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typesetting/quad/quadwriter/layout.rkt

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Racket

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#lang debug racket/base
(require racket/promise
racket/match
racket/list
sugar/list
txexpr/base
racket/date
pitfall
quad
racket/unsafe/ops
"attrs.rkt"
"param.rkt"
"font.rkt"
"log.rkt")
(provide (all-defined-out))
(define-quad string-quad quad ())
(define (q:string-draw q doc)
(when (pair? (quad-elems q))
(font doc (path->string (quad-ref q font-path-key default-font-face)))
(font-size doc (quad-ref q :font-size default-font-size))
(fill-color doc (quad-ref q :font-color default-font-color))
(define str (unsafe-car (quad-elems q)))
(match-define (list x y) (quad-origin q))
(text doc str x y
#:tracking (quad-ref q :font-tracking 0)
#:bg (quad-ref q :bg)
#:features (quad-ref q :font-features default-font-features)
#:link (quad-ref q :link))))
(define (q:string-draw-end q doc)
(when (draw-debug-string?)
(draw-debug q doc "#99f" "#ccf")))
(define (q:string-printable? q [sig #f])
;; printable unless single space, which is not printable at start or end
(match (quad-elems q)
[(cons elem _)
(case elem
[(" " #\space) (not (memq sig '(start end)))]
[else #true])]
[_ #true]))
(define q:string (q #:type string-quad
#:from 'bo
#:to 'bi
#:id 'str
#:printable q:string-printable?
#:draw q:string-draw
#:draw-end q:string-draw-end))
(define-quad image-quad quad ())
(define (q:image-draw q doc)
(define img (quad-ref q :image-object))
(match-define (list x y) (quad-origin q))
(match-define (list w h) (size q))
(image doc img x y
#:width w
#:height h))
(define (q:image-draw-end q doc)
(when (draw-debug-image?)
(draw-debug q doc "orange" "orange")))
(define q:image (q #:type image-quad
#:from 'bo
#:to 'bi
#:id 'image
#:printable #true
#:draw q:image-draw
#:draw-end q:image-draw-end))
(define (make-size-promise q [str-arg #f])
(delay
(define pdf (current-pdf))
(define str
(cond
[str-arg]
[(pair? (quad-elems q)) (unsafe-car (quad-elems q))]
[else #false]))
(define string-size
(cond
[str
(font-size pdf (quad-ref q :font-size default-font-size))
(font pdf (path->string (quad-ref q font-path-key default-font-face)))
(if (equal? str "\u00AD")
(quad-ref q :font-tracking 0)
(+ (string-width pdf str
#:tracking (quad-ref q :font-tracking 0)
#:features (quad-ref q :font-features default-font-features))))]
[else 0]))
(list string-size (quad-ref q :line-height (current-line-height pdf)))))
(define (generic->typed-quad q)
(cond
[(line-break-quad? q) q]
[(match (quad-ref q :image-file)
[#false #false]
[(? file-exists? path-string)
(define img-obj (open-image (current-pdf) path-string))
(define img-width ($img-width img-obj))
(define img-height ($img-height img-obj))
(match-define (list layout-width layout-height)
(match (list (quad-ref q :image-width) (quad-ref q :image-height))
[(list (? number? w) (? number? h)) (list w h)]
[(list #false (? number? h)) (define ratio (/ h img-height))
(list (* ratio img-width) h)]
[(list (? number? w) #false) (define ratio (/ w img-width))
(list w (* ratio img-height))]
[(list #false #false) (list img-width img-height)]))
(struct-copy
image-quad q:image
[attrs #:parent quad (let ([h (hash-copy (quad-attrs q))])
;; defeat 'bi 'bo positioning by removing font reference
(hash-set! h font-path-key #false)
;; save the img-obj for later
(hash-set! h :image-object img-obj)
h)]
[size #:parent quad (pt layout-width layout-height)])]
[bad-path (raise-argument-error 'quadwriter "image path that exists" bad-path)])]
[else
(struct-copy
string-quad q:string
[attrs #:parent quad (let ([attrs (quad-attrs q)])
(hash-ref! attrs :font-size default-font-size)
attrs)]
[elems #:parent quad (quad-elems q)]
[size #:parent quad (make-size-promise q)])]))
(define (draw-debug q doc [fill-color "#f99"] [stroke-color "#fcc"] [stroke-width 0.5])
(when (draw-debug?)
