChecked as boolean )
    ' BOTH edges arrive here. The option being vacated fires first with isChecked = false,
    ' then the one being taken fires with true.
    if isChecked then
        print "quality is now id " & str( PsOptionButton_GetID( hOpt ) )
    end if
end sub

Reading the answer back later, without holding any of the handles:

dim as long nQuality = PsOptionButton_FindCheckedID( hParent, 1 )   ' -1 = unanswered

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Concepts

The handle is a real window

PsOptionButton_Create returns an ordinary HWND. Move it with SetWindowPos, show it with ShowWindow, disable it with EnableWindow — all of that works, and the control keeps its own state in step when you do. There is no opaque handle type.

A group is a parent plus a group id

A group is the pair (parent window, group id). Every option button with the same parent and the same group id is in the same group, and exactly one of them can be checked.

The group id is a Create parameter rather than only a setter, because a forgotten grouping call does not fail — it silently merges two groups into one, and the form looks right until somebody clicks. It defaults to 0, so a window with a single logical group needs no grouping calls at all.

hOpt1 = PsOptionButton_Create( hParent, 1001, 1 )   ' group 1
hOpt2 = PsOptionButton_Create( hParent, 1002, 1 )   ' group 1
hOpt3 = PsOptionButton_Create( hParent, 1003, 2 )   ' a different group, same parent

Two groups on one parent never interfere. PsOptionButton_SetGroupID moves a button between groups later.

Exactly one member of a group carries WS_TABSTOP

The checked member, or the first enabled member when nothing is checked. It moves automatically when the check moves, when a member is disabled, and when a member is destroyed.

That is what makes the group a single tab stop, which is how a Windows radio group behaves: Tab enters the group at the checked option and the next Tab leaves the group entirely. Within the group you navigate with the arrows.

You do not manage this bit, and you should not set WS_TABSTOP on these controls yourself.

Arrow order is creation order

The arrow keys walk the group in the order the buttons were created, not in z-order and not by screen position. If you create a group out of visual order, the arrows will follow the order you created them in.

Geometry is derived, never set

The control owns its rects. You set inputs — padding, the box cell size, the gap, the ring band — and the layout produces the rects from them. You can read them, but you cannot assign them.

ringPad    = nFocusGap + nFocusThick        reserved ALWAYS, focused or not
textBlock  = hasText ? nBoxGap + textW : 0
contentH   = max( hasText ? textH : 0 , nBoxHeight )

idealW     = 2*ringPad + padLeft + boxWidth + textBlock + padRight
idealH     = 2*ringPad + padTop  + contentH + padBottom

rcContent  = client deflated by ringPad
rcVisual   = rcContent inflated by ringPad

PsOptionButton_GetIdealSize is valid before the control has ever been sized, which is what lets you use it to decide how big to make the control in the first place.

The focus-ring band is reserved whether or not the control has focus, so nothing moves when focus arrives.

The box cell is pinned; the caption gets the leftover

The box cell sits against the padding on whichever side OPT_BOXALIGN_* puts it, and the caption takes the whole span that is left over. One model gives both looks, decided only by how wide you make the control:

sized to GetIdealSize     (o) Highest quality          packed
sized to a full row width  Highest quality        (o)  settings row

A column of OPT_BOXALIGN_RIGHT buttons all sized to the same width line their circles up for free.

rcText is the span, not the ink. It runs from the box cell to the far padding so DT_END_ELLIPSIS has somewhere to ellipsize into. Drawing a background behind "the text" using that rect fills the whole span.

The circle is inscribed in the cell, not equal to it

rcBox is the declared cell the layout charges for. rcCircle is the largest centred square inside it — which is what actually gets drawn. They are identical for the default 16×16 cell and differ the moment you set a non-square one, at which point stroking rcBox would produce a stadium rather than a circle.

If you write a paint callback and want a round button, use rcCircle.

The dot scales with the circle by default

nDotSize is 0 by default, which means derive the dot as a percentage of the circle diameter. Set the box cell to 32px and the dot grows with it. A declared non-zero nDotSize overrides that and stays fixed — useful, but it decouples: scale the cell up afterwards and the dot will look wrong with nothing to warn you.

Setters are silent; user interaction notifies

PsOptionButton_SetChecked, SetGroupID and ClearGroup change state without firing any callback. Only a completed click, Space, an arrow-key move, or the explicit PsOptionButton_Click notifies.

