Release all images in MetalTextureHandler::releaseRenderResources (#2316)

This PR addresses #2303.

This brings the MetalTextureHandler inline with the GLTextureHandler for releasing all the images when `nullptr` is passed.

Without this - both CPU and Metal texture memory is being leaked if the image caches are flushed.  

Recursively releasing the resources fixes the Metal texture memory leak, but that just highlighted the CPU side memory leak.  This is due to the MetalTextureHandler also retaining an `ImagePtr` in `_imageBindingInfo`.  Removing the `ImagePtr` from this storage fixes the memory leak, and it doesn't seem to be necessary to store the image, the only thing the image is used for is to access the resource ID - which is the same as the key to the `unordered_map`.

Author: ld-kerley

source/MaterialXRenderMsl/MetalTextureHandler.h

@@ -89,7 +89,7 @@ class MX_RENDERMSL_API MetalTextureHandler : public ImageHandler
     std::vector<unsigned int> _boundTextureLocations;
 
     std::unordered_map<unsigned int, id<MTLTexture>> _metalTextureMap;
-    std::unordered_map<unsigned int, std::pair<ImagePtr, ImageSamplingProperties>> _imageBindingInfo;
+    std::unordered_map<unsigned int, ImageSamplingProperties> _imageBindingInfo;
     std::unordered_map<ImageSamplingProperties, id<MTLSamplerState>, ImageSamplingKeyHasher> _imageSamplerStateMap;
 
     id<MTLDevice> _device = nil;

source/MaterialXRenderMsl/MetalTextureHandler.mm

@@ -29,7 +29,7 @@
             return false;
         }
     }
-    _imageBindingInfo[image->getResourceId()] = std::make_pair(image, samplingProperties);
+    _imageBindingInfo[image->getResourceId()] = samplingProperties;
     return true;
 }
 
@@ -72,7 +72,7 @@
     _boundTextureLocations[textureUnit] = image->getResourceId();
 
     [renderCmdEncoder setFragmentTexture:_metalTextureMap[image->getResourceId()] atIndex:textureUnit];
-    [renderCmdEncoder setFragmentSamplerState:getSamplerState(_imageBindingInfo[image->getResourceId()].second) atIndex:textureUnit];
+    [renderCmdEncoder setFragmentSamplerState:getSamplerState(_imageBindingInfo[image->getResourceId()]) atIndex:textureUnit];
 
     return true;
 }
@@ -90,15 +90,10 @@
 
 id<MTLTexture> MetalTextureHandler::getMTLTextureForImage(unsigned int index) const
 {
-    auto imageInfo = _imageBindingInfo.find(index);
-    if (imageInfo != _imageBindingInfo.end())
+    auto metalTexture = _metalTextureMap.find(index);
+    if (metalTexture != _metalTextureMap.end())
     {
-        if (!imageInfo->second.first)
-            return nil;
-
-        auto metalTexture = _metalTextureMap.find(imageInfo->second.first->getResourceId());
-        if (metalTexture != _metalTextureMap.end())
-            return metalTexture->second;
+        return metalTexture->second;
     }
 
     return nil;
@@ -109,7 +104,7 @@
     auto imageInfo = _imageBindingInfo.find(index);
     if (imageInfo != _imageBindingInfo.end())
     {
-        return getSamplerState(imageInfo->second.second);
+        return getSamplerState(imageInfo->second);
     }
     return nil;
 }
@@ -281,7 +276,16 @@
 void MetalTextureHandler::releaseRenderResources(ImagePtr image)
 {
     if (!image)
+    {
+        for (auto iter : _imageCache)
+        {
+            if (iter.second)
+            {
+                releaseRenderResources(iter.second);
+            }
+        }
         return;
+    }
 
     if (image->getResourceId() == MslProgram::UNDEFINED_METAL_RESOURCE_ID)
     {