Fix T68826 Eevee: Multi-Mat not working if switching from Solid shading

The correct fix would be to avoid all those hacks but this is needed if
we want to be able to parallelize object vbo extractions.

1 files changed, 19 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index 884d39343c6..3bf9a03ddeb 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -1088,6 +1088,25 @@ void DRW_mesh_batch_cache_create_requested(
     }
   }
 
+  /* HACK: if MBC_SURF_PER_MAT is requested and ibo.tris is already available, it won't have it's
+   * index ranges initialized. So discard ibo.tris in order to recreate it. */
+  if ((batch_requested & MBC_SURF_PER_MAT) != 0 && (cache->batch_ready & MBC_SURF_PER_MAT) == 0) {
+    FOREACH_MESH_BUFFER_CACHE(cache, mbuffercache)
+    {
+      GPU_INDEXBUF_DISCARD_SAFE(mbuffercache->ibo.tris);
+    }
+    /* Clear all batches that reference ibo.tris. */
+    GPU_BATCH_CLEAR_SAFE(cache->batch.surface);
+    GPU_BATCH_CLEAR_SAFE(cache->batch.surface_weights);
+    GPU_BATCH_CLEAR_SAFE(cache->batch.edit_mesh_analysis);
+    GPU_BATCH_CLEAR_SAFE(cache->batch.edit_triangles);
+    GPU_BATCH_CLEAR_SAFE(cache->batch.edit_lnor);
+    GPU_BATCH_CLEAR_SAFE(cache->batch.edit_selection_faces);
+
+    cache->batch_ready &= ~(MBC_SURFACE | MBC_SURFACE_WEIGHTS | MBC_EDIT_MESH_ANALYSIS |
+                            MBC_EDIT_TRIANGLES | MBC_EDIT_LNOR | MBC_EDIT_SELECTION_FACES);
+  }
+
   /* Second chance to early out */
   if ((batch_requested & ~cache->batch_ready) == 0) {
 #ifdef DEBUG