feat(figment): add SVG to half-block rasterization pipeline

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

engine/figment_render.py

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+"""
+SVG to half-block terminal art rasterization.
+
+Pipeline: SVG -> cairosvg -> PIL -> greyscale threshold -> half-block encode.
+Follows the same pixel-pair approach as engine/render.py for OTF fonts.
+"""
+
+from __future__ import annotations
+
+from io import BytesIO
+
+import cairosvg
+from PIL import Image
+
+_cache: dict[tuple[str, int, int], list[str]] = {}
+
+
+def rasterize_svg(svg_path: str, width: int, height: int) -> list[str]:
+    """Convert SVG file to list of half-block terminal rows (uncolored).
+
+    Args:
+        svg_path: Path to SVG file.
+        width: Target terminal width in columns.
+        height: Target terminal height in rows.
+
+    Returns:
+        List of strings, one per terminal row, containing block characters.
+    """
+    cache_key = (svg_path, width, height)
+    if cache_key in _cache:
+        return _cache[cache_key]
+
+    # SVG -> PNG in memory
+    png_bytes = cairosvg.svg2png(
+        url=svg_path,
+        output_width=width,
+        output_height=height * 2,  # 2 pixel rows per terminal row
+    )
+
+    # PNG -> greyscale PIL image
+    # Composite RGBA onto white background so transparent areas become white (255)
+    # and drawn pixels retain their luminance values.
+    img_rgba = Image.open(BytesIO(png_bytes)).convert("RGBA")
+    img_rgba = img_rgba.resize((width, height * 2), Image.Resampling.LANCZOS)
+    background = Image.new("RGBA", img_rgba.size, (255, 255, 255, 255))
+    background.paste(img_rgba, mask=img_rgba.split()[3])
+    img = background.convert("L")
+
+    data = img.tobytes()
+    pix_w = width
+    pix_h = height * 2
+    # White (255) = empty space, dark (< threshold) = filled pixel
+    threshold = 128
+
+    # Half-block encode: walk pixel pairs
+    rows: list[str] = []
+    for y in range(0, pix_h, 2):
+        row: list[str] = []
+        for x in range(pix_w):
+            top = data[y * pix_w + x] < threshold
+            bot = data[(y + 1) * pix_w + x] < threshold if y + 1 < pix_h else False
+            if top and bot:
+                row.append("█")
+            elif top:
+                row.append("▀")
+            elif bot:
+                row.append("▄")
+            else:
+                row.append(" ")
+        rows.append("".join(row))
+
+    _cache[cache_key] = rows
+    return rows
+
+
+def clear_cache() -> None:
+    """Clear the rasterization cache (e.g., on terminal resize)."""
+    _cache.clear()

tests/test_figment_render.py

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+"""Tests for engine.figment_render module."""
+
+import os
+
+from engine.figment_render import rasterize_svg
+
+FIXTURE_SVG = os.path.join(os.path.dirname(__file__), "fixtures", "test.svg")
+
+
+class TestRasterizeSvg:
+    def test_returns_list_of_strings(self):
+        rows = rasterize_svg(FIXTURE_SVG, 40, 20)
+        assert isinstance(rows, list)
+        assert all(isinstance(r, str) for r in rows)
+
+    def test_output_height_matches_terminal_height(self):
+        rows = rasterize_svg(FIXTURE_SVG, 40, 20)
+        assert len(rows) == 20
+
+    def test_output_contains_block_characters(self):
+        rows = rasterize_svg(FIXTURE_SVG, 40, 20)
+        all_chars = "".join(rows)
+        block_chars = {"█", "▀", "▄"}
+        assert any(ch in all_chars for ch in block_chars)
+
+    def test_different_sizes_produce_different_output(self):
+        rows_small = rasterize_svg(FIXTURE_SVG, 20, 10)
+        rows_large = rasterize_svg(FIXTURE_SVG, 80, 40)
+        assert len(rows_small) == 10
+        assert len(rows_large) == 40
+
+    def test_nonexistent_file_raises(self):
+        import pytest
+        with pytest.raises(Exception):
+            rasterize_svg("/nonexistent/file.svg", 40, 20)
+
+
+class TestRasterizeCache:
+    def test_cache_returns_same_result(self):
+        rows1 = rasterize_svg(FIXTURE_SVG, 40, 20)
+        rows2 = rasterize_svg(FIXTURE_SVG, 40, 20)
+        assert rows1 == rows2
+
+    def test_cache_invalidated_by_size_change(self):
+        rows1 = rasterize_svg(FIXTURE_SVG, 40, 20)
+        rows2 = rasterize_svg(FIXTURE_SVG, 60, 30)
+        assert len(rows1) != len(rows2)