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Set font size to be the em square's size and decouple from the line height #8857

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Set font size to be the em square's size and decouple from the line height #8857

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23dde40
decouple line height from the font size
cfillion Aug 5, 2025
e8ce4fa
make font size be the em square's size when ImFontCfg::SizePixels is …
cfillion Aug 3, 2025
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37 changes: 18 additions & 19 deletions imgui.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4027,7 +4027,7 @@ ImGuiContext::ImGuiContext(ImFontAtlas* shared_font_atlas)
Initialized = false;
Font = NULL;
FontBaked = NULL;
FontSize = FontSizeBase = FontBakedScale = CurrentDpiScale = 0.0f;
FontSize = FontSizeBase = FontBakedScale = FontLineHeight = CurrentDpiScale = 0.0f;
FontRasterizerDensity = 1.0f;
IO.Fonts = shared_font_atlas ? shared_font_atlas : IM_NEW(ImFontAtlas)();
if (shared_font_atlas == NULL)
Expand Down Expand Up @@ -5990,10 +5990,9 @@ ImVec2 ImGui::CalcTextSize(const char* text, const char* text_end, bool hide_tex
text_display_end = text_end;

ImFont* font = g.Font;
const float font_size = g.FontSize;
if (text == text_display_end)
return ImVec2(0.0f, font_size);
ImVec2 text_size = font->CalcTextSizeA(font_size, FLT_MAX, wrap_width, text, text_display_end, NULL);
return ImVec2(0.0f, g.FontLineHeight);
ImVec2 text_size = font->CalcTextSizeA(g.FontSize, FLT_MAX, wrap_width, text, text_display_end, NULL);

// Round
// FIXME: This has been here since Dec 2015 (7b0bf230) but down the line we want this out.
Expand Down Expand Up @@ -7470,8 +7469,8 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
// Lock menu offset so size calculation can use it as menu-bar windows need a minimum size.
window->DC.MenuBarOffset.x = ImMax(ImMax(window->WindowPadding.x, style.ItemSpacing.x), g.NextWindowData.MenuBarOffsetMinVal.x);
window->DC.MenuBarOffset.y = g.NextWindowData.MenuBarOffsetMinVal.y;
window->TitleBarHeight = (flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : g.FontSize + g.Style.FramePadding.y * 2.0f;
window->MenuBarHeight = (flags & ImGuiWindowFlags_MenuBar) ? window->DC.MenuBarOffset.y + g.FontSize + g.Style.FramePadding.y * 2.0f : 0.0f;
window->TitleBarHeight = (flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : g.FontLineHeight + g.Style.FramePadding.y * 2.0f;
window->MenuBarHeight = (flags & ImGuiWindowFlags_MenuBar) ? window->DC.MenuBarOffset.y + g.FontLineHeight + g.Style.FramePadding.y * 2.0f : 0.0f;
window->FontRefSize = g.FontSize; // Lock this to discourage calling window->CalcFontSize() outside of current window.

// Depending on condition we use previous or current window size to compare against contents size to decide if a scrollbar should be visible.
Expand Down Expand Up @@ -7604,9 +7603,9 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
// Large values tend to lead to variety of artifacts and are not recommended.
window->WindowRounding = (flags & ImGuiWindowFlags_ChildWindow) ? style.ChildRounding : ((flags & ImGuiWindowFlags_Popup) && !(flags & ImGuiWindowFlags_Modal)) ? style.PopupRounding : style.WindowRounding;

// For windows with title bar or menu bar, we clamp to FrameHeight(FontSize + FramePadding.y * 2.0f) to completely hide artifacts.
// For windows with title bar or menu bar, we clamp to FrameHeight(LineHeight + FramePadding.y * 2.0f) to completely hide artifacts.
//if ((window->Flags & ImGuiWindowFlags_MenuBar) || !(window->Flags & ImGuiWindowFlags_NoTitleBar))
// window->WindowRounding = ImMin(window->WindowRounding, g.FontSize + style.FramePadding.y * 2.0f);
// window->WindowRounding = ImMin(window->WindowRounding, g.FontLineHeight + style.FramePadding.y * 2.0f);

