Use a fixed spacing between buttons specified in pixels

Right now the spacing between buttons is the equivalent of one additional button
distributed all over the button row as spacing. This is kind of tricky to imagine
and parse when reading the code, so let's us a fixed value specified in pixels instead.

Author: jonas2515

src/main.rs

@@ -42,6 +42,7 @@ use pixel_shift::PIXEL_SHIFT_WIDTH_PX;
 
 const DFR_WIDTH: i32 = 2008;
 const DFR_HEIGHT: i32 = 64;
+const BUTTON_SPACING_PX: i32 = 16;
 const BUTTON_COLOR_INACTIVE: f64 = 0.200;
 const BUTTON_COLOR_ACTIVE: f64 = 0.400;
 const TIMEOUT_MS: i32 = 10 * 1000;
@@ -115,8 +116,7 @@ impl FunctionLayer {
         let c = Context::new(&surface).unwrap();
         c.translate(DFR_HEIGHT as f64, 0.0);
         c.rotate((90.0f64).to_radians());
-        let button_width = (DFR_WIDTH as u64 - PIXEL_SHIFT_WIDTH_PX) as f64 / (self.buttons.len() + 1) as f64;
-        let spacing_width = ((DFR_WIDTH as u64 - PIXEL_SHIFT_WIDTH_PX) as f64 - self.buttons.len() as f64 * button_width) / (self.buttons.len() - 1) as f64;
+        let button_width = ((DFR_WIDTH - PIXEL_SHIFT_WIDTH_PX as i32) - (BUTTON_SPACING_PX * (self.buttons.len() - 1) as i32)) as f64 / self.buttons.len() as f64;
         let radius = 8.0f64;
         let bot = (DFR_HEIGHT as f64) * 0.2;
         let top = (DFR_HEIGHT as f64) * 0.85;
@@ -127,7 +127,7 @@ impl FunctionLayer {
         c.select_font_face("sans-serif", FontSlant::Normal, FontWeight::Bold);
         c.set_font_size(32.0);
         for (i, button) in self.buttons.iter().enumerate() {
-            let left_edge = i as f64 * (button_width + spacing_width) + pixel_shift_x + (PIXEL_SHIFT_WIDTH_PX / 2) as f64;
+            let left_edge = i as f64 * (button_width + BUTTON_SPACING_PX as f64) + pixel_shift_x + (PIXEL_SHIFT_WIDTH_PX / 2) as f64;
             let color = if active_buttons[i] {
                 BUTTON_COLOR_ACTIVE
             } else if config.show_button_outlines {
@@ -198,9 +198,8 @@ impl LibinputInterface for Interface {
 
 
 fn button_hit(num: u32, idx: u32, x: f64, y: f64) -> bool {
-    let button_width = DFR_WIDTH as f64 / (num + 1) as f64;
-    let spacing_width = (DFR_WIDTH as f64 - num as f64 * button_width) / (num - 1) as f64;
-    let left_edge = idx as f64 * (button_width + spacing_width);
+    let button_width = (DFR_WIDTH - (BUTTON_SPACING_PX * (num - 1) as i32)) as f64 / num as f64;
+    let left_edge = idx as f64 * (button_width + BUTTON_SPACING_PX as f64);
     if x < left_edge || x > (left_edge + button_width) {
         return false
     }