That split is what makes it safe to call a setter from inside your own change callback — the recursive call cannot notify.

Both edges notify, and the loser fires first

When the user checks B while A was checked, two callbacks fire, in this order:

OnChanged( hA, false )      ' first
OnChanged( hB, true  )      ' second

Both state writes land before either callback runs, so reading PsOptionButton_FindChecked() from inside either one gives a coherent answer — the group is never observably double-checked or momentarily empty.

If you only care about the winner, test isChecked and ignore the other call.

Mouse capture and the cancelled gesture

Pressing an option button takes mouse capture. Press it, slide the cursor off, release — and nothing gets checked. The control paints the press state only while the cursor is inside, so the gesture visibly cancels before the release confirms it.

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Behaviour and limits

• A group with nothing checked is legal, and it is the state a group starts in. PsOptionButton_FindCheckedID returns -1 for it. The user can never reach it — clicking the checked member is a silent no-op and no gesture unchecks. Only the host can empty a group, via SetChecked(h, false) or ClearGroup.
• Enter is not claimed. A focused option button lets Enter through to the dialog's default button, which is what a Win32 radio button does. Space is the activation key.
• Groups cannot span parents. A group is (parent, id); two buttons with different parents are never in the same group even with the same id.
• Arrow keys clamp to the group and wrap at both ends. They never move focus out of it.
• Disabled members are stepped over by the arrows and refuse clicks, but PsOptionButton_SetChecked still works on them — a host restoring saved settings onto a conditionally-greyed form has to be able to say which option is selected.
• Destroying the checked member leaves the group with nothing checked. The check is not reassigned to a survivor. The tab stop is handed on, so the group stays reachable by Tab.
• SetGroupID makes an arriving checked button lose if the destination group already has a checked member. Re-grouping is a layout operation, not a user answering a question.
• The box cell is declared, never measured. Set it larger and the control gets wider; the control never sizes the cell to fit anything.
• A caption-less option button is shorter than a captioned one, because the content height ignores the font when there is no text. A host laying out a mixed column takes the max itself.
• No mnemonics. The renderer forces DT_NOPREFIX, so &Highest draws a literal ampersand. PsOptionButton_Click is the door for a host accelerator.
• No tri-state, no multiline captions, no HICON, no WM_COMMAND sent to the parent, no hit-testing API. The whole client is the hit area, caption included.
• CS_DBLCLKS is not set. A rapid second click arrives as an ordinary WM_LBUTTONDOWN.
• Not thread-safe. Create and drive these from the UI thread only.

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API reference

Creation

Function	Behaviour
PsOptionButton_Create( hWndParent, CtrlID, nGroupID = 0 ) as HWND	Creates the control as a hidden 0×0 child. nGroupID places it in a group; buttons sharing hWndParent and nGroupID are mutually exclusive. Returns the control's HWND.

Group

Function	Behaviour
PsOptionButton_GetGroupID( hOpt ) as long	The button's group id.
PsOptionButton_SetGroupID( hOpt, nGroupID )	Moves the button to another group. Silent. Re-establishes the tab-stop rule in both the old and the new group. If the button was checked and the destination already has a checked member, the arriving button is unchecked. If it was the checked member of the group it left, that group is left with nothing checked.
PsOptionButton_GetGroupCount( hOpt ) as long	How many live members the button's group has, including itself.
PsOptionButton_GetGroupMember( hOpt, idx ) as HWND	The idx'th member of the group in creation order. 0 if idx is out of range.
PsOptionButton_GetGroupChecked( hOpt ) as HWND	The checked member of the button's group, or 0 when nothing is checked.
PsOptionButton_FindChecked( hWndParent, nGroupID ) as HWND	Same question asked without holding a member handle. 0 when nothing is checked.
PsOptionButton_FindCheckedID( hWndParent, nGroupID ) as long	The control id of the checked member, or -1 when nothing is checked. -1 means unanswered, not failed.
PsOptionButton_ClearGroup( hOpt )	Unchecks every member of the button's group. Silent. The group keeps its tab stop.

