Fix: vterm flickered a lot when using gemini cli as backend (#272)

* Improve Vterm rendering detection and add test

* Add no-flicker option and pass env to Claude Code

* add contributor

* Refine vterm redraw regex and add CRLF test

Author: tninja

ai-code-backends-infra.el

@@ -86,7 +86,7 @@ Can be either `vterm' or `eat'."
   :type 'boolean
   :group 'ai-code-backends-infra)
 
-(defcustom ai-code-backends-infra-vterm-render-delay 0.005
+(defcustom ai-code-backends-infra-vterm-render-delay 0.01
   "Rendering optimization delay for batched terminal updates."
   :type 'number
   :group 'ai-code-backends-infra)
@@ -167,6 +167,12 @@ if the AI session buffer is not currently visible."
 
 ;;; Vterm Rendering Optimization
 
+(defconst ai-code-backends-infra--vterm-redraw-regexp
+  "\033\\[[0-9;?]*[A-GJKMH]"
+  "Regexp to detect ANSI terminal redraw or movement sequences.
+Standalone carriage returns are intentionally excluded so simple CR-based
+updates are handled separately via carriage return counting.")
+
 (defvar-local ai-code-backends-infra--vterm-render-queue nil)
 (defvar-local ai-code-backends-infra--vterm-render-timer nil)
 
@@ -263,12 +269,14 @@ scrolling and copying are not disrupted by timer-driven redraws."
       (funcall orig-fun process input)
     (with-current-buffer (process-buffer process)
       (let* ((complex-redraw-detected
-              (string-match-p "\033\\[[0-9]*A.*\033\\[K.*\033\\[[0-9]*A.*\033\\[K" input))
+              (string-match-p ai-code-backends-infra--vterm-redraw-regexp input))
              (clear-count (1- (length (split-string input "\033\\[K"))))
+             (cr-count (cl-count ?\15 input))
              (escape-count (cl-count ?\033 input))
              (input-length (length input))
              (escape-density (if (> input-length 0) (/ (float escape-count) input-length) 0)))
         (if (or complex-redraw-detected
+                (>= cr-count 2)
                 (and (> escape-density 0.3) (>= clear-count 2))
                 ai-code-backends-infra--vterm-render-queue
                 (bound-and-true-p vterm-copy-mode))
@@ -946,8 +954,8 @@ CLEANUP-FN is called with no arguments when the process exits.
 INSTANCE-NAME overrides instance selection when non-nil.
 PREFIX enables instance selection when BUFFER-NAME is nil.
 When FORCE-PROMPT is non-nil, always prompt for a new instance name.
-ENV-VARS is a list of additional environment variable strings (e.g., \"VAR=value\")
-passed to the terminal session on creation.
+ENV-VARS is a list of additional environment variable strings, for example
+\"VAR=value\", passed to the terminal session on creation.
 MULTILINE-INPUT-SEQUENCE configures `S-<return>' and `C-<return>' to send
 that sequence inside the session buffer.
 POST-START-FN is called with (BUFFER PROCESS INSTANCE-NAME) after a new

ai-code-claude-code.el

@@ -1,6 +1,6 @@
 ;;; ai-code-claude-code.el --- Thin wrapper for Claude Code CLI  -*- lexical-binding: t; -*-
 
-;; Author: Kang Tu <tninja@gmail.com>
+;; Author: Kang Tu, Yoav Orot
 ;; SPDX-License-Identifier: Apache-2.0
 
 ;;; Commentary:
@@ -31,6 +31,11 @@
   :type '(repeat string)
   :group 'ai-code-claude-code)
 
+(defcustom ai-code-claude-code-no-flicker t
+  "Enable experimental flicker-free terminal renderer in Claude Code."
+  :type 'boolean
+  :group 'ai-code-claude-code)
+
 (defcustom ai-code-claude-code-multiline-input-sequence "\e\r"
   "Terminal sequence used for multiline input in Claude Code sessions.
 This mirrors the newline sequence Claude Code expects from `/terminal-setup'."
@@ -59,7 +64,9 @@ With prefix ARG, prompt for CLI args using
          (mcp-launch (ai-code-mcp-agent-prepare-launch 'claude-code working-dir command))
          (launch-command (or (plist-get mcp-launch :command) command))
          (cleanup-fn (plist-get mcp-launch :cleanup-fn))
-         (post-start-fn (plist-get mcp-launch :post-start-fn)))
+         (post-start-fn (plist-get mcp-launch :post-start-fn))
+         (env-vars (list (format "CLAUDE_CODE_NO_FLICKER=%s"
+                                 (if ai-code-claude-code-no-flicker "1" "0")))))
     (ai-code-backends-infra--toggle-or-create-session
      working-dir
      nil
@@ -70,7 +77,7 @@ With prefix ARG, prompt for CLI args using
      nil
      ai-code-claude-code--session-prefix
      nil
-     nil
+     env-vars
      ai-code-claude-code-multiline-input-sequence
      post-start-fn)))
 

test/test_ai-code-backends-infra.el

@@ -13,6 +13,8 @@
 (require 'ai-code-backends-infra)
 (require 'ai-code-notifications)
 
