276 lines
10 KiB
Markdown
276 lines
10 KiB
Markdown
# AGENTS.md — Prism
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## Project Identity
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**Prism** is a node-based image compositing tool. Images flow through a directed
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acyclic graph (DAG) of processing nodes (read, blend, colour-grade, etc.) and
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are rendered via GPU shaders.
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- **Language**: C11 / C++11 (dual-mode, like `src/wapp/`)
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- **GPU API**: Vulkan, abstracted behind a Rendering Hardware Interface (RHI)
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- **Shading language**: Slang, stored in external `.slang` files under `src/shaders/`
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- **Build**: `justfile` (Just) as a task runner
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- **Dependencies**: `src/wapp/` (local utility library, already vendored)
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## Coding Conventions
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All code follows the patterns established in `src/wapp/`. The project prefix is
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`pr` (functions/macros) / `Pr` (types).
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### Naming
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| Category | Convention | Examples |
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|-----------------------|------------------------|---------------------------------|
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| Types | `Pr` + PascalCase | `PrNode`, `PrGraph`, `PrImage` |
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| Functions | `pr` + PascalCase | `prGraphCreate`, `prNodeEval` |
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| Macros | `pr` + PascalCase | `prArrayOf`, `prNodeType` |
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| Enum constants | `PR_` + SCREAMING_SNAKE| `PR_NODE_BLEND`, `PR_OK` |
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| Internal/static funcs | `_` + camelCase | `_resolveTopology`, `_execCmd` |
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| File-scope globals | `_` + camelCase | `_default_allocator` |
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| File-scope constants | SCREAMING_SNAKE | `MAX_NODE_NAME` |
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| Variables | snake_case | `vertex_count`, `edge_node` |
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- **Variable names**: Prefer descriptive names (e.g. `vertex_count` over `vc`, `edge_node` over `en`). Short names (`i`, `j`, `n`) are acceptable only in tight loop counters or trivial index variables. Avoid single-letter names in non-trivial scopes, and avoid abbreviated names that require the reader to hold a mental dictionary.
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### Formatting
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- **Tabs for indentation**, 8-column tab width.
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- **Braces** on the same line as control statements (Attach style).
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- **Braces on single-line if statements**: Always use braces, even for single-line bodies:
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```c
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// correct
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if (!buffer) { return; }
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if (!texture) { _abort("alloc failed"); }
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// wrong
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if (!buffer) return;
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if (!texture) _abort("alloc failed");
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```
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- **Pointers**: `*` against the name, not the type (`PrRhiBuffer *buf`, not `PrRhiBuffer* buf`).
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- **Line width**: 120 columns.
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- **Continuation lines** align to the opening parenthesis.
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- **Return-type alignment**: Within each `// =====` section, align function
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declaration names so the first letter of every function occupies the same
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column. For pointer return types, place `*` directly against the function
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name (no space) and put all alignment padding between the type name and `*`.
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```c
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// correct — * against fn name, padding before *
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PrRhiSwapchain *prRhiCreateSwapchain(…);
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void prRhiDestroySwapchain(…);
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PrRhiSwapchainResult prRhiAcquireNextImage(…);
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```
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### Storage qualifiers
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Use the `wp_extern` / `wp_intern` / `wp_persist` aliases from wapp:
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```c
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wp_extern void prGraphInit(PrGraph *g); // extern linkage
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wp_intern void _helper(void); // static (file-scope)
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wp_persist u32 _counter; // static (file-scope, mutable)
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```
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### Structs
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POD structs with typedef, following `wapp/base/` patterns. Functions operate
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on structs by pointer rather than through vtables:
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```c
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typedef struct PrNode PrNode;
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struct PrNode {
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PrNodeType type;
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u32 input_count;
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PrNode **inputs;
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// ...
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};
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void prNodeInit(PrNode *n, PrAllocator *alloc);
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void prNodeEval(PrNode *n, PrRhiCmdList *cl);
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void prNodeDestroy(PrNode *n, PrAllocator *alloc);
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```
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### Memory management
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Use wapp allocators (`WpAllocator`, arena-based). Stack-allocate where
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possible; pass allocators explicitly.
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```c
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PrGraph *prGraphCreate(PrAllocator *alloc);
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void prGraphDestroy(PrGraph *g, PrAllocator *alloc);
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```
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### File organisation
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One `.h` / `.c` pair per module, grouped in subdirectories by subsystem.
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A top-level umbrella header re-exports everything (see `src/wapp/wapp.h`).
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```
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src/prism/prism.h ← umbrella include
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src/prism/core/ ← graph, node types, DAG
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src/prism/rhi/ ← rendering hardware interface
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src/prism/node/ ← node implementations
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src/prism/app/ ← entry point, window, main loop
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```
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Shaders live in a flat-ish `src/shaders/` tree:
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```
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src/shaders/blit.slang
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src/shaders/blend.slang
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src/shaders/common/ ← shared include files
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```
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### Data-oriented design
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For hot paths (per-frame graph evaluation, image transfers, shader dispatch)
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prefer SoA layouts, batch processing, and minimise pointer chasing. Keep
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the DAG in contiguous arrays (e.g. adjacency lists packed in flat buffers)
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rather than individually allocated linked structures.
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### Frame-by-frame command batching
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Commands that execute every frame must avoid arena allocation. Use stack
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arrays with a while-loop to batch operations in fixed-size chunks:
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```c
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while (count > 0) {
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VkTypeArray batch = wpArrayWithCapacity(VkType, 16, WP_ARRAY_INIT_FILLED);
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u32 batch_size = count < wpArrayCapacity(batch) ? count : (u32)wpArrayCapacity(batch);
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// ... process batch ...
