Feat: Line styles (dashed lines)

implot.cpp

@@ -4556,6 +4556,94 @@ ImPlotMarker NextMarker() {
     ++gp.CurrentItems->MarkerIdx;
     return idx;
 }
+
+void LoadDefaultLineStyles() {
+    const ImU32 Dash[] = {10, 6};
+    const ImU32 Dot[]  = {2, 6};
+    const ImU32 DashDot[] = {10, 6, 2, 6};
+    const ImU32 DashDotDot[] = {10, 6, 2, 6, 2, 6};
+
+    // The default line styles are added at fixed indices
+    // We use the internal add function with the desired index to ensure they are stored in the correct order and that user defined line styles are added after them
+    AddLineStyleInternal(ImPlotLineStyle_Dashed, Dash, sizeof(Dash)/sizeof(ImU32));
+    AddLineStyleInternal(ImPlotLineStyle_Dotted, Dot, sizeof(Dot)/sizeof(ImU32));
+    AddLineStyleInternal(ImPlotLineStyle_DashDot, DashDot, sizeof(DashDot)/sizeof(ImU32));
+    AddLineStyleInternal(ImPlotLineStyle_DashDotDot, DashDotDot, sizeof(DashDotDot)/sizeof(ImU32));
+}
+
+int AddLineStyle(const ImU32* keys, int count) {
+    IM_ASSERT_USER_ERROR(count > 1 && count % 2 == 0, "The line style size must be greater than 1 and even!");
+    // User defined line styles are added after the default line styles, so we start with an index of -1 to append to the end of the list
+    return AddLineStyleInternal(-1, keys, count);
+}
+
+int AddLineStyleInternal(const int ID, const ImU32* keys, const int count) {
+    IM_ASSERT(ID < ImPlotLineStyle_COUNT || ID == -1); // ID must be a valid default line style index or -1 for user defined styles
+    ImPlotContext& gp = *GImPlot;
+    int period = 0;
+    for (int i = 0; i < count; ++i){
+        period += keys[i];
+    }
+    // Reserve space for default line styles if they haven't been added yet
+    if (gp.LineStyleData.Size < ImPlotLineStyle_COUNT) {
+        gp.LineStyleData.resize(ImPlotLineStyle_COUNT);
+        for (int i = 0; i < ImPlotLineStyle_COUNT; ++i) gp.LineStyleData[i].RectID = -1;
+    }
+    if (ID >= 0 && gp.LineStyleData[ID].RectID != -1)
+        return ID; // If the ID is already used
+    // Get font atlas and add a custom rectangle to it
+    ImFontAtlas *atlas = ImGui::GetIO().Fonts;
+    ImFontAtlasRectId rectID = atlas->AddCustomRect(510, 1);
+    int keyIdx = 0;
+    ImU32 k = 0;
+    ImU32 color = ~0;
+    if (rectID != -1)
+    {
+        // Build the atlas and get the pixel data
+        unsigned char* pixels;
+        int width, height;
+        atlas->GetTexDataAsRGBA32(&pixels, &width, &height);
+        // Retrieve the rectangle location and fill it with data
+        ImFontAtlasRect rect;
+        if (atlas->GetCustomRect(rectID, &rect))
+        {
+            for (int i = 0; i < rect.h; i++)
+            {
+                // Calculate the pointer to the start of the row in the atlas
+                ImU32* row = (ImU32*)pixels + (rect.y + i) * width + rect.x;
+                for (int j = 0; j < rect.w; j++)
+                {
+                    row[j] = color;
+                    if (++k >= keys[keyIdx]) {
+                        color = ~color;
+                        keyIdx = (keyIdx + 1) % count;
+                        k = 0;
+                    }
+                }
+            }
+            // Add the line style data to the context
+            if (ID < 0)
+                gp.LineStyleData.push_back(ImPlotLineStyleData(rectID, period, 510));
+            else
+                gp.LineStyleData[ID] = ImPlotLineStyleData(rectID, period, 510);
+            return gp.LineStyleData.Size - 1;
+        }
+        else
+            IM_ASSERT(0 && "Failed to retrieve custom rectangle from font atlas for line style!");
+    }
+    else
+        IM_ASSERT(0 && "Failed to add custom rectangle to font atlas for line style!");
+    return -1;
+}
+
+const ImPlotLineStyleData& GetLineStyleData(ImPlotLineStyle style) {
+    ImPlotContext& gp = *GImPlot;
+    IM_ASSERT_USER_ERROR(style >= 0 && style < gp.LineStyleData.Size, "Invalid line style index!");
+    const ImPlotLineStyleData& data = gp.LineStyleData[style];
+    if (!ImGui::GetIO().Fonts->GetCustomRect(data.RectID, &data.Rect))
+        IM_ASSERT(0 && "Failed to retrieve custom rectangle from font atlas for line style!");
+    return data;
+}
 
