feat: add IsPlotChanging()

As pointed out in the `TODO.md`

Author: SamuMazzi

TODO.md

@@ -37,7 +37,6 @@ The list below represents a combination of high-priority work, nice-to-have feat
 
 ## Tools / Misc.
 
-- add `IsPlotChanging` to detect change in limits
 - add ability to extend plot/axis context menus
 - add LTTB downsampling for lines
 - add box selection to axes
@@ -80,6 +79,7 @@ Ideally every `PlotX` function should use our faster rendering pipeline when it
 |PlotDummy|-|-|-|-|
 
 ## Completed
+- add `IsPlotChanging` to detect change in limits
 - make BeginPlot take fewer args:
 - make query a tool -> `DragRect`
 - rework DragLine/Point to use ButtonBehavior

implot.cpp

@@ -2135,6 +2135,8 @@ void SetupAxis(ImAxis idx, const char* label, ImPlotAxisFlags flags) {
     if (plot.JustCreated || flags != axis.PreviousFlags)
         axis.Flags = flags;
     axis.PreviousFlags = flags;
+    // cache previous range
+    axis.PreviousRange = ImPlotRange(axis.Range.Min, axis.Range.Max);
     // enable axis
     axis.Enabled = true;
     // set label
@@ -3739,6 +3741,16 @@ bool IsPlotHovered() {
     return gp.CurrentPlot->Hovered;
 }
 
+bool IsPlotChanging() {
+    ImPlotContext& gp = *GImPlot;
+    IM_ASSERT_USER_ERROR(gp.CurrentPlot != nullptr, "IsPlotChanging() needs to be called between BeginPlot() and EndPlot()!");
+    SetupLock();
+    ImPlotPlot& plot = *gp.CurrentPlot;
+    bool differentX = plot.Axes[plot.CurrentX].Range.Min != plot.Axes[plot.CurrentX].PreviousRange.Min || plot.Axes[plot.CurrentX].Range.Max != plot.Axes[plot.CurrentX].PreviousRange.Max;
+    bool differentY = plot.Axes[plot.CurrentY].Range.Min != plot.Axes[plot.CurrentY].PreviousRange.Min || plot.Axes[plot.CurrentY].Range.Max != plot.Axes[plot.CurrentY].PreviousRange.Max;
+    return differentX || differentY;
+}
+
 bool IsAxisHovered(ImAxis axis) {
     ImPlotContext& gp = *GImPlot;
     IM_ASSERT_USER_ERROR(gp.CurrentPlot != nullptr, "IsPlotXAxisHovered() needs to be called between BeginPlot() and EndPlot()!");

implot.h

@@ -982,6 +982,8 @@ IMPLOT_API ImPlotRect GetPlotLimits(ImAxis x_axis = IMPLOT_AUTO, ImAxis y_axis =
 
 // Returns true if the plot area in the current plot is hovered.
 IMPLOT_API bool IsPlotHovered();
+// Returns true if the limits of the current plot are changing.
+IMPLOT_API bool IsPlotChanging();
 // Returns true if the axis label area in the current plot is hovered.
 IMPLOT_API bool IsAxisHovered(ImAxis axis);
 // Returns true if the bounding frame of a subplot is hovered.

