bgfx/3rdparty/ocornut-imgui/widgets/range_slider.inl

// https://github.com/ocornut/imgui/issues/76
// Taken from: https://github.com/wasikuss/imgui/commit/a50515ace6d9a62ebcd69817f1da927d31c39bb1

namespace ImGui
{

// ~80% common code with ImGui::SliderBehavior
bool RangeSliderBehavior(const ImRect& frame_bb, ImGuiID id, float* v1, float* v2, float v_min, float v_max, float power, int decimal_precision, ImGuiSliderFlags flags)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindow* window = GetCurrentWindow();
    const ImGuiStyle& style = g.Style;

    // Draw frame
    RenderFrame(frame_bb.Min, frame_bb.Max, GetColorU32(ImGuiCol_FrameBg), true, style.FrameRounding);

    const bool is_non_linear = (power < 1.0f-0.00001f) || (power > 1.0f+0.00001f);
    const bool is_horizontal = (flags & ImGuiSliderFlags_Vertical) == 0;

    const float grab_padding = 2.0f;
    const float slider_sz = is_horizontal ? (frame_bb.GetWidth() - grab_padding * 2.0f) : (frame_bb.GetHeight() - grab_padding * 2.0f);
    float grab_sz;
    if (decimal_precision > 0)
        grab_sz = ImMin(style.GrabMinSize, slider_sz);
    else
        grab_sz = ImMin(ImMax(1.0f * (slider_sz / ((v_min < v_max ? v_max - v_min : v_min - v_max) + 1.0f)), style.GrabMinSize), slider_sz);  // Integer sliders, if possible have the grab size represent 1 unit
    const float slider_usable_sz = slider_sz - grab_sz;
    const float slider_usable_pos_min = (is_horizontal ? frame_bb.Min.x : frame_bb.Min.y) + grab_padding + grab_sz*0.5f;
    const float slider_usable_pos_max = (is_horizontal ? frame_bb.Max.x : frame_bb.Max.y) - grab_padding - grab_sz*0.5f;

    // For logarithmic sliders that cross over sign boundary we want the exponential increase to be symmetric around 0.0f
    float linear_zero_pos = 0.0f;   // 0.0->1.0f
    if (v_min * v_max < 0.0f)
    {
        // Different sign
        const float linear_dist_min_to_0 = powf(fabsf(0.0f - v_min), 1.0f/power);
        const float linear_dist_max_to_0 = powf(fabsf(v_max - 0.0f), 1.0f/power);
        linear_zero_pos = linear_dist_min_to_0 / (linear_dist_min_to_0+linear_dist_max_to_0);
    }
    else
    {
        // Same sign
        linear_zero_pos = v_min < 0.0f ? 1.0f : 0.0f;
    }

    // Process clicking on the slider
    bool value_changed = false;
    if (g.ActiveId == id)
    {
        if (g.IO.MouseDown[0])
        {
            const float mouse_abs_pos = is_horizontal ? g.IO.MousePos.x : g.IO.MousePos.y;
            float clicked_t = (slider_usable_sz > 0.0f) ? ImClamp((mouse_abs_pos - slider_usable_pos_min) / slider_usable_sz, 0.0f, 1.0f) : 0.0f;
            if (!is_horizontal)
                clicked_t = 1.0f - clicked_t;

            float new_value;
            if (is_non_linear)
            {
                // Account for logarithmic scale on both sides of the zero
                if (clicked_t < linear_zero_pos)
                {
                    // Negative: rescale to the negative range before powering
                    float a = 1.0f - (clicked_t / linear_zero_pos);
                    a = powf(a, power);
                    new_value = ImLerp(ImMin(v_max,0.0f), v_min, a);
                }
                else
                {
                    // Positive: rescale to the positive range before powering
                    float a;
                    if (fabsf(linear_zero_pos - 1.0f) > 1.e-6f)
                        a = (clicked_t - linear_zero_pos) / (1.0f - linear_zero_pos);
                    else
                        a = clicked_t;
                    a = powf(a, power);
                    new_value = ImLerp(ImMax(v_min,0.0f), v_max, a);
                }
            }
            else
            {
                // Linear slider
                new_value = ImLerp(v_min, v_max, clicked_t);
            }

            // Round past decimal precision
            new_value = RoundScalar(new_value, decimal_precision);
            if (*v1 != new_value || *v2 != new_value)
            {
                if (fabsf(*v1 - new_value) < fabsf(*v2 - new_value))
                {
                    *v1 = new_value;
                }
                else
                {
                    *v2 = new_value;
                }
                value_changed = true;
            }
        }
        else
        {
            ClearActiveID();
        }
    }

    // Calculate slider grab positioning
    float grab_t = SliderBehaviorCalcRatioFromValue(*v1, v_min, v_max, power, linear_zero_pos);