// Apply window focus (new and reactivated windows are moved to front)
bool want_focus = false;
Expand Down Expand Up @@ -8775,8 +8774,8 @@ void ImGui::UpdateFontsNewFrame()
g.Font = font;
g.FontSizeBase = g.Style.FontSizeBase;
g.FontSize = 0.0f;
ImFontStackData font_stack_data = { font, g.Style.FontSizeBase, g.Style.FontSizeBase }; // <--- Will restore FontSize
SetCurrentFont(font_stack_data.Font, font_stack_data.FontSizeBeforeScaling, 0.0f); // <--- but use 0.0f to enable scale
ImFontStackData font_stack_data = { font, g.Style.FontSizeBase, g.Style.FontSizeBase }; // <--- Will restore FontSize
SetCurrentFont(font_stack_data.Font, font_stack_data.FontSizeBeforeScaling, 0.0f); // <--- but use 0.0f to enable scale
g.FontStack.push_back(font_stack_data);
IM_ASSERT(g.Font->IsLoaded());
}
Expand Down Expand Up @@ -8908,6 +8907,7 @@ void ImGui::UpdateCurrentFontSize(float restore_font_size_after_scaling)
g.Font->CurrentRasterizerDensity = g.FontRasterizerDensity;
g.FontSize = final_size;
g.FontBaked = (g.Font != NULL && window != NULL) ? g.Font->GetFontBaked(final_size) : NULL;
g.FontLineHeight = g.FontBaked ? g.FontBaked->LineHeight : g.FontSize;
g.FontBakedScale = (g.Font != NULL && window != NULL) ? (g.FontSize / g.FontBaked->Size) : 0.0f;
g.DrawListSharedData.FontSize = g.FontSize;
g.DrawListSharedData.FontScale = g.FontBakedScale;
Expand Down Expand Up @@ -11402,25 +11402,25 @@ ImVec2 ImGui::CalcItemSize(ImVec2 size, float default_w, float default_h)
float ImGui::GetTextLineHeight()
{
ImGuiContext& g = *GImGui;
return g.FontSize;
return g.FontLineHeight;
}

float ImGui::GetTextLineHeightWithSpacing()
{
ImGuiContext& g = *GImGui;
return g.FontSize + g.Style.ItemSpacing.y;
return g.FontLineHeight + g.Style.ItemSpacing.y;
}

float ImGui::GetFrameHeight()
{
ImGuiContext& g = *GImGui;
return g.FontSize + g.Style.FramePadding.y * 2.0f;
return g.FontLineHeight + g.Style.FramePadding.y * 2.0f;
}

float ImGui::GetFrameHeightWithSpacing()
{
ImGuiContext& g = *GImGui;
return g.FontSize + g.Style.FramePadding.y * 2.0f + g.Style.ItemSpacing.y;
return g.FontLineHeight + g.Style.FramePadding.y * 2.0f + g.Style.ItemSpacing.y;
}

ImVec2 ImGui::GetContentRegionAvail()
Expand Down Expand Up @@ -16695,8 +16695,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
{
char buf[32];
ImFormatString(buf, IM_ARRAYSIZE(buf), "%d", window->BeginOrderWithinContext);
float font_size = GetFontSize();
draw_list->AddRectFilled(window->Pos, window->Pos + ImVec2(font_size, font_size), IM_COL32(200, 100, 100, 255));
draw_list->AddRectFilled(window->Pos, window->Pos + ImVec2(g.FontSize, g.FontLineHeight), IM_COL32(200, 100, 100, 255));
draw_list->AddText(window->Pos, IM_COL32(255, 255, 255, 255), buf);
}
}
Expand Down Expand Up @@ -17079,7 +17078,7 @@ void ImGui::DebugNodeFont(ImFont* font)
baked->FindGlyph((ImWchar)base);