Content

Function	Behaviour
PsOptionButton_GetText( hOpt ) as DWSTRING	The caption.
PsOptionButton_SetText( hOpt, Text )	Sets the caption and re-measures. "" removes it, and the box gap is then not charged. Re-applies auto-size.
PsOptionButton_GetID( hOpt ) as long	The host command id. Defaults to the CtrlID passed to Create.
PsOptionButton_SetID( hOpt, id )	Sets the id reported by FindCheckedID. Does not change the window's GWLP_ID.
PsOptionButton_GetItemData( hOpt ) as integer	Free-form host payload.
PsOptionButton_SetItemData( hOpt, itemData )	Stores a host payload. The control never reads it.

WM_SETTEXT, WM_GETTEXT and WM_GETTEXTLENGTH all alias the caption, so SetWindowTextW and GetWindowTextW work on these controls and agree with Get/SetText.

State

Function	Behaviour
PsOptionButton_GetChecked( hOpt ) as boolean	Whether this button is the checked member.
PsOptionButton_SetChecked( hOpt, isChecked )	Silent. Checking unchecks every peer and moves the group's tab stop here. Unchecking is allowed and leaves the group with nothing checked. Works on a disabled button. A no-op if the state is already what you asked for.
PsOptionButton_GetEnabled( hOpt ) as boolean	Whether the control is enabled.
PsOptionButton_SetEnabled( hOpt, isEnabled )	Goes through EnableWindow, so the system enforces it. Clears any hover state. Disabling the member holding the group's tab stop hands it to another enabled member.
PsOptionButton_GetFocused( hOpt ) as boolean	Whether the control currently has keyboard focus.
PsOptionButton_Refresh( hOpt )	Marks the layout stale and requests a repaint. Rarely needed — every setter does it.

Action

Function	Behaviour
PsOptionButton_Click( hOpt )	Checks the button as if the user had clicked it — it FIRES the change callbacks, both edges, loser first. A silent no-op when the button is already checked or is disabled. With no mnemonics, this is the only door a host accelerator has.

Geometry and layout

Function	Behaviour
PsOptionButton_GetBoxAlign( hOpt ) as long	OPT_BOXALIGN_LEFT or OPT_BOXALIGN_RIGHT.
PsOptionButton_SetBoxAlign( hOpt, nBoxAlign )	Which side the circle sits on. Does not change the ideal size — the mirror is exact.
PsOptionButton_GetTextAlign( hOpt ) as long	OPT_TEXTALIGN_LEFT / CENTER / RIGHT.
PsOptionButton_SetTextAlign( hOpt, nTextAlign )	Where the caption sits within its span, which is the leftover after the box cell and padding — not within the control.
PsOptionButton_GetPadding( hOpt, nLeft, nTop, nRight, nBottom )	Reads the four paddings.
PsOptionButton_SetPadding( hOpt, nLeft, nTop, nRight, nBottom )	Raw pixels — you scale for DPI. Re-measures and re-applies auto-size.
PsOptionButton_GetBoxGap( hOpt ) as long	Gap between the box cell and the caption.
PsOptionButton_SetBoxGap( hOpt, nBoxGap )	Charged only when there is a caption. Re-measures.
PsOptionButton_GetBoxSize( hOpt, nBoxWidth, nBoxHeight )	Reads the declared box cell.
PsOptionButton_SetBoxSize( hOpt, nBoxWidth, nBoxHeight )	Sets the declared cell. Clamped to >= 0. The drawn circle is the largest centred square inside it. Re-measures.
PsOptionButton_GetRingThickness( hOpt ) as long	The unchecked ring's pen width, in raw pixels.
PsOptionButton_SetRingThickness( hOpt, nThickness )	Raw pixels — do not pre-scale for DPI. The painter scales the pen itself; pre-scaling doubles it. Clamped to >= 0 (0 draws no ring). Repaints without re-measuring.
PsOptionButton_GetDotSize( hOpt ) as long	The declared dot diameter, or 0 for derived.
PsOptionButton_SetDotSize( hOpt, nDotSize )	0 derives the dot from the circle diameter (the default, and what keeps them in proportion). Non-zero is a fixed diameter. Clamped to >= 0, and at paint time to at least 2px and at most the circle. Re-derives the layout.
PsOptionButton_GetFocusRing( hOpt, nGap, nThickness )	Reads the focus band.
PsOptionButton_SetFocusRing( hOpt, nGap, nThickness )	The band is reserved unconditionally, so both values contribute to the ideal size and this re-measures. nThickness is raw pixels — the painter scales it.
PsOptionButton_GetFocusCurvature( hOpt ) as long	Corner ellipse diameter of the focus ring.
PsOptionButton_SetFocusCurvature( hOpt, nCurvature )	Clamped to >= 0. 0 gives square corners. Repaints only.
PsOptionButton_GetAutoSize( hOpt ) as boolean	Whether the control resizes itself.
PsOptionButton_SetAutoSize( hOpt, bAutoSize )	Opt-in. When on, the control SetWindowPoses itself to its ideal size after any change that could alter it, preserving the top-left. Off by default: normally the host measures and places.
PsOptionButton_GetIdealSize( hOpt, nWidth, nHeight )	The size the control wants. Valid before the control has ever been sized.
PsOptionButton_GetContentRect( hOpt, rc ) as boolean	Client deflated by the focus band.
PsOptionButton_GetBoxRect( hOpt, rc ) as boolean	The declared box cell. Never empty.
PsOptionButton_GetCircleRect( hOpt, rc ) as boolean	The inscribed circle actually drawn. Never empty.
PsOptionButton_GetDotRect( hOpt, rc ) as boolean	The dot, centred in the circle. Computed whether or not the button is checked.
PsOptionButton_GetTextRect( hOpt, rc ) as boolean	The caption span. Returns FALSE and an empty rect when there is no caption.
PsOptionButton_GetVisualRect( hOpt, rc ) as boolean	Content inflated by the focus band — the outer visual bounds.

