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Font quality in Linux #2

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spworley opened this issue Aug 11, 2014 · 2 comments
Closed

Font quality in Linux #2

spworley opened this issue Aug 11, 2014 · 2 comments

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@spworley
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Running Ubuntu with the latest GLWF 3.0.4, fonts are very poorly rendered. The rightmost column of each glyph is clipped off, and the y baseline of each glyph is not consistent.

image

@ocornut
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ocornut commented Aug 11, 2014

In this function
void ImBitmapFont::RenderText(

You can replace

            const float s1 = (0.0f + glyph->X) * tex_scale_x;
            const float t1 = (0.0f + glyph->Y) * tex_scale_y;
            const float s2 = (0.0f + glyph->X + glyph->Width) * tex_scale_x;
            const float t2 = (0.0f + glyph->Y + glyph->Height) * tex_scale_y;

With

            const float s1 = (0.5f + glyph->X) * tex_scale_x;
            const float t1 = (0.5f + glyph->Y) * tex_scale_y;
            const float s2 = (0.5f + glyph->X + glyph->Width) * tex_scale_x;
            const float t2 = (0.5f + glyph->Y + glyph->Height) * tex_scale_y;

I am currently investigating the right way to expose that because the offset depends on your rendering architecture.

@ocornut
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ocornut commented Aug 11, 2014

I have commited a fix, added a 'float PixelCenterOffset' value in ImGuiIO which default to 0.5f (for OpenGL and DirectX 10+). The DirectX9 sample application sets it back to 0.0. Based on a suggestion by SimDietrich.

@ocornut ocornut closed this as completed Aug 11, 2014
@ocornut ocornut added the bug label Aug 11, 2014
Organic-Code added a commit to Organic-Code/imgui that referenced this issue Mar 5, 2019
I should update my settings, I guess
ocornut pushed a commit that referenced this issue Mar 6, 2019
Squashed commit of the following:

commit 1970d84
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 12:20:39 2019 -0500

    Removing sneaky tabulations #2 (why, editor T-T)

    I should update my settings, I guess

commit 219bdfc
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 12:17:27 2019 -0500

    Removing useless check introduced in b0d172

commit 8afd7a2
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 11:49:24 2019 -0500

    Removing sneaky tabulations

commit 8e04908
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 11:45:13 2019 -0500

    Moving InputTextHinted code to InputTextEx

commit b0d1723
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 00:23:02 2019 -0500

    C++11 to C++98

commit 9afeae3
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Mon Mar 4 23:43:28 2019 -0500

    Added InputTextHinted
guillermoblanca pushed a commit to guillermoblanca/imgui that referenced this issue Jun 18, 2019
supermerill added a commit to supermerill/imgui that referenced this issue Feb 12, 2024
pthom added a commit to pthom/imgui that referenced this issue Sep 6, 2024
…cornut#7669)

(fix for ocornut#7669)

There is a common user issue which is that developers may reuse the same ID, and will not understand why their widget is not responsive.

This PR will:
* detect when the same ID is used on different widgets (only if the widget is hovered, to avoid a O(n^2) search at each frame)
* display a warning tooltip to the user, with hints on how to fix the issue (e.g. use PushID, or add a ## to the label)
* allow the user to break in the debugger on any of the widgets that use the same ID

**View from 10,000 feet**
See this video for a quick overview of the feature and how it is implemented: https://traineq.org/ImGui/ImGui_PR_Warn_reuse_ID_Explanation.mp4

# Summary of changes

## struct ImGuiContext: added fields UidIXXX (UidsThisFrame & co)

```cpp
struct ImGuiContext
{
    ...
    // Declaration
    ImVector<ImGuiID>       UidsThisFrame;                      // A list of item IDs submitted this frame (used to detect and warn about duplicate ID usage).
    int                     UidAllowDuplicatesStack;            // Stack depth for allowing duplicate IDs (if > 0, duplicate IDs are allowed). See PushAllowDuplicateID / PopAllowDuplicateID
    ImGuiID                 UidHighlightedDuplicate;            // Will be set if a duplicated item is hovered (all duplicated items will appear with a red dot in the top left corner on the next frame)
    int                     UidHighlightedTimestamp;            // Timestamp (FrameCount) of the highlight (which will be shown on the next frame)
    bool                    UidWasTipDisplayed;                 // Will be set to true to avoid displaying multiple times the same tooltip
    ...

    // Constructor
    ImGuiContext(ImFontAtlas* shared_font_atlas) {
        ...
        UidsThisFrame.clear();
        UidAllowDuplicatesStack = 0;
        UidHighlightedDuplicate = 0;
        UidWasTipDisplayed = false;
        ...
    }
};
```

