Fix cryptomatte passes saved lossy into multilayer EXR

The DWA compression code in OpenEXR has hardcoded rules which decides
which channels are lossy or lossless. There is no control over these
rules via API.

This change makes it so channel names of xyzw is used for cryptomatte
passes in Cycles. This works around the hardcoded rules in the DWA code
making it so lossless compression is used. It is important to use lower
case y channel name as the upper case Y uses lossy compression.

The change in the channel naming also makes it so the write code uses
32bit for the cryptomatte even when saving half-float EXR.

Fixes T96933: Cryptomatte layers saved incorrectly with EXR DWA compression
Fixes T88049: Cryptomatte EXR Output Bit Depth should always be 32bit

Differential Revision: https://developer.blender.org/D15823

1 files changed, 7 insertions, 3 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_cryptomatte.c b/source/blender/draw/engines/eevee/eevee_cryptomatte.c
index 6ba71e2b2db..36ec1354375 100644
--- a/source/blender/draw/engines/eevee/eevee_cryptomatte.c
+++ b/source/blender/draw/engines/eevee/eevee_cryptomatte.c
@@ -421,27 +421,31 @@ void EEVEE_cryptomatte_output_accumulate(EEVEE_ViewLayerData *UNUSED(sldata), EE
 
 void EEVEE_cryptomatte_update_passes(RenderEngine *engine, Scene *scene, ViewLayer *view_layer)
 {
+  /* NOTE: Name channels lowercase xyzw so that compression rules check in OpenEXR DWA code uses
+   * loseless compression. It is important to use lowercase since the capital Y uses lossy
+   * compression in DWA. */
+
   char cryptomatte_pass_name[MAX_NAME];
   const short num_passes = eevee_cryptomatte_passes_per_layer(view_layer);
   if ((view_layer->cryptomatte_flag & VIEW_LAYER_CRYPTOMATTE_OBJECT) != 0) {
     for (short pass = 0; pass < num_passes; pass++) {
       BLI_snprintf_rlen(cryptomatte_pass_name, MAX_NAME, "CryptoObject%02d", pass);
       RE_engine_register_pass(
-          engine, scene, view_layer, cryptomatte_pass_name, 4, "RGBA", SOCK_RGBA);
+          engine, scene, view_layer, cryptomatte_pass_name, 4, "xyzw", SOCK_RGBA);
     }
   }
   if ((view_layer->cryptomatte_flag & VIEW_LAYER_CRYPTOMATTE_MATERIAL) != 0) {
     for (short pass = 0; pass < num_passes; pass++) {
       BLI_snprintf_rlen(cryptomatte_pass_name, MAX_NAME, "CryptoMaterial%02d", pass);
       RE_engine_register_pass(
-          engine, scene, view_layer, cryptomatte_pass_name, 4, "RGBA", SOCK_RGBA);
+          engine, scene, view_layer, cryptomatte_pass_name, 4, "xyzw", SOCK_RGBA);
     }
   }
   if ((view_layer->cryptomatte_flag & VIEW_LAYER_CRYPTOMATTE_ASSET) != 0) {
     for (short pass = 0; pass < num_passes; pass++) {
       BLI_snprintf_rlen(cryptomatte_pass_name, MAX_NAME, "CryptoAsset%02d", pass);
       RE_engine_register_pass(
-          engine, scene, view_layer, cryptomatte_pass_name, 4, "RGBA", SOCK_RGBA);
+          engine, scene, view_layer, cryptomatte_pass_name, 4, "xyzw", SOCK_RGBA);
     }
   }
 }