The text pipeline stages a glyph's rect *origin* per instance and carries the
rect's *size* once per draw, so a backend whose glyphs have differing rect sizes
-- a TrueType packing trimmed to ink, which is Task 8's shape -- would have drawn
every glyph at whichever size it happened to be told, with nothing downstream
able to tell. Make that constraint structural rather than documented:
- TextBackend::cell_uv() declares the one cell size, and the contract (an atlas
is a fixed-cell grid; a proportional face draws its glyphs *into* a uniform
cell instead of trimming each rect to its ink, and why the pipeline needs it)
is stated on the atlas accessors.
- glyph_is_cell() is the check; add_text()/set_cell() declare the cell from the
backend, and the staging path asserts it for every glyph in a debug build.
A release build draws on with the cell it was told, as before.
- Renderer::flush_text() takes u_glyph_uv from the backend, not from the batch,
so the draw's one rect size can never come from whichever glyph was staged
first.
- loader: add available(), true only after load() has resolved every
required entry point (false at the start of load()). Program::from_source
and the other fallible constructors return ErrorCode::Unsupported while it
is false, so a failed load() with a partially populated table can no longer
fault on an unresolved entry point.
- caps: GL_CONTEXT_PROFILE_MASK only exists from 3.2, so query it only on
3.2+ contexts. A 3.0/3.1 query latches GL_INVALID_ENUM in the context, which
the next unrelated glGetError() (e.g. read_pixel) then reports as failure.
- tests: gate the dlsym/libGL.so.1 fallback assertions on libGL being
resolvable, so the GL suite also passes on a GLES-only host.
Martino Ferrari