## struct ImGuiWindow: added ReserveUniqueID(), beside GetID()

imgui_internal.h:2572 / near GetID() existing methods
```cpp
struct ImGuiWindow {
    ...
    // ReserveUniqueID: returns GetID(), but may display a warning. Should be called only once per frame with a given ID
    ImGuiID     ReserveUniqueID(const char* str_id);
    ...
};
```

## Added PushAllowDuplicateID / PopAllowDuplicateID

imgui_internal.h:3057  / near related ID functions (SetActiveID, GetIDWithSeed, ...)
```cpp
    ...
    IMGUI_API void          PushAllowDuplicateID();         // Disables the tooltip warning when duplicate IDs are detected.
    IMGUI_API void          PopAllowDuplicateID();          // Re-enables the tooltip warning when duplicate IDs are detected.
    ...
```

imgui.cpp:3873 / near ReserveUniqueID() implementation
```cpp
IMGUI_API void ImGui::PushAllowDuplicateID()
{
    ImGuiContext& g = *GImGui;
    g.UidAllowDuplicatesStack++;
}

IMGUI_API void ImGui::PopAllowDuplicateID()
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(g.UidAllowDuplicatesStack > 0 && "Mismatched PopAllowDuplicateID()");
    g.UidAllowDuplicatesStack--;
}
```

## Main logic: ImGui::EndFrame(), NewFrame() and ImGuiWindow::ReserveUniqueID()

### ImGui::NewFrame():
```cpp
    ...
    g.UidsThisFrame.resize(0);  // Empty the list of items, but keep its allocated data
    g.UidWasTipDisplayed = false;
```

### ImGui::EndFrame():
```cpp
    IM_ASSERT(g.UidAllowDuplicatesStack == 0 && "Mismatched Push/PopAllowDuplicateID");
    if (g.UidHighlightedTimestamp != ImGui::GetFrameCount())
    {
        g.UidHighlightedTimestamp = 0;
        g.UidHighlightedDuplicate = 0;
    }
```

### ImGuiWindow::ReserveUniqueID() / imgui.cpp, at the end of "[SECTION] ID STACK"
The pseudocode below summarizes its behavior:
```cpp
IMGUI_API ImGuiID ImGuiWindow::ReserveUniqueID(const char* str_id)
{
    ImGuiContext& g = *GImGui;
    ImGuiID id = GetID(str_id);

    // If PushAllowDuplicateID was called, do not check for uniqueness
    if (g.UidAllowDuplicatesStack != 0)
    return id;

    // Visual aid: a red circle in the top-left corner of all widgets that use a duplicate of the id
    if (id == g.UidHighlightedDuplicate)
        Draw Red dot on top left corner

    // Only check for uniqueness if hovered (this avoid a O(n^2) search at each frame)
    if (id == ImGui::GetHoveredID())
    {
        if (g.UidsThisFrame.contains(id) && !g.UidWasTipDisplayed)
        {
            // Prepare highlight on the next frame for widgets that use this ID
            g.UidHighlightedDuplicate = id;
            g.UidHighlightedTimestamp = ImGui::GetFrameCount();
            if (ImGui::BeginTooltip())
            {
                if (! g.DebugItemPickerActive)
                {
                    // Display tooltip showing the duplicate Id as a string
                    ...
                    // Show hints for correction (PushID, ##)
                    ...

                    ImGui::Text("    Press Ctrl-P to break in any of those items    ");
                    if Ctrl-P
                        g.DebugItemPickerActive = true;
                }
                else
                {
                    // Add additional info at the bottom of the ItemPicker tooltip
                    ImGui::Text("Click on one of the widgets which uses a duplicated item");
                }
                ImGui::EndTooltip();
            }
            g.UidWasTipDisplayed = true;
        }
    }
    g.UidsThisFrame.push_back(id);
    return id;
}
```

## imgui_widgets.cpp: use ReserveUniqueID, allow duplicates when needed (TempInputText, BeginMenuEx):

I went through all the usages of window->GetID() and changed them to ReserveUniqueID when it was possible / desirable.

### Places with one-line changes

In all the places below, the change was extremely simple: I simply replaced `window->GetID` by `window->ReserveUniqueID`.