const int surface_sqrt = (int)ImSqrt((float)baked->MetricsTotalSurface);
Text("Ascent: %f, Descent: %f, Ascent-Descent: %f", baked->Ascent, baked->Descent, baked->Ascent - baked->Descent);
Text("Ascent: %f, Descent: %f, Ascent-Descent: %f, LineHeight: %f", baked->Ascent, baked->Descent, baked->Ascent - baked->Descent, baked->LineHeight);
Text("Texture Area: about %d px ~%dx%d px", baked->MetricsTotalSurface, surface_sqrt, surface_sqrt);
for (int src_n = 0; src_n < font->Sources.Size; src_n++)
{
Expand Down Expand Up @@ -17424,7 +17423,7 @@ void ImGui::ShowDebugLogWindow(bool* p_open)
{
ImGuiContext& g = *GImGui;
if ((g.NextWindowData.HasFlags & ImGuiNextWindowDataFlags_HasSize) == 0)
SetNextWindowSize(ImVec2(0.0f, GetFontSize() * 12.0f), ImGuiCond_FirstUseEver);
SetNextWindowSize(ImVec2(0.0f, GetTextLineHeight() * 12.0f), ImGuiCond_FirstUseEver);
if (!Begin("Dear ImGui Debug Log", p_open) || GetCurrentWindow()->BeginCount > 1)
{
End();
Expand Down Expand Up @@ -17751,7 +17750,7 @@ void ImGui::ShowIDStackToolWindow(bool* p_open)
{
ImGuiContext& g = *GImGui;
if ((g.NextWindowData.HasFlags & ImGuiNextWindowDataFlags_HasSize) == 0)
SetNextWindowSize(ImVec2(0.0f, GetFontSize() * 8.0f), ImGuiCond_FirstUseEver);
SetNextWindowSize(ImVec2(0.0f, GetTextLineHeight() * 8.0f), ImGuiCond_FirstUseEver);
if (!Begin("Dear ImGui ID Stack Tool", p_open) || GetCurrentWindow()->BeginCount > 1)
{
End();
Expand Down
1 change: 1 addition & 0 deletions imgui.h
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Expand Up @@ -3757,6 +3757,7 @@ struct ImFontBaked

// [Internal] Members: Cold
float Ascent, Descent; // 4+4 // out // Ascent: distance from top to bottom of e.g. 'A' [0..FontSize] (unscaled)
float LineHeight; // 4 // out // Vertical distance between two baselines
unsigned int MetricsTotalSurface:26;// 3 // out // Total surface in pixels to get an idea of the font rasterization/texture cost (not exact, we approximate the cost of padding between glyphs)
unsigned int WantDestroy:1; // 0 // // Queued for destroy
unsigned int LoadNoFallback:1; // 0 // // Disable loading fallback in lower-level calls.
Expand Down
9 changes: 5 additions & 4 deletions imgui_draw.cpp
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Expand Up @@ -4574,7 +4574,7 @@ static bool ImGui_ImplStbTrueType_FontSrcInit(ImFontAtlas* atlas, ImFontConfig*
if (src->MergeMode && src->SizePixels == 0.0f)
src->SizePixels = ref_size;

