fix: zoom around cursor when axes are equal

Author: brenocq

implot.cpp

@@ -2026,20 +2026,22 @@ bool UpdateInput(ImPlotPlot& plot) {
         float tx = ImRemap(IO.MousePos.x, plot.PlotRect.Min.x, plot.PlotRect.Max.x, 0.0f, 1.0f);
         float ty = ImRemap(IO.MousePos.y, plot.PlotRect.Min.y, plot.PlotRect.Max.y, 0.0f, 1.0f);
 
+        // Track which axis to use as reference for equal aspect
+        ImPlotAxis* equal_ref_axis = nullptr;
+
         for (int i = 0; i < IMPLOT_NUM_X_AXES; i++) {
             ImPlotAxis& x_axis = plot.XAxis(i);
             const bool equal_zoom   = axis_equal && x_axis.OrthoAxis != nullptr;
             const bool equal_locked = (equal_zoom != false) && x_axis.OrthoAxis->IsInputLocked();
             if (x_hov[i] && !x_axis.IsInputLocked() && !equal_locked) {
                 ImGui::SetKeyOwner(ImGuiKey_MouseWheelY, plot.ID);
                 if (zoom_rate != 0.0f) {
-                    float correction = (plot.Hovered && equal_zoom) ? 0.5f : 1.0f;
-                    const double plot_l = x_axis.PixelsToPlot(plot.PlotRect.Min.x - rect_size.x * tx * zoom_rate * correction);
-                    const double plot_r = x_axis.PixelsToPlot(plot.PlotRect.Max.x + rect_size.x * (1 - tx) * zoom_rate * correction);
+                    const double plot_l = x_axis.PixelsToPlot(plot.PlotRect.Min.x - rect_size.x * tx * zoom_rate);
+                    const double plot_r = x_axis.PixelsToPlot(plot.PlotRect.Max.x + rect_size.x * (1 - tx) * zoom_rate);
                     x_axis.SetMin(x_axis.IsInverted() ? plot_r : plot_l);
                     x_axis.SetMax(x_axis.IsInverted() ? plot_l : plot_r);
-                    if (axis_equal && x_axis.OrthoAxis != nullptr)
-                        x_axis.OrthoAxis->SetAspect(x_axis.GetAspect());
+                    if (equal_zoom)
+                        equal_ref_axis = &x_axis;
                     changed = true;
                 }
             }
@@ -2051,17 +2053,21 @@ bool UpdateInput(ImPlotPlot& plot) {
             if (y_hov[i] && !y_axis.IsInputLocked() && !equal_locked) {
                 ImGui::SetKeyOwner(ImGuiKey_MouseWheelY, plot.ID);
                 if (zoom_rate != 0.0f) {
-                    float correction = (plot.Hovered && equal_zoom) ? 0.5f : 1.0f;
-                    const double plot_t = y_axis.PixelsToPlot(plot.PlotRect.Min.y - rect_size.y * ty * zoom_rate * correction);
-                    const double plot_b = y_axis.PixelsToPlot(plot.PlotRect.Max.y + rect_size.y * (1 - ty) * zoom_rate * correction);
+                    const double plot_t = y_axis.PixelsToPlot(plot.PlotRect.Min.y - rect_size.y * ty * zoom_rate);
+                    const double plot_b = y_axis.PixelsToPlot(plot.PlotRect.Max.y + rect_size.y * (1 - ty) * zoom_rate);
                     y_axis.SetMin(y_axis.IsInverted() ? plot_t : plot_b);
                     y_axis.SetMax(y_axis.IsInverted() ? plot_b : plot_t);
-                    if (axis_equal && y_axis.OrthoAxis != nullptr)
-                        y_axis.OrthoAxis->SetAspect(y_axis.GetAspect());
+                    if (equal_zoom)
+                        equal_ref_axis = &y_axis;
                     changed = true;
                 }
             }
         }
+
+        // Apply equal aspect constraint after zooming both axes
+        if (equal_ref_axis != nullptr && equal_ref_axis->OrthoAxis != nullptr) {
+            equal_ref_axis->OrthoAxis->SetAspect(equal_ref_axis->GetAspect());
+        }
     }
 
     // BOX-SELECTION ----------------------------------------------------------