For example, in ImGui::ButtonEx
```cpp
bool ImGui::ButtonEx(const char* label, const ImVec2& size_arg, ImGuiButtonFlags flags)
    ...
    const ImGuiID id = window->ReserveUniqueID(label);  // Instead of window->GetID
```

Below is the list of all function where this simple change was applied:
```cpp
    InvisibleButton
    ArrowButtonEx
    GetWindowScrollbarID
    ImageButton  (both versions)
    Checkbox
    RadioButton
    BeginCombo
    DragScalar
    SliderScalar
    VSliderScalar
    InputTextEx
    ColorButton
    CollapsingHeader
    Selectable
    PlotEx
    BeginTabBar
    TabBarCalcTabID
    TreeNode(const char *)
    TreeNodeEx(const char *)
    TreeNodeExV(const char *)
```

### Places where duplicates are needed

#### TempInputText

TempInputText create text input in place of another active widget (e.g. used when doing a CTRL+Click on drag/slider widgets)
It reuses the widget ID, so we allow it temporarily via PushAllowDuplicateID / PopAllowDuplicateID
```
bool ImGui::TempInputText(const ImRect& bb, ImGuiID id, const char* label, char* buf, int buf_size, ImGuiInputTextFlags flags)
{
    ImGui::PushAllowDuplicateID();
    ...
    ImGui::PopAllowDuplicateID();
}

```

#### GetWindowScrollbarID
GetWindowScrollbarID had to be split in two: ReserveWindowScrollbarID will perform the ID reservation, while GetWindowScrollbarID is only a query
Luckily, this is the only instance where this was required.

#### BeginMenuEx

In BeginMenuEx, we initially call GetID() instead of ReserveUniqueID() because were are not "consuming" this ID:
instead, we are only querying IsPopupOpen().
The ID will be consumed later by calling ImGui::PushID(label) + Selectable("") (which will lead to the same ID)

```
bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
{
    const ImGuiID id = window->GetID(label);
    bool menu_is_open = IsPopupOpen(id, ImGuiPopupFlags_None);

    ...

    PushID(label);
    pressed = Selectable("", menu_is_open, selectable_flags, ImVec2(w, label_size.y));

    ...
}
```

#### Places with no changes, but worth mentioning

* TreeNode(const void *): unchanged
`TreeNode(const void* ptr_id)` and `TreeNodeExV(const void *)` are the only instances which call `window->GetID(const void *)`.
As a consequence, they cannot use the unique id mechanism, but I think their usage is rare enough that is not a big concern.

* ImGui::TabBarCalcTabID: unchanged
It still uses window->GetID, to avoid issues when merging with the docking branch.

* BeginChild, BeginPopup and co are unchanged:
  since they use ImGui::Begin()/End() internally), I suspect they might be called multiple times with the same string,
  since it is allowed with ImGui::Begin/End.

## imgui_demo.cpp: some minor changes

I went through the full demo Window to look for instances where a duplicate ID might be used, and corrected them.
Very few changes were required:

* "Layout/Text Baseline Alignment": simple ID fix  (ImGui::Button("Some framed item#ocornut#2"))
* Widgets/Plotting: simple id fix (ImGui::PlotLines("Lines#ocornut#2", ...), ImGui::PlotHistogram("Histogram#ocornut#2", ...))
* Columns (legacy API)/Borders: added ImGui::PushID for each cell
* Widgets/Drag and Drop/Drag to reorder items (simple): no change, but a transient duplicate ID may appear during reordering (for *one* frame only).