if (src->SizePixels >= 0.0f)
if (src->SizePixels > 0.0f)
bd_font_data->ScaleFactor = stbtt_ScaleForPixelHeight(&bd_font_data->FontInfo, 1.0f);
else
bd_font_data->ScaleFactor = stbtt_ScaleForMappingEmToPixels(&bd_font_data->FontInfo, 1.0f);
Expand Down Expand Up @@ -4617,6 +4617,7 @@ static bool ImGui_ImplStbTrueType_FontBakedInit(ImFontAtlas* atlas, ImFontConfig
stbtt_GetFontVMetrics(&bd_font_data->FontInfo, &unscaled_ascent, &unscaled_descent, &unscaled_line_gap);
baked->Ascent = ImCeil(unscaled_ascent * scale_for_layout);
baked->Descent = ImFloor(unscaled_descent * scale_for_layout);
baked->LineHeight = src->SizePixels > 0.0f ? baked->Size : baked->Ascent - baked->Descent;
}
return true;
}
Expand Down Expand Up @@ -5061,7 +5062,7 @@ void ImFontBaked::ClearOutputData()
IndexAdvanceX.clear();
IndexLookup.clear();
FallbackGlyphIndex = -1;
Ascent = Descent = 0.0f;
Ascent = Descent = LineHeight = 0.0f;
MetricsTotalSurface = 0;
}

Expand Down Expand Up @@ -5461,8 +5462,8 @@ ImVec2 ImFont::CalcTextSizeA(float size, float max_width, float wrap_width, cons
if (!text_end)
text_end = text_begin + ImStrlen(text_begin); // FIXME-OPT: Need to avoid this.

const float line_height = size;
ImFontBaked* baked = GetFontBaked(size);
const float line_height = baked->LineHeight;
const float scale = size / baked->Size;

ImVec2 text_size = ImVec2(0, 0);
Expand Down Expand Up @@ -5592,9 +5593,9 @@ void ImFont::RenderText(ImDrawList* draw_list, float size, const ImVec2& pos, Im
if (!text_end)
text_end = text_begin + ImStrlen(text_begin); // ImGui:: functions generally already provides a valid text_end, so this is merely to handle direct calls.

const float line_height = size;
ImFontBaked* baked = GetFontBaked(size);

const float line_height = baked->LineHeight;
const float scale = size / baked->Size;
const float origin_x = x;
const bool word_wrap_enabled = (wrap_width > 0.0f);
Expand Down
3 changes: 2 additions & 1 deletion imgui_internal.h
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Expand Up @@ -2149,8 +2149,9 @@ struct ImGuiContext
ImVector<ImFontAtlas*> FontAtlases; // List of font atlases used by the context (generally only contains g.IO.Fonts aka the main font atlas)
ImFont* Font; // Currently bound font. (== FontStack.back().Font)
ImFontBaked* FontBaked; // Currently bound font at currently bound size. (== Font->GetFontBaked(FontSize))
float FontSize; // Currently bound font size == line height (== FontSizeBase + externals scales applied in the UpdateCurrentFontSize() function).
float FontSize; // Currently bound font size (== FontSizeBase + externals scales applied in the UpdateCurrentFontSize() function).
float FontSizeBase; // Font size before scaling == style.FontSizeBase == value passed to PushFont() when specified.
float FontLineHeight; // Currently bound font's line height (+ externals scales applied in the UpdateCurrentFontSize() function).
float FontBakedScale; // == FontBaked->Size / FontSize. Scale factor over baked size. Rarely used nowadays, very often == 1.0f.
float FontRasterizerDensity; // Current font density. Used by all calls to GetFontBaked().
float CurrentDpiScale; // Current window/viewport DpiScale == CurrentViewport->DpiScale
Expand Down
2 changes: 1 addition & 1 deletion imgui_tables.cpp
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Expand Up @@ -3075,7 +3075,7 @@ float ImGui::TableGetHeaderRowHeight()
// In your custom header row you may omit this all together and just call TableNextRow() without a height...
ImGuiContext& g = *GImGui;
ImGuiTable* table = g.CurrentTable;
float row_height = g.FontSize;
float row_height = g.FontLineHeight;
for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
if (IM_BITARRAY_TESTBIT(table->EnabledMaskByIndex, column_n))
if ((table->Columns[column_n].Flags & ImGuiTableColumnFlags_NoHeaderLabel) == 0)
Expand Down
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