# lib-core.render

Colored-quad tile-grid renderer + tag-driven entity-render. Reads
`lib-core.maps`'s tilemap (v0.1: `draw_map`), and `lib-core.composition`'s
tag-index (v0.2: `draw_entities`).

**Version:** 0.3.0
**Lib-ID:** lib-core.render
**Requires:** lib-core.maps v>=0.5.7, lib-core.composition v>=0.4.0
**Tags:** render, tiles, draw, colored-quads, entities

## Topology

<!-- topology:start (auto-generated; do not edit) -->
```mermaid
graph LR
  this["lib-core.render"]
  lib_core_maps["lib-core.maps"]
  this --> lib_core_maps
  lib_core_composition["lib-core.composition"]
  this --> lib_core_composition
  engine["engine.*"]
  this --> engine
```
<!-- topology:end -->

## API

### `render.draw_map(map_id)`
**Syntax:** `render.draw_map(map_id: string | nil) -> integer`

**Example:**
```lua
function render(ctx)
    engine.render.clear_color(engine.render.rgb(20, 20, 30))
    local n = render.draw_map()  -- uses current-map
end
```

**Description:** Iterates the tiles of the specified map (or current-map when nil), drawing one colored rect per tile at `(tx * tile_size, ty * tile_size)`. Tile color is read from the tilemap's `tile.color = {r, g, b}`; if missing or malformed, falls back to magenta as a visible "missing-color" debug-marker. Must be called from inside a render hook. Returns the number of tiles drawn (for smoke verification + debug).

### `render.draw_entities(filter)`
**Syntax:** `render.draw_entities({tag: string}) -> integer`

**Example:**
```lua
function render_fn(ctx)
    camera.begin()
    render.draw_map()
    render.draw_entities{ tag = "renderable" }
    camera.finish()
end
```

**Description:** Iterates entities tagged with `filter.tag` (via
`composition.list_by_tag`) and renders each according to its
sprite-properties. `position.x`/`position.y` is treated as the visual
CENTER of the entity in all render-paths. Returns the number of
entities drawn.

Three sprite-property paths are tried per entity, in order:

1. **`sprite_atlas` (string, atlas-texture-path) + `sprite_uv.{x,y,w,h}`
   (numbers)** — renders the sub-rectangle of the atlas via
   `engine.render.draw_sprite_transform`. Optional `sprite_scale`
   (number, default 1.0) scales the rendered quad uniformly around its
   visual center; useful when a sprite-atlas's native pixel size
   doesn't match the project tile-scale. Atlas textures are loaded
   once and cached internally on first use; no eviction.
2. **`sprite_color` (uint32 0xRRGGBBAA) + `sprite_w` + `sprite_h`
   (numbers)** — renders a colored rect via `engine.render.draw_rect`.
3. **None of the above** — magenta 16×16 fallback rect (debug-marker).

Filter shape `{tag = "..."}` is the only supported form in v0.2.0;
template-id-based or property-predicate filters are deferred (loud-error
for malformed filters; see Phase-A Spec A-Q3).

## Conventions

- Colored-quads only in v0.1.0. Texture-rendering, multi-layer composition, post-processing, parallax, shaders, hot-reload all DEPRECATED-MVP.
- World-space coords; pair with `lib-core.camera` to support panning + zoom.
- Magenta fallback `[255, 0, 255]` is intentional: high-visibility debug-marker for malformed color-data.
- Y-down-positive per ADR-0031.

## Consumer pattern

```lua
local maps   = require("lib-core.maps")
local render = require("lib-core.render")
local camera = require("lib-core.camera")

function render_fn(ctx)
    engine.render.clear_color(engine.render.rgb(20, 20, 30))
    camera.begin()
    render.draw_map()
    camera.finish()
end
```

## CHANGELOG

### v0.3.0 (2026-06-20)
- Added optional `sprite_scale` (number) on path (1). Defaults to 1.0
  when absent — v0.2.0 consumers unchanged. Lets templates whose
  native sprite resolution doesn't match the project tile-scale
  rescale at render time without re-baking the atlas.
- Composition dep tightened to v0.3.0 (matches current sibling-tree
  state; no API impact, just resolution-correctness).

### v0.2.0 (Phase A.2 — 2026-06-09)
- Added `draw_entities(filter)` tag-driven entity-render. Two sprite-
  property paths (`sprite_atlas`+`sprite_uv` / `sprite_color`+`sprite_w`+
  `sprite_h`) plus magenta-fallback. `position.x`/`.y` is visual-center.
- Atlas-texture cache (no eviction in v0.2.0).
- New dep: `lib-core.composition` v0.1.0.

### v0.1.0 (P.0)
- Initial release: `draw_map` colored-quad iterator.

## References

- Spec v0.1.0 (P.0): `meta/docs/superpowers/specs/2026-05-09-p0-lib-render-design.md`
- Spec v0.2.0 (Phase A): `meta/docs/superpowers/specs/2026-06-09-phase-A-inactive-entities-composition-actor-reentry-design.md`
- Architecture: `meta/docs/architecture/render-pipeline.md`
- ADR-0001 (engine knows verbs, libs bring nouns)
- ADR-0031 (pixel-convention: Y-down-positive)
- ADR-0038 (API-Doc-Convention)