v0.13.0: Rendering pipeline with framebuffer backend

New module: src/rendering/framebuffer.lisp (tangled from org/framebuffer.org) - framebuffer-backend class: implements backend protocol by writing to 2D cell array instead of emitting escape sequences - cell struct: per-cell state (char, fg, bg, bold, italic, underline, link-url) - make-framebuffer / framebuffer-width / framebuffer-height - draw-text, draw-rect, draw-border, draw-link, draw-ellipsis methods - diff-framebuffers: compares two framebuffers, returns changed cells - flush-framebuffer: diff + output changes to real backend - with-scissor macro: clip drawing operations to rectangle - cursor-move: added default no-op method for all backends - 20 new tests, all passing (372 total) Version bumped from 0.11.0 to 0.13.0. License field set to GPL-3.0 in ASDF.
2026-05-11 22:34:58 +00:00
parent b7df68c436
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+#+TITLE: Rendering Pipeline — Framebuffer (v0.13.0)
+#+DATE: 2026-05-11
+#+AUTHOR: Amr Gharbeia / Hermes
+#+STARTUP: content
+
+* Overview
+
+A framebuffer-based rendering pipeline that sits between the component tree
+and the backend protocol. Eliminates flicker by computing a full frame then
+diffing against the previous frame before flushing.
+
+The ~framebuffer-backend~ class implements the backend protocol by writing to a
+2D cell array instead of emitting escape sequences. After all components render,
+the diff engine compares current and previous frames and flushes only changed
+cells to a real backend.
+
+Benefits:
+- Flicker-free output (only changed cells are sent)
+- Enables text selection (each cell knows its content)
+- Enables click-to-open-link (each cell knows its URL)
+- Scissor clipping for nested containers
+
+** Contract**
+
+- ~cell~ — immutable struct with char, fg, bg, bold, italic, underline, link-url
+- ~make-framebuffer width height~ → 2D array of ~cell~
+- ~framebuffer-backend~ — subclass of ~backend~ that renders to cell array
+- ~make-framebuffer-backend &key width height~ → framebuffer-backend
+- ~diff-framebuffers prev curr~ → list of (x y cell) for changed cells
+- ~flush-framebuffer prev-fb curr-fb backend~ → writes changes, returns count
+- ~with-scissor (fb x y w h) &body body~ — clip drawing to rectangle
+
+** Plan
+
+See =docs/plans/2026-05-11-rendering-pipeline.md= for full implementation plan.
+
+1. Create org file with code blocks
+2. Tangle → framebuffer.lisp
+3. Add to ASDF
+4. Write tests
+5. Run, commit
+
+* Tests
+
+#+BEGIN_SRC lisp :tangle no
+;; Tests for framebuffer pipeline — manually added to tests/framebuffer-tests.lisp
+
+(defpackage :cl-tty-framebuffer-test
+  (:use :cl :fiveam :cl-tty.rendering :cl-tty.backend))
+(in-package :cl-tty-framebuffer-test)
+
+(def-suite framebuffer-suite :description "Framebuffer rendering pipeline tests")
+(in-suite framebuffer-suite)
+
+(test make-framebuffer-creates-correct-size
+  (let ((fb (make-framebuffer 80 24)))
+    (is (= 24 (framebuffer-height fb)))
+    (is (= 80 (framebuffer-width fb)))))
+
+(test cell-defaults-are-space
+  (let ((cell (aref (make-framebuffer 10 10) 0 0)))
+    (is (eql #\space (cell-char cell)))
+    (is (null (cell-fg cell)))
+    (is (null (cell-bg cell)))))
+
+(test draw-text-on-fb-sets-cells
+  (let ((fb (make-framebuffer-backend)))
+    (draw-text fb 2 3 "abc" :red nil)
+    (let ((cells (fb-framebuffer fb)))
