Render: Lazily allocate render passes pixels storage

The idea is to only allocate pixel storage only when there is an actual
data to be written to them.

This moves the code forward a better support of high-res rendering when
pixel storage is not allocated until render engine is ready to provide
pixel data.

Is expected to be no functional changes for neither users no external
engines. The only difference is that the motion and depth passes will
be displayed as transparent for until render engine provides any tile
result (at which point the pixels will be allocated and initialized to
infinite depth).

Differential Revision: https://developer.blender.org/D12195

1 files changed, 38 insertions, 23 deletions

diff --git a/source/blender/draw/engines/image/image_engine.c b/source/blender/draw/engines/image/image_engine.c
index 438c95118ef..b4c0ade380e 100644
--- a/source/blender/draw/engines/image/image_engine.c
+++ b/source/blender/draw/engines/image/image_engine.c
@@ -115,33 +115,48 @@ static void space_image_gpu_texture_get(Image *image,
     BKE_image_multiview_index(image, &sima->iuser);
   }
 
-  if (ibuf) {
-    const int sima_flag = sima->flag & ED_space_image_get_display_channel_mask(ibuf);
-    if (sima_flag & SI_SHOW_ZBUF && (ibuf->zbuf || ibuf->zbuf_float || (ibuf->channels == 1))) {
-      if (ibuf->zbuf) {
-        BLI_assert_msg(0, "Integer based depth buffers not supported");
-      }
-      else if (ibuf->zbuf_float) {
-        *r_gpu_texture = GPU_texture_create_2d(
-            __func__, ibuf->x, ibuf->y, 0, GPU_R16F, ibuf->zbuf_float);
-        *r_owns_texture = true;
-      }
-      else if (ibuf->rect_float && ibuf->channels == 1) {
-        *r_gpu_texture = GPU_texture_create_2d(
-            __func__, ibuf->x, ibuf->y, 0, GPU_R16F, ibuf->rect_float);
-        *r_owns_texture = true;
-      }
+  if (ibuf == NULL) {
+    return;
+  }
+
+  if (ibuf->rect == NULL && ibuf->rect_float == NULL) {
+    /* This codepath is only supposed to happen when drawing a lazily-allocatable render result.
+     * In all the other cases the `ED_space_image_acquire_buffer()` is expected to return NULL as
+     * an image buffer when it has no pixels. */
+
+    BLI_assert(image->type == IMA_TYPE_R_RESULT);
+
+    float zero[4] = {0, 0, 0, 0};
+    *r_gpu_texture = GPU_texture_create_2d(__func__, 1, 1, 0, GPU_RGBA16F, zero);
+    *r_owns_texture = true;
+    return;
+  }
+
+  const int sima_flag = sima->flag & ED_space_image_get_display_channel_mask(ibuf);
+  if (sima_flag & SI_SHOW_ZBUF && (ibuf->zbuf || ibuf->zbuf_float || (ibuf->channels == 1))) {
+    if (ibuf->zbuf) {
+      BLI_assert_msg(0, "Integer based depth buffers not supported");
     }
-    else if (image->source == IMA_SRC_TILED) {
-      *r_gpu_texture = BKE_image_get_gpu_tiles(image, iuser, ibuf);
-      *r_tex_tile_data = BKE_image_get_gpu_tilemap(image, iuser, NULL);
-      *r_owns_texture = false;
+    else if (ibuf->zbuf_float) {
+      *r_gpu_texture = GPU_texture_create_2d(
+          __func__, ibuf->x, ibuf->y, 0, GPU_R16F, ibuf->zbuf_float);
+      *r_owns_texture = true;
     }
-    else {
-      *r_gpu_texture = BKE_image_get_gpu_texture(image, iuser, ibuf);
-      *r_owns_texture = false;
+    else if (ibuf->rect_float && ibuf->channels == 1) {
+      *r_gpu_texture = GPU_texture_create_2d(
+          __func__, ibuf->x, ibuf->y, 0, GPU_R16F, ibuf->rect_float);
+      *r_owns_texture = true;
     }
   }
+  else if (image->source == IMA_SRC_TILED) {
+    *r_gpu_texture = BKE_image_get_gpu_tiles(image, iuser, ibuf);
+    *r_tex_tile_data = BKE_image_get_gpu_tilemap(image, iuser, NULL);
+    *r_owns_texture = false;
+  }
+  else {
+    *r_gpu_texture = BKE_image_get_gpu_texture(image, iuser, ibuf);
+    *r_owns_texture = false;
+  }
 }
 
 static void space_node_gpu_texture_get(Image *image,