 //------------------------------------------------------------------------------
 // [Section] Colormaps

implot.h

@@ -115,6 +115,7 @@ typedef int ImPlotCond;               // -> enum ImPlotCond_
 typedef int ImPlotCol;                // -> enum ImPlotCol_
 typedef int ImPlotStyleVar;           // -> enum ImPlotStyleVar_
 typedef int ImPlotScale;              // -> enum ImPlotScale_
+typedef int ImPlotLineStyle;          // -> enum ImPlotLineStyle_
 typedef int ImPlotMarker;             // -> enum ImPlotMarker_
 typedef int ImPlotColormap;           // -> enum ImPlotColormap_
 typedef int ImPlotLocation;           // -> enum ImPlotLocation_
@@ -139,6 +140,7 @@ enum ImAxis_ {
 enum ImPlotProp_ {
     ImPlotProp_LineColor,       // line color (applies to lines, bar edges); IMPLOT_AUTO_COL will use next Colormap color or current item color
     ImPlotProp_LineWeight,      // line weight in pixels (applies to lines, bar edges, marker edges)
+    ImPlotProp_LineStyle,       // line style (applies to lines)
     ImPlotProp_FillColor,       // fill color (applies to shaded regions, bar faces); IMPLOT_AUTO_COL will use next Colormap color or current item color
     ImPlotProp_FillAlpha,       // alpha multiplier (applies to FillColor and MarkerFillColor)
     ImPlotProp_Marker,          // marker type; specify ImPlotMarker_Auto to use the next unused marker
@@ -429,6 +431,16 @@ enum ImPlotScale_ {
     ImPlotScale_SymLog,     // symmetric log scale
 };
 
+// Line style specifications.
+enum ImPlotLineStyle_ {
+    ImPlotLineStyle_Solid = -1,// default
+    ImPlotLineStyle_Dashed,    // 6px on, 6px off
+    ImPlotLineStyle_Dotted,    // 2px on, 6px off
+    ImPlotLineStyle_DashDot,   // 6px on, 2px off, 2px on, 2px off
+    ImPlotLineStyle_DashDotDot,// 6px on, 2px off, 2px on, 2px off, 2px on, 2px off
+    ImPlotLineStyle_COUNT
+};
+
 // Marker specifications.
 enum ImPlotMarker_ {
     ImPlotMarker_None = -2, // no marker
@@ -510,6 +522,7 @@ enum ImPlotBin_ {
 struct ImPlotSpec {
     ImVec4          LineColor       = IMPLOT_AUTO_COL;       // line color (applies to lines, bar edges); IMPLOT_AUTO_COL will use next Colormap color or current item color
     float           LineWeight      = 1.0f;                  // line weight in pixels (applies to lines, bar edges, marker edges)
+    ImPlotLineStyle LineStyle       = ImPlotLineStyle_Solid; // line style (applies to lines)
     ImVec4          FillColor       = IMPLOT_AUTO_COL;       // fill color (applies to shaded regions, bar faces); IMPLOT_AUTO_COL will use next Colormap color or current item color
     float           FillAlpha       = 1.0f;                  // alpha multiplier (applies to FillColor and MarkerFillColor)
     ImPlotMarker    Marker          = ImPlotMarker_None;     // marker type; specify ImPlotMarker_Auto to use the next unused marker
@@ -544,6 +557,7 @@ struct ImPlotSpec {
         switch (prop) {
         case ImPlotProp_LineColor       : LineColor       = ImGui::ColorConvertU32ToFloat4((ImU32)v); return;
         case ImPlotProp_LineWeight      : LineWeight      = (float)v;                                 return;
+        case ImPlotProp_LineStyle       : LineStyle       = (ImPlotLineStyle)v;                       return;
         case ImPlotProp_FillColor       : FillColor       = ImGui::ColorConvertU32ToFloat4((ImU32)v); return;
         case ImPlotProp_FillAlpha       : FillAlpha       = (float)v;                                 return;
         case ImPlotProp_Marker          : Marker          = (ImPlotMarker)v;                          return;
@@ -1216,6 +1230,11 @@ IMPLOT_API const char* GetMarkerName(ImPlotMarker idx);
 // Returns the next marker and advances the marker for the current plot. You need to call this between Begin/EndPlot!
 IMPLOT_API ImPlotMarker NextMarker();
 
