BControlLook: Introduce ComposeIconSize().

This takes an int32 (e.g. B_MINI_ICON or another constant) and
then returns a BSize scaled appropriately, the same as ComposeSpacing()
does already for the *_SPACING constants.

This will be used to replace icon size computations throughout the tree.

headers/os/interface/ControlLook.h

@@ -102,6 +102,7 @@ public:
 	virtual	float				DefaultItemSpacing() const = 0;
 
 	static	float				ComposeSpacing(float spacing);
+	static	BSize				ComposeIconSize(int32 size);
 
 	virtual uint32				Flags(BControl* control) const = 0;
 

src/kits/interface/ControlLook.cpp

@@ -45,6 +45,18 @@ BControlLook::ComposeSpacing(float spacing)
 }
 
 
+BSize
+BControlLook::ComposeIconSize(int32 size)
+{
+	float scale = be_plain_font->Size() / 12.0f;
+	if (scale < 1.0f)
+		scale = 1.0f;
+
+	const int32 scaled = size * scale;
+	return BSize(scaled - 1, scaled - 1);
+}
+
+
 void
 BControlLook::DrawLabel(BView* view, const char* label, const BBitmap* icon,
 	BRect rect, const BRect& updateRect, const rgb_color& base, uint32 flags,