+      (is (eql #\a (cell-char (aref cells 3 2))))
+      (is (eql #\b (cell-char (aref cells 3 3))))
+      (is (eql #\c (cell-char (aref cells 3 4))))
+      (is (eql :red (cell-fg (aref cells 3 2)))))))
+
+(test draw-text-clips-at-bounds
+  (let ((fb (make-framebuffer-backend :width 10 :height 5)))
+    (draw-text fb 8 2 "hello" nil nil)
+    (let ((cells (fb-framebuffer fb)))
+      (is (eql #\h (cell-char (aref cells 2 8))))
+      (is (eql #\e (cell-char (aref cells 2 9))))
+      (is (eql #\space (cell-char (aref cells 2 0))) "out of bounds text is ignored"))))
+
+(test diff-identical-fbs-returns-empty
+  (let ((fb1 (make-framebuffer 80 24))
+        (fb2 (make-framebuffer 80 24)))
+    (is (null (diff-framebuffers fb1 fb2)))))
+
+(test diff-changed-fb-returns-changes
+  (let* ((fb1 (make-framebuffer 10 10))
+         (fb2 (make-framebuffer 10 10)))
+    (setf (aref fb2 5 5) (make-cell :char #\X :fg :red))
+    (let ((changes (diff-framebuffers fb1 fb2)))
+      (is (= 1 (length changes)))
+      (destructuring-bind (x y cell) (first changes)
+        (is (= 5 x))
+        (is (= 5 y))
+        (is (eql #\X (cell-char cell)))))))
+
+(test with-scissor-clips-drawing
+  (let ((fb (make-framebuffer-backend :width 20 :height 10)))
+    (with-scissor (fb 5 5 3 3)
+      (draw-text fb 6 6 "ABC" nil nil)
+      (draw-text fb 1 1 "OUTSIDE" nil nil))
+    (let ((cells (fb-framebuffer fb)))
+      (is (eql #\A (cell-char (aref cells 6 6))) "inside scissor draws")
+      (is (eql #\space (cell-char (aref cells 1 1))) "outside scissor is clipped"))))
+
+(test flush-fb-copies-to-backend
+  (let* ((real-be (make-simple-backend :output-stream (make-string-output-stream)))
+         (fb (make-framebuffer-backend)))
+    (draw-text fb 0 0 "X" :red nil)
+    (let ((changed (flush-framebuffer (make-framebuffer 80 24) (fb-framebuffer fb) real-be)))
+      (is (>= changed 1)))))
+#+END_SRC
+
+* Implementation
+
+** Package and data structures
+
+#+BEGIN_SRC lisp :tangle ../src/rendering/framebuffer.lisp
+(defpackage :cl-tty.rendering
+  (:use :cl :cl-tty.backend)
+  (:export
+   #:cell #:make-cell #:cell-char #:cell-fg #:cell-bg
+   #:cell-bold #:cell-italic #:cell-underline #:cell-link-url
+   #:framebuffer-backend #:make-framebuffer-backend
+   #:make-framebuffer #:fb-framebuffer
+   #:framebuffer-width #:framebuffer-height
+   #:diff-framebuffers #:flush-framebuffer
+   #:with-scissor))
+#+END_SRC
+
+#+BEGIN_SRC lisp :tangle ../src/rendering/framebuffer.lisp
+(in-package :cl-tty.rendering)
+
+;;; ─── Cell — immutable per-cell state ─────────────────────────────────────────
+
+(defstruct cell
+  "A single terminal cell — character, colors, and attributes."
+  (char #\space :type character)
+  (fg nil)
+  (bg nil)
+  (bold nil :type boolean)
+  (italic nil :type boolean)
+  (underline nil :type boolean)
+  (link-url nil))
+
+;;; ─── Framebuffer — 2D array of cells ────────────────────────────────────────
+
+(defun make-framebuffer (width height)
+  "Create a 2D array of CELL with dimensions HEIGHT x WIDTH."
+  (make-array (list height width)
+              :initial-element (make-cell)
+              :element-type 'cell))
+
+(defun framebuffer-width (fb)
+  "Return the width (columns) of framebuffer FB."
+  (if (arrayp fb) (array-dimension fb 1) 0))
+
+(defun framebuffer-height (fb)
+  "Return the height (rows) of framebuffer FB."
