Fix T84398: Multiview images show only one view.

The `image_get_gpu_texture` didn't use the iuser->view_index but
recalculated the requested view again. This lead to inconsistent
behavior when switching between multi view textures or stereo textures.

This has been fixed by ensuring that the `iuser->view_index` is always
used.

An Image has only place to store 2 view textures. This is done for
right/left eye compositing. A multi view texture can have more views.
This would lead to reading and writing to unallocated space.

When a multiview texture is requested that is larger than 1. It will
always be cached as being the first eye. The `gpu_view` of the Image is
also used as a cache key to check this.

3 files changed, 16 insertions, 7 deletions

diff --git a/source/blender/blenkernel/intern/image_gpu.c b/source/blender/blenkernel/intern/image_gpu.c
index 05aa3c89a84..a6bd65227a0 100644
--- a/source/blender/blenkernel/intern/image_gpu.c
+++ b/source/blender/blenkernel/intern/image_gpu.c
@@ -271,6 +271,7 @@ static GPUTexture **get_image_gpu_texture_ptr(Image *ima,
 {
   const bool in_range = (textarget >= 0) && (textarget < TEXTARGET_COUNT);
   BLI_assert(in_range);
+  BLI_assert(multiview_eye == 0 || multiview_eye == 1);
 
   if (in_range) {
     return &(ima->gputexture[textarget][multiview_eye]);
@@ -310,9 +311,17 @@ static GPUTexture *image_get_gpu_texture(Image *ima,
    * the current `pass` and `layer` should be 0. */
   short requested_pass = iuser ? iuser->pass : 0;
   short requested_layer = iuser ? iuser->layer : 0;
-  if (ima->gpu_pass != requested_pass || ima->gpu_layer != requested_layer) {
+  short requested_view = iuser ? iuser->multi_index : 0;
+  /* There is room for 2 multiview textures. When a higher number is requested we should always
+   * target the first view slot. This is fine as multi view images aren't used together. */
+  if (requested_view < 2) {
+    requested_view = 0;
+  }
+  if (ima->gpu_pass != requested_pass || ima->gpu_layer != requested_layer ||
+      ima->gpu_view != requested_view) {
     ima->gpu_pass = requested_pass;
     ima->gpu_layer = requested_layer;
+    ima->gpu_view = requested_view;
     ima->gpuflag |= IMA_GPU_REFRESH;
   }
 
@@ -345,9 +354,10 @@ static GPUTexture *image_get_gpu_texture(Image *ima,
   BKE_image_tag_time(ima);
 
   /* Test if we already have a texture. */
-  const int current_view = iuser ? ((iuser->flag & IMA_SHOW_STEREO) != 0 ? iuser->multiview_eye :
-                                                                           iuser->view) :
-                                   0;
+  int current_view = iuser ? iuser->multi_index : 0;
+  if (current_view >= 2) {
+    current_view = 0;
+  }
   GPUTexture **tex = get_image_gpu_texture_ptr(ima, textarget, current_view);
   if (*tex) {
     return *tex;
diff --git a/source/blender/draw/engines/image/image_engine.c b/source/blender/draw/engines/image/image_engine.c
index 5445685b5ba..04bdee131d7 100644
--- a/source/blender/draw/engines/image/image_engine.c
+++ b/source/blender/draw/engines/image/image_engine.c
@@ -110,9 +110,7 @@ static void space_image_gpu_texture_get(Image *image,
     /* update multiindex and pass for the current eye */
     BKE_image_multilayer_index(image->rr, &sima->iuser);
   }
-  else {
-    BKE_image_multiview_index(image, &sima->iuser);
-  }
+  BKE_image_multiview_index(image, &sima->iuser);
 
   if (ibuf) {
     if (sima->flag & SI_SHOW_ZBUF && (ibuf->zbuf || ibuf->zbuf_float || (ibuf->channels == 1))) {
diff --git a/source/blender/makesdna/DNA_image_types.h b/source/blender/makesdna/DNA_image_types.h
index eb03e047c90..5db30b70449 100644
--- a/source/blender/makesdna/DNA_image_types.h
+++ b/source/blender/makesdna/DNA_image_types.h
@@ -157,6 +157,7 @@ typedef struct Image {
   short gpuflag;
   short gpu_pass;
   short gpu_layer;
+  short gpu_view;
   char _pad2[6];
 
   /** Deprecated. */