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Layers & Frames

How OpenGPEX organizes visual content into Frames (artboards) containing Layers (visual elements).

Frames

A Frame is a top-level canvas container with:

  • Canvas dimensions (width × height in pixels)
  • Camera state (pan position + zoom level)
  • Layer stack (ordered collection of layers)
  • Active layer reference

You can have multiple frames in a single project for multi-view workflows.

Layer Types

Type Description Use Case
Image Raster pixel data from imported files Photos, bitmaps
Text Editable text with styling Titles, captions
Vector Shape-based layers Geometric paths
Color Full-canvas solid fill Backgrounds
Paint Freehand raster drawing Pixel painting

Layer Properties

Every layer has:

  • Identity: unique ID, user-visible name
  • Visibility/Lock: toggle display and edit protection
  • Opacity & Blend Mode: 16 compositing modes available
  • Geometry: center position, rotation, flip, bounding dimensions
  • Masks: vector masks (shape-based) and bitmap masks (painted)
  • Adjustments: non-destructive brightness, contrast, saturation, hue, blur
  • Fragment metadata (optional): sourceLayerId (parent layer), assocMaskId (corresponding hole mask on parent) — see Cut-Link section below

Z-Order

Layers render bottom-to-top based on their position in an order array. Reordering only changes the array — layer objects stay referentially stable, making undo patches minimal.

Non-Destructive Editing

OpenGPEX preserves original pixel data at all times:

  1. Original asset stored immutably in CAS (Content-Addressable Storage)
  2. Layer metadata (position, masks, adjustments) stored as lightweight properties
  3. Rendering combines asset + metadata on-the-fly
  4. Undo simply reverts metadata — no need to restore pixel data

Cut-Link Fragment System

When a user performs Peel (Cut to Layer), OpenGPEX establishes a bidirectional link between the source layer and the resulting fragment:

  • Fragment → Source: metadata.sourceLayerId + metadata.assocMaskId identify the parent and its hole mask
  • Source → Fragment: an inverted VectorMask with assocLayerId pointing to the fragment

This enables:

  • Merge Back: recursively return fragments to their source (zero rasterization)
  • Union Merge: combine multiple fragments via polygon union (vector precision)
  • Auto-cleanup: deleting a fragment automatically removes its hole mask from the source
sourceLayerId assocMaskId Meaning
set set Cut fragment — bidirectional link, supports Merge Back
set empty Copy derivative — lineage only, no complementary constraint
empty — Independent layer

Sub-Layer System (Triplets)

Complex layers can contain child sub-layers:

  • Host: the main user-visible layer
  • Exchange: temporary drawing buffer
  • Frag: drawing fragment buffer

Geometry changes on a host layer automatically cascade to its children.

Last updated: 2026-08-30