GPUVertBuf: Add handle refcount

A handle refcount is here to avoid freeing of the GPUVertBuf datablock
if it is still referenced somewhere else.

This does not prevent deleting the actual data. This is to avoid too
much zombie data usage.

This is in order to avoid most hacks inside `draw_instance_data.c`.

2 files changed, 24 insertions, 1 deletions

diff --git a/source/blender/gpu/GPU_vertex_buffer.h b/source/blender/gpu/GPU_vertex_buffer.h
index 757255496e0..bd1019bb1f5 100644
--- a/source/blender/gpu/GPU_vertex_buffer.h
+++ b/source/blender/gpu/GPU_vertex_buffer.h
@@ -59,6 +59,8 @@ typedef struct GPUVertBuf {
   uint32_t vbo_id;
   /** Usage hint for GL optimisation. */
   GPUUsageType usage;
+  /** This counter will only avoid freeing the GPUVertBuf, not the data. */
+  char handle_refcount;
   /** Data has been touched and need to be reuploaded to GPU. */
   bool dirty;
   uchar *data; /* NULL indicates data in VRAM (unmapped) */
@@ -73,6 +75,10 @@ GPUVertBuf *GPU_vertbuf_create_with_format_ex(const GPUVertFormat *, GPUUsageTyp
 void GPU_vertbuf_clear(GPUVertBuf *verts);
 void GPU_vertbuf_discard(GPUVertBuf *);
 
+/* Avoid GPUVertBuf datablock being free but not its data. */
+void GPU_vertbuf_handle_ref_add(GPUVertBuf *verts);
+void GPU_vertbuf_handle_ref_remove(GPUVertBuf *verts);
+
 void GPU_vertbuf_init(GPUVertBuf *, GPUUsageType);
 void GPU_vertbuf_init_with_format_ex(GPUVertBuf *, const GPUVertFormat *, GPUUsageType);
 
diff --git a/source/blender/gpu/intern/gpu_vertex_buffer.cc b/source/blender/gpu/intern/gpu_vertex_buffer.cc
index 67ad8835b6a..debf9835c90 100644
--- a/source/blender/gpu/intern/gpu_vertex_buffer.cc
+++ b/source/blender/gpu/intern/gpu_vertex_buffer.cc
@@ -77,6 +77,7 @@ void GPU_vertbuf_init(GPUVertBuf *verts, GPUUsageType usage)
   memset(verts, 0, sizeof(GPUVertBuf));
   verts->usage = usage;
   verts->dirty = true;
+  verts->handle_refcount = 1;
 }
 
 void GPU_vertbuf_init_with_format_ex(GPUVertBuf *verts,
@@ -137,7 +138,23 @@ void GPU_vertbuf_clear(GPUVertBuf *verts)
 void GPU_vertbuf_discard(GPUVertBuf *verts)
 {
   GPU_vertbuf_clear(verts);
-  MEM_freeN(verts);
+  GPU_vertbuf_handle_ref_remove(verts);
+}
+
+void GPU_vertbuf_handle_ref_add(GPUVertBuf *verts)
+{
+  verts->handle_refcount++;
+}
+
+void GPU_vertbuf_handle_ref_remove(GPUVertBuf *verts)
+{
+  BLI_assert(verts->handle_refcount > 0);
+  verts->handle_refcount--;
+  if (verts->handle_refcount == 0) {
+    /* Should already have been cleared. */
+    BLI_assert(verts->vbo_id == 0 && verts->data == NULL);
+    MEM_freeN(verts);
+  }
 }
 
 uint GPU_vertbuf_size_get(const GPUVertBuf *verts)