+// Executes post-setup initialization
+IMPLOT_API void LoadDefaultLineStyles();
+
+IMPLOT_API int AddLineStyle(const ImU32* keys, int count);
+
 //-----------------------------------------------------------------------------
 // [SECTION] Colormaps
 //-----------------------------------------------------------------------------

implot_demo.cpp

@@ -1063,6 +1063,60 @@ void Demo_RealtimePlots() {
 
 //-----------------------------------------------------------------------------
 
+void Demo_LineStyles() {
+    IMGUI_DEMO_MARKER("Plots/Line Styles");
+    static ImPlotSpec spec;
+    static bool is_init = false;
+    static ImPlotLineStyle custom_style[2];
+    // Custom line styles are defined by an array of on/off lengths in pixels.
+    // The first element is the length of the dash, the second is the length of the gap, and so on.
+    static ImU32 styleA[] = {15, 6, 15, 6, 2, 6}; // dash, dash, dot
+    static ImU32 styleB[] = {20, 6, 10, 6}; // long dash, short dash
+
+    // ImPlot::LoadDefaultLineStyles() must be called before using line styles!
+    // It should be called once after context creation and backend initialization
+    // Called here for demo purposes, but you should call it in your initialization code.
+    if (!is_init) {
+        // Register custom line style before loading defaults
+        custom_style[0] = ImPlot::AddLineStyle(styleA, sizeof(styleA)/sizeof(ImU32));
+        // Load default line styles
+        ImPlot::LoadDefaultLineStyles();
+        // Register custom line style after loading defaults (order doesn't matter)
+        custom_style[1] = ImPlot::AddLineStyle(styleB, sizeof(styleB)/sizeof(ImU32));
+        is_init = true;
+    }
+    ImGui::DragFloat("Line Weight", &spec.LineWeight,0.05f,0.5f,32.0f,"%.2f px");
+
+    if (ImPlot::BeginPlot("##LineStyles", ImVec2(-1,0), ImPlotFlags_CanvasOnly)) {
+
+        ImPlot::SetupAxes(nullptr, nullptr, ImPlotAxisFlags_NoDecorations, ImPlotAxisFlags_NoDecorations);
+        ImPlot::SetupAxesLimits(0, 5, 0, 9);
+
+        ImS8 xs[2] = {1,4};
+        ImS8 ys[2] = {7,8};
+
+        // Line Styles
+        for (int m = 0; m < ImPlotLineStyle_COUNT; ++m) {
+            ImGui::PushID(m);
+            spec.LineStyle = (ImPlotLineStyle)m;
+            ImPlot::PlotLine("##Style", xs, ys, 2, spec);
+            ImGui::PopID();
+            ys[0]--; ys[1]--;
+        }
+        // Custom Line Styles
+        for (int m = 0; m < 2; ++m) {
+            ImGui::PushID(m);
+            spec.LineStyle = custom_style[m];
+            ImPlot::PlotLine("##Custom", xs, ys, 2, spec);
+            ImGui::PopID();
+            ys[0]--; ys[1]--;
+        }
+        ImPlot::EndPlot();
+    }
+}
+
+//-----------------------------------------------------------------------------
+
 void Demo_MarkersAndText() {
     IMGUI_DEMO_MARKER("Plots/Markers and Text");
     static ImPlotSpec spec(ImPlotProp_Marker, ImPlotMarker_Auto);
@@ -2499,6 +2553,7 @@ void ShowDemoWindow(bool* p_open) {
             DemoHeader("Histogram 2D", Demo_Histogram2D);
             DemoHeader("Digital Plots", Demo_DigitalPlots);
             DemoHeader("Images", Demo_Images);
+            DemoHeader("Line Styles", Demo_LineStyles);
             DemoHeader("Markers and Text", Demo_MarkersAndText);
             DemoHeader("NaN Values", Demo_NaNValues);
             ImGui::EndTabItem();

