Add shader cross-compilation pipeline for Hello examples

[jdolan]

Replaces hard-coded MSL string constants in Hello.c / HelloCompute.c with a proper cross-platform HLSL→blob pipeline.

What's new

Examples/Shaders/ (new subdirectory)

Five HLSL sources + pre-compiled blobs versioned in the repo so consumers never need shadercross installed to build:

Shader	Stage	Entry point
Hello.vert.hlsl	vertex	vs_main
Hello.frag.hlsl	fragment	fs_main
HelloCompute.comp.hlsl	compute	cs_main
HelloCompute.vert.hlsl	vertex	vs_main
HelloCompute.frag.hlsl	fragment	fs_main

Each ships as .msl + .spv (built via glslc + shadercross). .dxil stubs are committed as empty placeholders pending a DXC-enabled shadercross build.

Examples/Shaders/Makefile.am

make shadercross regenerates all blobs. Rules: glslc HLSL→SPIR-V, shadercross SPIR-V→MSL, shadercross HLSL→DXIL. EXTRA_DIST includes all sources and blobs. all-local symlinks blobs into the build dir for out-of-tree builds.

ObjectivelyGPU-shadercross Xcode aggregate target

"Compile Shaders" run-script build phase with declared input/output paths for incremental rebuilds.

ObjectivelyGPU-shadercross.vcxproj (new)

VS Utility project with CustomBuild items per HLSL file; added to ObjectivelyGPU.sln.

RenderDevice::loadComputePipeline()

Parallel to loadShader() for compute stages — resolves the platform blob by format priority (MSL → DXIL → SPIR-V), fills code/code_size/format in SDL_GPUComputePipelineCreateInfo, and calls createComputePipeline.

Hello.c / HelloCompute.c

• All inline MSL constants and create_shader() helpers removed
• Resource path set at startup: SDL_GetBasePath() + "Shaders"
• loadShader("Hello.vert", …) / loadShader("Hello.frag", …) etc.
• loadComputePipeline("HelloCompute.comp", …) for the compute stage

Entry-point convention

HLSL entry points vs_main / fs_main / cs_main are preserved verbatim in MSL and SPIR-V output (only a literal main is renamed to main0 by SPIRV-Cross). No loadShader patching needed.

One known gap

DXIL blobs are empty stubs — the installed shadercross was built without DXC support. The Makefile, Xcode, and VS rules are all wired up; they just need a DXC-enabled shadercross to produce real outputs.

[Copilot]

Pull request overview

This PR replaces inline Metal shader source in the Hello examples with a versioned, cross-platform shader asset pipeline (HLSL sources + precompiled blobs), and adds a RenderDevice helper for compute pipelines to load compiled blobs via the Resource system.

Changes:

• Added RenderDevice::loadComputePipeline() to load compute shader blobs via Resource and create compute pipelines.
• Added Examples/Shaders/ with HLSL sources plus committed platform blobs, and build-system wiring (Autotools + Xcode aggregate target + VS utility project) to regenerate them.
• Updated Hello.c / HelloCompute.c to load shaders/pipelines from the shader assets directory at runtime.

Reviewed changes

Copilot reviewed 20 out of 30 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
Sources/ObjectivelyGPU/RenderDevice.h	Adds public interface + Doxygen for loadComputePipeline.
Sources/ObjectivelyGPU/RenderDevice.c	Implements loadComputePipeline and wires it into the class interface.
ObjectivelyGPU.xcodeproj/project.pbxproj	Adds ObjectivelyGPU-shadercross aggregate target and a “Compile Shaders” run-script phase with declared inputs/outputs.
ObjectivelyGPU.vs15/ObjectivelyGPU.sln	Adds the ObjectivelyGPU-shadercross utility project to the solution.
ObjectivelyGPU.vs15/ObjectivelyGPU-shadercross.vcxproj	Adds per-shader CustomBuild steps to run shadercross for SPIR-V/MSL/DXIL.
Examples/Shaders/Makefile.am	Adds make shadercross rules, EXTRA_DIST, and out-of-tree symlink behavior for blob discovery.
Examples/Shaders/Hello.vert.hlsl	New HLSL source for Hello vertex stage.
Examples/Shaders/Hello.frag.hlsl	New HLSL source for Hello fragment stage.
Examples/Shaders/HelloCompute.comp.hlsl	New HLSL source for HelloCompute compute stage.
Examples/Shaders/HelloCompute.vert.hlsl	New HLSL source for HelloCompute vertex stage.
Examples/Shaders/HelloCompute.frag.hlsl	New HLSL source for HelloCompute fragment stage.
Examples/Shaders/Hello.vert.msl	New precompiled MSL blob for Hello vertex stage.
Examples/Shaders/Hello.frag.msl	New precompiled MSL blob for Hello fragment stage.
Examples/Shaders/HelloCompute.comp.msl	New precompiled MSL blob for HelloCompute compute stage.
Examples/Shaders/HelloCompute.vert.msl	New precompiled MSL blob for HelloCompute vertex stage.
Examples/Shaders/HelloCompute.frag.msl	New precompiled MSL blob for HelloCompute fragment stage.
Examples/Shaders/Hello.vert.dxil	Empty DXIL placeholder blob (stub).
Examples/Shaders/Hello.frag.dxil	Empty DXIL placeholder blob (stub).
Examples/Shaders/HelloCompute.comp.dxil	Empty DXIL placeholder blob (stub).
Examples/Shaders/HelloCompute.vert.dxil	Empty DXIL placeholder blob (stub).
Examples/Shaders/HelloCompute.frag.dxil	Empty DXIL placeholder blob (stub).
Examples/Makefile.am	Adds Shaders subdir so shader assets are included in the examples build/install flow.
Examples/Hello.c	Switches to Resource-based shader loading and sets shader resource path at startup.
Examples/HelloCompute.c	Switches to Resource-based shader + compute pipeline loading and sets shader resource path at startup.
configure.ac	Registers Examples/Shaders/Makefile for Autotools generation.