build

Iron Law

YOU MUST BUILD LOCALLY AND VERIFY IT PASSES BEFORE EVERY PUSH.
No exceptions.

Violating the letter of this rule is violating the spirit of this rule.

Announce at start: "I am using the build skill to [build/configure/troubleshoot] [description]."

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BEFORE PROCEEDING

Before pushing any change:

1. cmake --build build exits 0 - no build errors
2. ./build/tests/ParticleViewerTests exits 0 - all tests pass
3. Every FetchContent_Declare has a GIT_TAG pinned to a tag or commit SHA, not a branch name
4. No new dependency duplicates an existing transitive dependency at a different version
5. If shader files were changed: build was re-run so Viewer-Assets/shaders/ is current

[+] All met -> proceed to push [-] Any unmet -> fix before pushing

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Core Principle: CMake Is the Single Source of Build Truth

All build configuration lives in CMakeLists.txt. No manual file copying, no build scripts beyond convenience wrappers.

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Step 1: Build Commands

# Standard build
cmake -B build -S .
cmake --build build

# Development mode (all warnings + coverage)
cmake -B build -S . -Dalloutput=ON
cmake --build build

# Run the application
./build/Viewer

# Install (copies binary + shader assets to bin/)
cmake --install build

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Step 2: Build Requirements

Requirement	Minimum Version
CMake	3.24
C++ compiler	C++20 (GCC >= 10, Clang >= 11, MSVC 2019+)
OpenGL	Development libraries (OpenGL::GL target)
GLM	System-installed
SDL3	Auto-downloaded via FetchContent (local) or Flatpak module
clang-format	For code formatting
clang-tidy	For static analysis (advisory)

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Step 3: Dependency Management

SDL3

• Local builds: CMakeLists.txt calls find_package(SDL3) first, falls back to FetchContent if not found.
• Flatpak builds: SDL3 is built as a standalone Flatpak module (before the app) so the Freedesktop SDK pkg-config paths detect SDL_X11 and SDL_WAYLAND. FetchContent is NOT used in Flatpak.

Dear ImGui

• Always downloaded via FetchContent.

Embedded Libraries (no management needed)

• src/glad/ -- GLAD OpenGL loader
• src/stb_*.h -- stb single-header libraries

Dependency Upgrades

• Allowed as long as all tests pass and build succeeds
• Visual regression tests are a hard requirement -- must pass without modification unless the approver is explicitly shown the new output
• Test updates for API changes (e.g., GoogleTest) are acceptable

One Version Rule

Iron Gate: One version of each dependency in the build. No version aliases, no parallel installations, no if(FOUND v1) else(use v2) chains.

Rule: Before adding or upgrading any dependency:

1. Check if that library is already a transitive dependency of another component
2. If it is: use the existing version -- upgrade if needed, never add a parallel version
3. If a diamond dependency arises (A needs lib@v1, B needs lib@v2): resolve by upgrading to the higher version and confirming both A and B still work
4. Document the version pin (tag or commit SHA) in CMakeLists.txt -- never use HEAD or main as a FetchContent ref in production builds

Gate: grep -r "FetchContent_Declare" CMakeLists.txt -- every FetchContent_Declare must have a GIT_TAG pinned to a specific version, not a branch name.

[+] All tags pinned to a version tag or commit SHA -> proceed to add or upgrade the dependency [-] Any tag references a branch name -> fix the ref before proceeding

# CORRECT -- pinned to tag
FetchContent_Declare(some_lib GIT_REPOSITORY ... GIT_TAG v1.2.3)

# WRONG -- pinned to branch (non-reproducible)
FetchContent_Declare(some_lib GIT_REPOSITORY ... GIT_TAG main)

Rationalization: "The HEAD version has the fix we need." Counter: pin to the commit SHA that contains the fix, not to HEAD. Unpinned HEAD = a different build every cmake run.

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Step 4: Build Notes

• Shaders: Files in src/shaders/ are auto-copied to Viewer-Assets/shaders/ during build.
• Tests: Enabled by default (BUILD_TESTS=ON). Run with ./build/tests/ParticleViewerTests.
• Version: See versioning skill for how version is resolved at build time.

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Step 5: Troubleshooting

Missing SDL3: Run cmake -B build -S . -- SDL3 downloads automatically via FetchContent.

OpenGL headers not found: Install OpenGL development packages. Ensure OpenGL::GL CMake target is available.

Shader files not found at runtime: Run from the build directory, or ensure Viewer-Assets/shaders/ exists alongside the binary.

Flatpak build issues: See the flatpak skill for MSAA fallback, SDL3 module setup, NVIDIA GL workarounds, and setenv gotchas.

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Rationalization Prevention

Excuse	Reality
"Small change, can't break the build"	Even single-line changes break builds. Run cmake --build build first.
"CI will catch it if the build fails"	CI is a safety net. Don't push broken builds intentionally.
"It built fine yesterday"	Dependencies change. State changes. Build locally before every push.
"The CMake error is too confusing to parse"	Read the first 10 lines of error output -- that's always where the root cause is.
"I'll fix the FetchContent pin later"	Unpinned dependencies produce non-reproducible builds. Pin to tag/commit now.
"The tests don't need to be in the build target"	All test targets must build cleanly. No orphaned test binaries.

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Red Flags -- STOP

If you catch yourself thinking any of these, stop and follow the rule:

• "I'll push and see if CI builds it"
• "This small change couldn't break CMake"
• "The dependency version doesn't really matter"
• "I don't understand the CMake error but it probably works"
• "I'll update the dependency pin in a follow-up"
• About to push without running cmake --build build locally

All of these mean: Run cmake --build build locally. Read the full output. Fix errors before pushing.

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Reference

• Flatpak manifest: flatpak/org.particleviewer.ParticleViewer.yaml
• Flatpak GL/SDL3 gotchas: see the flatpak skill
• Build scripts: scripts/linuxBuildAndInstall.sh, scripts/build-flatpak.sh