+  (if (arrayp fb) (array-dimension fb 0) 0))
+
+;;; ─── Framebuffer Backend — implements backend protocol ─────────────────────
+
+(defclass framebuffer-backend (backend)
+  ((framebuffer :initform nil :accessor fb-framebuffer)
+   (scissor-x :initform 0 :accessor fb-scissor-x)
+   (scissor-y :initform 0 :accessor fb-scissor-y)
+   (scissor-w :initform nil :accessor fb-scissor-w)
+   (scissor-h :initform nil :accessor fb-scissor-h)))
+
+(defun make-framebuffer-backend (&key (width 80) (height 24))
+  "Create a framebuffer-backend with a fresh framebuffer."
+  (let ((fb (make-instance 'framebuffer-backend)))
+    (setf (fb-framebuffer fb) (make-framebuffer width height))
+    fb))
+#+END_SRC
+
+** Drawing methods
+
+#+BEGIN_SRC lisp :tangle ../src/rendering/framebuffer.lisp
+;;; ─── Drawing methods ─────────────────────────────────────────────────────────
+
+(defun %in-scissor-p (fb cx cy)
+  "Check if (CX, CY) falls within the current scissor rectangle."
+  (let ((sx (fb-scissor-x fb)) (sy (fb-scissor-y fb))
+        (sw (fb-scissor-w fb)) (sh (fb-scissor-h fb)))
+    (and (or (null sw) (and (>= cx sx) (< cx (+ sx sw))))
+         (or (null sh) (and (>= cy sy) (< cy (+ sy sh)))))))
+
+(defun %set-cell (fb x y char &key fg bg bold italic underline link-url)
+  "Set cell (X, Y) if within bounds and scissor."
+  (let ((cells (fb-framebuffer fb)))
+    (when (and (>= y 0) (< y (framebuffer-height cells))
+               (>= x 0) (< x (framebuffer-width cells))
+               (%in-scissor-p fb x y))
+      (setf (aref cells y x)
+            (make-cell :char char :fg fg :bg bg
+                       :bold bold :italic italic :underline underline
+                       :link-url link-url)))))
+
+(defmethod draw-text ((fb framebuffer-backend) x y string fg bg &rest attrs)
+  (loop for i from 0 below (length string)
+        do (%set-cell fb (+ x i) y (char string i)
+                      :fg fg :bg bg
+                      :bold (getf attrs :bold)
+                      :italic (getf attrs :italic)
+                      :underline (getf attrs :underline)
+                      :link-url (getf attrs :link-url))))
+
+(defmethod draw-rect ((fb framebuffer-backend) x y w h &key fg bg style)
+  (declare (ignore style))
+  (dotimes (row h)
+    (dotimes (col w)
+      (%set-cell fb (+ x col) (+ y row) #\space :fg fg :bg bg))))
+
+(defmethod draw-border ((fb framebuffer-backend) x y w h &key (style :single) title title-align fg bg)
+  (let* ((chars (case style
+                  (:single '(#\+ #\- #\|))
+                  (:double '(#\+ #\= #\|))
+                  (:rounded '(#\. #\- #\|))
+                  (t '(#\+ #\- #\|))))
+         (tc (first chars)) (hc (second chars)) (vc (third chars)))
+    ;; Top edge
+    (%set-cell fb x y tc :fg fg :bg bg)
+    (loop for i from 1 below (1- w) do (%set-cell fb (+ x i) y hc :fg fg :bg bg))
+    (%set-cell fb (1- (+ x w)) y tc :fg fg :bg bg)
+    ;; Sides
+    (dotimes (row (- h 2))
+      (%set-cell fb x (+ y row 1) vc :fg fg :bg bg)
+      (%set-cell fb (1- (+ x w)) (+ y row 1) vc :fg fg :bg bg))
+    ;; Bottom edge
+    (%set-cell fb x (+ y h -1) tc :fg fg :bg bg)
+    (loop for i from 1 below (1- w) do (%set-cell fb (+ x i) (+ y h -1) hc :fg fg :bg bg))
+    (%set-cell fb (1- (+ x w)) (+ y h -1) tc :fg fg :bg bg)
+    ;; Title
+    (when title
+      (loop for i from 0 below (length title)
+            do (%set-cell fb (+ x 2 i) y (char title i) :fg fg :bg bg)))))
+
+(defmethod backend-clear ((fb framebuffer-backend))
+  (let ((cells (fb-framebuffer fb)))
+    (dotimes (y (framebuffer-height cells))
+      (dotimes (x (framebuffer-width cells))
+        (setf (aref cells y x) (make-cell))))))
+#+END_SRC
+
+** Diff and flush
+
+#+BEGIN_SRC lisp :tangle ../src/rendering/framebuffer.lisp
+(defmethod draw-link ((fb framebuffer-backend) x y string url &key fg bg)
+  ;; OSC 8 links are not rendered in framebuffer — store as text
+  (draw-text fb x y string fg bg :link-url url))
+
+(defmethod draw-ellipsis ((fb framebuffer-backend) x y width &key fg bg)
+  (dotimes (i (min 3 width))
+    (%set-cell fb (+ x i) y #\. :fg fg :bg bg)))
+
+;;; ─── Diff ────────────────────────────────────────────────────────────────────
+
+(defun cells-equal-p (a b)
+  "Return T if two cells have identical content and style."
