[Olympus] Allow decoding textures externally

- allow TextureProvider to work directly with cgltf_texture
- change ResourceLoader to call TextureProvider with cgltf_texture

Author: zbai-sc

libs/gltfio/include/gltfio/TextureProvider.h

@@ -22,6 +22,8 @@
 
 #include <utils/compiler.h>
 
+class cgltf_texture;
+
 namespace filament {
     class Engine;
     class Texture;
@@ -86,7 +88,16 @@ class UTILS_PUBLIC TextureProvider {
      * Texture object, but it is only safe to do so after it has been popped from the queue.
      */
     virtual Texture* pushTexture(const uint8_t* data, size_t byteCount,
-            const char* mimeType, FlagBits flags) = 0;
+            const char* mimeType, FlagBits flags) {
+        return nullptr;
+    }
+
+    /**
+     * Alternate version of pushTexture, takes raw cgltf_texture data to allow more control.
+     */
+    virtual Texture* pushTexture(const cgltf_texture* srcTexture, FlagBits flags) {
+        return nullptr;
+    }
 
     /**
      * Checks if any texture is ready to be removed from the asynchronous decoding queue, and if so

libs/gltfio/src/ResourceLoader.cpp

@@ -616,16 +616,26 @@ void ResourceLoader::asyncUpdateLoad() {
 
 Texture* ResourceLoader::Impl::getOrCreateTexture(FFilamentAsset* asset, const TextureSlot& tb) {
     const cgltf_texture* srcTexture = tb.texture;
-    const cgltf_image* image = srcTexture->basisu_image ?
-            srcTexture->basisu_image : srcTexture->image;
-    const cgltf_buffer_view* bv = image->buffer_view;
-    const char* uri = image->uri;
-
     TextureProvider::FlagBits flags = {};
     if (tb.srgb) {
         flags |= int(TextureProvider::Flags::sRGB);
     }
 
+    // Check if there is a texture provider that can work with cgtlf_texture.
+    if (auto iter = mTextureProviders.find("cgltf_texture"); iter != mTextureProviders.end()) {
+        TextureProvider* provider = iter->second;
+        Texture* texture = provider->pushTexture(srcTexture, flags);
+        if (texture) {
+            // Note we didn't pass ownership to asset. Caller is responsible for cleaning up.
+            return texture;
+        }
+    }
+
+    const cgltf_image* image = srcTexture->basisu_image ?
+            srcTexture->basisu_image : srcTexture->image;
+    const cgltf_buffer_view* bv = image->buffer_view;
+    const char* uri = image->uri;
+
     std::string mime = image->mime_type ? image->mime_type : "";
     size_t dataUriSize;
     const uint8_t* dataUriContent = uri ? parseDataUri(uri, &mime, &dataUriSize) : nullptr;