ImDrawList: merge draw command better, cases of multiple Begin/End gets merged properly

imgui.cpp

@@ -705,6 +705,7 @@ static inline ImVec2& operator+=(ImVec2& lhs, const ImVec2& rhs)
 static inline ImVec2& operator-=(ImVec2& lhs, const ImVec2& rhs)                { lhs.x -= rhs.x; lhs.y -= rhs.y; return lhs; }
 static inline ImVec2& operator*=(ImVec2& lhs, const float rhs)                  { lhs.x *= rhs; lhs.y *= rhs; return lhs; }
 //static inline ImVec2& operator/=(ImVec2& lhs, const float rhs)                { lhs.x /= rhs; lhs.y /= rhs; return lhs; }
+static inline ImVec4 operator-(const ImVec4& lhs, const ImVec4& rhs)            { return ImVec4(lhs.x-rhs.x, lhs.y-rhs.y, lhs.z-rhs.z, lhs.w-lhs.w); }
 
 static inline int    ImMin(int lhs, int rhs)                                    { return lhs < rhs ? lhs : rhs; }
 static inline int    ImMax(int lhs, int rhs)                                    { return lhs >= rhs ? lhs : rhs; }
@@ -719,6 +720,7 @@ static inline float  ImSaturate(float f)
 static inline float  ImLerp(float a, float b, float t)                          { return a + (b - a) * t; }
 static inline ImVec2 ImLerp(const ImVec2& a, const ImVec2& b, const ImVec2& t)  { return ImVec2(a.x + (b.x - a.x) * t.x, a.y + (b.y - a.y) * t.y); }
 static inline float  ImLengthSqr(const ImVec2& lhs)                             { return lhs.x*lhs.x + lhs.y*lhs.y; }
+static inline float  ImLengthSqr(const ImVec4& lhs)                             { return lhs.x*lhs.x + lhs.y*lhs.y + lhs.z*lhs.z + lhs.w*lhs.w; }
 
 static int ImStricmp(const char* str1, const char* str2)
 {
@@ -8004,7 +8006,11 @@ void ImDrawList::UpdateClipRect()
     }
     else
     {
-        current_cmd->clip_rect = clip_rect_stack.empty() ? GNullClipRect : clip_rect_stack.back();
+        ImVec4 current_clip_rect = clip_rect_stack.empty() ? GNullClipRect : clip_rect_stack.back();
+        if (commands.size() > 2 && ImLengthSqr(commands[commands.size()-2].clip_rect - current_clip_rect) < 0.00001f)
+            commands.pop_back();
+        else
+            current_cmd->clip_rect = current_clip_rect;
     }
 }