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Metal: bake the glyph atlas at physical resolution (Retina/HiDPI)

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On a 2x display the static texture is physical-sized, but glyphs were
rasterized from the font at its logical point size and then stretched to
fill it, so text looked soft. Bake each glyph from a copy of the font
scaled by the backing factor (g_atlas_scale) and divide the physical
metrics back to logical pixels at the draw site, so the quad stays
logical-sized but is textured from a high-res glyph that maps ~1:1 onto
the physical texture. The atlas is dropped and rebuilt if the scale
changes (window moved to a different-DPI monitor).

No-op on 1x displays (scale == 1): verified AE unchanged at 0.98% vs NS.

Also add Fase I to TODO.org: a neutral drawing-backend abstraction so
macOS uses Metal and Linux/Windows use OpenGL.
This commit is contained in:
Andros Fenollosa 2026-06-02 16:04:00 +02:00
parent df8a190e28
commit d1cd7b2405
1 changed files with 44 additions and 10 deletions
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54
src/mtlterm.m
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@ -239,6 +239,12 @@ static id<MTLTexture> g_atlas = nil;
static int g_atlas_next_x = 0;
static int g_atlas_next_y = 0;
static int g_atlas_row_h = 0;
/* Backing scale the atlas glyphs are rasterized at (1.0 on a 1x display, 2.0 on
Retina). Glyphs are baked at physical resolution so they stay crisp on the
physical-pixel static texture; draw sites divide the physical metrics back to
logical pixels. Reset the atlas when this changes (e.g. window moves to a
monitor with a different DPI). See TODO.org Fase C-bis. */
static CGFloat g_atlas_scale = 1.0;
/* Phase 4: global animation configuration (Lisp-configurable) */
MtlCursorMode g_mtl_cursor_mode = MTL_CURSOR_SPRING;
@ -581,13 +587,22 @@ mtl_rasterize_glyph_id (CTFontRef font, CGGlyph cgGlyph, uint64_t key)
if (!g_atlas) return NULL;
MtlGlyphCacheEntry *entry;
CGFloat s = g_atlas_scale;
CGRect bbox = CTFontGetBoundingRectsForGlyphs (font,
/* Rasterize at physical resolution: bake the glyph from a copy of the font
scaled by the backing factor. Bbox/advance then come out in physical
pixels; draw sites divide the stored metrics by g_atlas_scale to get back to
logical pixels. On a 1x display this is a no-op (s == 1). */
CTFontRef rfont = (s != 1.0)
? CTFontCreateCopyWithAttributes (font, CTFontGetSize (font) * s, NULL, NULL)
: (CTFontRef) CFRetain (font);
CGRect bbox = CTFontGetBoundingRectsForGlyphs (rfont,
kCTFontOrientationDefault, &cgGlyph, NULL, 1);
/* Glyph advance */
/* Glyph advance (physical → store logical) */
CGSize adv;
CTFontGetAdvancesForGlyphs (font, kCTFontOrientationDefault,
CTFontGetAdvancesForGlyphs (rfont, kCTFontOrientationDefault,
&cgGlyph, &adv, 1);
int bw = (int)ceil (bbox.size.width) + 2;
@ -596,8 +611,9 @@ mtl_rasterize_glyph_id (CTFontRef font, CGGlyph cgGlyph, uint64_t key)
{
/* Space or zero-size glyph: cache as empty with correct advance */
entry = glyph_cache_insert (key);
CFRelease (rfont);
if (!entry) return NULL;
entry->advance_x = (float)adv.width;
entry->advance_x = (float)(adv.width / s);
entry->width = entry->height = 0;
return entry;
}
@ -635,8 +651,9 @@ mtl_rasterize_glyph_id (CTFontRef font, CGGlyph cgGlyph, uint64_t key)
CGContextSetGrayFillColor (ctx, 1.0, 1.0);
CGPoint origin = CGPointMake (floor (-bbox.origin.x) + 1,
floor (-bbox.origin.y) + 1);
CTFontDrawGlyphs (font, &cgGlyph, &origin, 1, ctx);
CTFontDrawGlyphs (rfont, &cgGlyph, &origin, 1, ctx);
CGContextRelease (ctx);
CFRelease (rfont);
/* Upload to atlas */
MTLRegion region = MTLRegionMake2D ((NSUInteger)g_atlas_next_x,
@ -663,7 +680,7 @@ mtl_rasterize_glyph_id (CTFontRef font, CGGlyph cgGlyph, uint64_t key)
entry->height = bh;
entry->bearing_x = (int)(floor (-bbox.origin.x) + 1);
entry->bearing_y = bh - 1 - raster_oy;
entry->advance_x = (float)adv.width;
entry->advance_x = (float)(adv.width / s);
g_atlas_next_x += bw + 1;
if (bh > g_atlas_row_h) g_atlas_row_h = bh;
@ -1098,6 +1115,18 @@ easing_apply (MtlScrollEasing mode, float t)
{
CGSize dsz = self.metalLayer.drawableSize;
/* Track the backing scale so the glyph atlas is baked at physical resolution.
If it changes (window moved to a different-DPI monitor), drop the atlas so
glyphs re-rasterize at the new scale. */
NSSize fsz = self.metalLayer.frame.size;
CGFloat scale = fsz.width > 0 ? dsz.width / fsz.width : 1.0;
if (scale > 0 && fabs (scale - g_atlas_scale) > 0.01)
{
g_atlas_scale = scale;
g_atlas_next_x = g_atlas_next_y = g_atlas_row_h = 0;
glyph_cache_init ();
}
/* Ensure staticTexture exists and matches drawable size.
Bug fix: multiple update_begin/end cycles happen per Emacs redisplay pass
(cursor blink, modeline, etc.). Using MTLLoadActionClear on every beginFrame
@ -1158,10 +1187,15 @@ easing_apply (MtlScrollEasing mode, float t)
float fr, fg, fb;
unpack_color (fgcolor, &fr, &fg, &fb);
float x0 = (float)(origin.x - ge->bearing_x);
float y0 = (float)(origin.y - ge->bearing_y);
float x1 = x0 + ge->width;
float y1 = y0 + ge->height;
/* The atlas glyph is baked at physical resolution (g_atlas_scale); the draw
site works in logical pixels, so divide the physical metrics back down. The
quad ends up logical-sized but textured from a high-res glyph, which maps
~1:1 onto the physical static texture and stays crisp on Retina. */
CGFloat s = g_atlas_scale;
float x0 = (float)(origin.x - ge->bearing_x / s);
float y0 = (float)(origin.y - ge->bearing_y / s);
float x1 = x0 + ge->width / s;
float y1 = y0 + ge->height / s;
float u0 = (float)ge->atlas_x / MTL_ATLAS_WIDTH;
float v0 = (float)ge->atlas_y / MTL_ATLAS_HEIGHT;