pt-or-px: heed the dpi-aware setting

Before this patch, pt-or-px values, like letter-spacing, were *always*
scaled using the current DPI value.

This is wrong; if the fonts are scaled using the output’s scaling
factor, then so should all other point values.

This also fixes an issue where e.g. letter-spacing would use one DPI
value at startup, but then when increasing/decreasing or resetting the
font size, would be re-calculated using a different DPI value, leading
to completely different spacing.

This happened when there were multiple monitors, with different DPI
values, and foot guessed the initial DPI value wrong. Normally, foot
would correct itself as soon as the window was mapped, and the
“correct” DPI value known. But if the fonts were scaled using the
scaling factor, it was possible that the font reload never happened.

This patch also updates the thickness calculation (for LIGHT and HEAVY
box drawing characters) to use the scaling factor when appropriate.

Closes #680

CHANGELOG.md

@@ -56,6 +56,11 @@
 * Foot now sends `SIGTERM`/`SIGKILL` to the client application’s process group,
   instead of just to the client application’s process.
 * `kmous` terminfo capability from `\E[M` to `\E[<`.
+* pt-or-px values (`letter-spacing`, etc) and the line thickness
+  (`tweak.box-drawing-base-thickness`) in box drawing characters are
+  now translated to pixel values using the monitor’s scaling factor
+  when `dpi-aware=no`, or `dpi-aware=auto` and the scaling factor is
+  larger than 1 (https://codeberg.org/dnkl/foot/issues/680).
 
 
 ### Deprecated

box-drawing.c

@@ -25,9 +25,6 @@ struct buf {
     int width;
     int height;
     int stride;
-    int dpi;
-    float cell_size;
-    float base_thickness;
     bool solid_shades;
 
     int thickness[2];
@@ -63,17 +60,15 @@ change_buffer_format(struct buf *buf, pixman_format_code_t new_format)
 }
 
 static int NOINLINE
-_thickness(struct buf *buf, enum thickness thick)
+_thickness(int base_thickness, enum thickness thick)
 {
     int multiplier = thick * 2 + 1;
 
+    xassert(base_thickness >= 1);
     xassert((thick == LIGHT && multiplier == 1) ||
             (thick == HEAVY && multiplier == 3));
 
-    return
-        max(
-            (int)(buf->base_thickness * buf->dpi / 72.0 * buf->cell_size), 1)
-        * multiplier;
+    return base_thickness * multiplier;
 }
 #define thickness(thick) buf->thickness[thick]
 
@@ -2751,25 +2746,13 @@ box_drawing(const struct terminal *term, wchar_t wc)
         abort();
     }
 
-    struct buf buf = {
-        .data = data,
-        .pix = pix,
-        .format = fmt,
-        .width = width,
-        .height = height,
-        .stride = stride,
-        .dpi = term->font_dpi,
-        .cell_size = sqrt(pow(term->cell_width, 2) + pow(term->cell_height, 2)),
-        .base_thickness = term->conf->tweak.box_drawing_base_thickness,
-        .solid_shades = term->conf->tweak.box_drawing_solid_shades,
-    };
+    double dpi = term_font_sized_by_dpi(term, term->scale) ? term->font_dpi : 96.;
+    double scale = term_font_sized_by_scale(term, term->scale) ? term->scale : 1.;
+    double cell_size = sqrt(pow(term->cell_width, 2) + pow(term->cell_height, 2));
 
-    buf.thickness[LIGHT] = _thickness(&buf, LIGHT);
-    buf.thickness[HEAVY] = _thickness(&buf, HEAVY);
-
-    /* Overlap when width is odd */
-    buf.x_halfs[0] = round(width / 2.); /* Endpoint first half */
-    buf.x_halfs[1] = width / 2;         /* Startpoint second half */
+    int base_thickness =
+        (double)term->conf->tweak.box_drawing_base_thickness * scale * cell_size * dpi / 72.0;
+    base_thickness = max(base_thickness, 1);
 
     int y0 = 0, y1 = 0;
     switch (height % 3) {
@@ -2789,8 +2772,31 @@ box_drawing(const struct terminal *term, wchar_t wc)
         break;
     }
 