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vkCmd*(cb->handle, ...);
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count -= batch_size;
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first += batch_size;
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}
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```
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This avoids per-frame arena churn while handling arbitrarily large inputs.
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### Graph / adjacency lists
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Adjacency list nodes must be **separately allocated from the vertex array**.
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Never use the vertex struct itself as a linked-list node in another vertex's
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adjacency chain — that shares the `next` pointer between two roles (vertex state
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vs. edge linking) and causes edges to splice into unintended chains.
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```c
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// correct — per-edge copy on the arena
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static void addEdge(PrGraph *g, const WpAllocator *alloc, u64 from, u64 to) {
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PrVertex *src = &g->vertices[from];
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PrVertex *dst = wpMemAllocatorAlloc(alloc, sizeof(PrVertex));
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if (!dst) { /* handle OOM */ return; }
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dst->id = g->vertices[to].id;
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dst->value = g->vertices[to].value;
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dst->next = src->next;
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src->next = dst;
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}
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// wrong — reuses the destination vertex as the list node
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static void addEdge_bad(PrGraph *g, u64 from, u64 to) {
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PrVertex *src = &g->vertices[from];
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PrVertex *dest = &g->vertices[to];
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dest->next = src->next;
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src->next = dest; // overwrites dest->next used elsewhere
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}
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```
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Arena bump allocation (`wpMemAllocatorAlloc`) is the natural fit for building
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graph structures: per-edge nodes live in the arena and are freed in one shot
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when the arena is destroyed.
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Always NULL-check the result of `wpMemAllocatorAlloc` — even arena allocators
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can fail if the backing buffer is exhausted.
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### WpArray usage
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| Scenario | API | Size must be… |
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|----------|-----|---------------|
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| Stack (local, short-lived) | `wpArrayWithCapacity` | compile-time constant |
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| Heap (arena-backed) | `wpArrayAllocCapacity` | runtime value |
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`wpArrayWithCapacity` creates a VLA-like compound literal on the stack —
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passing a runtime variable triggers undefined behaviour and compiler warnings.
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Use `wpArrayAllocCapacity` with an arena allocator for runtime sizes.
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Always use typed array aliases (`WpU64Array`, `PrNodeIdArray`, etc.) rather
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than raw pointers when declaring array variables. Follow the existing typedef
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pattern in the module (`typedef Type *TypeArray`).
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Typedef pattern:
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- Opaque handles use `**` (pointer-to-pointer)
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- Value types use `*` (contiguous block)
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```c
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typedef PrRhiBuffer **PrRhiBufferArray; // opaque handles → **
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typedef PrRhiColorAttachment *PrRhiColorAttachmentArray; // value types → *
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```
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Group opaque handle arrays first, value type arrays second, separated by a
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blank line.
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Use named init flags (`WP_ARRAY_INIT_NONE`, `WP_ARRAY_INIT_FILLED`) instead of
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bare `0` — they make the initialisation policy explicit.
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- `WP_ARRAY_INIT_FILLED`: sets `count = capacity` on allocation. Required when
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you plan to index into the array directly (not via append/push), since the
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array's `count` must reflect valid elements for any downstream use.
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- `WP_ARRAY_INIT_NONE`: leaves `count = 0`. Use when you'll fill the array
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incrementally via `wpArrayAppendCapped` / `wpArrayAppendAlloc`.
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Use `wpArrayCapacity(arr)`, `wpArrayCount(arr)`, `wpArraySetCount(arr, n)` to
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query and control array state rather than computing sizes manually.
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### Local/scratch arenas
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For function-local scratch allocations, use `wpMemArenaAllocatorInitZero` with a
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fixed size rather than a stack buffer + `InitWithBuffer`:
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```c
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WpAllocator scratch = wpMemArenaAllocatorInitZero(KiB(16));
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```
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## Documentation
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Save research notes and implementation plans as markdown in `documents/`:
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```
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documents/
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├── ARCHITECTURE.md
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├── RENDERING_HARDWARE_INTERFACE.md
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├── NODE_SYSTEM.md
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├── ROADMAP.md
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├── research/
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│ └── <topic>.md
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└── session-logs/
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└── YYYY-MM-DD.md
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```
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## Skills
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Domain-specific conventions are stored as skills in `.opencode/skills/<name>/SKILL.md`.
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These are loaded on-demand by the AI agent when a task matches their description,
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keeping AGENTS.md lean.
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- **`prism-rhi`** — RHI backend dispatch, by-value descs, file layout
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- **`prism-dag`** — DAG adjacency lists, arena allocation, Kahn's algorithm
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## Workflows for AI agents
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### Research / planning
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1. Save findings to `documents/research/<topic>.md`.
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2. When asked for a plan, write it to `documents/<PLAN_NAME>.md` and present
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a summary; iterate on the plan before writing any code.
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3. Only start implementing after the plan is approved.
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### Skill maintenance
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When you observe the user correcting your output (e.g. formatting, conventions),
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infer the rule and add it to the relevant skill's `SKILL.md`. If no skill
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matches, add a new one. This keeps AGENTS.md focused on project identity and
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critical workflow rules rather than accumulating domain details.
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### Committing
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Only commit when explicitly asked. When asked:
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- Stage only intended files.
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- Write a short, conventional commit message in present tense.
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- Never amend, force-push, or create PRs without a request.
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