Basic gimp gradient loader

[clinton/scratch.git] / gimp-gradient.scm

diff --git a/gimp-gradient.scm b/gimp-gradient.scm
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+;;; Load GIMP Gradients. Kind of.
+;;; 2014
+
+(use-modules (ice-9 match)
+            (ice-9 rdelim)
+
+            (rnrs enums)
+            (srfi srfi-9)
+            (srfi srfi-26))
+
+(define +default-steps+ 1024)
+
+(define-enumeration blend-function
+  (linear curved sinusoidal spherical-increasing spherical-decreaing)
+  blend-functions)
+
+(define-enumeration color-model
+  (rgb hsv-counter hsv-clockwise)
+  color-models)
+
+;; Gradients are just a list of gradient-segment
+#;(define-record-type <gradient-segment>
+  (make-gradient-segment left-pos left-color mid-pos mid-color right-pos right-color)
+  gradient-segment?
+  (left-position ))
+
+
+;; returna list of ((#(left-pos r g b) #(right-pos r g b)))
+;; ignore alpha, blending function, midpoint... whatever, for now.
+(define (parse-gradient file-name)
+  (call-with-input-file file-name
+    (lambda (instream)
+      (read-line instream) ; Gimp Gradient
+      (let* ((name (read-line instream))
+            (segments (string->number (read-line instream))))
+       (let loop ((next-line (read-line instream))
+                  (segments (list)))
+         (if (eof-object? next-line)
+             (reverse segments)
+             (let ((bits (string-split next-line #\space)))
+               (format #t "bits (~A): ~A~%" (length bits) bits)
+               (match (map string->number bits)
+                 ((left-stop mid right-stop lr lg lb la rr rg rb ra blend color)
+                  (loop (read-line instream)
+                        (cons (list (vector left-stop lr lg lb)
+                                    #;(vector mid mr mg mb)
+                                    (vector right-stop rr rg rb))
+                              segments)))))))))))
+
+(define (segment->rgb segment total-steps)
+  (match segment
+    ((#(l lr lg lb) #(r rr rg rb))
+     (linear-blend lr lg lb rr rg rb
+                  (inexact->exact (floor (* total-steps (- r l))))))))
+
+(define (segments->rgb segments total-steps)
+  (apply append (map (cut segment->rgb <> total-steps) segments)))
+
+(define* (linear-blend r1 g1 b1 r2 g2 b2 steps)
+  (let ((rd (/ (- r2 r1) steps))
+       (gd (/ (- g2 g1) steps))
+       (bd (/ (- g2 g1) steps)))
+    (let loop ((remaining steps)
+              (colors (list)))
+      (if (= remaining 0)
+         (reverse colors)
+         (let ((step (- steps remaining)))
+           (loop (1- remaining)
+                 (cons (vector (+ r1 (* rd step))
+                               (+ g1 (* gd step))
+                               (+ b1 (* bd step)))
+                       colors)))))))