+(defvar vterm-copy-mode-hook)
+
 (ert-deftest test-ai-code-backends-infra-output-meaningful-p-noise ()
   "Ensure terminal noise is not considered meaningful output."
   (should-not (ai-code-backends-infra--output-meaningful-p nil))
@@ -1246,6 +1248,56 @@
       (when (buffer-live-p buffer)
         (kill-buffer buffer)))))
 
+(ert-deftest test-ai-code-backends-infra-vterm-smart-renderer-queues-on-carriage-return ()
+  "Incoming vterm data is queued when it contains multiple carriage returns."
+  (with-temp-buffer
+    (rename-buffer "*testgemini[test-dir]*" t)
+    (setq-local ai-code-backends-infra--vterm-render-queue nil)
+    (setq-local ai-code-backends-infra--vterm-render-timer nil)
+    (setq-local vterm-copy-mode nil)
+    (let* ((rendered nil)
+           (orig-fun (lambda (_process input) (push input rendered)))
+           (mock-process 'mock-proc))
+      (cl-letf (((symbol-function 'process-buffer)
+                 (lambda (_proc) (current-buffer)))
+                ((symbol-function 'run-at-time)
+                 (lambda (&rest _args) 'mock-timer))
+                ((symbol-function 'cancel-timer)
+                 (lambda (&rest _args) nil)))
+        ;; Send input with multiple \r (common in TUI progress bars/updates).
+        (ai-code-backends-infra--vterm-smart-renderer
+         orig-fun mock-process "Loading... 10%\rLoading... 20%\r")
+        ;; It should NOT be rendered immediately.
+        (should (null rendered))
+        ;; It should be in the queue.
+        (should (equal ai-code-backends-infra--vterm-render-queue "Loading... 10%\rLoading... 20%\r"))))))
+
+(ert-deftest test-ai-code-backends-infra-vterm-smart-renderer-allows-crlf-pass-through ()
+  "Simple CRLF output should render immediately instead of being queued."
+  (with-temp-buffer
+    (rename-buffer "*testgemini[test-crlf]*" t)
+    (setq-local ai-code-backends-infra--vterm-render-queue nil)
+    (setq-local ai-code-backends-infra--vterm-render-timer nil)
+    (setq-local vterm-copy-mode nil)
+    (let* ((rendered nil)
+           (timer-scheduled nil)
+           (orig-fun (lambda (_process input) (push input rendered)))
+           (mock-process 'mock-proc))
+      (cl-letf (((symbol-function 'process-buffer)
+                 (lambda (_proc) (current-buffer)))
+                ((symbol-function 'run-at-time)
+                 (lambda (&rest _args)
+                   (setq timer-scheduled t)
+                   'mock-timer))
+                ((symbol-function 'cancel-timer)
+                 (lambda (&rest _args) nil)))
+        (ai-code-backends-infra--vterm-smart-renderer
+         orig-fun mock-process "hello\r\n")
+        (should (equal rendered '("hello\r\n")))
+        (should-not timer-scheduled)
+        (should-not ai-code-backends-infra--vterm-render-queue)
+        (should-not ai-code-backends-infra--vterm-render-timer)))))
+
 (provide 'test_ai-code-backends-infra)
 
 ;;; test_ai-code-backends-infra.el ends here

test/test_ai-code-claude-code.el

@@ -40,6 +40,28 @@
         (ai-code-claude-code)
         (should (equal captured-sequence "\e\r"))))))
 
+(ert-deftest ai-code-test-claude-code-start-passes-no-flicker-env ()
+  "Starting Claude Code should pass CLAUDE_CODE_NO_FLICKER env var based on config."
+  (let ((captured-env-vars :unset))
+    (cl-letf (((symbol-function 'ai-code-backends-infra--session-working-directory)
+               (lambda () "/tmp/test-claude"))
+              ((symbol-function 'ai-code-backends-infra--resolve-start-command)
+               (lambda (&rest _args)
+                 (list :command "claude")))
+              ((symbol-function 'ai-code-mcp-agent-prepare-launch)
+               (lambda (&rest _args) nil))
+              ((symbol-function 'ai-code-backends-infra--toggle-or-create-session)
+               (lambda (&rest args)
+                 (let ((env-vars (nth 9 args)))
+                   (setq captured-env-vars env-vars))
+                 nil)))
+      (let ((ai-code-claude-code-no-flicker t))
+        (ai-code-claude-code)
+        (should (member "CLAUDE_CODE_NO_FLICKER=1" captured-env-vars)))
+      (let ((ai-code-claude-code-no-flicker nil))
+        (ai-code-claude-code)
+        (should (member "CLAUDE_CODE_NO_FLICKER=0" captured-env-vars))))))
+
 (provide 'test_ai-code-claude-code)
 
 ;;; test_ai-code-claude-code.el ends here