Easing in and out of center using a sin function

Each credit has its own draw function

Credits outside of the visible game area are not drawn

game.js

@@ -81,7 +81,12 @@ window.addEventListener("load", async () => {
           translate: (ctx, x, y) => ctx.translate(x, y),
           rotate: (ctx, angle) => ctx.rotate(angle),
           setTransform: (ctx, a, b, c, d, e, f) => ctx.setTransform(a, b, c, d, e, f),
-          setImageSmoothingEnabled: (ctx, enabled) => ctx.imageSmoothingEnabled = (enabled == 1)
+          setImageSmoothingEnabled: (ctx, enabled) => ctx.imageSmoothingEnabled = (enabled == 1),
+          measureText: (ctx, text) => ctx.measureText(text),
+        },
+        textMetrics: {
+          actualBoundingBoxAscent: (metrics) => metrics.actualBoundingBoxAscent,
+          actualBoundingBoxDescent: (metrics) => metrics.actualBoundingBoxDescent,
         },
         math: {
           random: () => Math.random()

game.scm

@@ -20,6 +20,7 @@
 ;;; Code:
 
 (use-modules (dom canvas)
+             (dom text-metrics)
              (dom document)
              (dom element)
              (dom event)
@@ -62,7 +63,8 @@
              (math)
              (math rect)
              (math vector)
-             (scheme base))
+             (scheme base)
+             (srfi srfi-1))
 
 (define game-width 320.0)
 (define game-height 240.0)
@@ -225,14 +227,6 @@
    (set! *level* ((vector-ref levels idx) (collected-gem? idx)))
    (update-objects!)))
 
-(define (load-credits!)
-  (replace-game-state! 'credits)
-  (set! *actormap* (make-whactormap))
-  (set-vec2-y! *credits-scroll* 0.0)
-  (clear-snapshots!)
-  (with-goblins
-   (set! *level* (load-credits #f))
-   (update-objects!)))
 
 (define (load-level! idx)
     ;; TODO: Maybe show a little achievement popup when all gems
@@ -287,6 +281,8 @@
        (set-level! *level-idx*)
        (media-play audio:bg-music)))))
 
+(define text-offset-y (* 0.75 tile-height))
+
 ;; Menu types
 
 (define-record-type <menu>
@@ -396,6 +392,251 @@
       (pop-menu-history!)
       ((cdr (vector-ref (menu-items (current-menu)) (current-menu-index))))))
 