(save doc)
;; draw layout box
(line-width doc stroke-width)
; subtracting stroke-width keeps adjacent boxes from overlapping
(save doc)
(apply rect doc (append (pt+ (quad-origin q)) (map (λ (x) (- x stroke-width)) (size q))))
(clip doc)
(define pt (to-point q))
(circle doc (pt-x pt) (pt-y pt) (+ 3 stroke-width))
(fill doc fill-color)
(restore doc)
(apply rect doc (append (pt+ (quad-origin q)) (map (λ (x) (- x stroke-width)) (size q))))
(stroke doc stroke-color)
(restore doc)))
(define-quad line-break-quad quad ())
(define q:line-break (make-line-break-quad #:printable #f
#:id 'line-break))
(define-quad para-break-quad line-break-quad ())
(define q:para-break (make-para-break-quad #:printable #f
#:id 'para-break))
(define-quad hr-break-quad line-break-quad ())
(define q:hr-break (make-hr-break-quad #:printable #t
#:id 'hr-break))
(define-quad column-break-quad line-break-quad ())
(define q:column-break (make-column-break-quad #:printable #f
#:id 'column-break))
(define-quad page-break-quad column-break-quad ())
(define q:page-break (make-page-break-quad #:printable #f
#:id 'page-break))
(define q:line (q #:size (pt 0 default-line-height)
#:from 'sw
#:to 'nw
#:printable #true
#:id 'line
#:draw-start (if draw-debug-line? draw-debug void)))
(define-quad line-spacer-quad line-break-quad ())
(define only-prints-in-middle (λ (q sig) (not (memq sig '(start end)))))
(define (make-paragraph-spacer maybe-first-line-q key default-val)
(define arbitrary-width 20)
(q #:type line-spacer-quad
#:size (pt arbitrary-width (cond
[(and maybe-first-line-q (quad-ref maybe-first-line-q key))]
[else default-val]))
#:from 'sw
#:to 'nw
#:printable only-prints-in-middle
#:draw-start (if (draw-debug-line?) draw-debug void)))
(define softies (map string '(#\space #\- #\u00AD)))
(define (soft-break-for-line? q)
(and (pair? (quad-elems q))
(member (unsafe-car (quad-elems q)) softies)))
(define (consolidate-runs pcs ending-q)
(let loop ([runs empty][pcs pcs])
(match pcs
[(? empty?) (reverse runs)]
[(cons (? string-quad? strq) rest)
(define-values (run-pcs rest) (splitf-at pcs (λ (p) (same-run? strq p))))
(define new-run (quad-copy q:string
[attrs (quad-attrs strq)]
[elems (merge-adjacent-strings (apply append (for/list ([pc (in-list run-pcs)])
(quad-elems pc))))]
[size (delay (pt (for/sum ([pc (in-list run-pcs)])
(pt-x (size pc)))
(pt-y (size strq))))]))
(loop (cons new-run runs) rest)]
[(cons first rest) (loop (cons first runs) rest)])))
(define (render-hyphen qs ending-q)
;; naive handling of soft hyphen:
;; if soft hyphen cause the break, then append a printing hyphen to the end of the run.
;; this assumes that there is room for the hyphen on the line
;; and does not take into account hyphen-break transformations found in other languages.
;; However we do want the hyphen joined into the string so the final shaping / positioning is correct
;; for instance, kerning between last letter and hyphen.
