refactor!: de-virtualize IC and TS (#4384)

Background: The ImageCache and TextureSystem had historically been
implemented as pure virtual abstract base classe defining an interface,
then a hidden concrete subclass. The flexibility this was intended to
provide was never really used; instead the imagined main client for the
flexibility, OSL, has a different mechanism for customizing the texture
system (via their RendererServices class). Meanwhile, this has made the
interfaces to IC and TS impossible to change without breaking the ABI.

So this PR does the following:

* ImageCache and TextureSytem are fullly de-virtualized, and are now
concrete classes, no hidden subclassing, no virtual methods. As such,
removing or changing existing methods will be an ABI break, but adding
new methods is not.

* Each now use a PIMPL idiom, where all the data and internal methods
are hidden from the public interface and do not affect the ABI.

* Roughly speaking, we added the PIMPL pointers and made the
ImageCacheImpl/TextureSystemImpl -- what used to be the hidden concrete
subclasses -- into the hidden PIMPL classes.

* Moved a lot of classes that used to be in a "pvt" namespace into the
main namespace. If they are opaque types not exposed in public headers
or as symbols exported from the library, it doesn't matter, so this just
removes some arbitrary clutter.

* Had to rearrange some of the recently added heapsize/footprint code,
moved some inline functions in the headers into methods of the classes,
defined in the cpp files.

This itself is a huge ABI change, so will only be merged into master, to
become part of the 3.0 release. This is not an API change, though! This
is all about the internals, and should not require any client software
to change a single line of code.

I may do further simplification or refactoring of this code in the
future, but that will all be smaller and have no further API/ABI changes
that break compatibility.

Although the structure of the class hierarchy has changed around, none
of the logic about how IC and TS actually *work* has changed, so there
should be no change in observable behavior.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/include/OpenImageIO/imagebuf.h

@@ -25,10 +25,7 @@ OIIO_NAMESPACE_BEGIN
 class ImageBuf;
 class ImageBufImpl;  // Opaque type for the unique_ptr.
 class ImageCache;
-
-namespace pvt {
 class ImageCacheTile;
-};  // namespace pvt
 
 
 
@@ -1369,7 +1366,7 @@ class OIIO_API ImageBuf {
         int m_rng_xbegin, m_rng_xend, m_rng_ybegin, m_rng_yend, m_rng_zbegin,
             m_rng_zend;
         int m_x, m_y, m_z;
-        pvt::ImageCacheTile* m_tile = nullptr;
+        ImageCacheTile* m_tile = nullptr;
         int m_tilexbegin, m_tileybegin, m_tilezbegin;
         int m_tilexend;
         int m_nchannels;
@@ -1638,7 +1635,7 @@ class OIIO_API ImageBuf {
     // tile for the given pixel, and return the ptr to the actual pixel
     // within the tile. If any read errors occur, set haderror=true (but
     // if there are no errors, do not modify haderror).
-    const void* retile(int x, int y, int z, pvt::ImageCacheTile*& tile,
+    const void* retile(int x, int y, int z, ImageCacheTile*& tile,
                        int& tilexbegin, int& tileybegin, int& tilezbegin,
                        int& tilexend, bool& haderr, bool exists,
                        WrapMode wrap) const;

src/include/OpenImageIO/imagecache.h

@@ -203,6 +203,54 @@ OIIO_NAMESPACE_BEGIN
 using namespace pvt;
 using namespace simd;
 
+
+bool
+TextureSystem::environment(ustring filename, TextureOpt& options, V3fParam R,
+                           V3fParam dRdx, V3fParam dRdy, int nchannels,
+                           float* result, float* dresultds, float* dresultdt)
+{
+    return m_impl->environment(filename, options, R, dRdx, dRdy, nchannels,
+                               result, dresultds, dresultdt);
+}
+
+
+bool
+TextureSystem::environment(TextureHandle* texture_handle,
+                           Perthread* thread_info, TextureOpt& options,
+                           V3fParam R, V3fParam dRdx, V3fParam dRdy,
+                           int nchannels, float* result, float* dresultds,
+                           float* dresultdt)
+{
+    return m_impl->environment(texture_handle, thread_info, options, R, dRdx,
+                               dRdy, nchannels, result, dresultds, dresultdt);
+}
+
+
+bool
+TextureSystem::environment(ustring filename, TextureOptBatch& options,
+                           Tex::RunMask mask, const float* R, const float* dRdx,
+                           const float* dRdy, int nchannels, float* result,
+                           float* dresultds, float* dresultdt)
+{
+    return m_impl->environment(filename, options, mask, R, dRdx, dRdy,
+                               nchannels, result, dresultds, dresultdt);
+}
+
+
+bool
+TextureSystem::environment(TextureHandle* texture_handle,
+                           Perthread* thread_info, TextureOptBatch& options,
+                           Tex::RunMask mask, const float* R, const float* dRdx,
+                           const float* dRdy, int nchannels, float* result,
+                           float* dresultds, float* dresultdt)
+{
+    return m_impl->environment(texture_handle, thread_info, options, mask, R,
+                               dRdx, dRdy, nchannels, result, dresultds,
+                               dresultdt);
+}
+
+
+
 namespace pvt {
 
 
@@ -225,6 +273,8 @@ vector_to_latlong(const Imath::V3f& R, bool y_is_up, float& s, float& t)
         t = 0.0f;
 }
 
+}  // namespace pvt
+
 
 
 bool
@@ -594,6 +644,4 @@ TextureSystemImpl::environment(ustring filename, TextureOptBatch& options,
 }
 
 
-}  // end namespace pvt
-
 OIIO_NAMESPACE_END