+
+;; Credits
+
+(define credits-margin 0.0) ;; lines
+(define credits-pace 15.0) ;; ticks per line (inverse speed)
+(define credits-start (+ game-height text-offset-y))
+(define credits-end text-offset-y)
+
+(define line-height
+  (let ((lh #f))
+    (lambda ()
+      (unless lh
+        (set-font! context "normal 16px monogram")
+        (let ((metrics (measure-text context "Aj")))
+          (set! lh
+                (* (+ (text-metrics-actual-bounding-box-ascent metrics)
+                      (text-metrics-actual-bounding-box-descent metrics))
+                   1.25))))
+      lh)))
+
+(define-record-type <credit>
+  (_make-credit lines draw update on-enter on-leave)
+  credit?
+  (lines credit-lines)
+  (draw credit-draw)
+  (update credit-update)
+  (on-enter credit-on-enter)
+  (on-leave credit-on-leave))
+
+(define* (make-credit #:key (lines 1)
+                      (draw (lambda (y) #f))
+                      (update (lambda (t) #f))
+                      (on-enter (lambda () #f))
+                      (on-leave (lambda () #f)))
+  (_make-credit lines draw update on-enter on-leave))
+
+(define* (make-credit-group #:rest credits)
+  (let ((accumulate (lambda* (accessor #:key (init 0.0) preproc)
+                      (fold (lambda (c sum)
+                              (when preproc ((preproc c) sum))
+                              (+ sum (accessor c)))
+                            init credits)))
+        (call (lambda (proc)
+                (lambda ()
+                  (map (lambda (c) ((proc c))) credits)))))
+    (make-credit
+     #:lines (accumulate credit-lines)
+     #:draw (lambda (top)
+              (accumulate credit-height #:init top #:preproc credit-draw))
+     #:update (lambda (top)
+                (accumulate credit-height #:init top #:preproc credit-update))
+     #:on-enter (call credit-on-enter)
+     #:on-leave (call credit-on-leave))))
+
+(define (make-credit-text text)
+  (make-credit
+   #:draw
+   (lambda (y)
+     (set-fill-color! context "#fff")
+     (set-text-align! context "center")
+     (set-font! context "normal 16px monogram")
+     (fill-text context text
+                (* 0.7 game-width) y))))
+
+(define (make-credit-underline text)
+  (make-credit-group
+   (make-credit-text text)
+   (make-credit-text (make-string (string-length text) #\-))))
+
+(define* (make-credit-centering credit #:key (padding 6.0) (easing 4.0)
+                                (on-enter-center (lambda () #f))
+                                (on-leave-center (lambda () #f)))
+  (let* ((pi 3.14159)
+         (offset 0.0)
+         (speed (/ (line-height) credits-pace))
+         (center (/ (- (+ credits-start credits-end) (credit-height credit)) 2.0))
+         (ease-height (* (line-height) easing))
+         (ease-speed (lambda (y) (* speed (sin (/ y ease-height)))))
+         ;; Amount that credits scroll up during easing
+         (ease-travel (* ease-height (/ pi 2.0)))
+         ;; Start below center so that it eases right into the center
+         (beg (+ center (- ease-travel ease-height)))
+         (beg-mid (- beg ease-travel))
+         (end-mid (- beg-mid (* (line-height) padding)))
+         (end (- end-mid ease-travel)))
+    (make-credit
+     #:lines (+ padding (* 2 easing) (credit-lines credit))
+     #:draw (lambda (y) ((credit-draw credit) (+ y offset)))
+     #:update
+     ;; Remember that y is decreasing as credits rise up the screen
+     ;; toward y=0, so the comparators might seem to be flipped but
+     ;; that's how they need to be.
+     (lambda (y)
+       (when (and (<= y beg) (> y end)) 
+         (cond
+          ((> y beg-mid)
+           ;; Accelerate
+           (set! offset (+ offset (ease-speed (- beg y)))))
+          ((> y end-mid)
+           ;; Match speed
+           (set! offset (+ offset speed))
+           (when on-enter-center
+             (on-enter-center)
+             (set! on-enter-center #f)))
+          (else
+           ;; Decelerate
+           (when on-leave-center
+             (on-leave-center)
+             (set! on-leave-center #f))
+           (set! offset (+ offset (ease-speed (- y end)))))))
+       ;; Call on-leave-center even if no easing is used
+       (when (and (<= y end) on-leave-center)
+         (on-leave-center)
+         (set! on-leave-center #f))
+       ((credit-update credit) (+ y offset)))
+     #:on-enter (credit-on-enter credit)
+     #:on-leave (credit-on-leave credit))))
+
+(define (make-credits)
+  (vector (make-credit-centering
+           (make-credit-group
+            (make-credit-text "Phew, you made it!")
+            (make-credit-text "Time to relax.")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-text "Cirkoban was made by the")
+            (make-credit-text "Spritely Institute")))
+          (make-credit-centering
