Webasm terminal fixes.

Reverse video, not reverse text.
Provide an XTERM equivalent default palette.
Reset colors should go to silver on black.
Black color 0 should be rendered properly.

webfiles/tcell.js

@@ -62,14 +62,19 @@ function drawCell(x, y, mainc, combc, fg, bg, attrs) {
     var span = document.createElement("span")
     var use = false
 
-    if (fg) { span.style.color = intToHex(fg); use = true }
-    if (bg) { span.style.backgroundColor = intToHex(bg); use = true }
+    if ((attrs & (1<<2)) != 0) { // reverse video
+        var temp = bg
+        bg = fg
+        fg = temp
+        use = true
+    }
+    if (fg != -1) { span.style.color = intToHex(fg); use = true }
+    if (bg != -1) { span.style.backgroundColor = intToHex(bg); use = true }
 
     if (attrs != 0) {
         use = true
         if ((attrs & 1) != 0) { span.classList.add("bold") }
         if ((attrs & (1<<1)) != 0) { span.classList.add("blink") }
-        if ((attrs & (1<<2)) != 0) { span.classList.add("reverse") }
         if ((attrs & (1<<3)) != 0) { span.classList.add("underline") }
         if ((attrs & (1<<4)) != 0) { span.classList.add("dim") }
         if ((attrs & (1<<5)) != 0) { span.classList.add("italic") }

webfiles/termstyle.css

@@ -25,8 +25,6 @@
 
 .blink { animation: blinker 1s step-start infinite; }
 
-.reverse { unicode-bidi: bidi-override; direction: rtl; }
-
 .underline { text-decoration: underline; }
 
 .dim { filter: brightness(50) }

wscreen.go

@@ -109,6 +109,39 @@ func (t *wScreen) SetCell(x, y int, style Style, ch ...rune) {
 	}
 }
 
+// paletteColor gives a more natural palette color actually matching
+// typical XTerm.  We might in the future want to permit styling these
+// via CSS.
+
+var palette = map[Color]int32{
+	ColorBlack: 0x000000,
+	ColorMaroon: 0xcd0000,
+	ColorGreen: 0x00cd00,
+	ColorOlive: 0xcdcd00,
+	ColorNavy: 0x0000ee,
+	ColorPurple: 0xcd00cd,
+	ColorTeal: 0x00cdcd,
+	ColorSilver: 0xe5e5e5,
+	ColorGray: 0x7f7f7f,
+	ColorRed: 0xff0000,
+	ColorLime: 0x00ff00,
+	ColorYellow: 0xffff00,
+	ColorBlue: 0x5c5cff,
+	ColorFuchsia: 0xff00ff,
+	ColorAqua: 0x00ffff,
+	ColorWhite: 0xffffff,
+}
+
+func paletteColor(c Color) int32 {
+	if (c.IsRGB()) {
+		return int32(c & 0xffffff);
+	}
+	if (c >= ColorBlack && c <= ColorWhite) {
+		return palette[c]
+	}
+	return c.Hex()
+}
+
 func (t *wScreen) drawCell(x, y int) int {
 	mainc, combc, style, width := t.cells.GetContent(x, y)
 
@@ -120,7 +153,13 @@ func (t *wScreen) drawCell(x, y int) int {
 		style = t.style
 	}
 
-	fg, bg := style.fg.Hex(), style.bg.Hex()
+	fg, bg := paletteColor(style.fg), paletteColor(style.bg)
+	if (fg == -1) {
+		fg = 0xe5e5e5;
+	}
+	if (bg == -1) {
+		bg = 0x000000;
+	}
 
 	var combcarr []interface{} = make([]interface{}, len(combc))
 	for i, c := range combc {