implot_demo.cpp

@@ -2128,6 +2128,24 @@ void Demo_ColormapWidgets() {
 
 //-----------------------------------------------------------------------------
 
+void Demo_PlotLimitsChanging() {
+    unsigned int lin[10] = {8,8,9,7,8,8,8,9,7,8};
+    unsigned int bar[10] = {1,2,5,3,4,1,2,5,3,4};
+    unsigned int dot[10] = {7,6,6,7,8,5,6,5,8,7};
+
+    if (ImPlot::BeginPlot("##LimitsChanging")) {
+        ImPlot::SetupAxes( "x-axis", "y-axis");
+        ImPlot::SetupAxesLimits(-0.5f, 9.5f, 0, 10);
+        ImPlot::PlotBars("Bars", bar, 10, 0.5f);
+        ImPlot::PlotLine("Line", lin, 10);
+        bool is_changing = ImPlot::IsPlotChanging();
+        ImGui::Text("Axes are changing: %s", (is_changing ? "true" : "false"));
+        ImPlot::EndPlot();
+    }
+}
+
+//-----------------------------------------------------------------------------
+
 void Demo_CustomPlottersAndTooltips()  {
     ImGui::BulletText("You can create custom plotters or extend ImPlot using implot_internal.h.");
     double dates[]  = {1546300800,1546387200,1546473600,1546560000,1546819200,1546905600,1546992000,1547078400,1547164800,1547424000,1547510400,1547596800,1547683200,1547769600,1547942400,1548028800,1548115200,1548201600,1548288000,1548374400,1548633600,1548720000,1548806400,1548892800,1548979200,1549238400,1549324800,1549411200,1549497600,1549584000,1549843200,1549929600,1550016000,1550102400,1550188800,1550361600,1550448000,1550534400,1550620800,1550707200,1550793600,1551052800,1551139200,1551225600,1551312000,1551398400,1551657600,1551744000,1551830400,1551916800,1552003200,1552262400,1552348800,1552435200,1552521600,1552608000,1552867200,1552953600,1553040000,1553126400,1553212800,1553472000,1553558400,1553644800,1553731200,1553817600,1554076800,1554163200,1554249600,1554336000,1554422400,1554681600,1554768000,1554854400,1554940800,1555027200,1555286400,1555372800,1555459200,1555545600,1555632000,1555891200,1555977600,1556064000,1556150400,1556236800,1556496000,1556582400,1556668800,1556755200,1556841600,1557100800,1557187200,1557273600,1557360000,1557446400,1557705600,1557792000,1557878400,1557964800,1558051200,1558310400,1558396800,1558483200,1558569600,1558656000,1558828800,1558915200,1559001600,1559088000,1559174400,1559260800,1559520000,1559606400,1559692800,1559779200,1559865600,1560124800,1560211200,1560297600,1560384000,1560470400,1560729600,1560816000,1560902400,1560988800,1561075200,1561334400,1561420800,1561507200,1561593600,1561680000,1561939200,1562025600,1562112000,1562198400,1562284800,1562544000,1562630400,1562716800,1562803200,1562889600,1563148800,1563235200,1563321600,1563408000,1563494400,1563753600,1563840000,1563926400,1564012800,1564099200,1564358400,1564444800,1564531200,1564617600,1564704000,1564963200,1565049600,1565136000,1565222400,1565308800,1565568000,1565654400,1565740800,1565827200,1565913600,1566172800,1566259200,1566345600,1566432000,1566518400,1566777600,1566864000,1566950400,1567036800,1567123200,1567296000,1567382400,1567468800,1567555200,1567641600,1567728000,1567987200,1568073600,1568160000,1568246400,1568332800,1568592000,1568678400,1568764800,1568851200,1568937600,1569196800,1569283200,1569369600,1569456000,1569542400,1569801600,1569888000,1569974400,1570060800,1570147200,1570406400,1570492800,1570579200,1570665600,1570752000,1571011200,1571097600,1571184000,1571270400,1571356800,1571616000,1571702400,1571788800,1571875200,1571961600};
@@ -2277,6 +2295,7 @@ void ShowDemoWindow(bool* p_open) {
             DemoHeader("Legend Options", Demo_LegendOptions);
             DemoHeader("Legend Popups", Demo_LegendPopups);
             DemoHeader("Colormap Widgets", Demo_ColormapWidgets);
+            DemoHeader("Plot limits changing", Demo_PlotLimitsChanging);
             ImGui::EndTabItem();
         }
         if (ImGui::BeginTabItem("Custom")) {

implot_internal.h

@@ -627,6 +627,7 @@ struct ImPlotAxis
     ImPlotAxisFlags      Flags;
     ImPlotAxisFlags      PreviousFlags;
     ImPlotRange          Range;
+    ImPlotRange          PreviousRange;
     ImPlotCond           RangeCond;
     ImPlotScale          Scale;
     ImPlotRange          FitExtents;