    // Draw
    if (!is_horizontal)
        grab_t = 1.0f - grab_t;
    float grab_pos = ImLerp(slider_usable_pos_min, slider_usable_pos_max, grab_t);
    ImRect grab_bb1;
    if (is_horizontal)
        grab_bb1 = ImRect(ImVec2(grab_pos - grab_sz*0.5f, frame_bb.Min.y + grab_padding), ImVec2(grab_pos + grab_sz*0.5f, frame_bb.Max.y - grab_padding));
    else
        grab_bb1 = ImRect(ImVec2(frame_bb.Min.x + grab_padding, grab_pos - grab_sz*0.5f), ImVec2(frame_bb.Max.x - grab_padding, grab_pos + grab_sz*0.5f));
    window->DrawList->AddRectFilled(grab_bb1.Min, grab_bb1.Max, GetColorU32(g.ActiveId == id ? ImGuiCol_SliderGrabActive : ImGuiCol_SliderGrab), style.GrabRounding);

    // Calculate slider grab positioning
    grab_t = SliderBehaviorCalcRatioFromValue(*v2, v_min, v_max, power, linear_zero_pos);

    // Draw
    if (!is_horizontal)
        grab_t = 1.0f - grab_t;
    grab_pos = ImLerp(slider_usable_pos_min, slider_usable_pos_max, grab_t);
    ImRect grab_bb2;
    if (is_horizontal)
        grab_bb2 = ImRect(ImVec2(grab_pos - grab_sz*0.5f, frame_bb.Min.y + grab_padding), ImVec2(grab_pos + grab_sz*0.5f, frame_bb.Max.y - grab_padding));
    else
        grab_bb2 = ImRect(ImVec2(frame_bb.Min.x + grab_padding, grab_pos - grab_sz*0.5f), ImVec2(frame_bb.Max.x - grab_padding, grab_pos + grab_sz*0.5f));
    window->DrawList->AddRectFilled(grab_bb2.Min, grab_bb2.Max, GetColorU32(g.ActiveId == id ? ImGuiCol_SliderGrabActive : ImGuiCol_SliderGrab), style.GrabRounding);

    ImRect connector(grab_bb1.Min, grab_bb2.Max);
    connector.Min.x += grab_sz;
    connector.Min.y += grab_sz*0.3f;
    connector.Max.x -= grab_sz;
    connector.Max.y -= grab_sz*0.3f;

    window->DrawList->AddRectFilled(connector.Min, connector.Max, GetColorU32(ImGuiCol_SliderGrab), style.GrabRounding);

    return value_changed;
}

// ~95% common code with ImGui::SliderFloat
bool RangeSliderFloat(const char* label, float* v1, float* v2, float v_min, float v_max, const char* display_format, float power)
{
    ImGuiWindow* window = GetCurrentWindow();
    if (window->SkipItems)
        return false;

    ImGuiContext& g = *GImGui;
    const ImGuiStyle& style = g.Style;
    const ImGuiID id = window->GetID(label);
    const float w = CalcItemWidth();

    const ImVec2 label_size = CalcTextSize(label, NULL, true);
    const ImRect frame_bb(window->DC.CursorPos, window->DC.CursorPos + ImVec2(w, label_size.y + style.FramePadding.y*2.0f));
    const ImRect total_bb(frame_bb.Min, frame_bb.Max + ImVec2(label_size.x > 0.0f ? style.ItemInnerSpacing.x + label_size.x : 0.0f, 0.0f));

    // NB- we don't call ItemSize() yet because we may turn into a text edit box below
    if (!ItemAdd(total_bb, &id))
    {
        ItemSize(total_bb, style.FramePadding.y);
        return false;
    }

    const bool hovered = ItemHoverable(frame_bb, id);
    if (hovered)
        SetHoveredID(id);

    if (!display_format)
        display_format = "(%.3f, %.3f)";
    int decimal_precision = ParseFormatPrecision(display_format, 3);

    // Tabbing or CTRL-clicking on Slider turns it into an input box
    bool start_text_input = false;
    const bool tab_focus_requested = FocusableItemRegister(window, g.ActiveId == id);
    if (tab_focus_requested || (hovered && g.IO.MouseClicked[0]))
    {
        SetActiveID(id, window);
        FocusWindow(window);

        if (tab_focus_requested || g.IO.KeyCtrl)
        {
            start_text_input = true;
            g.ScalarAsInputTextId = 0;
        }
    }
    if (start_text_input || (g.ActiveId == id && g.ScalarAsInputTextId == id))
        return InputScalarAsWidgetReplacement(frame_bb, label, ImGuiDataType_Float, v1, id, decimal_precision);

    ItemSize(total_bb, style.FramePadding.y);

    // Actual slider behavior + render grab
    const bool value_changed = RangeSliderBehavior(frame_bb, id, v1, v2, v_min, v_max, power, decimal_precision, 0);

    // Display value using user-provided display format so user can add prefix/suffix/decorations to the value.
    char value_buf[64];
    const char* value_buf_end = value_buf + ImFormatString(value_buf, IM_ARRAYSIZE(value_buf), display_format, *v1, *v2);
    RenderTextClipped(frame_bb.Min, frame_bb.Max, value_buf, value_buf_end, NULL, ImVec2(0.5f,0.5f));

    if (label_size.x > 0.0f)
        RenderText(ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y), label);

    return value_changed;
}

} // namespace ImGui