api(ImageBuf): IB::localpixels_as_[writable_]byte_image_span (AcademySoftwareFoundation#5011)

Utilities to ask the IB for the local pixels as an untyped span of
bytes. This is a "safe" alternative to `localpixels()`, which just
returned a single pointer, instead returning an image_span that
understands the sizes and strides of the buffer.

---------

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

Author: lgritz

src/include/OpenImageIO/imagebuf.h

@@ -1369,6 +1369,16 @@ class OIIO_API ImageBuf {
     void* localpixels();
     const void* localpixels() const;
 
+    /// Return an `image_span<const std::byte>` giving the extent and layout
+    /// of "local" pixel memory, if they are fully in RAM and not backed by an
+    /// ImageCache, or an empty span otherwise.
+    image_span<const std::byte> localpixels_as_byte_image_span() const;
+
+    /// Return an `image_span<std::byte>` giving the extent and layout of
+    /// "local" pixel memory, if they are fully in RAM and not backed by an
+    /// ImageCache, and it is a writable IB, or an empty span otherwise.
+    image_span<std::byte> localpixels_as_writable_byte_image_span();
+
     /// Pixel-to-pixel stride within the localpixels memory.
     stride_t pixel_stride() const;
     /// Scanline-to-scanline stride within the localpixels memory.

src/libOpenImageIO/imagebuf.cpp

@@ -2140,6 +2140,22 @@ ImageBuf::localpixels()
 
 
 
+image_span<const std::byte>
+ImageBuf::localpixels_as_byte_image_span() const
+{
+    return m_impl->m_bufspan;
+}
+
+
+
+image_span<std::byte>
+ImageBuf::localpixels_as_writable_byte_image_span()
+{
+    return m_impl->m_readonly ? image_span<std::byte>() : m_impl->m_bufspan;
+}
+
+
+
 const void*
 ImageBuf::localpixels() const
 {