glTF images with data URI lose their URI during parsing

[ptc-tgamper]

Describe the issue

During parsing of glTF Images that store their data in a data URI, the latter is discarded. Only images that reference an external file keep their URI, see

tinygltf/tiny_gltf.h

Line 4398 in 10b23b6

image->uri = uri;

Therefore, when one uses a custom image loader that leaves image.image empty, the image data cannot be loaded later from the original data URI.

To Reproduce

• OS
• Compiler, compiler version, compile options
• Please attach minimal and reproducible .glTF file if you got an issue related to .glTF data

Expected behaviour

The image's URI should not be discarded if it is not loaded into image.image

Screenshots

If applicable, add screenshots to help explain your problem.

Additional context
We are using a custom image loaderto avoid loading images into memory, since our models have Gigabytes of images. Naturally then the custom image writer needs to have access to the original image data. But the original image.uri has been lost during parsing.

[syoyo]

You should describe the issue in clear manner. Also should attach minimal reproducible code&gltf file.

[ptc-tgamper]

#498 has a respective test case. It generates a glTF file that shows the problem on the fly.

I can rework the description here, if that is ok? And attach a glTF that shows the problem.