ImDrawList: Add LegacyPolyline flag for backward compatibility

Author: thedmd

imgui.cpp

@@ -1309,6 +1309,7 @@ ImGuiStyle::ImGuiStyle()
     AntiAliasedLines            = true;             // Enable anti-aliased lines/borders. Disable if you are really tight on CPU/GPU.
     AntiAliasedLinesUseTex      = true;             // Enable anti-aliased lines/borders using textures where possible. Require backend to render with bilinear filtering (NOT point/nearest filtering).
     AntiAliasedFill             = true;             // Enable anti-aliased filled shapes (rounded rectangles, circles, etc.).
+    LegacyPolyline              = false;            // Enable fallback to legacy AddPolyline() to trade feature and precission for speed.
     CurveTessellationTol        = 1.25f;            // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
     CircleTessellationMaxError  = 0.30f;            // Maximum error (in pixels) allowed when using AddCircle()/AddCircleFilled() or drawing rounded corner rectangles with no explicit segment count specified. Decrease for higher quality but more geometry.
 
@@ -4774,6 +4775,8 @@ static void SetupDrawListSharedData()
         g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AntiAliasedLinesUseTex;
     if (g.Style.AntiAliasedFill)
         g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AntiAliasedFill;
+    if (g.Style.LegacyPolyline)
+        g.DrawListSharedData.InitialFlags |= ImDrawListFlags_LegacyPolyline;
     if (g.IO.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset)
         g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AllowVtxOffset;
 }

imgui.h

@@ -2179,6 +2179,7 @@ struct ImGuiStyle
     bool        AntiAliasedLines;           // Enable anti-aliased lines/borders. Disable if you are really tight on CPU/GPU. Latched at the beginning of the frame (copied to ImDrawList).
     bool        AntiAliasedLinesUseTex;     // Enable anti-aliased lines/borders using textures where possible. Require backend to render with bilinear filtering (NOT point/nearest filtering). Latched at the beginning of the frame (copied to ImDrawList).
     bool        AntiAliasedFill;            // Enable anti-aliased edges around filled shapes (rounded rectangles, circles, etc.). Disable if you are really tight on CPU/GPU. Latched at the beginning of the frame (copied to ImDrawList).
+    bool        LegacyPolyline;             // Enable fallback to legacy AddPolyline() to trade feature and precission for speed.
     float       CurveTessellationTol;       // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
     float       CircleTessellationMaxError; // Maximum error (in pixels) allowed when using AddCircle()/AddCircleFilled() or drawing rounded corner rectangles with no explicit segment count specified. Decrease for higher quality but more geometry.
     ImVec4      Colors[ImGuiCol_COUNT];
@@ -3022,6 +3023,7 @@ enum ImDrawListFlags_
     ImDrawListFlags_AntiAliasedLinesUseTex  = 1 << 1,  // Enable anti-aliased lines/borders using textures when possible. Require backend to render with bilinear filtering (NOT point/nearest filtering).
     ImDrawListFlags_AntiAliasedFill         = 1 << 2,  // Enable anti-aliased edge around filled shapes (rounded rectangles, circles).
     ImDrawListFlags_AllowVtxOffset          = 1 << 3,  // Can emit 'VtxOffset > 0' to allow large meshes. Set when 'ImGuiBackendFlags_RendererHasVtxOffset' is enabled.
+    ImDrawListFlags_LegacyPolyline          = 1 << 4,  // (Legacy) For AddPolyline() to trade features and precission for a bit of extra performance.
 };
 
 // Draw command list
@@ -3116,7 +3118,7 @@ struct ImDrawList
     inline    void  PathLineToMergeDuplicate(const ImVec2& pos)                 { if (_Path.Size == 0 || memcmp(&_Path.Data[_Path.Size - 1], &pos, 8) != 0) _Path.push_back(pos); }
     inline    void  PathFillConvex(ImU32 col)                                   { AddConvexPolyFilled(_Path.Data, _Path.Size, col); _Path.Size = 0; }
     inline    void  PathFillConcave(ImU32 col)                                  { AddConcavePolyFilled(_Path.Data, _Path.Size, col); _Path.Size = 0; }
-    inline    void  PathStroke(ImU32 col, ImDrawFlags flags = 0, float thickness = 1.0f, float miter_limit = -1.0f) { AddPolyline(_Path.Data, _Path.Size, col, flags, thickness, miter_limit); _Path.Size = 0; }
+    inline    void  PathStroke(ImU32 col, ImDrawFlags flags = 0, float thickness = 1.0f, float miter_limit = -1.0f) { if (Flags & ImDrawListFlags_LegacyPolyline) AddPolylineLegacy(_Path.Data, _Path.Size, col, flags, thickness); else AddPolyline(_Path.Data, _Path.Size, col, flags, thickness, miter_limit); _Path.Size = 0; }
     IMGUI_API void  PathArcTo(const ImVec2& center, float radius, float a_min, float a_max, int num_segments = 0);
     IMGUI_API void  PathArcToFast(const ImVec2& center, float radius, int a_min_of_12, int a_max_of_12);                // Use precomputed angles for a 12 steps circle
     IMGUI_API void  PathEllipticalArcTo(const ImVec2& center, const ImVec2& radius, float rot, float a_min, float a_max, int num_segments = 0); // Ellipse

imgui_demo.cpp

@@ -8021,6 +8021,11 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             HelpMarker("Faster lines using texture data. Require backend to render with bilinear filtering (not point/nearest filtering).");
 
             ImGui::Checkbox("Anti-aliased fill", &style.AntiAliasedFill);
+
+            ImGui::Checkbox("Legacy polyline", &style.LegacyPolyline);
+            ImGui::SameLine();
+            HelpMarker("Legacy polyline is faster for drawing lots of geometry, but does lack of features and robustness.");
+
             ImGui::PushItemWidth(ImGui::GetFontSize() * 8);
             ImGui::DragFloat("Curve Tessellation Tolerance", &style.CurveTessellationTol, 0.02f, 0.10f, 10.0f, "%.2f");
             if (style.CurveTessellationTol < 0.10f) style.CurveTessellationTol = 0.10f;