# Demo code in order to test this PR

Add and call this function in any imgui example. This code will trigger the warnings for duplicated IDs,
and will also enable to make sure that the fixes that had to be done are OK.

```cpp
char text1[500] = "Hello,";
char text2[500] = "world!";
char text3[500] = "Hello,";
char text4[500] = "world!";
int value = 0;
bool flag1 = false, flag2 = false;
float f1 = 0.f, f2 = 0.f, f3 = 0.f, f4 = 0.f;

void Gui()
{
    // Some widgets to show the duplicated ID warnings
    ImGui::SetNextWindowSize(ImVec2(400, 500));
    if (ImGui::Begin("Duplicated ID examples", nullptr, ImGuiWindowFlags_MenuBar))
    {
        ImGui::TextWrapped("Example of widgets using duplicated IDs");
        ImGui::Separator();

        ImGui::TextWrapped("Only the first button is clickable (same ID)");
        if (ImGui::Button("button")) printf("Button1 pressed\n");
        if (ImGui::Button("button")) printf("Button2 pressed\n");

        ImGui::Separator();

        ImGui::TextWrapped("Those text inputs will share the same value (editing one will overwrite the other)");
        ImGui::InputText("text", text1, IM_ARRAYSIZE(text1));
        ImGui::InputText("text", text2, IM_ARRAYSIZE(text2));

        ImGui::Separator();

        ImGui::TextWrapped("Those radio buttons will share the same value (selecting one will overwrite the other)");
        ImGui::RadioButton("radio", &value, 0);
        ImGui::RadioButton("radio", &value, 1);

        ImGui::Separator();

        ImGui::TextWrapped("The second checkbox cannot be toggled");
        ImGui::Checkbox("checkbox", &flag1);
        ImGui::Checkbox("checkbox", &flag2);

        ImGui::Separator();

        ImGui::TextWrapped("Those two sliders will share the same value (editing one will overwrite the other");
        ImGui::SliderFloat("slider", &f1, 0.f, 1.f);
        ImGui::SliderFloat("slider", &f2, 0.f, 1.f);

        ImGui::Separator();
    }
    ImGui::End();

    // Some widgets to test the fixes that had to be done
    ImGui::SetNextWindowSize(ImVec2(400, 400));
    if (ImGui::Begin("Regression tests", nullptr, ImGuiWindowFlags_MenuBar))
    {
        ImGui::TextWrapped("Small issues had to be fixed inside DragFloat (cf TempInputText), InputTextMultiline and BeginMenuBar.\n"
            "This window is here to test those fixes.");

        ImGui::Separator();

        if (ImGui::BeginMenuBar())
        {
            if (ImGui::BeginMenu("My Menu"))
            {
                ImGui::MenuItem("Item 1");
                ImGui::EndMenu();
            }
            ImGui::EndMenuBar();
        }

        ImGui::TextWrapped("DragFloat will reuse the Item ID when double clicking. This is allowed via Push/PopAllowDuplicateID");
        ImGui::DragFloat("dragf", &f3);

        ImGui::Separator();

        ImGui::TextWrapped("An issue was fixed with the InputTextMultiline vertical scrollbar, which trigerred a duplicate ID warning, which was fixed");
        ImGui::InputTextMultiline("multiline", text1, 500);

    }
    ImGui::End();

    // A window that is populated in several steps should still detect duplicates
    {
        ImGui::SetNextWindowSize(ImVec2(400, 200));

        ImGui::Begin("Window populated in several steps");
        ImGui::TextWrapped("This window is populated between several ImGui::Begin/ImGui::End calls (with the same window name).\n"
                           "Duplicates should be detected anyhow.");
        ImGui::Text("A first InputText");
        ImGui::InputText("TTT", text3, 500);
        ImGui::End();

        ImGui::Begin("Window populated in several steps");
        ImGui::Separator();
        ImGui::Text("The second InputText below reuses the same ID, \nin a different ImGui::Begin/ImGui::End context \n(but with the same window name)");
        ImGui::InputText("TTT", text4, 500);
        ImGui::End();
    }
}
```
pthom added a commit to pthom/imgui that referenced this issue Sep 6, 2024
(fix for ocornut#7669)

There is a common user issue which is that developers may reuse the same ID, and will not understand why their widget is not responsive.

This PR will:
* detect when the same ID is used on different widgets (only if the widget is hovered, to avoid a O(n^2) search at each frame)
* display a warning tooltip to the user, with hints on how to fix the issue (e.g. use PushID, or add a ## to the label)
* allow the user to break in the debugger on any of the widgets that use the same ID
* enable to disable the warning when needed (e.g. when reusing the ID is intentional, via PushAllowDuplicateID / PopAllowDuplicateID)
* enable to debug all duplicates at once (by defining IMGUI_DEBUG_PARANOID)

**View from 10,000 feet**

This PR adds a distinction between

```cpp
    // Same as before (computes the hash of the string)
    ImGuiID     GetID(const char* str, const char* str_end = NULL);
 ```
and
```cpp

    ImGuiID     ReserveUniqueID(const char* str_id);  // returns GetID(), but may display a warning tooltip if the ID is not unique. Should be called only once per frame with a given ID stack.
```

This distinction was applied to several widgets inside imgui_widgets.cpp which now call ReserveUniqueID instead of GetID,
when their intention is to reserve a unique ID for the widget.

