ImBuf: add IMB_allocFromBufferOwn that takes ownership of the buffer

Avoids duplicating the image buffer when saving thumbnails.

source/blender/blenkernel/intern/studiolight.c

@@ -439,17 +439,15 @@ static void studiolight_load_equirect_image(StudioLight *sl)
         if (ctx.diffuse_pass != NULL) {
           float *converted_pass = studiolight_multilayer_convert_pass(
               ibuf, ctx.diffuse_pass, ctx.num_diffuse_channels);
-          diffuse_ibuf = IMB_allocFromBuffer(
+          diffuse_ibuf = IMB_allocFromBufferOwn(
               NULL, converted_pass, ibuf->x, ibuf->y, ctx.num_diffuse_channels);
-          MEM_freeN(converted_pass);
         }
 
         if (ctx.specular_pass != NULL) {
           float *converted_pass = studiolight_multilayer_convert_pass(
               ibuf, ctx.specular_pass, ctx.num_specular_channels);
-          specular_ibuf = IMB_allocFromBuffer(
+          specular_ibuf = IMB_allocFromBufferOwn(
               NULL, converted_pass, ibuf->x, ibuf->y, ctx.num_specular_channels);
-          MEM_freeN(converted_pass);
         }
 
         IMB_exr_close(ibuf->userdata);
@@ -1148,12 +1146,11 @@ static void studiolight_calculate_irradiance_equirect_image(StudioLight *sl)
     }
     ITER_PIXELS_END;
 
-    sl->equirect_irradiance_buffer = IMB_allocFromBuffer(NULL,
-                                                         colbuf,
-                                                         STUDIOLIGHT_IRRADIANCE_EQUIRECT_WIDTH,
-                                                         STUDIOLIGHT_IRRADIANCE_EQUIRECT_HEIGHT,
-                                                         4);
-    MEM_freeN(colbuf);
+    sl->equirect_irradiance_buffer = IMB_allocFromBufferOwn(NULL,
+                                                            colbuf,
+                                                            STUDIOLIGHT_IRRADIANCE_EQUIRECT_WIDTH,
+                                                            STUDIOLIGHT_IRRADIANCE_EQUIRECT_HEIGHT,
+                                                            4);
   }
   sl->flag |= STUDIOLIGHT_EQUIRECT_IRRADIANCE_IMAGE_CALCULATED;
 }

source/blender/imbuf/IMB_imbuf.h

@@ -148,6 +148,14 @@ struct ImBuf *IMB_allocImBuf(unsigned int x,
 bool IMB_initImBuf(
     struct ImBuf *ibuf, unsigned int x, unsigned int y, unsigned char planes, unsigned int flags);
 
+/**
+ * Create a copy of a pixel buffer and wrap it to a new ImBuf
+ * (transferring ownership to the in imbuf).
+ * \attention Defined in allocimbuf.c
+ */
+struct ImBuf *IMB_allocFromBufferOwn(
+    unsigned int *rect, float *rectf, unsigned int w, unsigned int h, unsigned int channels);
+
 /**
  * Create a copy of a pixel buffer and wrap it to a new ImBuf
  * \attention Defined in allocimbuf.c

source/blender/imbuf/intern/allocimbuf.c

@@ -430,6 +430,41 @@ bool imb_addrectImBuf(ImBuf *ibuf)
   return false;
 }
 
+/**
+ * \param take_ownership: When true, the buffers become owned by the resulting image.
+ */
+struct ImBuf *IMB_allocFromBufferOwn(
+    unsigned int *rect, float *rectf, unsigned int w, unsigned int h, unsigned int channels)
+{
+  ImBuf *ibuf = NULL;
+
+  if (!(rect || rectf)) {
+    return NULL;
+  }
+
+  ibuf = IMB_allocImBuf(w, h, 32, 0);
+
+  ibuf->channels = channels;
+
+  /* Avoid #MEM_dupallocN since the buffers might not be allocated using guarded-allocation. */
+  if (rectf) {
+    BLI_assert(MEM_allocN_len(rectf) == sizeof(float[4]) * w * h);
+    ibuf->rect_float = rectf;
+
+    ibuf->flags |= IB_rectfloat;
+    ibuf->mall |= IB_rectfloat;
+  }
+  if (rect) {
+    BLI_assert(MEM_allocN_len(rect) == sizeof(uchar[4]) * w * h);
+    ibuf->rect = rect;
+
+    ibuf->flags |= IB_rect;
+    ibuf->mall |= IB_rect;
+  }
+
+  return ibuf;
+}
+
 struct ImBuf *IMB_allocFromBuffer(const unsigned int *rect,
                                   const float *rectf,
                                   unsigned int w,

source/blender/windowmanager/intern/wm_files.c

@@ -1539,7 +1539,7 @@ static ImBuf *blend_file_thumb_from_screenshot(bContext *C, BlendThumbnail **thu
 
   int win_size[2];
   uint *buffer = WM_window_pixels_read(CTX_wm_manager(C), win, win_size);
-  ImBuf *ibuf = IMB_allocFromBuffer(buffer, NULL, win_size[0], win_size[1], 24);
+  ImBuf *ibuf = IMB_allocFromBufferOwn(buffer, NULL, win_size[0], win_size[1], 24);
 
   if (ibuf) {
     int ex, ey;
@@ -1561,7 +1561,6 @@ static ImBuf *blend_file_thumb_from_screenshot(bContext *C, BlendThumbnail **thu
 
     BlendThumbnail *thumb = BKE_main_thumbnail_from_imbuf(NULL, thumb_ibuf);
     IMB_freeImBuf(thumb_ibuf);
-    MEM_freeN(buffer);
     *thumb_pt = thumb;
   }
   WM_cursor_wait(false);