add public API for horizontal and vertical guide lines

implot.cpp

@@ -1185,7 +1185,7 @@ bool BeginPlot(const char* title, const char* x_label, const char* y_label, cons
 
     // capture scroll with a child region
     if (!ImHasFlag(plot.Flags, ImPlotFlags_NoChild)) {
-        ImGui::BeginChild(title, ImVec2(size.x == 0 ? IMPLOT_DEFAULT_W : size.x, size.y == 0 ? IMPLOT_DEFAULT_H : size.y));
+        ImGui::BeginChild(title, ImVec2(size.x == 0 ? IMPLOT_DEFAULT_W : size.x, size.y == 0 ? IMPLOT_DEFAULT_H : size.y), false, ImGuiWindowFlags_NoScrollbar);
         Window = ImGui::GetCurrentWindow();
         Window->ScrollMax.y = 1.0f;
         gp.ChildWindowMade = true;
@@ -2479,6 +2479,68 @@ ImPlotLimits GetPlotQuery(int y_axis_in) {
     return result;
 }
 
+bool HorizontalGuide(const char* id, double* value, const ImVec4& col, float thickness) {
+    ImPlotContext& gp = *GImPlot;
+    IM_ASSERT_USER_ERROR(gp.CurrentPlot != NULL, "HorizontalGuide() needs to be called between BeginPlot() and EndPlot()!");
+    const float grab_size = 2*thickness;
+    float xl = gp.BB_Plot.Min.x;
+    float xr = gp.BB_Plot.Max.x;
+    float y  = PlotToPixels(0, *value).y;
+    ImU32 col32 = IsColorAuto(col) ? GetStyleColorU32(ImPlotCol_Query) : ImGui::ColorConvertFloat4ToU32(col);
+    PushPlotClipRect();
+    GetPlotDrawList()->AddLine(ImVec2(xl,y), ImVec2(xr,y), col32, thickness);
+    PopPlotClipRect();
+    const bool outside = (y < gp.BB_Plot.Min.y - grab_size / 2 || y > gp.BB_Plot.Max.y + grab_size / 2);
+    if (outside)
+        return false;
+    ImVec2 old_cursor_pos = ImGui::GetCursorScreenPos();
+    ImVec2 new_cursor_pos = ImVec2(xl, y - grab_size / 2.0f);    
+    ImGui::SetItemAllowOverlap();
+    ImGui::SetCursorScreenPos(new_cursor_pos);
+    ImGui::InvisibleButton(id, ImVec2(xr - xl, grab_size));
+    ImGui::SetCursorScreenPos(old_cursor_pos);
+    if (ImGui::IsItemHovered() || ImGui::IsItemActive()) {
+        ImGui::SetMouseCursor(ImGuiMouseCursor_ResizeNS);
+    }
+    bool dragging = false;
+    if (ImGui::IsItemActive() && ImGui::IsMouseDragging(0)) {
+        *value = ImPlot::GetPlotMousePos().y;
+        dragging = true;
+    }
+    return dragging;
+}
+
+bool VerticalGuide(const char* id, double* value, const ImVec4& col, float thickness) {
+    ImPlotContext& gp = *GImPlot;
+    IM_ASSERT_USER_ERROR(gp.CurrentPlot != NULL, "VerticalGuide() needs to be called between BeginPlot() and EndPlot()!");
+    const float grab_size = 2*thickness;
+    float yt = gp.BB_Plot.Min.y;
+    float yb = gp.BB_Plot.Max.y;
+    float x  = PlotToPixels(*value,0).x;
+    ImU32 col32 = IsColorAuto(col) ? GetStyleColorU32(ImPlotCol_Query) : ImGui::ColorConvertFloat4ToU32(col);
+    PushPlotClipRect();
+    GetPlotDrawList()->AddLine(ImVec2(x,yt), ImVec2(x,yb), col32, thickness);
+    PopPlotClipRect();
+    const bool outside = (x < gp.BB_Plot.Min.x - grab_size / 2 || x > gp.BB_Plot.Max.x + grab_size / 2);
+    if (outside)
+        return false;
+    ImVec2 old_cursor_pos = ImGui::GetCursorScreenPos();
+    ImVec2 new_cursor_pos = ImVec2(x - grab_size / 2.0f, yt);    
+    ImGui::SetItemAllowOverlap();
+    ImGui::SetCursorScreenPos(new_cursor_pos);
+    ImGui::InvisibleButton(id, ImVec2(grab_size, yb-yt));
+    ImGui::SetCursorScreenPos(old_cursor_pos);
+    if (ImGui::IsItemHovered() || ImGui::IsItemActive()) {
+        ImGui::SetMouseCursor(ImGuiMouseCursor_ResizeEW);
+    }
+    bool dragging = false;
+    if (ImGui::IsItemActive() && ImGui::IsMouseDragging(0)) {
+        *value = ImPlot::GetPlotMousePos().x;
+        dragging = true;
+    }
+    return dragging;
+}
+
 bool IsLegendEntryHovered(const char* label_id) {
     ImPlotContext& gp = *GImPlot;
     IM_ASSERT_USER_ERROR(gp.CurrentPlot != NULL, "IsPlotItemHighlight() needs to be called between BeginPlot() and EndPlot()!");