-    buf.y_thirds[0] = y0;  /* Endpoint first third, start point second third */
-    buf.y_thirds[1] = y1;  /* Endpoint second third, start point last third */
+    struct buf buf = {
+        .data = data,
+        .pix = pix,
+        .format = fmt,
+        .width = width,
+        .height = height,
+        .stride = stride,
+        .solid_shades = term->conf->tweak.box_drawing_solid_shades,
+
+        .thickness = {
+            [LIGHT] = _thickness(base_thickness, LIGHT),
+            [HEAVY] = _thickness(base_thickness, HEAVY),
+        },
+
+        /* Overlap when width is odd */
+        .x_halfs = {
+            round(width / 2.), /* Endpoint first half */
+            width / 2,         /* Startpoint second half */
+        },
+
+        .y_thirds = {
+            y0,  /* Endpoint first third, start point second third */
+            y1,  /* Endpoint second third, start point last third */
+        },
+    };
 
     LOG_DBG("LIGHT=%d, HEAVY=%d",
             _thickness(&buf, LIGHT), _thickness(&buf, HEAVY));

terminal.c

@@ -627,15 +627,6 @@ err_sem_destroy:
     return false;
 }
 
-int
-term_pt_or_px_as_pixels(const struct terminal *term,
-                        const struct pt_or_px *pt_or_px)
-{
-    return pt_or_px->px == 0
-        ? round(pt_or_px->pt * term->font_dpi / 72)
-        : pt_or_px->px;
-}
-
 static void
 free_box_drawing(struct fcft_glyph **box_drawing)
 {
@@ -802,19 +793,30 @@ get_font_subpixel(const struct terminal *term)
     return FCFT_SUBPIXEL_DEFAULT;
 }
 
-static bool
-font_sized_by_dpi(const struct terminal *term, int scale)
+bool
+term_font_sized_by_dpi(const struct terminal *term, int scale)
 {
     return term->conf->dpi_aware == DPI_AWARE_YES ||
         (term->conf->dpi_aware == DPI_AWARE_AUTO && scale <= 1);
 }
 
-static bool
-font_sized_by_scale(const struct terminal *term, int scale)
+bool
+term_font_sized_by_scale(const struct terminal *term, int scale)
 {
-    return !font_sized_by_dpi(term, scale);
+    return !term_font_sized_by_dpi(term, scale);
 }
 
+int
+term_pt_or_px_as_pixels(const struct terminal *term,
+                        const struct pt_or_px *pt_or_px)
+{
+    double scale = term_font_sized_by_scale(term, term->scale) ? term->scale : 1.;
+    double dpi = term_font_sized_by_dpi(term, term->scale) ? term->font_dpi : 96.;
+
+    return pt_or_px->px == 0
+        ? round(pt_or_px->pt * scale * dpi / 72)
+        : pt_or_px->px;
+}
 
 struct font_load_data {
     size_t count;
@@ -857,7 +859,7 @@ reload_fonts(struct terminal *term)
             char size[64];
 
             const int scale =
-                font_sized_by_scale(term, term->scale) ? term->scale : 1;
+                term_font_sized_by_scale(term, term->scale) ? term->scale : 1;
 
             if (use_px_size)
                 snprintf(size, sizeof(size), ":pixelsize=%d",
@@ -892,7 +894,7 @@ reload_fonts(struct terminal *term)
     const size_t count_bold_italic = custom_bold_italic ? counts[3] : counts[0];
     const char **names_bold_italic = (const char **)(custom_bold_italic ? names[3] : names[0]);
 
-    const bool use_dpi = font_sized_by_dpi(term, term->scale);
+    const bool use_dpi = term_font_sized_by_dpi(term, term->scale);
 
     char *attrs[4] = {NULL};
     int attr_len[4] = {-1, -1, -1, -1};  /* -1, so that +1 (below) results in 0 */
@@ -1981,8 +1983,8 @@ term_font_dpi_changed(struct terminal *term, int old_scale)
     float dpi = get_font_dpi(term);
     xassert(term->scale > 0);
 
-    bool was_scaled_using_dpi = font_sized_by_dpi(term, old_scale);
-    bool will_scale_using_dpi = font_sized_by_dpi(term, term->scale);
+    bool was_scaled_using_dpi = term_font_sized_by_dpi(term, old_scale);
+    bool will_scale_using_dpi = term_font_sized_by_dpi(term, term->scale);
 
     bool need_font_reload =
         was_scaled_using_dpi != will_scale_using_dpi ||

terminal.h

@@ -643,6 +643,9 @@ bool term_font_size_decrease(struct terminal *term);
 bool term_font_size_reset(struct terminal *term);
 bool term_font_dpi_changed(struct terminal *term, int old_scale);
 void term_font_subpixel_changed(struct terminal *term);
+
+bool term_font_sized_by_dpi(const struct terminal *term, int scale);
+bool term_font_sized_by_scale(const struct terminal *term, int scale);
 int term_pt_or_px_as_pixels(
     const struct terminal *term, const struct pt_or_px *pt_or_px);