+           (make-credit-text "https://spritely.institute"))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Game Design")
+            (make-credit-text "Christine Lemmer-Webber")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Level Design")
+            (make-credit-text "Christine Lemmer-Webber")
+            (make-credit-text "Juliana Sims")
+            (make-credit-text "David Thompson"))
+           #:on-enter-center (lambda () (pk "Level Design centering!!"))
+           #:on-leave-center (lambda () (pk "Level Design leaving center!!")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Pixel Art")
+            (make-credit-text "Christine Lemmer-Webber"))
+           #:easing 0
+           #:on-enter-center (lambda () (pk "Pixel Art centering!!"))
+           #:on-leave-center (lambda () (pk "Pixel Art leaving center!!")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Music")
+            (make-credit-text "EncryptedWhispers")
+            (make-credit-text "Christine Lemmer-Webber")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Programming")
+            (make-credit-text "Juliana Sims")
+            (make-credit-text "David Thompson")
+            (make-credit-text "Amy Grinn")))
+          (make-credit-centering
+           (make-credit-group
+            (make-credit-underline "Other")
+            (make-credit-text "monogram font by datagoblin")))
+          (make-credit-centering
+           (make-credit-text "Thank you for playing!"))))
+
+(define-record-type <credits>
+  (make-credits-state credits top first-visible-index next-visible-index)
+  credits-state?
+  (credits credits-state-credits)
+  (top credits-state-top set-credits-state-top!)
+  (first-visible-index
+   credits-state-first-visible-index
+   set-credits-state-first-visible-index!)
+  (next-visible-index
+   credits-state-next-visible-index
+   set-credits-state-next-visible-index!))
+
+(define *credits* #f)
+
+(define (credits)
+  (credits-state-credits *credits*))
+(define (credits-top)
+  (credits-state-top *credits*))
+(define (credits-first-visible-index)
+  (credits-state-first-visible-index *credits*))
+(define (credits-next-visible-index)
+  (credits-state-next-visible-index *credits*))
+(define (set-credits-top! top)
+  (set-credits-state-top! *credits* top))
+(define (set-credits-first-visible-index! index)
+  (set-credits-state-first-visible-index! *credits* index))
+(define (set-credits-next-visible-index! index)
+  (set-credits-state-next-visible-index! *credits* index))
+(define (credits-reset!)
+  (set! *credits* (make-credits-state (make-credits) credits-start 0 -1)))  
+
+(define (load-credits!)
+  (credits-reset!)
+  (replace-game-state! 'credits)
+  (set! *actormap* (make-whactormap))
+  (clear-snapshots!)
+  (with-goblins
+   (set! *level* (load-credits #f))
+   (update-objects!)))
+
+(define (credit-height credit)
+  (* (credit-lines credit) (line-height)))
+
+(define (draw-credits)
+  (draw-level)
+  (let lp ((i (credits-first-visible-index))
+           (y (credits-top)))
+    (when (and (< i (vector-length (credits)))
+               (<= y credits-start))
+      (let ((c (vector-ref (credits) i)))
+        ((credit-draw c) y)
+        (lp (1+ i) (+ y (credit-height c) (* (line-height)
+                                             credits-margin)))))))
+
+(define (update-credits!)
+  (let ((i (credits-first-visible-index)))
+    (when (< i (vector-length (credits)))
+      ;; Update credits
+      (let lp ((i i)
+               (y (credits-top)))
+        (when (and (< i (vector-length (credits)))
+                   (<= y credits-start))
+          (let ((c (vector-ref (credits) i)))
+            ;; Call on-enter as credits enter the screen
+            (when (> i (credits-next-visible-index))
+              ((credit-on-enter c))
+              (set-credits-next-visible-index! i))
+            ((credit-update c) y)
+            (lp (1+ i) (+ y (credit-height c) (* (line-height) credits-margin))))))
+      ;; Remove credits as they leave the screen
+      (let* ((c (vector-ref (credits) i))
+             (bottom (+ (credits-top) (credit-height c))))
+        (when (< bottom credits-end)
+          (set-credits-top! (+ bottom (* (line-height) credits-margin)))
+          (set-credits-first-visible-index! (1+ i))
+          ((credit-on-leave c))))
+      ;; Advance credits
+      (set-credits-top! (- (credits-top) (/ (line-height) credits-pace))))))
+
 (define (reset-game!)
   (run-script
    (lambda ()
@@ -533,7 +774,9 @@
   (maybe-poll-gamepad)
   (scheduler-tick! (current-scheduler))
   (particle-pool-update! particles)
-  (timeout update-callback dt))
+  (timeout update-callback dt)
+  (when (equal? (current-game-state) 'credits)
+    (update-credits!)))
 (define update-callback (procedure->external update))
 