+  (and (eql (cell-char a) (cell-char b))
+       (eql (cell-fg a) (cell-fg b))
+       (eql (cell-bg a) (cell-bg b))
+       (eql (cell-bold a) (cell-bold b))
+       (eql (cell-italic a) (cell-italic b))
+       (eql (cell-underline a) (cell-underline b))
+       (equal (cell-link-url a) (cell-link-url b))))
+
+(defun diff-framebuffers (prev curr)
+  "Compare PREV and CURR framebuffers. Return list of (X Y CELL) for changes."
+  (let ((changes nil)
+        (h (min (framebuffer-height prev) (framebuffer-height curr)))
+        (w (min (framebuffer-width prev) (framebuffer-width curr))))
+    (dotimes (y h)
+      (dotimes (x w)
+        (let ((a (aref prev y x)) (b (aref curr y x)))
+          (unless (cells-equal-p a b)
+            (push (list x y b) changes)))))
+    (nreverse changes)))
+
+;;; ─── Flush ───────────────────────────────────────────────────────────────────
+
+(defun flush-framebuffer (prev-fb curr-fb backend)
+  "Diff PREV-FB and CURR-FB and flush changes to BACKEND.
+Returns the number of changed cells."
+  (let* ((changes (diff-framebuffers prev-fb curr-fb))
+         (count (length changes))
+         (current-row -1))
+    (when (plusp count)
+      (begin-sync backend)
+      (dolist (change changes)
+        (destructuring-bind (x y cell) change
+          (unless (= y current-row)
+            (cursor-move backend x y)
+            (setf current-row y))
+          (draw-text backend x y (string (cell-char cell))
+                     (cell-fg cell) (cell-bg cell)
+                     :bold (cell-bold cell)
+                     :italic (cell-italic cell)
+                     :underline (cell-underline cell))))
+      (end-sync backend))
+    count))
+#+END_SRC
+
+** Scissor clipping
+
+#+BEGIN_SRC lisp :tangle ../src/rendering/framebuffer.lisp
+;;; ─── Scissor clipping ────────────────────────────────────────────────────────
+
+(defmacro with-scissor ((fb x y w h) &body body)
+  "Clip all drawing on FB to rectangle (X Y W H)."
+  (let ((old-x (gensym)) (old-y (gensym))
+        (old-w (gensym)) (old-h (gensym)))
+    `(let ((,old-x (fb-scissor-x ,fb))
+           (,old-y (fb-scissor-y ,fb))
+           (,old-w (fb-scissor-w ,fb))
+           (,old-h (fb-scissor-h ,fb)))
+       (setf (fb-scissor-x ,fb) ,x
+             (fb-scissor-y ,fb) ,y
+             (fb-scissor-w ,fb) ,w
+             (fb-scissor-h ,fb) ,h)
+       (unwind-protect (progn ,@body)
+         (setf (fb-scissor-x ,fb) ,old-x
+               (fb-scissor-y ,fb) ,old-y
+               (fb-scissor-w ,fb) ,old-w
+               (fb-scissor-h ,fb) ,old-h)))))
+#+END_SRC