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Auto-detect output scale

If the screen DPI is high enough, auto-enable scale=2 (if the user
hasn't set the scale).

Uses heuristics based on [1].

[1]: https://gitlab.gnome.org/GNOME/mutter/blob/05217066171992b0bc50882869aad6385285c878/src/backends/meta-monitor.c#L1590

Closes: #1800
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emersion authored and RedSoxFan committed Dec 10, 2019
1 parent 2f3c6cc commit 2f84d6e349d12f3293c44268bc5c8551340e5787
Showing with 53 additions and 3 deletions.
  1. +53 −3 sway/config/output.c
@@ -263,6 +263,49 @@ static bool set_mode(struct wlr_output *output, int width, int height,
return wlr_output_set_mode(output, best);
}

/* Some manufacturers hardcode the aspect-ratio of the output in the physical
* size field. */
static bool phys_size_is_aspect_ratio(struct wlr_output *output) {
return (output->phys_width == 1600 && output->phys_height == 900) ||
(output->phys_width == 1600 && output->phys_height == 1000) ||
(output->phys_width == 160 && output->phys_height == 90) ||
(output->phys_width == 160 && output->phys_height == 100) ||
(output->phys_width == 16 && output->phys_height == 9) ||
(output->phys_width == 16 && output->phys_height == 10);
}

// The minimum DPI at which we turn on a scale of 2
#define HIDPI_DPI_LIMIT (2 * 96)
// The minimum screen height at which we turn on a scale of 2
#define HIDPI_MIN_HEIGHT 1200
// 1 inch = 25.4 mm
#define MM_PER_INCH 25.4

static int compute_default_scale(struct wlr_output *output) {
int width, height;
wlr_output_transformed_resolution(output, &width, &height);
if (height < HIDPI_MIN_HEIGHT) {
return 1;
}

if (output->phys_width == 0 || output->phys_height == 0) {
return 1;
}

if (phys_size_is_aspect_ratio(output)) {
return 1;
}

double dpi_x = (double) width / (output->phys_width / MM_PER_INCH);
double dpi_y = (double) height / (output->phys_height / MM_PER_INCH);
sway_log(SWAY_DEBUG, "Output DPI: %fx%f", dpi_x, dpi_y);
if (dpi_x <= HIDPI_DPI_LIMIT || dpi_y <= HIDPI_DPI_LIMIT) {
return 1;
}

return 2;
}

bool apply_output_config(struct output_config *oc, struct sway_output *output) {
if (output == root->noop_output) {
return false;
@@ -313,9 +356,16 @@ bool apply_output_config(struct output_config *oc, struct sway_output *output) {
}
output->current_mode = wlr_output->current_mode;

float scale;
if (oc && oc->scale > 0) {
sway_log(SWAY_DEBUG, "Set %s scale to %f", oc->name, oc->scale);
wlr_output_set_scale(wlr_output, oc->scale);
scale = oc->scale;
} else {
scale = compute_default_scale(wlr_output);
sway_log(SWAY_DEBUG, "Auto-detected output scale: %f", scale);
}
if (scale != wlr_output->scale) {
sway_log(SWAY_DEBUG, "Set %s scale to %f", oc->name, scale);
wlr_output_set_scale(wlr_output, scale);

enum scale_filter_mode scale_filter_old = output->scale_filter;
switch (oc->scale_filter) {
@@ -388,7 +438,7 @@ static void default_output_config(struct output_config *oc,
oc->refresh_rate = mode->refresh / 1000.f;
}
oc->x = oc->y = -1;
oc->scale = 1;
oc->scale = 0; // auto
oc->scale_filter = SCALE_FILTER_DEFAULT;
struct sway_output *output = wlr_output->data;
oc->subpixel = output->detected_subpixel;

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