(match (and ending-q (equal? (quad-elems ending-q) '("\u00AD")) qs)
[(list head ... last-q)
(define str (car (quad-elems last-q)))
(define str+hyphen (string-append str "-"))
(append head
(list (quad-copy last-q
[elems (list str+hyphen)]
[size (make-size-promise last-q str+hyphen)])))]
[_ qs]))
(module+ test
(require rackunit)
(check-true (line-break-quad? (second (quad-elems (q "foo" q:page-break "bar")))))
(check-true (line-break-quad? (second (atomize (q "foo" q:page-break "bar"))))))
(define-quad filler-quad quad ())
(define (sum-of-widths qss)
(for*/sum ([qs (in-list qss)]
[q (in-list qs)])
(pt-x (size q))))
(define (space-quad? q) (equal? (quad-elems q) (list " ")))
(define (fill-wrap qs ending-q line-q)
(match (and (pair? qs) (quad-ref (car qs) (if ending-q
:line-align
:line-align-last) "left"))
[align-value
;; words may still be in hyphenated fragments
;; (though soft hyphens would have been removed)
;; so group them (but no need to consolidate — that happens elsewhere)
(define-values (word-space-sublists word-sublists) (partition* space-quad? qs))
(match (length word-sublists)
[1 #:when (equal? align-value "justify") qs] ; can't justify single word
[word-count
(match-define (list line-width line-height) (quad-size line-q))
(define hung-word-sublists
(match word-sublists
[(list sublists ... (list prev-qs ... last-q))
#:when (pair? (quad-elems last-q))
(define last-char-str (regexp-match #rx"[.,:;-]$" (car (quad-elems last-q))))
(match last-char-str
[#false word-sublists]
[_ (define hanger-q (quad-copy last-q
[elems null]
[size (let ([p (make-size-promise last-q (car last-char-str))])
(delay
(match-define (list x y) (force p))
(pt (- x) y)))]))
(define last-sublist (append prev-qs (list last-q hanger-q)))
(append sublists (list last-sublist))])]
[_ word-sublists]))
(define word-width (sum-of-widths hung-word-sublists))
(define word-space-width (sum-of-widths word-space-sublists))
(define empty-hspace (- line-width
(quad-ref (car qs) :inset-left 0)
word-width
(quad-ref (car qs) :inset-right 0)))
(define line-overfull? (negative? (- empty-hspace word-space-width)))
(cond
[(or (equal? align-value "justify")
;; force justification upon overfull lines
(and line-overfull? (> word-count 1)))
(define justified-space-width (/ empty-hspace (sub1 word-count)))
(apply append (add-between hung-word-sublists (list (make-quad
#:from 'bo
#:to 'bi
#:draw-end q:string-draw-end
#:size (pt justified-space-width line-height)))))]
[(equal? align-value "left") qs] ; no filling needed
[else
(define space-multiplier (match align-value
["center" 0.5]
["right" 1]))
;; subtact space-width because that appears between words
;; we only care about redistributing the space on the ends
(define end-hspace (- empty-hspace word-space-width))
; make filler a leading quad, not a parent / grouping quad,
;; so that elements can still be reached by consolidate-runs
(list* (make-quad #:type filler-quad
#:from-parent (quad-from-parent (car qs))
#:from 'bo
#:to 'bi
#:size (pt (* end-hspace space-multiplier) 0)
#:attrs (quad-attrs (car qs)))
(quad-copy (car qs) [from-parent #f])
(cdr qs))])])]))
(define-quad offsetter-quad quad ())
(define (hr-draw dq doc)
(match-define (list left top) (quad-origin dq))
(match-define (list right bottom) (size dq))
(save doc)
(translate doc left (+ top (/ bottom 2)))
(move-to doc 0 0)
(line-to doc right 0)
(line-width doc 0.5)
(stroke doc "black")
(restore doc))
(define (make-hr-quad line-q)
(quad-copy line-q [draw-start hr-draw]))
(define ((finish-line-wrap line-q) pcs-in opening-q ending-q idx)
;; we curry line-q so that the wrap size can be communicated to this operation
;; remove unused soft hyphens so they don't affect final shaping
(define pcs-printing (for/list ([pc (in-list pcs-in)]
#:unless (equal? (quad-elems pc) '("\u00AD")))
pc))
(define new-lines
(cond
[(empty? pcs-printing) null]
[(hr-break-quad? ending-q) (list (make-hr-quad line-q))]
[else
;; render hyphen first so that all printable characters are available for size-dependent ops.
(define pcs-with-hyphen (render-hyphen pcs-printing ending-q))
;; fill wrap so that consolidate-runs works properly
;; (justified lines won't be totally consolidated)
(define pcs (fill-wrap pcs-with-hyphen ending-q line-q))
(match (consolidate-runs pcs ending-q)
[(? pair? elems)
(define elem (unsafe-car elems))
(match-define (list line-width line-height) (quad-size line-q))
(define new-size (let ()
(define line-heights
(filter-map (λ (q) (or (quad-ref q :line-height) (pt-y (size q)))) pcs))
(pt line-width (if (empty? line-heights) line-height (apply max line-heights)))))
(list
(struct-copy
quad line-q
;; move block attrs up, so they are visible in col wrap
[attrs (copy-block-attrs (quad-attrs elem)
(hash-copy (quad-attrs line-q)))]
;; line width is static
;; line height is the max 'line-height value or the natural height of q:line
[size new-size]
;; handle list indexes. drop new quad into line to hold list index
;; could also use this for line numbers
[elems
;; we assume here that a list item has already had extra inset-left
;; with room for a bullet
;; which we just insert at the front.