See this video for a quick overview of the feature and how it is implemented: https://traineq.org/ImGui/ImGui_PR_Warn_reuse_ID_Explanation.mp4

# Summary of changes

## struct ImGuiContext: added fields UidIXXX (UidsThisFrame & co)

```cpp
struct ImGuiContext
{
    ...
    // Declaration
    ImVector<ImGuiID>       UidsThisFrame;                      // A list of item IDs submitted this frame (used to detect and warn about duplicate ID usage).
    int                     UidAllowDuplicatesStack;            // Stack depth for allowing duplicate IDs (if > 0, duplicate IDs are allowed). See PushAllowDuplicateID / PopAllowDuplicateID
    ImGuiID                 UidHighlightedDuplicate;            // Will be set if a duplicated item is hovered (all duplicated items will appear with a red dot in the top left corner on the next frame)
    int                     UidHighlightedTimestamp;            // Timestamp (FrameCount) of the highlight (which will be shown on the next frame)
    bool                    UidWasTipDisplayed;                 // Will be set to true to avoid displaying multiple times the same tooltip
    ...

    // Constructor
    ImGuiContext(ImFontAtlas* shared_font_atlas) {
        ...
        UidsThisFrame.clear();
        UidAllowDuplicatesStack = 0;
        UidHighlightedDuplicate = 0;
        UidWasTipDisplayed = false;
        ...
    }
};
```

## struct ImGuiWindow: added ReserveUniqueID(), beside GetID()

imgui_internal.h:2572 / near GetID() existing methods
```cpp
struct ImGuiWindow {
    ...
    // ReserveUniqueID: returns GetID(), but may display a warning. Should be called only once per frame with a given ID
    ImGuiID     ReserveUniqueID(const char* str_id);
    ...
};
```

## Added PushAllowDuplicateID / PopAllowDuplicateID

imgui_internal.h:3057  / near related ID functions (SetActiveID, GetIDWithSeed, ...)
```cpp
    ...
    IMGUI_API void          PushAllowDuplicateID();         // Disables the tooltip warning when duplicate IDs are detected.
    IMGUI_API void          PopAllowDuplicateID();          // Re-enables the tooltip warning when duplicate IDs are detected.
    ...
```

imgui.cpp:3873 / near ReserveUniqueID() implementation
```cpp
IMGUI_API void ImGui::PushAllowDuplicateID()
{
    ImGuiContext& g = *GImGui;
    g.UidAllowDuplicatesStack++;
}

IMGUI_API void ImGui::PopAllowDuplicateID()
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(g.UidAllowDuplicatesStack > 0 && "Mismatched PopAllowDuplicateID()");
    g.UidAllowDuplicatesStack--;
}
```

## Main logic: ImGui::EndFrame(), NewFrame() and ImGuiWindow::ReserveUniqueID()

### ImGui::NewFrame():
```cpp
    ...
    g.UidsThisFrame.resize(0);  // Empty the list of items, but keep its allocated data
    g.UidWasTipDisplayed = false;
```

### ImGui::EndFrame():
```cpp
    IM_ASSERT(g.UidAllowDuplicatesStack == 0 && "Mismatched Push/PopAllowDuplicateID");
    if (g.UidHighlightedTimestamp != ImGui::GetFrameCount())
    {
        g.UidHighlightedTimestamp = 0;
        g.UidHighlightedDuplicate = 0;
    }
```

### ImGuiWindow::ReserveUniqueID() / imgui.cpp, at the end of "[SECTION] ID STACK"
The pseudocode below summarizes its behavior:
```cpp
IMGUI_API ImGuiID ImGuiWindow::ReserveUniqueID(const char* str_id)
{
    ImGuiContext& g = *GImGui;
    ImGuiID id = GetID(str_id);

    // If PushAllowDuplicateID was called, do not check for uniqueness
    if (g.UidAllowDuplicatesStack != 0)
    return id;

    // Visual aid: a red circle in the top-left corner of all widgets that use a duplicate of the id
    if (id == g.UidHighlightedDuplicate)
        Draw Red dot on top left corner

    // Only check for uniqueness if hovered (this avoid a O(n^2) search at each frame)
    if (id == ImGui::GetHoveredID())
    {
        if (g.UidsThisFrame.contains(id) && !g.UidWasTipDisplayed)
        {
            // Prepare highlight on the next frame for widgets that use this ID
            g.UidHighlightedDuplicate = id;
            g.UidHighlightedTimestamp = ImGui::GetFrameCount();
            if (ImGui::BeginTooltip())
            {
                if (! g.DebugItemPickerActive)
                {
                    // Display tooltip showing the duplicate Id as a string
                    ...
                    // Show hints for correction (PushID, ##)
                    ...

                    ImGui::Text("    Press Ctrl-P to break in any of those items    ");
                    if Ctrl-P
                        g.DebugItemPickerActive = true;
                }
                else
                {
                    // Add additional info at the bottom of the ItemPicker tooltip
                    ImGui::Text("Click on one of the widgets which uses a duplicated item");
                }
                ImGui::EndTooltip();
            }
            g.UidWasTipDisplayed = true;
        }
    }
    g.UidsThisFrame.push_back(id);
    return id;
}
```

