ImDrawList: added AddBezier(), PathBezierTo() for cubic bezier curves (#311)

imgui.cpp

@@ -620,6 +620,7 @@ ImGuiStyle::ImGuiStyle()
     DisplaySafeAreaPadding  = ImVec2(4,4);      // If you cannot see the edge of your screen (e.g. on a TV) increase the safe area padding. Covers popups/tooltips as well regular windows.
     AntiAliasedLines        = true;             // Enable anti-aliasing on lines/borders. Disable if you are really short on CPU/GPU.
     AntiAliasedShapes       = true;             // Enable anti-aliasing on filled shapes (rounded rectangles, circles, etc.)
+    CurveTessellationTol    = 1.25f;            // Tessellation tolerance. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
 
     Colors[ImGuiCol_Text]                   = ImVec4(0.90f, 0.90f, 0.90f, 1.00f);
     Colors[ImGuiCol_TextDisabled]           = ImVec4(0.60f, 0.60f, 0.60f, 1.00f);
@@ -1790,6 +1791,7 @@ void ImGui::NewFrame()
     IM_ASSERT(g.IO.RenderDrawListsFn != NULL);       // Must be implemented
     IM_ASSERT(g.IO.Fonts->Fonts.Size > 0);           // Font Atlas not created. Did you call io.Fonts->GetTexDataAsRGBA32 / GetTexDataAsAlpha8 ?
     IM_ASSERT(g.IO.Fonts->Fonts[0]->IsLoaded());     // Font Atlas not created. Did you call io.Fonts->GetTexDataAsRGBA32 / GetTexDataAsAlpha8 ?
+	IM_ASSERT(g.Style.CurveTessellationTol > 0.0f);  // Invalid
 
     if (!g.Initialized)
     {

imgui.h

@@ -647,6 +647,7 @@ struct ImGuiStyle
     ImVec2      DisplaySafeAreaPadding;     // If you cannot see the edge of your screen (e.g. on a TV) increase the safe area padding. Covers popups/tooltips as well regular windows.
     bool        AntiAliasedLines;           // Enable anti-aliasing on lines/borders. Disable if you are really tight on CPU/GPU.
     bool        AntiAliasedShapes;          // Enable anti-aliasing on filled shapes (rounded rectangles, circles, etc.)
+    float       CurveTessellationTol;       // Tessellation tolerance. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
     ImVec4      Colors[ImGuiCol_COUNT];
 
     IMGUI_API ImGuiStyle();
@@ -1100,15 +1101,18 @@ struct ImDrawList
     IMGUI_API void  AddImage(ImTextureID user_texture_id, const ImVec2& a, const ImVec2& b, const ImVec2& uv0, const ImVec2& uv1, ImU32 col = 0xFFFFFFFF);
     IMGUI_API void  AddPolyline(const ImVec2* points, const int num_points, ImU32 col, bool closed, float thickness, bool anti_aliased);
     IMGUI_API void  AddConvexPolyFilled(const ImVec2* points, const int num_points, ImU32 col, bool anti_aliased);
+	inline    void  AddBezier(const ImVec2& pos0, const ImVec2& cp0, const ImVec2& cp1, const ImVec2& pos1, ImU32 col, float thickness, int num_segments = 0) { PathBezierTo(pos0, cp0, cp1, pos1, num_segments); PathStroke(col, false, thickness); }
 
     // Stateful path API, add points then finish with PathFill() or PathStroke()
     inline    void  PathClear()                                                 { _Path.resize(0); }
-    inline    void  PathLineTo(const ImVec2& p)                                 { _Path.push_back(p); }
+    inline    void  PathLineTo(const ImVec2& pos)                               { _Path.push_back(pos); }
-    IMGUI_API void  PathArcTo(const ImVec2& centre, float radius, float a_min, float a_max, int num_segments = 10);
+    inline    void  PathLineToMergeDuplicate(const ImVec2& pos)                 { if (_Path.Size == 0 || _Path[_Path.Size-1].x != pos.x || _Path[_Path.Size-1].y != pos.y) _Path.push_back(pos); }
-    IMGUI_API void  PathArcToFast(const ImVec2& centre, float radius, int a_min_of_12, int a_max_of_12);
-    IMGUI_API void  PathRect(const ImVec2& a, const ImVec2& b, float rounding = 0.0f, int rounding_corners = 0x0F);
     inline    void  PathFill(ImU32 col)                                         { AddConvexPolyFilled(_Path.Data, _Path.Size, col, true); PathClear(); }
 	inline    void  PathStroke(ImU32 col, bool closed, float thickness = 1.0f)  { AddPolyline(_Path.Data, _Path.Size, col, closed, thickness, true); PathClear(); }
+	IMGUI_API void  PathArcTo(const ImVec2& centre, float radius, float a_min, float a_max, int num_segments = 10);
+    IMGUI_API void  PathArcToFast(const ImVec2& centre, float radius, int a_min_of_12, int a_max_of_12);                 // Use precomputed angles for a 12 steps circle
+	IMGUI_API void  PathBezierTo(const ImVec2& p0, const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, int num_segments = 0);
+    IMGUI_API void  PathRect(const ImVec2& rect_min, const ImVec2& rect_max, float rounding = 0.0f, int rounding_corners = 0x0F);
 