;; this is safe because line has already been filled.
(append
;; only put bullet into line if we're at the first line of the list item
(match (and (eq? idx 1) (quad-ref elem :list-index))
[#false null]
[bullet
(define bq (struct-copy
quad q:string ;; copy q:string to get draw routine
;; borrow attrs from elem
[attrs (quad-attrs elem)]
;; use bullet as elems
[elems (list (if (number? bullet) (format "~a." bullet) bullet))]
;; size doesn't matter because nothing refers to this quad
;; just for debugging box
[size (pt 15 (pt-y (size line-q)))]))
(from-parent (list bq) 'sw)])
(from-parent
(match (quad-ref elem :inset-left 0)
[0 elems]
[inset-val
(cons (make-quad
#:draw-end q:string-draw-end
#:to 'sw
#:size (pt inset-val 5)
#:type offsetter-quad)
elems)]) 'sw))]))]
[_ null])]))
(define maybe-first-line (match new-lines [(cons line0 _) line0][_ #false]))
(append (match opening-q
[#false (list (make-paragraph-spacer maybe-first-line :space-before 0))] ; paragraph break
[_ null])
new-lines
(match ending-q
[(? page-break-quad? page-break) (list page-break)] ; hard page break
[#false (list (make-paragraph-spacer maybe-first-line :space-after (* default-line-height 0.6)))] ; paragraph break
[_ null]))) ; hard line break
(define (line-wrap qs wrap-size)
(match qs
[(? null?) null]
[_
(unless (positive? wrap-size)
(raise-argument-error 'line-wrap "positive number" wrap-size))
(define line-q (quad-copy q:line [size (pt wrap-size (pt-y (size q:line)))]))
(define permitted-justify-overfill
(match (quad-ref (car qs) :line-align)
;; allow justified lines to go wider,
;; and then fill-wrap will tighten thes word spaces
;; this makes justified paragraphs more even, becuase
;; some lines are a little tight, as opposed to all of them being loose
["justify" 1.04]
[_ 1]))
(apply append
;; next line removes all para-break? quads as a consequence
(for/list ([qs (in-list (filter-split qs para-break-quad?))])
(wrap qs
(λ (q idx) (* (- wrap-size
(quad-ref (car qs) :inset-left 0)
(quad-ref (car qs) :inset-right 0))
permitted-justify-overfill))
#:nicely (match (or (current-line-wrap) (quad-ref (car qs) :line-wrap))
[(or "best" "kp") #true]
[_ #false])
#:hard-break line-break-quad?
#:soft-break soft-break-for-line?
#:finish-wrap (finish-line-wrap line-q))))]))
(define (make-nobreak! q) (quad-set! q :no-colbr #true)) ; cooperates with col-wrap
(define (do-keep-with-next! reversed-lines)
;; paints nobreak onto spacers that follow keep-with-next lines
;; (we are iterating backward, so the geometrically previous ln follows the spacer)
(match reversed-lines
[(? null?) null]
[_ (for ([this-ln (in-list reversed-lines)]
[prev-ln (in-list (cdr reversed-lines))]
#:when (and (line-spacer-quad? this-ln)
(quad-ref prev-ln :keep-with-next)))
(make-nobreak! this-ln)
(make-nobreak! prev-ln))]))
(define (apply-keeps lines)
(define groups-of-lines (contiguous-group-by (λ (x) (quad-ref x :display)) lines))
(for*/fold ([reversed-lines null]
#:result (begin
(do-keep-with-next! reversed-lines)
(reverse reversed-lines)))
([group (in-list groups-of-lines)]
[group-len (in-value (length group))]
[(ln idx0) (in-indexed group)])
(define idx (add1 idx0))
;; always catch last line of block in this case
;; so later cases are guaranteed to have earlier lines.
