fix(sdl2): pixel-perfect rendering across DPI levels#2222
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theangelperalta merged 2 commits intoJun 6, 2026
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Fixes several SDL2 rendering artefacts and adds a headless test suite: - Baseline drift: anchor glyphs via cached font ascent/descent (glyph_y = bottom_y - ascent - |descent|) instead of surface height. - AA tail erosion at attribute boundaries: lift the two-pass bg/glyph rendering to span the whole physical line in redraw-physical-line. - Oversized icon/folder/emoji glyphs: plain-text-object-p routes only base text-objects through the per-character path, leaving subclasses their scale-to-fit draw-object methods. - Stepped highlight rectangles: pin text-object height to the stable display-char-height rather than per-string SDL_ttf surface height. - DPI transitions (Retina <-> standard): handle :size-changed / :display-changed by re-deriving scale, re-opening the font, and refreshing per-view textures via *post-display-change-hooks*. Adds lem-sdl2/tests (font + drawing) wired into make test.
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- Move *post-display-change-hooks* defvar into the declarations section at the top of display.lisp (file_structure_rule), and reword its docstring to note it is a hook registry analogous to Lem's other *...-hooks* variables. - Export make-letter-object from lem-core/display and reference it unqualified in drawing.lisp instead of reaching through lem-core:: internal access (internal_symbol_rule).
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Summary
Fixes a set of SDL2 frontend rendering artefacts and adds a headless test suite to lock the invariants in.
p/g/T/y/Y):bg/:glyphrendering to span the whole physical line inredraw-physical-line— pass 1 paints all backgrounds, pass 2 blits all glyphs, so a 1px right-edge AA overhang isn't erased by the next run's background.plain-text-object-proutes only basetext-objectinstances through the per-character path;icon-object/folder-object/emoji-objectkeep their scale-to-fitdraw-objectmethods.object-heightfor basetext-objectto the stabledisplay-char-heightinstead of per-string SDL_ttf surface height, so adjacent attribute runs paint identical vertical extents.:size-changed/:display-changedwindow events: re-derive display scale, re-open the font at the new effective size, and refresh per-view textures via the new*post-display-change-hooks*mechanism.Tests
Adds
lem-sdl2/tests(tests/font.lisp,tests/drawing.lisp), wired intomake test:TTF_FontAscent/TTF_FontDescent, sign sanity, baseline band fits within font height, and metrics refresh on reopen at a new size.text-objectheight equalsdisplay-char-heightregardless of string content, and tracksdisplay-char-heightchanges (DPI swap).12 expectations across 6 deftests, all passing (verified locally via
asdf:test-system "lem-sdl2/tests"). The drawing tests use a minimalstub-displayso they run headlessly without an SDL window/renderer.