## imgui_widgets.cpp: use ReserveUniqueID, allow duplicates when needed (TempInputText, BeginMenuEx):

I went through all the usages of window->GetID() and changed them to ReserveUniqueID when it was possible / desirable.

### Places with one-line changes

In all the places below, the change was extremely simple: I simply replaced `window->GetID` by `window->ReserveUniqueID`.

For example, in ImGui::ButtonEx
```cpp
bool ImGui::ButtonEx(const char* label, const ImVec2& size_arg, ImGuiButtonFlags flags)
    ...
    const ImGuiID id = window->ReserveUniqueID(label);  // Instead of window->GetID
```

Below is the list of all function where this simple change was applied:
```cpp
    InvisibleButton
    ArrowButtonEx
    GetWindowScrollbarID
    ImageButton  (both versions)
    Checkbox
    RadioButton
    BeginCombo
    DragScalar
    SliderScalar
    VSliderScalar
    InputTextEx
    ColorButton
    CollapsingHeader
    Selectable
    PlotEx
    BeginTabBar
    TabBarCalcTabID
    TreeNode(const char *)
    TreeNodeEx(const char *)
    TreeNodeExV(const char *)
```

### Places where duplicates are needed

#### TempInputText

TempInputText create text input in place of another active widget (e.g. used when doing a CTRL+Click on drag/slider widgets)
It reuses the widget ID, so we allow it temporarily via PushAllowDuplicateID / PopAllowDuplicateID
```
bool ImGui::TempInputText(const ImRect& bb, ImGuiID id, const char* label, char* buf, int buf_size, ImGuiInputTextFlags flags)
{
    ImGui::PushAllowDuplicateID();
    ...
    ImGui::PopAllowDuplicateID();
}

```

#### GetWindowScrollbarID
GetWindowScrollbarID had to be split in two: ReserveWindowScrollbarID will perform the ID reservation, while GetWindowScrollbarID is only a query
Luckily, this is the only instance where this was required.

#### BeginMenuEx

In BeginMenuEx, we initially call GetID() instead of ReserveUniqueID() because were are not "consuming" this ID:
instead, we are only querying IsPopupOpen().
The ID will be consumed later by calling ImGui::PushID(label) + Selectable("") (which will lead to the same ID)

```
bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
{
    const ImGuiID id = window->GetID(label);
    bool menu_is_open = IsPopupOpen(id, ImGuiPopupFlags_None);

    ...

    PushID(label);
    pressed = Selectable("", menu_is_open, selectable_flags, ImVec2(w, label_size.y));

    ...
}
```

#### Places with no changes, but worth mentioning

* TreeNode(const void *): unchanged
`TreeNode(const void* ptr_id)` and `TreeNodeExV(const void *)` are the only instances which call `window->GetID(const void *)`.
As a consequence, they cannot use the unique id mechanism, but I think their usage is rare enough that is not a big concern.

* ImGui::TabBarCalcTabID: unchanged
It still uses window->GetID, to avoid issues when merging with the docking branch.

* BeginChild, BeginPopup and co are unchanged:
  since they use ImGui::Begin()/End() internally), I suspect they might be called multiple times with the same string,
  since it is allowed with ImGui::Begin/End.

