Fail loudly on a touch read, stop the workers before their sockets close, and file down the small edges

input.go

@@ -119,8 +119,11 @@ func watchTouch(w, h int) (*touchState, error) {
 		var down bool
 		for {
 			n, err := f.Read(buf)
+			// Nothing else feeds this state, so returning here would freeze the
+			// last touch in place and leave the reset button dead while the panel
+			// goes on looking alive.
 			if err != nil {
-				return
+				panic(fmt.Sprintf("reading touchscreen events: %v", err))
 			}
 			for o := 0; o+sizeofInputEvent <= n; o += sizeofInputEvent {
 				typ := *(*uint16)(unsafe.Pointer(&buf[o+16]))
@@ -142,9 +145,11 @@ func watchTouch(w, h int) (*touchState, error) {
 					if code != synReport {
 						break
 					}
+					// Scaled onto [0, w-1], so full deflection is the last pixel
+					// rather than one past it.
 					state.set(
-						int(int64(rawX-minX)*int64(w)/int64(maxX-minX)),
-						int(int64(rawY-minY)*int64(h)/int64(maxY-minY)),
+						int(int64(rawX-minX)*int64(w-1)/int64(maxX-minX)),
+						int(int64(rawY-minY)*int64(h-1)/int64(maxY-minY)),
 						down)
 				}
 			}