Simplify texture reader/writer code

[WeirdRubberDuck]

Simplifies the code by:

• Removing the possibility of adding new readers/writers (which were essentially unused). Now there is just one file for reading and one file for writing, both using STB
• Getting rid of the class and singleton pattern, and replacing the calls with normal functions in a texture namespace

Note that this breaks the support for reading .cmap files as textures. This has been reimplemented in the OpenSpace part of the PR:

Also not that this is a first step as part of a bigger rewrite to give us more flexibility in the texture reading, now that we can't change the format, etc., of a texture after it's created.

[Copilot]

Pull request overview

This PR refactors Ghoul’s texture IO by removing the extensible reader/writer registry and replacing it with STB-based free functions under ghoul::io::texture, updating call sites and build files accordingly.

Changes:

• Removed TextureReaderBase/TextureWriterBase plus the STB/CMAP concrete reader/writer classes, and simplified the public API to functions in ghoul::io::texture.
• Implemented STB-based loadTexture/imageSize and saveTexture directly in texturereader.cpp / texturewriter.cpp.
• Updated Assimp model loading to use the new texture reader API and cleaned up src/CMakeLists.txt sources/headers lists.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
src/io/texture/texturewriter.cpp	Inlined STB-based texture writing into a free-function API
include/ghoul/io/texture/texturewriter.h	Replaced class-based writer API with ghoul::io::texture functions/exceptions
src/io/texture/texturereader.cpp	Inlined STB-based texture reading and extension support helpers
include/ghoul/io/texture/texturereader.h	Replaced class-based reader API with ghoul::io::texture functions/exceptions
src/io/model/modelreaderassimp.cpp	Updated embedded/local texture loading to call texture::loadTexture and new exception types
src/CMakeLists.txt	Removed deleted texture IO sources/headers from the build
src/io/texture/texturewriterstb.cpp (deleted)	Removed STB writer class implementation
include/ghoul/io/texture/texturewriterstb.h (deleted)	Removed STB writer class declaration
src/io/texture/texturewriterbase.cpp (deleted)	Removed writer base exception implementation
include/ghoul/io/texture/texturewriterbase.h (deleted)	Removed writer base abstraction
src/io/texture/texturereaderstb.cpp (deleted)	Removed STB reader class implementation
include/ghoul/io/texture/texturereaderstb.h (deleted)	Removed STB reader class declaration
src/io/texture/texturereadercmap.cpp (deleted)	Removed CMAP reader implementation (per PR note)
include/ghoul/io/texture/texturereadercmap.h (deleted)	Removed CMAP reader declaration
src/io/texture/texturereaderbase.cpp (deleted)	Removed reader base exception implementation
include/ghoul/io/texture/texturereaderbase.h (deleted)	Removed reader base abstraction

Comments suppressed due to low confidence (1)

src/io/model/modelreaderassimp.cpp:156

• The embedded-texture load path catches texture::InvalidLoadException, but texture::loadTexture(void* memory, ...) no longer throws InvalidLoadException when the format is unsupported; it throws MissingReaderException instead. As a result, unsupported embedded textures may now escape this try/catch and fail the model load rather than falling back to a debug texture.

Either update this catch list to handle texture::MissingReaderException (and/or std::exception) for the embedded case, or restore throwing InvalidLoadException from the reader for unsupported embedded formats.

                    try {
                        textureEntry.texture = texture::loadTexture(
                            static_cast<void*>(texture->pcData),
                            texture->mWidth,
                            2,
                            {},
                            texture->achFormatHint
                        );
                        textureEntry.texture->setName(path.C_Str());
                        meshTexture.texture = textureEntry.texture.get();
                    }
                    catch (const texture::InvalidLoadException& e) {
                        LWARNING(std::format(
                            "Could not load unsupported texture from '{}' with size "
                            "'{}': Replacing with flashy color", e._memory, e._size
                        ));

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[Copilot]

saveTexture unconditionally calls std::filesystem::create_directory(path(filename).parent_path()). If filename is in the current directory (no parent path), parent_path() is empty and create_directory("") can throw std::filesystem::filesystem_error.

Consider guarding with if (!parent.empty()) and using create_directories to handle nested paths.

[Copilot]

The STB write calls (stbi_write_*) return a success/failure value, but the return is currently ignored. This means write failures (permissions, disk full, invalid path) will silently succeed from the caller's perspective.

Capture the return value and throw TextureWriteException when a write fails so callers can handle errors deterministically.