Fix #34779: Channels disappear from multilayer exr sequence

Issue was caused by delayed or missing image user frame
number update, which lead to image loading failure in
cases node is updating from image signal callback.

Solved in a way that file from image datablock is used
for sockets detection instead of loading image for
current frame.

3 files changed, 30 insertions, 3 deletions

diff --git a/source/blender/blenkernel/BKE_image.h b/source/blender/blenkernel/BKE_image.h
index 26ac2cc8bb4..0f8e25b9df5 100644
--- a/source/blender/blenkernel/BKE_image.h
+++ b/source/blender/blenkernel/BKE_image.h
@@ -232,6 +232,8 @@ void BKE_image_buf_fill_checker_color(unsigned char *rect, float *rect_float, in
 unsigned char *BKE_image_get_pixels_for_frame(struct Image *image, int frame);
 float *BKE_image_get_float_pixels_for_frame(struct Image *image, int frame);
 
+/* Guess offset for the first frame in the sequence */
+int BKE_image_sequence_guess_offset(struct Image *image);
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/blender/blenkernel/intern/image.c b/source/blender/blenkernel/intern/image.c
index 26651d76f68..c9034cfe7bb 100644
--- a/source/blender/blenkernel/intern/image.c
+++ b/source/blender/blenkernel/intern/image.c
@@ -3430,3 +3430,15 @@ float *BKE_image_get_float_pixels_for_frame(struct Image *image, int frame)
 
 	return pixels;
 }
+
+int BKE_image_sequence_guess_offset(Image *image)
+{
+	unsigned short numlen;
+	char head[FILE_MAX], tail[FILE_MAX];
+	char num[FILE_MAX] = {0};
+
+	BLI_stringdec(image->name, head, tail, &numlen);
+	BLI_strncpy(num, image->name + strlen(head), numlen + 1);
+
+	return atoi(num);
+}
diff --git a/source/blender/nodes/composite/nodes/node_composite_image.c b/source/blender/nodes/composite/nodes/node_composite_image.c
index c09903ad6c5..e2c4db55fd8 100644
--- a/source/blender/nodes/composite/nodes/node_composite_image.c
+++ b/source/blender/nodes/composite/nodes/node_composite_image.c
@@ -174,11 +174,24 @@ static void cmp_node_image_create_outputs(bNodeTree *ntree, bNode *node)
 {
 	Image *ima= (Image *)node->id;
 	if (ima) {
-		ImageUser *iuser= node->storage;
+		ImageUser *iuser = node->storage;
+		ImageUser load_iuser = {0};
 		ImBuf *ibuf;
-		
+		int offset = BKE_image_sequence_guess_offset(ima);
+
+		/* It is possible that image user in this node is not
+		 * properly updated yet. In this case loading image will
+		 * fail and sockets detection will go wrong.
+		 *
+		 * So we manually construct image user to be sure first
+		 * image from sequence (that one which is set as fileanme
+		 * for image datablock) is used for sockets detection
+		 */
+		load_iuser.ok = 1;
+		load_iuser.framenr = offset;
+
 		/* make sure ima->type is correct */
-		ibuf = BKE_image_acquire_ibuf(ima, iuser, NULL);
+		ibuf = BKE_image_acquire_ibuf(ima, &load_iuser, NULL);
 		
 		if (ima->rr) {
 			RenderLayer *rl= BLI_findlink(&ima->rr->layers, iuser->layer);