## imgui_demo.cpp: some minor changes

I went through the full demo Window to look for instances where a duplicate ID might be used, and corrected them.
Very few changes were required:

* "Layout/Text Baseline Alignment": simple ID fix  (ImGui::Button("Some framed item#ocornut#2"))
* Widgets/Plotting: simple id fix (ImGui::PlotLines("Lines#ocornut#2", ...), ImGui::PlotHistogram("Histogram#ocornut#2", ...))
* Columns (legacy API)/Borders: added ImGui::PushID for each cell
* Widgets/Drag and Drop/Drag to reorder items (simple): no change, but a transient duplicate ID may appear during reordering (for *one* frame only).

# Demo code in order to test this PR

Add and call this function in any imgui example. This code will trigger the warnings for duplicated IDs,
and will also enable to make sure that the fixes that had to be done are OK.

```cpp
char text1[500] = "Hello,";
char text2[500] = "world!";
char text3[500] = "Hello,";
char text4[500] = "world!";
int value = 0;
bool flag1 = false, flag2 = false;
float f1 = 0.f, f2 = 0.f, f3 = 0.f, f4 = 0.f;

void Gui()
{
    // Some widgets to show the duplicated ID warnings
    ImGui::SetNextWindowSize(ImVec2(400, 500));
    if (ImGui::Begin("Duplicated ID examples", nullptr, ImGuiWindowFlags_MenuBar))
    {
        ImGui::TextWrapped("Example of widgets using duplicated IDs");
        ImGui::Separator();

        ImGui::TextWrapped("Only the first button is clickable (same ID)");
        if (ImGui::Button("button")) printf("Button1 pressed\n");
        if (ImGui::Button("button")) printf("Button2 pressed\n");

        ImGui::Separator();

        ImGui::TextWrapped("Those text inputs will share the same value (editing one will overwrite the other)");
        ImGui::InputText("text", text1, IM_ARRAYSIZE(text1));
        ImGui::InputText("text", text2, IM_ARRAYSIZE(text2));

        ImGui::Separator();

        ImGui::TextWrapped("Those radio buttons will share the same value (selecting one will overwrite the other)");
        ImGui::RadioButton("radio", &value, 0);
        ImGui::RadioButton("radio", &value, 1);

        ImGui::Separator();

        ImGui::TextWrapped("The second checkbox cannot be toggled");
        ImGui::Checkbox("checkbox", &flag1);
        ImGui::Checkbox("checkbox", &flag2);

        ImGui::Separator();

        ImGui::TextWrapped("Those two sliders will share the same value (editing one will overwrite the other");
        ImGui::SliderFloat("slider", &f1, 0.f, 1.f);
        ImGui::SliderFloat("slider", &f2, 0.f, 1.f);

        ImGui::Separator();
    }
    ImGui::End();

    // Some widgets to test the fixes that had to be done
    ImGui::SetNextWindowSize(ImVec2(400, 400));
    if (ImGui::Begin("Regression tests", nullptr, ImGuiWindowFlags_MenuBar))
    {
        ImGui::TextWrapped("Small issues had to be fixed inside DragFloat (cf TempInputText), InputTextMultiline and BeginMenuBar.\n"
            "This window is here to test those fixes.");

        ImGui::Separator();

        if (ImGui::BeginMenuBar())
        {
            if (ImGui::BeginMenu("My Menu"))
            {
                ImGui::MenuItem("Item 1");
                ImGui::EndMenu();
            }
            ImGui::EndMenuBar();
        }

        ImGui::TextWrapped("DragFloat will reuse the Item ID when double clicking. This is allowed via Push/PopAllowDuplicateID");
        ImGui::DragFloat("dragf", &f3);

        ImGui::Separator();

        ImGui::TextWrapped("An issue was fixed with the InputTextMultiline vertical scrollbar, which trigerred a duplicate ID warning, which was fixed");
        ImGui::InputTextMultiline("multiline", text1, 500);

    }
    ImGui::End();

    // A window that is populated in several steps should still detect duplicates
    {
        ImGui::SetNextWindowSize(ImVec2(400, 200));

        ImGui::Begin("Window populated in several steps");
        ImGui::TextWrapped("This window is populated between several ImGui::Begin/ImGui::End calls (with the same window name).\n"
                           "Duplicates should be detected anyhow.");
        ImGui::Text("A first InputText");
        ImGui::InputText("TTT", text3, 500);
        ImGui::End();

        ImGui::Begin("Window populated in several steps");
        ImGui::Separator();
        ImGui::Text("The second InputText below reuses the same ID, \nin a different ImGui::Begin/ImGui::End context \n(but with the same window name)");
        ImGui::InputText("TTT", text4, 500);
        ImGui::End();
    }
}
```
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