Fix installer GUI ghosting: add double-buffer, fix text baseline

Ghosting root cause: all X11 drawing (XFillRectangle, XDrawLine, XDrawArc,
XDrawRectangle) and XRender Xft text rendering were going directly to the
window. XRender composites text on top of pixels without clearing underneath,
so previous log lines bled through on every update.

Fix:
- Added Pixmap buf to Ins struct (created at WIN_W × WIN_H after window init)
- Redirected all drawing calls (fill_rect, draw_line, XDrawRectangle,
  XDrawArc, XFillArc) from s->win to s->buf
- XftDrawCreate in redraw() now targets s->buf
- At end of redraw(): XCopyArea(buf → win) blits the complete frame at once
- Also fixed xft_text baseline: was y + ext.height - ext.y (glyph-specific,
  varied per string); now y + f->ascent (consistent font metric)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

installer/orioninstall-gui.c

@@ -126,6 +126,7 @@ typedef struct {
     Display  *dpy;
     int       scr;
     Window    win;
+    Pixmap    buf;   /* double-buffer — all drawing goes here, then blit */
     GC        gc;
     Colormap  cmap;
     Visual   *vis;
@@ -195,12 +196,12 @@ static void xftcol(Ins *s, unsigned long rgb, XftColor *out) {
 
 static void fill_rect(Ins *s, int x, int y, int w, int h, unsigned long rgb) {
     XSetForeground(s->dpy, s->gc, mkcolor(s, rgb));
-    XFillRectangle(s->dpy, s->win, s->gc, x, y, w, h);
+    XFillRectangle(s->dpy, s->buf, s->gc, x, y, w, h);
 }
 
 static void draw_line(Ins *s, int x1, int y1, int x2, int y2, unsigned long rgb) {
     XSetForeground(s->dpy, s->gc, mkcolor(s, rgb));
-    XDrawLine(s->dpy, s->win, s->gc, x1, y1, x2, y2);
+    XDrawLine(s->dpy, s->buf, s->gc, x1, y1, x2, y2);
 }
 
 /* Draw text and return pixel width */
@@ -210,7 +211,8 @@ static int xft_text(Ins *s, XftDraw *xd, XftFont *f, unsigned long rgb,
     XftColor col; xftcol(s, rgb, &col);
     XGlyphInfo ext;
     XftTextExtentsUtf8(s->dpy, f, (const FcChar8 *)str, strlen(str), &ext);
-    XftDrawStringUtf8(xd, &col, f, x, y + ext.height - ext.y,
+    /* y is the TOP of the text row; compute baseline from font metrics */
+    XftDrawStringUtf8(xd, &col, f, x, y + f->ascent,
                       (const FcChar8 *)str, strlen(str));
     XftColorFree(s->dpy, s->vis, s->cmap, &col);
     return ext.width;
@@ -264,7 +266,7 @@ static void draw_textfield(Ins *s, XftDraw *xd, int x, int y, int w,
     fill_rect(s, x, y, w, 32, C_INPUT_BG);
     /* border */
     XSetForeground(s->dpy, s->gc, mkcolor(s, bord));
-    XDrawRectangle(s->dpy, s->win, s->gc, x, y, w - 1, 31);
+    XDrawRectangle(s->dpy, s->buf, s->gc, x, y, w - 1, 31);
 
     /* content */
     if (tf->len == 0 && !focused && placeholder) {
@@ -321,10 +323,10 @@ static void draw_radio(Ins *s, XftDraw *xd, int x, int y, int w,
     /* radio circle */
     int cx = x + 20, cy = y + 22;
     XSetForeground(s->dpy, s->gc, mkcolor(s, C_SEP));
-    XDrawArc(s->dpy, s->win, s->gc, cx-8, cy-8, 16, 16, 0, 360*64);
+    XDrawArc(s->dpy, s->buf, s->gc, cx-8, cy-8, 16, 16, 0, 360*64);
     if (selected) {
         XSetForeground(s->dpy, s->gc, mkcolor(s, C_BTN_PRI));
-        XFillArc(s->dpy, s->win, s->gc, cx-5, cy-5, 10, 10, 0, 360*64);
+        XFillArc(s->dpy, s->buf, s->gc, cx-5, cy-5, 10, 10, 0, 360*64);
     }
 
     xft_text(s, xd, s->f_body,  C_TXT,     x+38, y+8,  label);
@@ -335,7 +337,7 @@ static void draw_radio(Ins *s, XftDraw *xd, int x, int y, int w,
 static void draw_progress(Ins *s, int x, int y, int w, int h, int pct) {
     fill_rect(s, x, y, w, h, C_BAR_BG);
     XSetForeground(s->dpy, s->gc, mkcolor(s, C_BORDER));
-    XDrawRectangle(s->dpy, s->win, s->gc, x, y, w-1, h-1);
+    XDrawRectangle(s->dpy, s->buf, s->gc, x, y, w-1, h-1);
 
