Fix uv height computation.

CHANGES.md

@@ -2,6 +2,7 @@
 =====
 - Fix note names (#18).
 - Fix GC pace when allocating bigarrays with custom memory.
+- Fix UV height calculation in `caml_yuv420_fill`.
 
 0.8.4 (2023-07-01)
 =====

src/imageYUV420.ml

@@ -48,6 +48,7 @@ type t = {
 
 let width img = img.width
 let height img = img.height
+let uv_height height = Data.round 2 ((height + 1) / 2)
 let dimensions img = (width img, height img)
 let y img = img.y
 let y_stride img = img.y_stride
@@ -65,7 +66,9 @@ let ensure_alpha img =
     Data.fill a 0xff;
     img.alpha <- Some a)
 
-external fill : t -> Pixel.yuv -> unit = "caml_yuv420_fill"
+external fill : t -> Pixel.yuv -> int -> unit = "caml_yuv420_fill"
+
+let fill img pix = fill img pix (uv_height img.height)
 
 let fill_alpha img a =
   if a = 0xff then img.alpha <- None
@@ -104,7 +107,7 @@ let create ?(blank = false) ?y_stride ?uv_stride width height =
   let y_stride, uv_stride = default_stride width y_stride uv_stride in
   let y = Data.aligned align (height * y_stride) in
   let u, v =
-    let height = Data.round 2 ((height + 1) / 2) in
+    let height = uv_height height in
     ( Data.aligned align (height * uv_stride),
       Data.aligned align (height * uv_stride) )
   in

src/image_yuv420.c

@@ -17,9 +17,8 @@
 
 #define max(a, b) (a > b ? a : b)
 #define min(a, b) (a < b ? a : b)
-#define round(r, n) (((n + (r - 1)) / r) * r)
 
-CAMLprim value caml_yuv420_fill(value img, value p) {
+CAMLprim value caml_yuv420_fill(value img, value p, value uv_height) {
   CAMLparam2(img, p);
   int y = Int_val(Field(p, 0));
   int u = Int_val(Field(p, 1));
@@ -28,8 +27,8 @@ CAMLprim value caml_yuv420_fill(value img, value p) {
   int y_stride = YUV420_y_stride(img);
   int uv_stride = YUV420_uv_stride(img);
   memset(YUV420_y(img), y, height * y_stride);
-  memset(YUV420_u(img), u, round(2, height / 2) * uv_stride);
-  memset(YUV420_v(img), v, round(2, height / 2) * uv_stride);
+  memset(YUV420_u(img), u, Int_val(uv_height) * uv_stride);
+  memset(YUV420_v(img), v, Int_val(uv_height) * uv_stride);
   CAMLreturn(Val_unit);
 }