 ;; Rendering
@@ -741,7 +984,6 @@
   ;; + num menu items + 1 for ellipses if num items is too big
   ;; + the y padding again
   (let* ((padding-y 1)
-         (text-offset-y (* 0.75 tile-height))
          (width 8.0)
          (num-items (vector-length (menu-items (current-menu))))
          (height (+ 2 ;; Menu title + back/ellipses
@@ -786,7 +1028,7 @@
                        (vec2-x center) y-text))
           (set-text-align! context "left")
           ;; indicator
-          (when (= (+ r r-page-offset) (current-menu-index))
+          (when (= r-page (current-menu-index))
             (fill-text context "▸" x-gutter y-text))
           ;; Menu items
           (when (>= r -1)
@@ -842,77 +1084,6 @@
 (define (draw-interstitial)
   (draw-level))
 
-(define *credits-scroll* (vec2 0.0 0.0))
-(define credits
-  #("Phew, you made it!"
-    "Time to relax."
-    #f
-    #f
-    "Cirkoban was made by the"
-    "Spritely Institute"
-    #f
-    "https://spritely.institute"
-    #f
-    "Game Design"
-    "-----------"
-    "Christine Lemmer-Webber"
-    #f
-    "Level Design"
-    "------------"
-    "Christine Lemmer-Webber"
-    "Juliana Sims"
-    "David Thompson"
-    #f
-    "Pixel Art"
-    "---------"
-    "Christine Lemmer-Webber"
-    #f
-    "Music"
-    "-----"
-    "EncryptedWhispers"
-    "Christine Lemmer-Webber"
-    #f
-    "Programming"
-    "-----------"
-    "Juliana Sims"
-    "David Thompson"
-    #f
-    "Other"
-    "-----"
-    "monogram font by datagoblin"
-    #f
-    #f
-    #f
-    #f
-    #f
-    #f
-    #f
-    #f
-    "Thank you for playing!"))
-(define credits-line-spacing 16.0)
-(define max-credits-scroll
-  (+ game-height (* (- (vector-length credits) 9) credits-line-spacing)))
-(define (draw-credits)
-  (draw-level)
-  (set-fill-color! context "#ffffff")
-  (set-text-align! context "center")
-  (set-font! context "normal 16px monogram")
-  (set-vec2-y! *credits-scroll*
-               (min (+ (vec2-y *credits-scroll*) 0.5)
-                    max-credits-scroll))
-  (let* ((x (* game-width 0.7))
-         (lines-on-screen 15)
-         (scroll-y (vec2-y *credits-scroll*))
-         ;; TODO: Only render the lines on screen.
-         (start 0)
-         (end (vector-length credits)))
-    (let lp ((i start) (y (- game-height scroll-y)))
-      (when (< i end)
-        (match (vector-ref credits i)
-          (#f #f)
-          (str (fill-text context str x y)))
-        (lp (1+ i) (+ y credits-line-spacing))))))
-
 (define *frame-time* (current-time*))
 (define (draw time)
   (unless (and (real? time) (inexact? time))

modules/dom/canvas.scm

@@ -39,7 +39,8 @@
             translate!
             rotate!
             set-transform!
-            set-image-smoothing-enabled!))
+            set-image-smoothing-enabled!
+            measure-text))
 
 ;; HTMLCanvasElement
 (define-foreign get-context
@@ -98,3 +99,6 @@
 (define-foreign set-image-smoothing-enabled!
   "canvas" "setImageSmoothingEnabled"
   (ref extern) i32 -> none)
+(define-foreign measure-text
+  "canvas" "measureText"
+  (ref extern) (ref string) -> (ref extern))

modules/dom/text-metrics.scm

@@ -0,0 +1,34 @@
+;;; Copyright (C) 2025 Amy Grinn <amy@spritely.institute>
+;;;
+;;; Licensed under the Apache License, Version 2.0 (the "License");
+;;; you may not use this file except in compliance with the License.
+;;; You may obtain a copy of the License at
+;;;
+;;;    http://www.apache.org/licenses/LICENSE-2.0
+;;;
+;;; Unless required by applicable law or agreed to in writing, software
+;;; distributed under the License is distributed on an "AS IS" BASIS,
+;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;;; See the License for the specific language governing permissions and
+;;; limitations under the License.
+
+;;; Commentary:
+;;;
+;;; HTML canvas TextMetrics interface bindings
+;;;
+;;; Code:
+
+(define-module (dom text-metrics)
+  #:pure
+  #:use-module (scheme base)
+  #:use-module (hoot ffi)
+  #:export (text-metrics-actual-bounding-box-ascent
+            text-metrics-actual-bounding-box-descent))
+
+(define-foreign text-metrics-actual-bounding-box-ascent
+  "textMetrics" "actualBoundingBoxAscent"
+  (ref extern) -> i32)
+
+(define-foreign text-metrics-actual-bounding-box-descent
+  "textMetrics" "actualBoundingBoxDescent"
+  (ref extern) -> i32)

modules/srfi/srf-1.scm

@@ -0,0 +1,3 @@
+(define-module (srfi srfi-1)
+  #:use-module ((scheme base) #:select (fold))
+  #:re-export (fold))