Tip/Demo: Log example as helper class.

[ocornut]

I have added a simple Log example in imgui_demo.cpp

The way you use it is:

static ExampleAppLog my_log;
[...]
my_log.AddLog("Hello %d world\n", 123);
[...]
my_log.Draw("title");

Complete code below.
The reason I added it is that it is a very common and desirable pattern to have a log window.

Now, this pattern is SO common that I am considering promoting this to a helper, e.g. ImGuiAppLog.
The only reason to do that is most people are too lazy to build their own log window. But if you build own you can make something that's more suited to your application (add multiple channels, add options to find the log emitter object in your game scene, click on filename to open them or folder in Windows Explorer, etc.). So I am on the fence as to whether I should provide this sort of stuff in the main library code. Opinion?

Similar to the memory editor I've posted here #270 (comment) , perhaps this is the sign that we could start a wiki or repository to post that sort of higher-level stuff ?

Demo code

struct ExampleAppLog
{
    ImGuiTextBuffer     Buf;
    ImGuiTextFilter     Filter;
    ImVector<int>       LineOffsets;        // Index to lines offset
    bool                ScrollToBottom;

    void    Clear()     { Buf.clear(); LineOffsets.clear(); }

    void    AddLog(const char* fmt, ...) IM_PRINTFARGS(2)
    {
        int old_size = Buf.size();
        va_list args;
        va_start(args, fmt);
        Buf.appendv(fmt, args);
        va_end(args);
        for (int new_size = Buf.size(); old_size < new_size; old_size++)
            if (Buf[old_size] == '\n')
                LineOffsets.push_back(old_size);
        ScrollToBottom = true;
    }

    void    Draw(const char* title, bool* p_opened = NULL)
    {
        ImGui::SetNextWindowSize(ImVec2(500,400), ImGuiSetCond_FirstUseEver);
        ImGui::Begin(title, p_opened);
        if (ImGui::Button("Clear")) Clear();
        ImGui::SameLine();
        bool copy = ImGui::Button("Copy");
        ImGui::SameLine();
        Filter.Draw("Filter", -100.0f);
        ImGui::Separator();
        ImGui::BeginChild("scrolling");
        ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(0,1));
        if (copy) ImGui::LogToClipboard();

        if (Filter.IsActive())
        {
            const char* buf_begin = Buf.begin();
            const char* line = buf_begin;
            for (int line_no = 0; line != NULL; line_no++)
            {
                const char* line_end = (line_no < LineOffsets.Size) ? buf_begin + LineOffsets[line_no] : NULL;
                if (Filter.PassFilter(line, line_end))
                    ImGui::TextUnformatted(line, line_end);
                line = line_end && line_end[1] ? line_end + 1 : NULL;
            }
        }
        else
        {
            ImGui::TextUnformatted(Buf.begin());
        }

        if (ScrollToBottom)
            ImGui::SetScrollHere(1.0f);
        ScrollToBottom = false;
        ImGui::PopStyleVar();
        ImGui::EndChild();
        ImGui::End();
    }
};

Same without filter

struct ExampleAppLog
{
    ImGuiTextBuffer     Buf;
    bool                ScrollToBottom;

    void    Clear()     { Buf.clear(); }

    void    AddLog(const char* fmt, ...) IM_PRINTFARGS(2)
    {
        va_list args;
        va_start(args, fmt);
        Buf.appendv(fmt, args);
        va_end(args);
        ScrollToBottom = true;
    }

    void    Draw(const char* title, bool* p_opened = NULL)
    {
        ImGui::SetNextWindowSize(ImVec2(500,400), ImGuiSetCond_FirstUseEver);
        ImGui::Begin(title, p_opened);
        if (ImGui::Button("Clear")) Clear();
        ImGui::SameLine();
        bool copy = ImGui::Button("Copy");
        ImGui::Separator();
        ImGui::BeginChild("scrolling");
        ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(0,1));
        if (copy) ImGui::LogToClipboard();
        ImGui::TextUnformatted(Buf.begin());
        if (ScrollToBottom)
            ImGui::SetScrollHere(1.0f);
        ScrollToBottom = false;
        ImGui::PopStyleVar();
        ImGui::EndChild();
        ImGui::End();
    }
};

Minimal version with no option, no filter:

struct ExampleAppLog
{
    ImGuiTextBuffer     Buf;
    bool                ScrollToBottom;

    void    Clear()     { Buf.clear(); }

    void    AddLog(const char* fmt, ...) IM_PRINTFARGS(2)
    {
        va_list args;
        va_start(args, fmt);
        Buf.appendv(fmt, args);
        va_end(args);
        ScrollToBottom = true;
    }

    void    Draw(const char* title, bool* p_opened = NULL)
    {
        ImGui::Begin(title, p_opened);
        ImGui::TextUnformatted(Buf.begin());
        if (ScrollToBottom)
            ImGui::SetScrollHere(1.0f);
        ScrollToBottom = false;
        ImGui::End();
    }
};

[hypernewbie]

yes. yes. yes.
thank you sir.

it would be extra nice if you could provide one that only draws the visible lines of text, using imgui's clipping mechanisms.

[Zardoz89]

Could be possible to use GetWindowDrawList().AddText() to emulate this (Zandronum/ZDooM console) ?

With TextUnformatted (&cia) and changing style per call, looks that I can only archive setting colours per line.

[ocornut]

Please open a new topic for that.

[ocornut]

Moved to https://github.com/ocornut/imgui/wiki/log_window_example

[ocornut]

FYI if you are stumbling on this thread: this is old code. Prefer using the equivalent code in imgui_demo.cpp as a base.

[richardeakin]

The wiki link appears to be dead. Code in imgui_demo.cpp was very helpful though thanks!

[moebiussurfing]

Here is that code updated on the official demo:

imgui/imgui_demo.cpp

Line 6859 in 0359f6e

// [SECTION] Example App: Debug Log / ShowExampleAppLog()

Anybody can clarify on here:

for (int line_no = 0; line != NULL; line_no++)
{
    const char* line_end = (line_no < LineOffsets.Size) ? buf_begin + LineOffsets[line_no] : NULL;
    if (Filter.PassFilter(line, line_end))
        ImGui::TextUnformatted(line, line_end);
    line = line_end && line_end[1] ? line_end + 1 : NULL;
}

What are line and line_end intended to be on here ImGui::TextUnformatted(line, line_end); ?

I understand that this kind of accelerated, as uses special types from ImGui like ImGuiTextBuffer, ImGuiTextFilter.
It should be faster than loggers that commonly we can do on custom cpp?

I tried to replace my code with that but I ended using my old system,
that uses STRINGS. I suspect that string are slow.

Any suggestions for learning / good practices are appreciated!