Fix Cycles standalone float textures not taking into account colorspace metadata

This got lost in colorspace refactoring at some point. It probably does not
affect many files in practice, but implementation was wrong regardless.

intern/cycles/scene/colorspace.cpp

@@ -95,16 +95,19 @@ bool ColorSpaceManager::colorspace_is_data(ustring colorspace)
 }
 
 ustring ColorSpaceManager::detect_known_colorspace(ustring colorspace,
+                                                   const char *file_colorspace,
                                                    const char *file_format,
                                                    bool is_float)
 {
   if (colorspace == u_colorspace_auto) {
     /* Auto detect sRGB or raw if none specified. */
     if (is_float) {
-      bool srgb = (colorspace == "sRGB" || colorspace == "GammaCorrected" ||
-                   (colorspace.empty() &&
-                    (strcmp(file_format, "png") == 0 || strcmp(file_format, "tiff") == 0 ||
-                     strcmp(file_format, "dpx") == 0 || strcmp(file_format, "jpeg2000") == 0)));
+      bool srgb = (strcmp(file_colorspace, "sRGB") == 0 ||
+                   strcmp(file_colorspace, "GammaCorrected") == 0 ||
+                   (file_colorspace[0] == '\0' &&
+                    (strcmp(file_format, "png") == 0 || strcmp(file_format, "jpeg") == 0 ||
+                     strcmp(file_format, "tiff") == 0 || strcmp(file_format, "dpx") == 0 ||
+                     strcmp(file_format, "jpeg2000") == 0)));
       return srgb ? u_colorspace_srgb : u_colorspace_raw;
     }
     else {

intern/cycles/scene/colorspace.h

@@ -21,6 +21,7 @@ class ColorSpaceManager {
    * convert to and from. If the colorspace is u_colorspace_auto, we auto
    * detect a colospace. */
   static ustring detect_known_colorspace(ustring colorspace,
+                                         const char *file_colorspace,
                                          const char *file_format,
                                          bool is_float);
 

intern/cycles/scene/image.cpp

@@ -261,7 +261,7 @@ void ImageMetaData::detect_colorspace()
 {
   /* Convert used specified color spaces to one we know how to handle. */
   colorspace = ColorSpaceManager::detect_known_colorspace(
-      colorspace, colorspace_file_format, is_float());
+      colorspace, colorspace_file_hint.c_str(), colorspace_file_format, is_float());
 
   if (colorspace == u_colorspace_raw) {
     /* Nothing to do. */

intern/cycles/scene/image.h

@@ -69,6 +69,7 @@ class ImageMetaData {
 
   /* Optional color space, defaults to raw. */
   ustring colorspace;
+  string colorspace_file_hint;
   const char *colorspace_file_format;
 
   /* Optional transform for 3D images. */

intern/cycles/scene/image_oiio.cpp

@@ -85,6 +85,7 @@ bool OIIOImageLoader::load_metadata(const ImageDeviceFeatures & /*features*/,
   }
 
   metadata.colorspace_file_format = in->format_name();
+  metadata.colorspace_file_hint = spec.get_string_attribute("oiio:ColorSpace");
 
   in->close();