All six rect getters force any pending layout first, so they never hand back a stale value. They return FALSE when the control has no geometry yet or the rect is legitimately empty.

Appearance

Function	Behaviour
PsOptionButton_GetColors( hOpt, pColors )	Copies the colour struct out.
PsOptionButton_SetColors( hOpt, pColors )	Copies the struct in and repaints. Read-modify-write it; do not build one from scratch unless you intend to set all 21 fields.
PsOptionButton_GetFont( hOpt ) as HFONT	The caption font. The caller owns it.
PsOptionButton_SetFont( hOpt, hTextFont )	The measuring font: it drives the ideal width, so this re-measures and re-applies auto-size. The control never deletes it.

Colour resolution

Both are pure functions — they take no control handle and touch no global, so you can call them from a paint callback to get exactly the colours the built-in painter would use.

Function	Behaviour
PsOptionButton_ResolveMood( isEnabled, isPressed, isHot ) as long	Returns one of OPT_MOOD_*. Precedence: disabled > pressed > hot > idle.
PsOptionButton_ResolveColors( pColors, nMood, isChecked, clrBack, clrFore, clrRing, clrDot )	Fills the four output colours for a mood. isChecked selects between the ring and ring-checked sets inside each mood. clrDot is resolved even when unchecked.

Tooltips

Function	Behaviour
PsOptionButton_GetTooltipText( hOpt ) as DWSTRING	The control's own tooltip text.
PsOptionButton_SetTooltipText( hOpt, Text )	Sets it. When non-empty it wins over the tooltip callback.
PsOptionButton_GetTooltipHandle( hOpt ) as HWND	The control's tooltip window, for TTM_* messages. The control owns and destroys it.
PsOptionButton_SetHoverTime( hOpt, milliseconds )	Initial hover delay before a tip appears.

There is no caption fallback: a control with neither its own tooltip text nor a callback answer shows nothing, rather than popping a tip that repeats the caption already on screen.

Callback registration

Function	Behaviour
PsOptionButton_SetPaintCallback( hOpt, usersub )	Replaces the built-in painter entirely.
PsOptionButton_SetMessageCallback( hOpt, userfunc )	Observes messages; can suppress most default handling.
PsOptionButton_SetTooltipCallback( hOpt, userfunc )	Supplies tooltip text on demand.
PsOptionButton_SetCheckChangedCallback( hOpt, usersub )	Reports user-driven check changes.

Render probes

Public so that a host supplying its own paint callback can assert it has not destroyed the control. Both render the control offscreen with its current painter.

Function	Behaviour
PsOptionButton_CountRenderedTones( hOpt, nPart ) as long	Number of distinct colours in one part, capped at 64. 0 if the control has no geometry. A part filled by a single rectangle reports 1 or 2 — calibrate any threshold against a deliberately broken render rather than assuming a low number means "not flooded".
PsOptionButton_HashRenderedPart( hOpt, nPart ) as ulong	FNV-1a over the same render. Two different states must hash differently; the same state twice must hash identically. It can prove a difference, never correctness. 0 is also the failure return.

nPart is one of the OPT_PART_* constants. Both force isFocused true internally so the focus ring is included, and restore it afterwards.

