zfm: navigating directories

assets/disk0/tvdos/include/wintex.js

@@ -81,4 +81,102 @@ class WindowObject {
 
 }
 
-exports = { WindowObject }
+/**
+ * @param dy cursor change (positive or negative)
+ * @param listSize size of the list to scroll
+ * @param listHeight size of the list window
+ * @param currentCursorPos ABSOLUTE position of the cursor
+ * @param currentScrollPos current scroll position of the list
+ * @param scrollPeek size of the scroll "peek"
+ * @return [new cursor pos, new scroll pos]
+ */
+function scrollVert(dy, listSize, listHeight, currentCursorPos, currentScrollPos, scrollPeek) {
+    let peek = 1
+
+    // clamp dy
+    if (currentCursorPos + dy > listSize - 1)
+        dy = (listSize - 1) - currentCursorPos
+    else if (currentCursorPos + dy < 0)
+        dy = -currentCursorPos
+
+    let nextRow = currentCursorPos + dy
+    
+    // update vertical scroll stats
+    if (dy != 0) {
+        let visible = listHeight - 1 - peek
+
+        if (nextRow - currentScrollPos > visible) {
+            currentScrollPos = nextRow - visible
+        }
+        else if (nextRow - currentScrollPos < 0 + peek) {
+            currentScrollPos = nextRow - peek // nextRow is less than zero
+        }
+
+        // NOTE: future-proofing here -- scroll clamping is moved outside of go-up/go-down
+        // if-statements above because horizontal movements can disrupt vertical scrolls as well because
+        // "normally" when you go right at the end of the line, you appear at the start of the next line
+
+        // scroll to the bottom?
+        if (listSize > listHeight && currentScrollPos > listSize - listHeight)
+            // to make sure not show buncha empty lines
+            currentScrollPos = listSize - listHeight
+        // scroll to the top? (order is important!)
+        if (currentScrollPos <= -1)
+            currentScrollPos = 0 // scroll of -1 would result to show "Line 0" on screen
+    }
+    
+    // move editor cursor
+    currentCursorPos = nextRow
+    return [currentCursorPos, currentScrollPos]
+}
+
+/**
+ * @param dx cursor change (positive or negative)
+ * @param stringSize length of the string to scroll
+ * @param stringViewSize size of the string view
+ * @param currentCursorPos ABSOLUTE position of the cursor
+ * @param currentScrollPos current scroll position of the list
+ * @param scrollPeek size of the scroll "peek"
+ * @return [new cursor pos, new scroll pos]
+ */
+function scrollHorz(dx, stringSize, stringViewSize, currentCursorPos, currentScrollPos, scrollPeek) {
+    let peek = 1
+
+    // clamp dx
+    if (currentCursorPos + dx > stringSize - 1)
+        dx = (stringSize - 1) - currentCursorPos
+    else if (currentCursorPos + dx < 0)
+        dx = -currentCursorPos
+
+    let nextCol = currentCursorPos + dx
+
+    // update vertical scroll stats
+    if (dx != 0) {
+        let visible = stringViewSize - 1 - peek
+
+        if (nextCol - currentScrollPos > visible) {
+            currentScrollPos = nextCol - visible
+        }
+        else if (nextCol - currentScrollPos < 0 + peek) {
+            currentScrollPos = nextCol - peek // nextCol is less than zero
+        }
+
+        // NOTE: future-proofing here -- scroll clamping is moved outside of go-up/go-down
+        // if-statements above because horizontal movements can disrupt vertical scrolls as well because
+        // "normally" when you go right at the end of the line, you appear at the start of the next line
+
+        // scroll to the bottom?
+        if (stringSize > stringViewSize && currentScrollPos > stringSize - stringViewSize)
+            // to make sure not show buncha empty lines
+            currentScrollPos = stringSize - stringViewSize
+        // scroll to the top? (order is important!)
+        if (currentScrollPos <= -1)
+            currentScrollPos = 0 // scroll of -1 would result to show "Line 0" on screen
+    }
+
+    // move editor cursor
+    currentCursorPos = nextCol
+    return [currentCursorPos, currentScrollPos]
+}
+
+exports = { WindowObject, scrollVert, scrollHorz }