Added RenderCheckMark() helper following the font size

Pretty ugly, not sure what's the right way to solve that automatically,
better shown as an "icon" so it doesn't have to necessarily look like
the font.

imgui.cpp

@@ -501,6 +501,7 @@ static void         RenderTextWrapped(ImVec2 pos, const char* text, const char*
 static void         RenderTextClipped(ImVec2 pos, const char* text, const char* text_end, const ImVec2* text_size_if_known, const ImVec2& clip_max);
 static void         RenderFrame(ImVec2 p_min, ImVec2 p_max, ImU32 fill_col, bool border = true, float rounding = 0.0f);
 static void         RenderCollapseTriangle(ImVec2 p_min, bool opened, float scale = 1.0f, bool shadow = false);
+static void         RenderCheckMark(ImVec2 pos);
 
 static void         SetFont(ImFont* font);
 static bool         ItemAdd(const ImRect& bb, const ImGuiID* id);
@@ -2528,6 +2529,22 @@ static void RenderCollapseTriangle(ImVec2 p_min, bool opened, float scale, bool
     window->DrawList->AddTriangleFilled(a, b, c, window->Color(ImGuiCol_Text));
 }
 
+static void RenderCheckMark(ImVec2 pos)
+{
+    ImGuiState& g = *GImGui;
+    ImGuiWindow* window = GetCurrentWindow();
+
+    float ax = (float)(int)(g.FontSize * 0.307f + 0.5f);        // Spacing
+    float rem_third = (float)(int)((g.FontSize - ax) / 3.0f);
+    float bx = ax + rem_third;
+    float cx = ax + rem_third * 3.0f;
+    float by = (float)(int)(g.Font->BaseLine * (g.FontSize / g.Font->FontSize) + 0.5f) + (float)(int)(g.Font->DisplayOffset.y);
+    float ay = by - rem_third;
+    float cy = by - rem_third * 2.0f;
+    window->DrawList->AddLine(ImVec2(pos.x + ax, pos.y + ay), ImVec2(pos.x + bx, pos.y + by), window->Color(ImGuiCol_Text));
+    window->DrawList->AddLine(ImVec2(pos.x + bx, pos.y + by), ImVec2(pos.x + cx, pos.y + cy), window->Color(ImGuiCol_Text));
+}
+
 // Calculate text size. Text can be multi-line. Optionally ignore text after a ## marker.
 // CalcTextSize("") should return ImVec2(0.0f, GImGui->FontSize)
 ImVec2 ImGui::CalcTextSize(const char* text, const char* text_end, bool hide_text_after_double_hash, float wrap_width)
@@ -8595,6 +8612,7 @@ bool    ImFontAtlas::Build()
         const float font_scale = stbtt_ScaleForPixelHeight(&data.FontInfo, data.SizePixels);
         int font_ascent, font_descent, font_line_gap;
         stbtt_GetFontVMetrics(&data.FontInfo, &font_ascent, &font_descent, &font_line_gap);
+        data.OutFont->BaseLine = (font_ascent * font_scale);
 
         const float uv_scale_x = 1.0f / TexWidth;
         const float uv_scale_y = 1.0f / TexHeight;
@@ -8754,6 +8772,7 @@ void    ImFont::Clear()
 {
     FontSize = 0.0f;
     DisplayOffset = ImVec2(-0.5f, 0.5f);
+    BaseLine = 0.0f;
     ContainerAtlas = NULL;
     Glyphs.clear();
     FallbackGlyph = NULL;

imgui.h

@@ -1018,6 +1018,7 @@ struct ImFont
         signed short    XOffset, YOffset;
         float           U0, V0, U1, V1;     // Texture coordinates
     };
+    float               BaseLine;           // Distance from top to bottom of e.g. 'A' [0..FontSize]
     ImFontAtlas*        ContainerAtlas;     // What we has been loaded into
     ImVector<Glyph>     Glyphs;
     const Glyph*        FallbackGlyph;      // == FindGlyph(FontFallbackChar)