implot.h

@@ -459,6 +459,11 @@ IMPLOT_API bool IsPlotQueried();
 // Returns the current plot query bounds.
 IMPLOT_API ImPlotLimits GetPlotQuery(int y_axis = IMPLOT_AUTO);
 
+// Shows a draggable horizontal guide line.
+IMPLOT_API bool HorizontalGuide(const char* id, double* value, const ImVec4& col = IMPLOT_AUTO_COL, float thickness = 2);
+// Shows a draggable vertical guide line.
+IMPLOT_API bool VerticalGuide(const char* id, double* value, const ImVec4& col = IMPLOT_AUTO_COL, float thickness = 2);
+
 //-----------------------------------------------------------------------------
 // Plot and Item Styling
 //-----------------------------------------------------------------------------

implot_demo.cpp

@@ -785,6 +785,23 @@ void ShowDemoWindow(bool* p_open) {
         }
     }
     //-------------------------------------------------------------------------
+    if (ImGui::CollapsingHeader("Guide Lines")) {
+        static double v1 = 0.2;
+        static double v2 = 0.6;
+        static double h1 = 0.25;
+        static double h2 = 0.75;
+        static double h3 = 0.5;
+        if (ImPlot::BeginPlot("##guides",0,0,ImVec2(-1,0),ImPlotFlags_YAxis2)) {            
+            ImPlot::VerticalGuide("v1",&v1, ImVec4(0,1,0,1));
+            ImPlot::VerticalGuide("v2",&v2, ImVec4(0,1,0,1));
+            ImPlot::HorizontalGuide("h1",&h1, ImVec4(1,0,0,1));
+            ImPlot::HorizontalGuide("h2",&h2, ImVec4(1,0,0,1));
+            ImPlot::SetPlotYAxis(1);
+            ImPlot::HorizontalGuide("h3",&h3, ImVec4(1,1,0,1));
+            ImPlot::EndPlot();
+        }
+    }
+    //-------------------------------------------------------------------------
     if (ImGui::CollapsingHeader("Drag and Drop")) {
         const int K_CHANNELS = 9;
         srand((int)(10000000 * DEMO_TIME));
@@ -1218,38 +1235,6 @@ void ShowDemoWindow(bool* p_open) {
         }
     }
     //-------------------------------------------------------------------------
-    if (ImGui::CollapsingHeader("Custom Dragable Lines")) {
-        static float line_value = 0.5f;
-        const float line_width = 3.0f;
-        const float grabbable_width = 5.0f;
-        if (ImPlot::BeginPlot("Dragable Lines")) {
-
-            auto x0 = ImPlot::GetPlotPos().x;
-            auto x1 = ImPlot::GetPlotPos().x + ImPlot::GetPlotSize().x;
-            auto y = ImPlot::PlotToPixels(0, line_value).y;
-            ImPlot::PushPlotClipRect();
-            ImPlot::GetPlotDrawList()->AddLine({ x0, y }, { x1, y }, IM_COL32_WHITE, line_width);
-            ImPlot::PopPlotClipRect();
-
-            ImVec2 old_cursor_pos = ImGui::GetCursorScreenPos();
-            ImVec2 new_cursor_pos = ImVec2(x0, y - grabbable_width / 2.0f);
-            ImGui::SetItemAllowOverlap();
-            ImGui::SetCursorScreenPos(new_cursor_pos);
-            ImGui::InvisibleButton("horizontal_line", ImVec2(x1 - x0, grabbable_width));
-            ImGui::SetCursorScreenPos(old_cursor_pos);
-
-            if (ImGui::IsItemHovered() || ImGui::IsItemActive()) {
-                ImGui::SetMouseCursor(ImGuiMouseCursor_ResizeNS);
-            }
-
-            if (ImGui::IsItemActive() && ImGui::IsMouseDragging(0)) {
-                line_value = ImPlot::GetPlotMousePos().y;
-            }
-
-            ImPlot::EndPlot();
-        }
-    }
-    //-------------------------------------------------------------------------
     ImGui::End();
 }