ImDrawList: fixed AddCircle, AddCircleFilled buffer read overflow with (rad > 0.0f && rad < 1.0f && num_segments == 0). (#3738)

Amend 051ce076. Maximum cached count becomes 63 instead of 64.

docs/CHANGELOG.txt

@@ -31,10 +31,22 @@ HOW TO UPDATE?
 - Please report any issue!
 
 
+-----------------------------------------------------------------------
+ VERSION 1.8X (In Progress)
+-----------------------------------------------------------------------
+
+Other Changes:
+
+- ImDrawList: fixed AddCircle()/AddCircleFilled() with (rad > 0.0f && rad < 1.0f && num_segments == 0). (#3738)
+  Would lead to a buffer read overflow.
+
+
 -----------------------------------------------------------------------
  VERSION 1.80 (Released 2021-01-21)
 -----------------------------------------------------------------------
 
+Decorated log: https://github.com/ocornut/imgui/releases/tag/v1.80
+
 Breaking Changes:
 
 - Added imgui_tables.cpp file! Manually constructed project files will need the new file added! (#3740)

imgui.cpp

@@ -1130,7 +1130,7 @@ void ImGuiIO::ClearInputCharacters()
 
 ImVec2 ImBezierCubicClosestPoint(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, const ImVec2& p4, const ImVec2& p, int num_segments)
 {
-    IM_ASSERT(num_segments > 0); // Use ImBezierClosestPointCasteljau()
+    IM_ASSERT(num_segments > 0); // Use ImBezierCubicClosestPointCasteljau()
     ImVec2 p_last = p1;
     ImVec2 p_closest;
     float p_closest_dist2 = FLT_MAX;

imgui.h

@@ -59,7 +59,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.80"
-#define IMGUI_VERSION_NUM           18000
+#define IMGUI_VERSION_NUM           18001
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE
 

imgui_draw.cpp

@@ -377,7 +377,7 @@ void ImDrawListSharedData::SetCircleSegmentMaxError(float max_error)
     CircleSegmentMaxError = max_error;
     for (int i = 0; i < IM_ARRAYSIZE(CircleSegmentCounts); i++)
     {
-        const float radius = i + 1.0f;
+        const float radius = (float)i;
         const int segment_count = IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(radius, CircleSegmentMaxError);
         CircleSegmentCounts[i] = (ImU8)ImMin(segment_count, 255);
     }
@@ -1278,7 +1278,7 @@ void ImDrawList::AddCircle(const ImVec2& center, float radius, ImU32 col, int nu
     if (num_segments <= 0)
     {
         // Automatic segment count
-        const int radius_idx = (int)radius - 1;
+        const int radius_idx = (int)radius;
         if (radius_idx < IM_ARRAYSIZE(_Data->CircleSegmentCounts))
             num_segments = _Data->CircleSegmentCounts[radius_idx]; // Use cached value
         else
@@ -1308,7 +1308,7 @@ void ImDrawList::AddCircleFilled(const ImVec2& center, float radius, ImU32 col,
     if (num_segments <= 0)
     {
         // Automatic segment count
-        const int radius_idx = (int)radius - 1;
+        const int radius_idx = (int)radius;
         if (radius_idx < IM_ARRAYSIZE(_Data->CircleSegmentCounts))
             num_segments = _Data->CircleSegmentCounts[radius_idx]; // Use cached value
         else

imgui_internal.h

@@ -610,6 +610,7 @@ struct IMGUI_API ImChunkStream
 //-----------------------------------------------------------------------------
 
 // ImDrawList: Helper function to calculate a circle's segment count given its radius and a "maximum error" value.
+// FIXME: the minimum number of auto-segment may be undesirably high for very small radiuses (e.g. 1.0f)
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN                     12
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX                     512
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(_RAD,_MAXERROR)    ImClamp((int)((IM_PI * 2.0f) / ImAcos(((_RAD) - (_MAXERROR)) / (_RAD))), IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX)
@@ -633,7 +634,7 @@ struct IMGUI_API ImDrawListSharedData
 
     // [Internal] Lookup tables
     ImVec2          ArcFastVtx[12 * IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER];  // FIXME: Bake rounded corners fill/borders in atlas
-    ImU8            CircleSegmentCounts[64];    // Precomputed segment count for given radius (array index + 1) before we calculate it dynamically (to avoid calculation overhead)
+    ImU8            CircleSegmentCounts[64];    // Precomputed segment count for given radius before we calculate it dynamically (to avoid calculation overhead)
     const ImVec4*   TexUvLines;                 // UV of anti-aliased lines in the atlas
 
     ImDrawListSharedData();