Method firstVisibleLine

texteditor/render.go:505–530

firstVisibleLine finds the first visible line, starting at given line (typically cursor -- if zero, a visible line is first found) -- returns stln if nothing found above it.

(stln int)

// (typically cursor -- if zero, a visible line is first found) -- returns
// stln if nothing found above it.
func (ed *Editor) firstVisibleLine(stln int) int {
	bb := ed.renderBBox()
	if stln == 0 {
		perln := float32(ed.linesSize.Y) / float32(ed.NumLines)
		stln = int(ed.Geom.Scroll.Y/perln) - 1
		if stln < 0 {
			stln = 0
		}
		for ln := stln; ln < ed.NumLines; ln++ {
			lbb := ed.lineBBox(ln)
			if int(math32.Ceil(lbb.Max.Y)) > bb.Min.Y { // visible
				stln = ln
				break
			}
		}
	}
	lastln := stln
	for ln := stln - 1; ln >= 0; ln-- {
		cpos := ed.charStartPos(lexer.Pos{Ln: ln})
		if int(math32.Ceil(cpos.Y)) < bb.Min.Y { // top just offscreen
			break
		}
		lastln = ln
	}
	return lastln
}

// lastVisibleLine finds the last visible line, starting at given line
// (typically cursor) -- returns stln if nothing found beyond it.