Cycles: Fix rendering of packed UDIM tiles with different sizes

The packed image loader was not aware of the fact that UDIM tiles
can be of a different size.

Exposed Python API required to access this information. It has the
same complexity as the "regular" packed files: in both cases the
ImBuf will be acquired and released to access the information.

While the current workflow of packing UDIMs is not very streamlined,
it is still possible and is something what the studio is using here.

Test file:
{F13130516}

Expected behavior achieved with this patch: a bigger checker board
pattern in viewport render

Actual behavior prior to this patch: either memory corruption, or
wrong/black render result on the plane

Differential Revision: https://developer.blender.org/D15111

1 files changed, 26 insertions, 3 deletions

diff --git a/intern/cycles/blender/image.cpp b/intern/cycles/blender/image.cpp
index 98ca16fe678..058fe3d46ac 100644
--- a/intern/cycles/blender/image.cpp
+++ b/intern/cycles/blender/image.cpp
@@ -28,10 +28,33 @@ BlenderImageLoader::BlenderImageLoader(BL::Image b_image,
 
 bool BlenderImageLoader::load_metadata(const ImageDeviceFeatures &, ImageMetaData &metadata)
 {
-  metadata.width = b_image.size()[0];
-  metadata.height = b_image.size()[1];
+  if (b_image.source() != BL::Image::source_TILED) {
+    /* Image sequence might have different dimensions, and hence needs to be handled in a special
+     * manner.
+     * NOTE: Currently the sequences are not handled by this image laoder. */
+    assert(b_image.source() != BL::Image::source_SEQUENCE);
+
+    metadata.width = b_image.size()[0];
+    metadata.height = b_image.size()[1];
+    metadata.channels = b_image.channels();
+  }
+  else {
+    /* Different UDIM tiles might have different resolutions, so get resolution from the actual
+     * tile. */
+    BL::UDIMTile b_udim_tile = b_image.tiles.get(tile_number);
+    if (b_udim_tile) {
+      metadata.width = b_udim_tile.size()[0];
+      metadata.height = b_udim_tile.size()[1];
+      metadata.channels = b_udim_tile.channels();
+    }
+    else {
+      metadata.width = 0;
+      metadata.height = 0;
+      metadata.channels = 0;
+    }
+  }
+
   metadata.depth = 1;
-  metadata.channels = b_image.channels();
 
   if (b_image.is_float()) {
     if (metadata.channels == 1) {