(unless (eq? idx group-len)
(cond
;; if we have :keep-all we can skip :keep-first and :keep-last cases
[(quad-ref ln :keep-all-lines) (make-nobreak! ln)]
;; to keep n lines, we only paint the first n - 1
;; (because each nobr line sticks to the next)
[(let ([keep-first (quad-ref ln :keep-first-lines)])
(and (number? keep-first) (< idx keep-first)))
(make-nobreak! ln)]
[(let ([keep-last (quad-ref ln :keep-last-lines)])
(and (number? keep-last) (< (- group-len keep-last) idx)))
(make-nobreak! ln)]))
(cons ln reversed-lines)))
(define (page-draw-start q doc)
(add-page doc)
(scale doc (zoom-factor) (zoom-factor))
(draw-debug q doc "aliceblue" "aliceblue" 3))
(define (draw-page-footer q doc)
(match-define (list x y) (quad-origin q))
(font-size doc (* .8 default-font-size))
(font doc default-font-face)
(fill-color doc default-font-color)
(text doc (format "~a · ~a at ~a" (quad-ref q :page-number 0)
(quad-ref q :doc-title "untitled")
(date->string (current-date) #t))
x y))
(define (make-footer-quad col-q page-idx path)
(define-values (dir name _) (split-path (path-replace-extension path #"")))
(q #:size (pt 50 default-line-height)
#:attrs (hasheq :page-number (+ (quad-ref col-q :page-number-start 1) (sub1 page-idx))
:doc-title (string-titlecase (path->string name)))
#:from-parent 'sw
#:to 'nw
#:shift (pt 0 (* 1.5 default-line-height))
#:printable #true
#:draw-start (λ (q doc)
(when draw-debug-line?
(draw-debug q doc "goldenrod" "goldenrod"))
(unless (quadwriter-test-mode)
(draw-page-footer q doc)))))
(define q:column (q
#:id 'col
#:from 'ne
#:to 'nw))
(struct column-spacer-quad quad () #:transparent)
(define q:column-spacer (q #:type column-spacer-quad
#:from 'ne
#:to 'nw
#:printable only-prints-in-middle))
(define q:page (q
#:id 'page
#:from-parent 'nw
#:draw-start page-draw-start))
(define q:doc (q #:draw-start (λ (q doc) (start-doc doc))
#:draw-end (λ (q doc) (end-doc doc))))
(define ((block-draw-start first-line) q doc)
;; adjust drawing coordinates for border inset
(match-define (list bil bit bir bib)
(for/list ([k (in-list (list :border-inset-left :border-inset-top :border-inset-right :border-inset-bottom))])
(quad-ref first-line k 0)))
(match-define (list left top) (pt+ (quad-origin q) (list bil bit)))
(match-define (list width height) (pt- (size q) (list (+ bil bir) (+ bit bib))))
;; fill rect
(cond
[(quad-ref first-line :background-color)
=> (λ (bgcolor)
(rect doc left top width height)
(fill doc bgcolor))])
;; draw border
(match-define (list bw-left bw-top bw-right bw-bottom)
(map (λ (k) (max 0 (quad-ref first-line k 0))) (list
:border-width-left
:border-width-top
:border-width-right
:border-width-bottom)))
;; adjust start and end points based on adjacent border width
;; so all borders overlap rectangularly
(define (half x) (/ x 2.0))
(define right (+ left width))
(define bottom (+ top height))
(define (box-side x1 y1 x2 y2 color stroke-width)
(when (positive? stroke-width)
(move-to doc x1 y1)
(line-to doc x2 y2)
(stroke doc (or color "black") stroke-width)))
(box-side (- left (half bw-left)) top (+ right (half bw-right)) top
(quad-ref first-line :border-color-top) bw-top)
(box-side right (- top (half bw-top)) right (+ bottom (half bw-bottom))
(quad-ref first-line :border-color-right) bw-right)
(box-side (+ right (half bw-right)) bottom (- left (half bw-left)) bottom
(quad-ref first-line :border-color-bottom) bw-bottom)
(box-side left (+ bottom (half bw-bottom)) left (- top (half bw-top))
(quad-ref first-line :border-color-left) bw-left)
(case (quad-ref first-line :block-clip)
[(#true)
(when (eq? (log-clipping?) 'warn)
(for ([line (in-list (quad-elems q))])
(define line-width (pt-x (size line)))
(define line-elem-width (for/sum ([q (in-list (quad-elems line))])
(pt-x (size q))))
(when (< line-width line-elem-width)
(define error-str (apply string-append (for/list ([q (in-list (quad-elems line))])
(match (quad-elems q)
[(list (? string? str)) str]
[_ ""]))))
(log-quadwriter-warning (format "clipping overfull line: ~v" error-str)))))
(save doc)
(rect doc left top width height)
(clip doc)]))
(define ((block-draw-end first-line) q doc)
(case (quad-ref first-line :block-clip)
[(#true) (restore doc)])
(when (draw-debug-block?)
