feat: add dpi detection and configuration for mouse distance

include/config.h

@@ -39,6 +39,7 @@ struct Config {
     int panel_height;
     int gap;
     char font_name[128];
+    double mouse_distance_dpi;
     ColorScheme colors;
 
     float default_master_ratio;

include/dwn.h

@@ -215,6 +215,9 @@ typedef struct {
     int last_mouse_x;
     int last_mouse_y;
     bool mouse_tracking_initialized;
+
+    double pixels_per_cm;
+    bool dpi_auto_detected;
 } DWNState;
 
 #define PHASE_OFFSET_PANEL_BG      0.0f

src/config.c

@@ -61,6 +61,7 @@ void config_set_defaults(Config *cfg)
     cfg->panel_height = DEFAULT_PANEL_HEIGHT;
     cfg->gap = DEFAULT_GAP;
     strncpy(cfg->font_name, "fixed", sizeof(cfg->font_name) - 1);
+    cfg->mouse_distance_dpi = 0.0;
 
     cfg->default_master_ratio = 0.55f;
     cfg->default_master_count = 1;
@@ -158,6 +159,9 @@ static void handle_config_entry(const char *section, const char *key,
             cfg->gap = (val >= 0 && val <= 100) ? val : DEFAULT_GAP;
         } else if (strcmp(key, "font") == 0) {
             strncpy(cfg->font_name, value, sizeof(cfg->font_name) - 1);
+        } else if (strcmp(key, "mouse_distance_dpi") == 0) {
+            double val = atof(value);
+            cfg->mouse_distance_dpi = (val > 0.0) ? val : 0.0;
         }
     } else if (strcmp(section, "layout") == 0) {
         if (strcmp(key, "master_ratio") == 0) {

src/main.c

@@ -218,6 +218,42 @@ static void handle_xi2_event(XGenericEventCookie *cookie)
     XFreeEventData(dwn->display, cookie);
 }
 
+static double calculate_pixels_per_cm(void)
+{
+    if (dwn->config->mouse_distance_dpi > 0.0) {
+        LOG_DEBUG("Using manual DPI override: %.1f", dwn->config->mouse_distance_dpi);
+        return dwn->config->mouse_distance_dpi / 2.54;
+    }
+
+    int width_mm = DisplayWidthMM(dwn->display, dwn->screen);
+    int height_mm = DisplayHeightMM(dwn->display, dwn->screen);
+
+    if (width_mm > 0 && height_mm > 0) {
+        double diag_pixels = sqrt((double)dwn->screen_width * dwn->screen_width +
+                                 (double)dwn->screen_height * dwn->screen_height);
+        double diag_mm = sqrt((double)width_mm * width_mm + (double)height_mm * height_mm);
+        double diag_cm = diag_mm / 10.0;
+
+        double pixels_per_cm = diag_pixels / diag_cm;
+
+        if (pixels_per_cm >= 20.0 && pixels_per_cm <= 200.0) {
+            dwn->dpi_auto_detected = true;
+            double dpi = pixels_per_cm * 2.54;
+            LOG_INFO("Auto-detected DPI: %.1f (%.2f pixels/cm) from EDID: %dx%dmm for %dx%dpx",
+                     dpi, pixels_per_cm, width_mm, height_mm,
+                     dwn->screen_width, dwn->screen_height);
+            return pixels_per_cm;
+        } else {
+            LOG_WARN("EDID data appears corrupt: %.1f pixels/cm detected, ignoring",
+                     pixels_per_cm);
+        }
+    }
+
+    LOG_WARN("Could not detect screen DPI from EDID, using default 96 DPI");
+    dwn->dpi_auto_detected = false;
+    return 37.8;
+}
+
 static void init_monitors(void)
 {
     if (!XineramaIsActive(dwn->display)) {
@@ -842,6 +878,8 @@ int dwn_init(void)
     extern void config_init_colors(Config *cfg);
     config_init_colors(dwn->config);
 
+    dwn->pixels_per_cm = calculate_pixels_per_cm();
+
     dwn->font = XLoadQueryFont(dwn->display, dwn->config->font_name);
     if (dwn->font == NULL) {
         dwn->font = XLoadQueryFont(dwn->display, "fixed");

src/panel.c

@@ -1348,7 +1348,7 @@ static void panel_render_mouse_distance(Panel *panel, int x, int *width)
     int text_y = panel_text_y(panel->height);
 
     char buf[32];
-    double cm = dwn->mouse_distance_pixels / 37.8;
+    double cm = dwn->mouse_distance_pixels / dwn->pixels_per_cm;
     int len;
 
     if (cm >= 100000.0) {