implot_internal.h

@@ -123,6 +123,8 @@ template <typename T>
 static inline T ImRemap01(T x, T x0, T x1) { return (x - x0) / (x1 - x0); }
 // Returns always positive modulo (assumes r != 0)
 static inline int ImPosMod(int l, int r) { return (l % r + r) % r; }
+// Returns the modulo of x by y (assumes y != 0)
+static inline double ImMod(double x, double y) { return fmod(x, y); }
 // Returns true if val is NAN
 static inline bool ImNan(double val) { return isnan(val); }
 // Returns true if val is NAN or INFINITY
@@ -285,6 +287,18 @@ typedef void (*ImPlotLocator)(ImPlotTicker& ticker, const ImPlotRange& range, fl
 // [SECTION] Structs
 //-----------------------------------------------------------------------------
 
+struct ImPlotLineStyleData {
+    ImPlotLineStyleData() {}
+    ImPlotLineStyleData(ImFontAtlasRectId rect_id, float period, float max_length) :
+        RectID(rect_id),
+        Period(period),
+        MaxLength(max_length) {}
+    ImFontAtlasRectId RectID;  // texture atlas rect ID for line style
+    float  Period;                  // period of line style in pixels
+    float  MaxLength;               // maximum length of line style in pixels
+    mutable ImFontAtlasRect Rect;   // cached rectangle for line style (filled in on demand)
+};
+
 // Combined date/time format spec
 struct ImPlotDateTimeSpec {
     ImPlotDateTimeSpec() {}
@@ -1243,11 +1257,12 @@ struct ImPlotContext {
     ImPlotTagCollection        Tags;
 
     // Style and Colormaps
-    ImPlotStyle                 Style;
-    ImVector<ImGuiColorMod>     ColorModifiers;
-    ImVector<ImGuiStyleMod>     StyleModifiers;
-    ImPlotColormapData          ColormapData;
-    ImVector<ImPlotColormap>    ColormapModifiers;
+    ImPlotStyle                     Style;
+    ImVector<ImGuiColorMod>         ColorModifiers;
+    ImVector<ImGuiStyleMod>         StyleModifiers;
+    ImPlotColormapData              ColormapData;
+    ImVector<ImPlotColormap>        ColormapModifiers;
+    ImVector<ImPlotLineStyleData>   LineStyleData;
 
     // Time
     tm Tm;
@@ -1508,6 +1523,12 @@ IMPLOT_API ImU32  SampleColormapU32(float t, ImPlotColormap cmap);
 // Render a colormap bar
 IMPLOT_API void RenderColorBar(const ImU32* colors, int size, ImDrawList& DrawList, const ImRect& bounds, bool vert, bool reversed, bool continuous);
 
+// Adds a line style with the given ID to ImPlot context. Set ID to -1 to add a line style with an automatically generated ID.
+IMPLOT_API int AddLineStyleInternal(const int ID, const ImU32* keys, const int count);
+
+// Returns line style data for a given line style. Do not store the returned value between frames as it may be invalidated if texture atlas is rebuilt.
+IMPLOT_API const ImPlotLineStyleData& GetLineStyleData(ImPlotLineStyle style);
+
 //-----------------------------------------------------------------------------
 // [SECTION] Math and Misc Utils
 //-----------------------------------------------------------------------------