Crate retroglyph_gl 

GPU rendering backend for retroglyph: native OpenGL 3.3 core and browser WebGL2, from a single codebase via [glow].

Architecture

config::GlBackendBuilder holds configuration (fonts, grid size, integer scale) and builds a GlRenderer. The glyph source is a static FontChain (a single BitmapFont is a chain of one); every font in the chain is grid-packed into one TEXTURE_2D_ARRAY atlas and addressed by a flat slot id (issue #367’s grid-packing half, lifting the 256-layer cap). The renderer maintains per-layer CPU-side instance arrays (one entry per cell: glyph slot + fg/bg RGB + flags) and a GL context that is created lazily when the windowing loop calls Presenter::init_surface:

GlBackendBuilder (font, grid size, scale)
  |  .build()
  v
GlRenderer
  implements retroglyph_window::presenter::Presenter (an Output supertrait)
  wrapped by retroglyph_window::backend::WindowBackend to become a full Backend
  (WindowBackend owns the input event queue and the no-op Cursor)
  |
  |  init_surface(window) -> GlContext (glutin native / WebGL2 wasm) + GlResources
  v
two instanced passes (backgrounds, then coverage-blended glyphs) per grid layer per present():
a unit quad instanced cols*rows times, sampling an R8 glyph atlas (TEXTURE_2D_ARRAY).

This backend composites grid layers itself on the GPU (compositing returns retroglyph_core::backend::Compositing::PixelLayered): it receives the raw layered stream from the core Terminal and draws each layer back-to-front, so an empty cell in a higher layer lets the layer beneath show through while an occupied cell is opaque (issue #368), matching retroglyph-software’s per-pixel occlusion. It requests full frames (needs_full_frame: true) and redraws every cell of every layer each frame, so there is no orphaned-pixel problem from sub-cell glyph spill.

Platform split

Native builds create the GL context from the window’s raw handles via glutin (context_native.rs); wasm builds acquire a WebGL2 context from the winit <canvas> (context_wasm.rs). Both expose the same internal GlContext API, so the renderer body has no cfg.

Features

This crate has no default features; every feature below is optional and off unless enabled.

default-font

⚪ Optional.

Embeds the Unscii 16 default font so a caller can build a renderer with no font of its own.

Forwards to retroglyph-window’s default-font feature.

dev

⚪ Optional.

Forwards retroglyph-core’s dev feature, which forces development diagnostics on in a build that would otherwise compile them out (see retroglyph_core::dev).

tilesets

⚪ Optional.

PNG sprite/tileset support (issue #366): decodes sprite sheets into an RGBA TEXTURE_2D_ARRAY atlas and draws them in a second, source-over blended pass.

Forwards to retroglyph-window’s shared tileset decode, and (Linux only, where it’s a dependency at all) to the retroglyph-software dev-dependency’s own tilesets, so the two stay in lockstep: without this, cargo test -p retroglyph-gl (this feature off) still pulls in retroglyph-window/tilesets transitively through that dev-dependency’s forced-on tilesets below, and the PresenterBuilder impl’s tileset method (gated on this crate’s own tilesets feature, matching every other tileset-gated item in this crate) would then be missing an item the trait requires whenever retroglyph-window/tilesets is on, regardless of this crate’s own flag (retroglyph#1192). Harmless outside a test build: retroglyph-software is dev-only, so this half of the forward is a no-op for a plain cargo build/check.

Modules

config

Configuration, builder, and error types for the GL backend.

error

SurfaceError: the GL backend’s surface-lifecycle error type.

font

Bitmap glyph fonts and CP437 mapping, shared by retroglyph’s graphical backends.

Structs

BitmapFont

A 1-bit-per-pixel bitmap glyph font.

FontChain

The glyph source a backend draws from: a primary BitmapFont plus an ordered list of fallback fonts.

GlRenderer

The live GL renderer: a Presenter, wrapped in WindowBackend to form a full Backend for the windowing loop.