render: use output's subpixel mode when rasterizing glyphs

render.c

@@ -404,7 +404,7 @@ render_cell(struct terminal *term, pixman_image_t *pix,
 
     struct font *font = attrs_to_font(term, &cell->attrs);
     const struct glyph *glyph = cell->wc != 0
-        ? font_glyph_for_wc(font, cell->wc, term->colors.alpha == 0xffff)
+        ? font_glyph_for_wc(font, cell->wc, term->font_subpixel)
         : NULL;
 
     int cell_cols = glyph != NULL ? max(1, glyph->cols) : 1;

terminal.c

@@ -579,6 +579,50 @@ get_font_dpi(const struct terminal *term)
     return dpi;
 }
 
+static enum subpixel_order
+get_font_subpixel(const struct terminal *term)
+{
+    if (term->colors.alpha != 0xffff) {
+        /* Can't do subpixel rendering on transparent background */
+        return FCFT_SUBPIXEL_ORDER_NONE;
+    }
+
+    enum wl_output_subpixel wl_subpixel;
+
+    /*
+     * Wayland doesn't tell us *which* part of the surface that goes
+     * on a specific output, only whether the surface is mapped to an
+     * output or not.
+     *
+     * Thus, when determining which subpixel mode to use, we can't do
+     * much but select *an* output. So, we pick the first one.
+     *
+     * If we're not mapped at all, we pick the first available
+     * monitor, and hope that's where we'll eventually get mapped.
+     *
+     * If there aren't any monitors we use the "default" subpixel
+     * mode.
+     */
+
+    if (tll_length(term->window->on_outputs) > 0)
+        wl_subpixel = tll_front(term->window->on_outputs)->subpixel;
+    else if (tll_length(term->wl->monitors) > 0)
+        wl_subpixel = tll_front(term->wl->monitors).subpixel;
+    else
+        wl_subpixel = WL_OUTPUT_SUBPIXEL_UNKNOWN;
+
+    switch (wl_subpixel) {
+    case WL_OUTPUT_SUBPIXEL_UNKNOWN:        return FCFT_SUBPIXEL_ORDER_DEFAULT;
+    case WL_OUTPUT_SUBPIXEL_NONE:           return FCFT_SUBPIXEL_ORDER_NONE;
+    case WL_OUTPUT_SUBPIXEL_HORIZONTAL_RGB: return FCFT_SUBPIXEL_ORDER_HORIZONTAL_RGB;
+    case WL_OUTPUT_SUBPIXEL_HORIZONTAL_BGR: return FCFT_SUBPIXEL_ORDER_HORIZONTAL_BGR;
+    case WL_OUTPUT_SUBPIXEL_VERTICAL_RGB:   return FCFT_SUBPIXEL_ORDER_VERTICAL_RGB;
+    case WL_OUTPUT_SUBPIXEL_VERTICAL_BGR:   return FCFT_SUBPIXEL_ORDER_VERTICAL_BGR;
+    }
+
+    return FCFT_SUBPIXEL_ORDER_DEFAULT;
+}
+
 static bool
 load_fonts_from_conf(const struct terminal *term, const struct config *conf,
                      struct font *fonts[static 4])
@@ -686,6 +730,9 @@ term_init(const struct config *conf, struct fdm *fdm, struct wayland *wayl,
         .ptmx_buffer = tll_init(),
         .font_dpi = 0,
         .font_adjustments = 0,
+        .font_subpixel = (conf->colors.alpha == 0xffff  /* Can't do subpixel rendering on transparent background */
+                          ? FCFT_SUBPIXEL_ORDER_DEFAULT
+                          : FCFT_SUBPIXEL_ORDER_NONE),
         .cursor_keys_mode = CURSOR_KEYS_NORMAL,
         .keypad_keys_mode = KEYPAD_NUMERICAL,
         .auto_margin = true,
@@ -1331,6 +1378,31 @@ term_font_dpi_changed(struct terminal *term)
     return false;
 }
 
+void
+term_font_subpixel_changed(struct terminal *term)
+{
+    enum subpixel_order subpixel = get_font_subpixel(term);
+
+    if (term->font_subpixel == subpixel)
+        return;
+
+#if defined(_DEBUG) && LOG_ENABLE_DBG
+    static const char *const str[] = {
+        [FCFT_SUBPIXEL_ORDER_DEFAULT] = "default",
+        [FCFT_SUBPIXEL_ORDER_NONE] = "disabled",
+        [FCFT_SUBPIXEL_ORDER_HORIZONTAL_RGB] = "RGB",
+        [FCFT_SUBPIXEL_ORDER_HORIZONTAL_BGR] = "BGR",
+        [FCFT_SUBPIXEL_ORDER_VERTICAL_RGB] = "V-RGB",
+        [FCFT_SUBPIXEL_ORDER_VERTICAL_BGR] = "V-BGR",
+    };
+#endif
+
+    LOG_DBG("subpixel mode changed: %s -> %s", str[term->font_subpixel], str[subpixel]);
+    term->font_subpixel = subpixel;
+    term_damage_view(term);
+    render_refresh(term);
+}
+
 void
 term_damage_rows(struct terminal *term, int start, int end)
 {

terminal.h

@@ -217,6 +217,7 @@ struct terminal {
     struct font *fonts[4];
     int font_dpi;
     int font_adjustments;
+    enum subpixel_order font_subpixel;
 
     tll(struct ptmx_buffer) ptmx_buffer;
 
@@ -445,6 +446,8 @@ bool term_font_size_increase(struct terminal *term);
 bool term_font_size_decrease(struct terminal *term);
 bool term_font_size_reset(struct terminal *term);
 bool term_font_dpi_changed(struct terminal *term);
+void term_font_subpixel_changed(struct terminal *term);
+
 
 void term_damage_rows(struct terminal *term, int start, int end);
 void term_damage_rows_in_view(struct terminal *term, int start, int end);

wayland.c

@@ -146,6 +146,7 @@ update_term_for_output_change(struct terminal *term)
 
     render_resize(term, term->width / term->scale, term->height / term->scale);
     term_font_dpi_changed(term);
+    term_font_subpixel_changed(term);
     wayl_reload_cursor_theme(term->wl, term);
 }
 
@@ -193,6 +194,7 @@ output_geometry(void *data, struct wl_output *wl_output, int32_t x, int32_t y,
     mon->inch = sqrt(pow(mon->dim.mm.width, 2) + pow(mon->dim.mm.height, 2)) * 0.03937008;
     mon->make = make != NULL ? strdup(make) : NULL;
     mon->model = model != NULL ? strdup(model) : NULL;
+    mon->subpixel = subpixel;
     output_update_ppi(mon);
 }
 

wayland.h

@@ -60,6 +60,7 @@ struct monitor {
 
     int scale;
     float refresh;
+    enum wl_output_subpixel subpixel;
 
     char *make;
     char *model;