     // Channels
     // - Use to simulate layers. By switching channels to can render out-of-order (e.g. submit foreground primitives before background primitives)

imgui_demo.cpp

@@ -1392,6 +1392,10 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
     {
         ImGui::Checkbox("Anti-aliased lines", &style.AntiAliasedLines);
         ImGui::Checkbox("Anti-aliased shapes", &style.AntiAliasedShapes);
+        ImGui::PushItemWidth(100);
+        ImGui::DragFloat("Curve Tessellation Tolerance", &style.CurveTessellationTol, 0.02f, 0.10f, FLT_MAX, NULL, 2.0f);
+        if (style.CurveTessellationTol < 0.0f) style.CurveTessellationTol = 0.10f;
+        ImGui::PopItemWidth();
         ImGui::TreePop();
     }
 

imgui_draw.cpp

@@ -639,6 +639,56 @@ void ImDrawList::PathArcTo(const ImVec2& centre, float radius, float amin, float
     }
 }
 
+static void PathBezierToCasteljau(ImVector<ImVec2>* path, float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4, float tess_tol, int level)
+{
+    float dx = x4 - x1;
+    float dy = y4 - y1;
+    float d2 = ((x2 - x4) * dy - (y2 - y4) * dx); 
+    float d3 = ((x3 - x4) * dy - (y3 - y4) * dx); 
+    d2 = (d2 >= 0) ? d2 : -d2;
+    d3 = (d3 >= 0) ? d3 : -d3;
+    if ((d2+d3) * (d2+d3) < tess_tol * (dx*dx + dy*dy)) 
+    {
+        path->push_back(ImVec2(x4, y4));
+    }
+    else if (level < 10)
+    {
+        float x12 = (x1+x2)*0.5f,       y12 = (y1+y2)*0.5f;
+        float x23 = (x2+x3)*0.5f,       y23 = (y2+y3)*0.5f;
+        float x34 = (x3+x4)*0.5f,       y34 = (y3+y4)*0.5f;
+        float x123 = (x12+x23)*0.5f,    y123 = (y12+y23)*0.5f;
+        float x234 = (x23+x34)*0.5f,    y234 = (y23+y34)*0.5f;
+        float x1234 = (x123+x234)*0.5f, y1234 = (y123+y234)*0.5f;
+
+        PathBezierToCasteljau(path, x1,y1,        x12,y12,    x123,y123,  x1234,y1234, tess_tol, level+1); 
+        PathBezierToCasteljau(path, x1234,y1234,  x234,y234,  x34,y34,    x4,y4,       tess_tol, level+1); 
+    }
+}
+
+void ImDrawList::PathBezierTo(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, const ImVec2& p4, int num_segments)
+{
+    PathLineToMergeDuplicate(p1);
+    if (num_segments == 0)
+    {
+        // Auto-tessellated
+        PathBezierToCasteljau(&_Path, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y, p4.x, p4.y, GImGui->Style.CurveTessellationTol, 0);
+    }
+    else
+    {
+        float t_step = 1.0f / (float)num_segments;
+        for (int i_step = 1; i_step <= num_segments; i_step++)
+        {
+            float t = t_step * i_step;
+            float u = 1.0f - t;
+            float w1 = u*u*u;
+            float w2 = 3*u*u*t;
+            float w3 = 3*u*t*t;
+            float w4 = t*t*t;
+            _Path.push_back(ImVec2(w1*p1.x + w2*p2.x + w3*p3.x + w4*p4.x, w1*p1.y + w2*p2.y + w3*p3.y + w4*p4.y));
+        }
+    }
+}
+
 void ImDrawList::PathRect(const ImVec2& a, const ImVec2& b, float rounding, int rounding_corners)
 {
     float r = rounding;