RTL image bitmap library

• Type: feature
• Track: B
• Status: done
• Owner: —
• Opened: 2026-06-20
• Closed: 2026-06-20
• Relation: Track B RTL foundation for PNG import, image conversion, and future graphics/image libraries.

Goal

Provide a small image core unit with an in-memory bitmap type, deliberately not tied to any file format or renderer. This is the shared data model for decoders and converters.

Prefer a neutral name such as Image or Bitmap. TBitmap is attractive and FPC/Lazarus-familiar, but it can imply a GUI toolkit object. A plain RTL TImage/TBitmap record with owned pixel storage is enough for the first slice.

Surface sketch

• TRGB / TRGBA pixel records
• TBitmap or TImage with Width, Height, and pixel storage
• CreateBitmap(w, h), FreeBitmap
• GetPixel, SetPixel
• helpers for RGB/RGBA conversion and alpha flattening
• optional later: views/slices, resize, palette expansion

Acceptance

• Library tests create small images, set/get pixels, copy/clear them, and verify deterministic pixel values.
• The type is usable by both PNG decode and image-to-ASCII conversion without depending on either unit.
• Memory ownership is explicit and works on hosted and constrained targets.

Notes

• Keep the first version byte-oriented and simple: 8-bit channels, row-major layout.
• Avoid GUI concepts such as canvases, handles, fonts, or windows in this unit.

Log

• 2026-06-20 — Landed lib/rtl/image.pas with TRGBA pixel and TImage bitmap records, initializers, boundary check, set/get pixel, and clear helpers. Tested in test/lib_png.pas (commit 44f7371).