(draw-debug q doc "#6c6" "#9c9")))
(define/match (lines->block lines)
[((cons ln0 _))
(q #:from 'sw
#:to 'nw
#:elems (from-parent lines 'nw)
#:id 'block
#:attrs (quad-attrs ln0)
#:size (delay (pt (pt-x (size ln0)) ;
(+ (for/sum ([line (in-list lines)])
(pt-y (size line)))
(quad-ref ln0 :inset-top 0)
(quad-ref ln0 :inset-bottom 0))))
#:shift-elems (pt 0 (+ (quad-ref ln0 :inset-top 0)))
#:draw-start (block-draw-start ln0)
#:draw-end (block-draw-end ln0))])
(define/match (from-parent qs [where #f])
;; doesn't change any positioning. doesn't depend on state. can happen anytime.
;; can be repeated without damage.
[((? null?) _) null]
[((cons q rest) where)
(cons (quad-copy q [from-parent (or where (quad-from q))]) rest)])
(define ((col-finish-wrap col-quad) lns . _)
(match lns
[(cons first-line _)
(list (quad-copy col-quad
;; move block attrs up, so they are visible in page wrap
[attrs (copy-block-attrs (quad-attrs first-line)
(hash-copy (quad-attrs col-quad)))]
[elems (from-parent (insert-blocks lns) 'nw)]))]
[_ null]))
(define (column-wrap qs vertical-height column-gap [column-quad q:column])
(unless (positive? vertical-height)
(raise-argument-error 'col-wrap "positive number" vertical-height))
;; on timing of `insert-blocks`:
;; can't do it before because it depends on where columns are broken.
;; could do it after, but it would require going back inside each col quad
;; which seems overly interdependent, because `insert-blocks` is used to determine break locations.
;; `col-wrap` should emit quads that are complete.
(define col-spacer (quad-copy q:column-spacer [size (pt column-gap 100)]))
(add-between
(wrap qs vertical-height
#:soft-break #true
#:hard-break column-break-quad?
#:no-break (λ (q) (quad-ref q :no-colbr)) ; cooperates with make-nobreak
#:distance (λ (q dist-so-far wrap-qs)
;; do trial block insertions
(for/sum ([x (in-list (insert-blocks wrap-qs))])
(pt-y (size x))))
#:finish-wrap (col-finish-wrap column-quad))
col-spacer))
(define ((page-finish-wrap page-quad path) cols q0 q page-idx)
(define elems
(match (quad-ref (car cols) :footer-display #true)
[(or #false "none") (from-parent cols 'nw)]
[_ (cons (make-footer-quad (car cols) page-idx path) (from-parent cols 'nw))]))
(list (quad-copy page-quad [elems elems])))
(define (page-wrap qs width [page-quad q:page])
(unless (positive? width)
(raise-argument-error 'page-wrap "positive number" width))
(wrap qs width
#:soft-break #true
#:hard-break page-break-quad?
#:no-break (λ (q) (quad-ref q :no-pbr))
#:distance (λ (q dist-so-far wrap-qs)
(for/sum ([x (in-list wrap-qs)])
(pt-x (size x))))
#:finish-wrap (page-finish-wrap page-quad (pdf-output-path (current-pdf)))))
(define (insert-blocks lines)
(define groups-of-lines (contiguous-group-by (λ (x) (quad-ref x :display)) lines))
(append* (for/list ([line-group (in-list groups-of-lines)])
(if (quad-ref (car line-group) :display)
(list (lines->block line-group))
line-group))))
(define-quad first-line-indent-quad quad ())
(define (insert-first-line-indents qs-in)
;; first line indents are quads inserted at the beginning of a paragraph
;; (that is, just after a paragraph break)
;; they need to be installed before line wrap
;; to be compatible with first-fit and best-fit.
;; stick a pbr on the front if there isn't one already
;; because of the "lookahead" style of iteration
(define qs (match qs-in
[(list (? para-break-quad?) _ ...) qs-in]
[_ (cons q:page-break qs-in)]))
(for/fold ([qs-out null]
#:result (reverse qs-out))
([q (in-list qs)]
[next-q (in-list (cdr qs))])
(match (and (para-break-quad? q) (quad-ref next-q :first-line-indent 0))
[(or #false 0) (cons next-q qs-out)]
[indent-val (list* next-q (make-quad #:from 'bo
#:to 'bi
#:draw-end q:string-draw-end
#:type first-line-indent-quad
#:attrs (quad-attrs next-q)
#:size (pt indent-val 10)) qs-out)])))