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Colors

PSOPTIONBUTTON_COLORS, copied on SetColors. Twenty-one fields.

Field	Paints	When
BackColor	the control's background	idle
BackColorHot	"	cursor over the control
BackColorPressed	"	left button down, cursor inside
BackColorDisabled	"	disabled
ForeColor	the caption	idle
ForeColorHot	"	hot
ForeColorPressed	"	pressed
ForeColorDisabled	"	disabled
RingColor	the unchecked circle — a stroked outline, no fill	idle
RingColorHot	"	hot
RingColorPressed	"	pressed
RingColorDisabled	"	disabled
RingColorChecked	the checked circle — a solid accent fill	idle
RingColorCheckedHot	"	hot
RingColorCheckedPressed	"	pressed
RingColorCheckedDisabled	"	disabled
DotColor	the dot drawn on top of the checked fill	idle
DotColorHot	"	hot
DotColorPressed	"	pressed
DotColorDisabled	"	disabled
FocusRingColor	the focus ring around the whole control	whenever focused

Precedence: disabled > pressed > hot > idle. isChecked is not a mood — it selects between the RingColor* and RingColorChecked* sets inside whichever mood resolved, so it works in all four without doubling the table.

The control reads completely flat by default, because BackColorHot, BackColorPressed and BackColorDisabled all default equal to BackColor. Hovering therefore changes only the circle and the caption. If you want a menu-style highlight across the whole row, set one field:

dim as PSOPTIONBUTTON_COLORS c
PsOptionButton_GetColors( hOpt, @c )
c.BackColorHot     = BGR( 44, 49, 58 )
c.BackColorPressed = BGR( 44, 49, 58 )
PsOptionButton_SetColors( hOpt, @c )

DotColor defaults to white rather than to ForeColor, because it sits on the accent fill rather than on the control background. DotColorDisabled defaults to the background colour, so a disabled checked button reads as a hollow ring.

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Callbacks

OPT_CheckChangedCallbackSub

type OPT_CheckChangedCallbackSub as sub( byval hOptionButton as HWND, byval isChecked as boolean )

Fires when the checked state changes through user interaction — a completed click, Space, an arrow-key move within the group, or the explicit PsOptionButton_Click.

Both edges fire, and the loser fires first. Checking B while A was checked produces OnChanged(hA, false) then OnChanged(hB, true). Both state writes land before either call, so PsOptionButton_FindChecked() is coherent from inside either one.

Fired after the state is updated, so PsOptionButton_GetChecked() agrees with isChecked.

SetChecked, SetGroupID and ClearGroup do not fire it — which is what makes it safe to call them from inside this handler.

OPT_PaintCallbackSub

type OPT_PaintCallbackSub as sub( byval p as PSOPTIONBUTTON_PAINTINFO ptr )

Draws the whole control instead of the built-in painter. Paint through p->b, the control's double buffer for this repaint — do not touch the screen DC.

The control has already filled the client with the resolved mood's BackColor before calling you, so a callback that only adds a foreground does not have to repaint the background.

Two contracts worth honouring:

• Draw the caption with the same font you handed to PsOptionButton_SetFont. The ideal width was measured with it; a different font means the width lies.
• Do not use PaintBorderRect to draw an outline. It fills unconditionally before it strokes, so used as a frame or a focus ring it erases everything beneath it. PaintRoundOutline strokes without filling. PaintEllipse always fills regardless of its pen argument. PsOptionButton_CountRenderedTones exists so you can assert you have not done this.

More generally: a callback that fills a rectangle covering the whole control erases everything the control already drew. Draw your additions, not a background.

OPT_MessageCallbackFunc

type OPT_MessageCallbackFunc as function( byval m as PSOPTIONBUTTON_MESSAGEINFO ptr ) as boolean

Observes messages. Return TRUE to suppress the control's default handling, FALSE to let it proceed. Focus and keyboard messages are handed over as well as mouse ones. Arrow keys reach you before they move the group selection, so you can veto navigation.

