screen.Clear() sets background color to last used style in v2.5.0

[wedaly]

In tcell v2.4.0, the following program clears the screen back to the default background color. In tcell v2.5.0, the program clears the screen to the last used style in screen.SetContent()

Here's a program that reproduces the issue:

package main

import (
	"time"
	"github.com/gdamore/tcell/v2"
)

func main() {
	s, err := tcell.NewScreen()
	if err != nil {
		panic(err)
	}

	if err := s.Init(); err != nil {
		panic(err)
	}

	s.Clear()
	s.Show()

	style := tcell.StyleDefault.
		Background(tcell.ColorMaroon).
		Foreground(tcell.ColorWhite).Bold(true)

	s.SetContent(0, 0, 'a', nil, style)
	s.SetContent(1, 0, 'b', nil, style)
	s.SetContent(2, 0, 'c', nil, style)
	s.Show()

	time.Sleep(time.Second)

	// In tcell v2.4.0, this clears the screen back to its default color.
	// In tcell v2.5.0, this clears the screen to maroon.
	s.Clear()
	s.Show()

	time.Sleep(time.Second * 5)

	s.Fini()
}

I was able to reproduce the issue in:

• Fedora 35, with gnome-terminal (both with and without tmux)
• macOS, with Terminal.app

Git bisecting shows 62f5502 as the commit that introduced the change in behavior.

Is this a regression? Or am I using SetContent / Clear / Show incorrectly?

(Thanks again for maintaining this project. I've been a happy user for several years now!)

[wedaly]

Stepping through the program with a debugger, I see that when tScreen.clearScreen() calls t.sendFgBg(fg, bg) with fg and bg set to ColorDefault, sendFgBg doesn't actually send anything (all the if statements evaluate false).

Maybe something like this would help?

diff --git a/tscreen.go b/tscreen.go
index 2c161cc..d7df641 100644
--- a/tscreen.go
+++ b/tscreen.go
@@ -859,6 +859,12 @@ func (t *tScreen) Show() {
 
 func (t *tScreen) clearScreen() {
        fg, bg, _ := t.style.Decompose()
+       if fg == ColorDefault {
+               fg = ColorReset
+       }
+       if bg == ColorDefault {
+               bg = ColorReset
+       }
        t.sendFgBg(fg, bg)
        t.TPuts(t.ti.Clear)
        t.clear = false

[wedaly]

This also seems to restore the old behavior:

diff --git a/tscreen.go b/tscreen.go
index 2ed73a2..676084e 100644
--- a/tscreen.go
+++ b/tscreen.go
@@ -859,6 +859,7 @@ func (t *tScreen) Show() {
 
 func (t *tScreen) clearScreen() {
        fg, bg, _ := t.style.Decompose()
+       t.TPuts(t.ti.AttrOff)
        t.sendFgBg(fg, bg)
        t.TPuts(t.ti.Clear)
        t.clear = false

I think ti.AttrOff used to get set by drawCell after ClearScreen filled the cells, but this stopped happening when the dirty flagged started getting set to false in 62f5502

[tobiassjosten]

Well dug, @wedaly! I'm seeing this exact same problem and have resorted to using Sync() after Clear() to bypass it for now.

[gdamore]

This is fixed in #523

I'll create a patch release today to get this out.