     if (pct > 0) {
         int fw = (w - 2) * pct / 100;
@@ -439,7 +441,7 @@ static void draw_footer(Ins *s, XftDraw *xd,
         int dy = fy + FOOT_H/2;
         unsigned long dc = (i == dot_step) ? C_BTN_PRI : C_SEP;
         XSetForeground(s->dpy, s->gc, mkcolor(s, dc));
-        XFillArc(s->dpy, s->win, s->gc, dx-4, dy-4, 8, 8, 0, 360*64);
+        XFillArc(s->dpy, s->buf, s->gc, dx-4, dy-4, 8, 8, 0, 360*64);
     }
 
     int bw = 120, bh = 36, by = fy + (FOOT_H - bh) / 2;
@@ -592,21 +594,21 @@ static void draw_locale(Ins *s, XftDraw *xd) {
     unsigned long fbd = factive ? C_INPUT_ACT : C_INPUT_BD;
     fill_rect(s, lx, fy, LC_PANE_W, 26, C_INPUT_BG);
     XSetForeground(s->dpy, s->gc, mkcolor(s, fbd));
-    XDrawRectangle(s->dpy, s->win, s->gc, lx, fy, LC_PANE_W-1, 25);
+    XDrawRectangle(s->dpy, s->buf, s->gc, lx, fy, LC_PANE_W-1, 25);
     const char *fdisp = s->tz_filter_len ? s->tz_filter : "";
     xft_text(s, xd, s->f_body, s->tz_filter_len ? C_TXT_INP : C_TXT_DIM,
              lx + 6, fy + 17, s->tz_filter_len ? fdisp : "Filter…");
     if (factive) {
         int cx = lx + 6 + text_w(s, s->f_body, fdisp);
         XSetForeground(s->dpy, s->gc, mkcolor(s, C_TXT_INP));
-        XDrawLine(s->dpy, s->win, s->gc, cx, fy + 4, cx, fy + 21);
+        XDrawLine(s->dpy, s->buf, s->gc, cx, fy + 4, cx, fy + 21);
     }
 
     /* timezone list */
     int ly = fy + 32;
     fill_rect(s, lx, ly, LC_PANE_W, LC_LIST_H, C_PANEL);
     XSetForeground(s->dpy, s->gc, mkcolor(s, C_SEP));
-    XDrawRectangle(s->dpy, s->win, s->gc, lx, ly, LC_PANE_W-1, LC_LIST_H-1);
+    XDrawRectangle(s->dpy, s->buf, s->gc, lx, ly, LC_PANE_W-1, LC_LIST_H-1);
 
     int vis = 0, row = 0;
     for (int i = 0; i < NTZ && vis < LC_ROWS_VIS + s->tz_scroll; i++) {
@@ -631,7 +633,7 @@ static void draw_locale(Ins *s, XftDraw *xd) {
     int kly = ty + 22 + 32; /* align with timezone list (below filter) */
     fill_rect(s, rx, kly, LC_PANE_W, LC_LIST_H + 26, C_PANEL);
     XSetForeground(s->dpy, s->gc, mkcolor(s, C_SEP));
-    XDrawRectangle(s->dpy, s->win, s->gc, rx, kly, LC_PANE_W-1, LC_LIST_H+25);
+    XDrawRectangle(s->dpy, s->buf, s->gc, rx, kly, LC_PANE_W-1, LC_LIST_H+25);
 
     int kvis = NKB < LC_ROWS_VIS + 1 ? NKB : LC_ROWS_VIS + 1;
     for (int i = s->kb_scroll; i < NKB && (i - s->kb_scroll) < kvis; i++) {
@@ -908,7 +910,7 @@ static void draw_done(Ins *s, XftDraw *xd) {
 /* ══════════════════════════════════════════════════════════════════ */
 
 static void redraw(Ins *s) {
-    XftDraw *xd = XftDrawCreate(s->dpy, s->win, s->vis, s->cmap);
+    XftDraw *xd = XftDrawCreate(s->dpy, s->buf, s->vis, s->cmap);
     fill_rect(s, 0, 0, WIN_W, WIN_H, C_BG);
 
     switch (s->step) {
@@ -923,9 +925,12 @@ static void redraw(Ins *s) {
 
     /* outer border */
     XSetForeground(s->dpy, s->gc, mkcolor(s, C_BORDER));
-    XDrawRectangle(s->dpy, s->win, s->gc, 0, 0, WIN_W-1, WIN_H-1);
+    XDrawRectangle(s->dpy, s->buf, s->gc, 0, 0, WIN_W-1, WIN_H-1);
 
     XftDrawDestroy(xd);
+
+    /* blit double-buffer → window in one shot (eliminates ghosting) */
+    XCopyArea(s->dpy, s->buf, s->win, s->gc, 0, 0, WIN_W, WIN_H, 0, 0);
     XFlush(s->dpy);
 }
 
@@ -1258,7 +1263,8 @@ static void init(Ins *s) {
         (sw - WIN_W)/2, (sh - WIN_H)/2, WIN_W, WIN_H,
         0, s->depth, InputOutput, s->vis,
         CWBackPixel | CWEventMask, &swa);
-    s->gc = XCreateGC(s->dpy, s->win, 0, NULL);
+    s->gc  = XCreateGC(s->dpy, s->win, 0, NULL);
+    s->buf = XCreatePixmap(s->dpy, s->win, WIN_W, WIN_H, s->depth);
 
     /* window title + WM hints */
     XStoreName(s->dpy, s->win, "OrionOS Installer");