The result is ignored for three messages:

Message	Why
WM_LBUTTONUP	The control holds mouse capture across a press and this message releases it. A callback that suppressed it would strand capture and route every later click to this control. Suppressing WM_LBUTTONDOWN suppresses the press without touching the capture bookkeeping.
WM_SETFOCUS	Focus is a fact the system reports, not an action to veto. The state is already updated by the time you are called.
WM_KILLFOCUS	"

A host that does not want the control focusable must not make it a tab stop.

OPT_TooltipCallbackFunc

type OPT_TooltipCallbackFunc as function( byval hOptionButton as HWND ) as DWSTRING

Supplies tooltip text on demand, only when a tip is about to show, and only when the control has no tooltip text of its own. Return "" for no tooltip.

PSOPTIONBUTTON_PAINTINFO

Field	Meaning
hOptionButton	the control, so the callback can query it
b	the control's PsBufferPaint for this repaint (not a copy)
rcClient	the whole client area
rcContent	rcClient deflated by the focus-ring band
rcBox	the declared box cell. Never empty
rcCircle	the inscribed circle — the largest centred square in rcBox. Use this for a round button
rcDot	the dot, centred in rcCircle. Computed whether or not the button is checked
rcText	the caption span, not the ink. Empty when there is no caption; degenerate when the client is too narrow
rcVisual	rcContent inflated by the focus-ring band
isChecked	this button is the group's checked member
isHot	the mouse is over the control
isPressed	a live left press and the cursor is still inside
isEnabled
isFocused	draw a focus ring when true
wszText	the caption
nRingThick	ring pen width in raw pixels — PaintRoundOutline scales it for you
nBoxAlign	OPT_BOXALIGN_*
nTextAlign	OPT_TEXTALIGN_*; map to DT_LEFT / DT_CENTER / DT_RIGHT

PSOPTIONBUTTON_MESSAGEINFO

Field	Meaning
hOptionButton	the control
uMsg	the message
wParam
lParam

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Constants

Box side

Constant	Meaning
OPT_BOXALIGN_LEFT	circle pinned to the left padding (default)
OPT_BOXALIGN_RIGHT	circle pinned to the right padding

Caption alignment within the span

Constant	Meaning
OPT_TEXTALIGN_LEFT	default
OPT_TEXTALIGN_CENTER
OPT_TEXTALIGN_RIGHT

Moods

Constant
OPT_MOOD_IDLE
OPT_MOOD_HOT
OPT_MOOD_PRESSED
OPT_MOOD_DISABLED

Probe parts

Constant	Rect measured
OPT_PART_CONTROL	rcContent
OPT_PART_BOX	rcBox, the declared cell
OPT_PART_TEXT	rcText, the caption span

Default geometry

DPI-scaled once at Create, except where noted. Every setter afterwards takes raw pixels.

Constant	Value
PSOPTIONBUTTON_DEFAULT_PADLEFT	4
PSOPTIONBUTTON_DEFAULT_PADTOP	2
PSOPTIONBUTTON_DEFAULT_PADRIGHT	4
PSOPTIONBUTTON_DEFAULT_PADBOTTOM	2
PSOPTIONBUTTON_DEFAULT_BOXGAP	8	charged only when there is a caption
PSOPTIONBUTTON_DEFAULT_BOXWIDTH	16	the declared cell
PSOPTIONBUTTON_DEFAULT_BOXHEIGHT	16
PSOPTIONBUTTON_DEFAULT_RINGTHICK	1	not scaled at Create — the painter scales the pen
PSOPTIONBUTTON_DEFAULT_FOCUSTHICK	1	not scaled at Create — same reason
PSOPTIONBUTTON_DEFAULT_DOTSIZE	0	0 = derive from the circle diameter
PSOPTIONBUTTON_DOTRATIO_PCT	40	the derived dot, as a percentage of the circle
PSOPTIONBUTTON_DEFAULT_FOCUSGAP	2
PSOPTIONBUTTON_DEFAULT_FOCUSCURV	4	ellipse diameter, not a radius
PSOPTIONBUTTON_DEFAULT_GROUPID	0

The two pen widths are the exception worth remembering: PaintRoundOutline DPI-scales the pen it is handed, so scaling them at creation as well would double them at any scale above 100%. They are DPI-aware — the painter is simply the thing that does it.

Hover tracking

Constant	Value
PSOPTIONBUTTON_HOTTRACK_MS	100	poll interval for the hover safety net, since WM_MOUSELEAVE is not guaranteed on a fast exit