CalcSaver template, optimize TextWidget measure

src/dlangui/core/types.d

@@ -513,6 +513,55 @@ struct Ref(T) { // if (T is RefCountedObject)
 }
 
 
+/**
+    This struct allows to not execute some code if some variables was not changed since the last check.
+    Used for optimizations.
+
+    Reference types, arrays and pointers are compared by reference.
+ */
+struct CalcSaver(Params...) {
+    import std.typecons : Tuple;
+    Tuple!Params values;
+
+    bool check(Params args) {
+        bool changed;
+        foreach (i, arg; args) {
+            if (values[i] !is arg) {
+                values[i] = arg;
+                changed = true;
+            }
+        }
+        return changed;
+    }
+}
+
+///
+unittest {
+
+    class A { }
+
+    CalcSaver!(uint, double[], A) saver;
+
+    uint x = 5;
+    double[] arr = [1, 2, 3];
+    A a = new A();
+
+    assert(saver.check(x, arr, a));
+    // values are not changing
+    assert(!saver.check(x, arr, a));
+    assert(!saver.check(x, arr, a));
+    assert(!saver.check(x, arr, a));
+    assert(!saver.check(x, arr, a));
+
+    x = 8;
+    arr ~= 25;
+    a = new A();
+    // values are changed
+    assert(saver.check(x, arr, a));
+    assert(!saver.check(x, arr, a));
+}
+
+
 //================================================================================
 // some utility functions
 

src/dlangui/widgets/controls.d

@@ -115,20 +115,26 @@ class TextWidget : Widget {
         return this;
     }
 
+    private CalcSaver!(Font, dstring, uint, uint) _measureSaver;
+
     override void measure(int parentWidth, int parentHeight) {
         FontRef font = font();
-        //auto measureStart = std.datetime.Clock.currAppTick;
+        uint w = (maxLines == 1) ? MAX_WIDTH_UNSPECIFIED :
+                                   parentWidth - margins.left - margins.right - padding.left - padding.right;
+        uint flags = textFlags;
+
+        // optimization: do not measure if nothing changed
+        if (_measureSaver.check(font.get, text, w, flags) || _needLayout) {
             Point sz;
             if (maxLines == 1) {
-            sz = font.textSize(text, MAX_WIDTH_UNSPECIFIED, 4, 0, textFlags);
+                sz = font.textSize(text, w, 4, 0, flags);
             } else {
-            sz = font.measureMultilineText(text,maxLines,parentWidth-margins.left-margins.right-padding.left-padding.right, 4, 0, textFlags);
+                sz = font.measureMultilineText(text, maxLines, w, 4, 0, flags);
+            }
+            // it's not very correct, but in such simple widget it doesn't make issues
+            measuredContent(SIZE_UNSPECIFIED, SIZE_UNSPECIFIED, sz.x, sz.y);
+            _needLayout = false;
         }
-        //auto measureEnd = std.datetime.Clock.currAppTick;
-        //auto duration = measureEnd - measureStart;
-        //if (duration.length > 10)
-        //    Log.d("TextWidget measureText took ", duration.length, " ticks");
-        measuredContent(parentWidth, parentHeight, sz.x, sz.y);
     }
 
     override void onDraw(DrawBuf buf) {