openFramewokrs / ImGui circular knob

ofApp.cpp

//https://github.com/ocornut/imgui/issues/942#issuecomment-268369298

//put code into ofApp.cpp and use between begin/end:
if (MyKnob("attack", &myKnob, 0.f, 10.f))
{
    cout << "knob:" << myKnob << endl;
}


// Implementing a simple custom widget using the public API.
// You may also use the <imgui_internal.h> API to get raw access to more data/helpers, however the internal API isn't guaranteed to be forward compatible.
// FIXME: Need at least proper label centering + clipping (internal functions RenderTextClipped provides both but api is flaky/temporary)
static bool MyKnob(const char* label, float* p_value, float v_min, float v_max)
{
    ImGuiIO& io = ImGui::GetIO();
    ImGuiStyle& style = ImGui::GetStyle();

    float radius_outer = 20.0f;
    ImVec2 pos = ImGui::GetCursorScreenPos();
    ImVec2 center = ImVec2(pos.x + radius_outer, pos.y + radius_outer);
    float line_height = ImGui::GetTextLineHeight();
    ImDrawList* draw_list = ImGui::GetWindowDrawList();

    float ANGLE_MIN = 3.141592f * 0.75f;
    float ANGLE_MAX = 3.141592f * 2.25f;

    ImGui::InvisibleButton(label, ImVec2(radius_outer*2, radius_outer*2 + line_height + style.ItemInnerSpacing.y));
    bool value_changed = false;
    bool is_active = ImGui::IsItemActive();
    bool is_hovered = ImGui::IsItemActive();
    if (is_active && io.MouseDelta.x != 0.0f)
    {
        float step = (v_max - v_min) / 200.0f;
        *p_value += io.MouseDelta.x * step;
        if (*p_value < v_min) *p_value = v_min;
        if (*p_value > v_max) *p_value = v_max;
        value_changed = true;
    }

    float t = (*p_value - v_min) / (v_max - v_min);
    float angle = ANGLE_MIN + (ANGLE_MAX - ANGLE_MIN) * t;
    float angle_cos = cosf(angle), angle_sin = sinf(angle);
    float radius_inner = radius_outer*0.40f;
    draw_list->AddCircleFilled(center, radius_outer, ImGui::GetColorU32(ImGuiCol_FrameBg), 16);
    draw_list->AddLine(ImVec2(center.x + angle_cos*radius_inner, center.y + angle_sin*radius_inner), ImVec2(center.x + angle_cos*(radius_outer-2), center.y + angle_sin*(radius_outer-2)), ImGui::GetColorU32(ImGuiCol_SliderGrabActive), 2.0f);
    draw_list->AddCircleFilled(center, radius_inner, ImGui::GetColorU32(is_active ? ImGuiCol_FrameBgActive : is_hovered ? ImGuiCol_FrameBgHovered : ImGuiCol_FrameBg), 16);
    draw_list->AddText(ImVec2(pos.x, pos.y + radius_outer * 2 + style.ItemInnerSpacing.y), ImGui::GetColorU32(ImGuiCol_Text), label);

    if (is_active || is_hovered)
    {
        ImGui::SetNextWindowPos(ImVec2(pos.x - style.WindowPadding.x, pos.y - line_height - style.ItemInnerSpacing.y - style.WindowPadding.y));
        ImGui::BeginTooltip();
        ImGui::Text("%.3f", *p_value);
        ImGui::EndTooltip();
    }

    return value_changed;
}