<*PRAGMA LL*>
The Palette interface allows you to implement your own screen-independent resources by registering a closure to produce an appropriate screen-dependent resource for any given screentype.
INTERFACE Palette; IMPORT VBT, PaintOp, Cursor, Pixmap, Font, ScrnPaintOp, ScrnCursor, ScrnPixmap, ScrnFont;
Translating a screen-independent resource into its screen-dependent form is called resolving the resource. Here are the closure types for resolving resources:
TYPE OpClosure = OBJECT METHODS <* LL.sup <= VBT.mu *> apply(st: VBT.ScreenType): ScrnPaintOp.T; END; CursorClosure = OBJECT METHODS <* LL.sup <= VBT.mu *> apply(st: VBT.ScreenType): ScrnCursor.T; END; PixmapClosure = OBJECT METHODS <* LL.sup <= VBT.mu *> apply(st: VBT.ScreenType): ScrnPixmap.T; END; FontClosure = OBJECT METHODS <* LL.sup <= VBT.mu *> apply(st: VBT.ScreenType): ScrnFont.T; END;
When an apply method is called, st # NIL. If the method returns NIL, then some default screen-dependent resource will be used; for example, the built-in font or the transparent painting operation.
The following procedures produce screen-independent resources from closures:
PROCEDURE FromOpClosure(cl: OpClosure): PaintOp.T; <* LL.sup <= VBT.mu *>
PROCEDURE FromCursorClosure (cl: CursorClosure): Cursor.T; <* LL.sup <= VBT.mu *>
Return a Cursor.T that behaves like cl.apply(st) on st.
PROCEDURE FromPixmapClosure (cl: PixmapClosure): Pixmap.T; <* LL.sup <= VBT.mu *>
Return a Pixmap.T that behaves like cl.apply(st) on st.
PROCEDURE FromFontClosure(cl: FontClosure): Font.T; <* LL.sup <= VBT.mu *>
Return a Font.T that behaves like cl.apply(st) on st.
If your apply method that resolves a resource needs to resolve some other resource, you should use one of the following procedures to do so. In all cases, st must be non-NIL.
PROCEDURE ResolveOp(st: VBT.ScreenType; op: PaintOp.T) : ScrnPaintOp.T;
Resolve op for st.
PROCEDURE ResolveCursor(st: VBT.ScreenType; cursor: Cursor.T): ScrnCursor.T;
Resolve cursor for st.
PROCEDURE ResolvePixmap(st: VBT.ScreenType; pixmap: Pixmap.T): ScrnPixmap.T;
Resolve pixmap for st.
PROCEDURE ResolveFont(st: VBT.ScreenType; font: Font.T) : ScrnFont.T;
Resolve font for st.
If you create a cycle of screen-independent resources each of which tries to resolve the next resource in the cycle, then the program will deadlock.
To implement screen-independent resources, every screentype includes a palette, which is a table of screen-dependent resources appropriate for that screentype. Most clients don't need to worry about the palette, but if you are implementing a VBT class that translates to some other window system---like X or Microsoft Windows---here is the procedure for building the palette in the screentype for a top-level window: palette
PROCEDURE Init(st: VBT.ScreenType); <* LL.sup = VBT.mu.v *>
Initialize st's palette, if it is not already initialized, by resolving all screen-independent resources for st and storing the results.
END Palette.
Return a PaintOp.T that behaves like cl.apply(st) on st.