I would like to draw on the TVirtualStringTree header columns but I have a problem. I need the tree columns to use it's "default draw" and add my own graphics on it.
If I use hoOwnerDraw with Header.Options and use OnHeaderDraw, I need to completely draw the columns myself (which is no good).
There is the OnAdvancedHeaderDraw which seems to be what I hope for (see example):
Used when owner draw is enabled for the header and a column is set to owner draw mode. But only if OnHeaderDrawQueryElements returns at least one element to be drawn by the application.
If I use OnAdvancedHeaderDraw (I must also use OnHeaderDrawQueryElements) I get what I want, but I need to substitute at-least one element in the OnHeaderDrawQueryElements (i.e. hpeBackground/hpeDropMark/hpeHeaderGlyph/hpeSortGlyph/hpeText) and draw it myself in the OnAdvancedHeaderDraw event.
When for example I return the hpeSortGlyph element, returning ShowSortGlyph := True in the var PaintInfo: THeaderPaintInfo of the OnAdvancedHeaderDraw does not make any difference, and the sort glyph is not painted, which means I must paint it myself. Since there is no DefaultDrawSortGlyph I need to reinvent to weal, so to speak, and copy big parts of code from VT source just to paint the sort glyph :/
I use/need all the elements in the columns, I just want to add my own graphics on top of the default column graphics (a drop down arrow) without substituting one of them. How can I avoid this behavior? Is it possible to draw on top of the exists column without patching the source?
I hope my question is clear.