Images: change alpha settings to support channel packing

This also replaces the Use Alpha setting. We now have these alpha modes:

* Straight: store RGB and alpha channels separately with alpha acting as a
  mask, also known as unassociated alpha.
* Premultiplied: transparent RGB pixels are multiplied by the alpha channel.
  The natural format for renders.
* Channel Packed: different images are packed in the RGB and alpha channels,
  and they should not influence each other. Channel packing is commonly used
  by game engines to save memory.
* None: ignore alpha channel from the file and make image fully opaque.

Cycles OSL does not correctly support Channel Packed and None yet, we are
missing fine control over the OpenImageIO texture cache to do that.

Fixes T53672

1 files changed, 16 insertions, 14 deletions

diff --git a/intern/cycles/render/image.cpp b/intern/cycles/render/image.cpp
index 6301b416724..160e7d9ff1e 100644
--- a/intern/cycles/render/image.cpp
+++ b/intern/cycles/render/image.cpp
@@ -299,12 +299,12 @@ static bool image_equals(ImageManager::Image *image,
                          void *builtin_data,
                          InterpolationType interpolation,
                          ExtensionType extension,
-                         bool use_alpha,
+                         ImageAlphaType alpha_type,
                          ustring colorspace)
 {
   return image->filename == filename && image->builtin_data == builtin_data &&
          image->interpolation == interpolation && image->extension == extension &&
-         image->use_alpha == use_alpha && image->colorspace == colorspace;
+         image->alpha_type == alpha_type && image->colorspace == colorspace;
 }
 
 int ImageManager::add_image(const string &filename,
@@ -313,7 +313,7 @@ int ImageManager::add_image(const string &filename,
                             float frame,
                             InterpolationType interpolation,
                             ExtensionType extension,
-                            bool use_alpha,
+                            ImageAlphaType alpha_type,
                             ustring colorspace,
                             ImageMetaData &metadata)
 {
@@ -338,14 +338,15 @@ int ImageManager::add_image(const string &filename,
   /* Fnd existing image. */
   for (slot = 0; slot < images[type].size(); slot++) {
     img = images[type][slot];
-    if (img && image_equals(
-                   img, filename, builtin_data, interpolation, extension, use_alpha, colorspace)) {
+    if (img &&
+        image_equals(
+            img, filename, builtin_data, interpolation, extension, alpha_type, colorspace)) {
       if (img->frame != frame) {
         img->frame = frame;
         img->need_load = true;
       }
-      if (img->use_alpha != use_alpha) {
-        img->use_alpha = use_alpha;
+      if (img->alpha_type != alpha_type) {
+        img->alpha_type = alpha_type;
         img->need_load = true;
       }
       if (img->colorspace != colorspace) {
@@ -399,7 +400,7 @@ int ImageManager::add_image(const string &filename,
   img->interpolation = interpolation;
   img->extension = extension;
   img->users = 1;
-  img->use_alpha = use_alpha;
+  img->alpha_type = alpha_type;
   img->colorspace = colorspace;
   img->mem = NULL;
 
@@ -445,7 +446,7 @@ void ImageManager::remove_image(const string &filename,
                                 void *builtin_data,
                                 InterpolationType interpolation,
                                 ExtensionType extension,
-                                bool use_alpha,
+                                ImageAlphaType alpha_type,
                                 ustring colorspace)
 {
   size_t slot;
@@ -457,7 +458,7 @@ void ImageManager::remove_image(const string &filename,
                                              builtin_data,
                                              interpolation,
                                              extension,
-                                             use_alpha,
+                                             alpha_type,
                                              colorspace)) {
         remove_image(type_index_to_flattened_slot(slot, (ImageDataType)type));
         return;
@@ -474,7 +475,7 @@ void ImageManager::tag_reload_image(const string &filename,
                                     void *builtin_data,
                                     InterpolationType interpolation,
                                     ExtensionType extension,
-                                    bool use_alpha,
+                                    ImageAlphaType alpha_type,
                                     ustring colorspace)
 {
   for (size_t type = 0; type < IMAGE_DATA_NUM_TYPES; type++) {
@@ -484,7 +485,7 @@ void ImageManager::tag_reload_image(const string &filename,
                                              builtin_data,
                                              interpolation,
                                              extension,
-                                             use_alpha,
+                                             alpha_type,
                                              colorspace)) {
         images[type][slot]->need_load = true;
         break;
@@ -516,7 +517,8 @@ bool ImageManager::file_load_image_generic(Image *img, unique_ptr<ImageInput> *i
     /* For typical RGBA images we let OIIO convert to associated alpha,
      * but some types we want to leave the RGB channels untouched. */
     const bool associate_alpha = !(ColorSpaceManager::colorspace_is_data(img->colorspace) ||
-                                   img->use_alpha == false);
+                                   img->alpha_type == IMAGE_ALPHA_IGNORE ||
+                                   img->alpha_type == IMAGE_ALPHA_CHANNEL_PACKED);
 
     if (!associate_alpha) {
       config.attribute("oiio:UnassociatedAlpha", 1);
@@ -692,7 +694,7 @@ bool ImageManager::file_load_image(Image *img,
     }
 
     /* Disable alpha if requested by the user. */
-    if (img->use_alpha == false) {
+    if (img->alpha_type == IMAGE_ALPHA_IGNORE) {
       for (size_t i = num_pixels - 1, pixel = 0; pixel < num_pixels; pixel++, i--) {
         pixels[i * 4 + 3] = one;
       }