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Tweak CalcTextSize() awkward width rounding/ceiling code to reduce floating-point imprecisions altering the result by 1 even at relatively small width. (#791) + apply same fudge factor to less important roundings.

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ceilf() is still measurable e.g. ballpark +0.5 for 200k calls.
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ocornut
2026-05-28 19:19:11 +02:00
parent 33bb693b4c
commit 12b7977555
4 changed files with 10 additions and 9 deletions
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2
docs/CHANGELOG.txt
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@@ -55,6 +55,8 @@ Other Changes:
- Fonts:
- Added `IMGUI_DISABLE_DEFAULT_FONT_BITMAP`/`IMGUI_DISABLE_DEFAULT_FONT_VECTOR` to
disable embedding either fonts separately. (#9407)
- Tweak CalcTextSize() awkward width rounding/ceiling code to reduce floating-point
imprecisions altering the result by 1 even at relatively small width. (#791)
- DrawList:
- Minor optimization to AddLine(), AddLineH(), AddLineV() functions. (#4091)
- Demo:

9
imgui.cpp
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@@ -6199,11 +6199,10 @@ ImVec2 ImGui::CalcTextSize(const char* text, const char* text_end, bool hide_tex
ImVec2 text_size = font->CalcTextSizeA(font_size, 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.
// FIXME: Investigate using ceilf or e.g.
// - https://git.musl-libc.org/cgit/musl/tree/src/math/ceilf.c
// - https://embarkstudios.github.io/rust-gpu/api/src/libm/math/ceilf.rs.html
text_size.x = IM_TRUNC(text_size.x + 0.99999f);
// FIXME: This has been here since Dec 2015 (7b0bf230 then 4622fa4b6) but down the line we want this out. See #791.
// Investigate using ceilf or e.g. https://git.musl-libc.org/cgit/musl/tree/src/math/ceilf.c, https://embarkstudios.github.io/rust-gpu/api/src/libm/math/ceilf.rs.html
// The problem is that ceilf() has a measurable cost. Not high, but measurable!
text_size.x = IM_TRUNC(text_size.x + 0.999f);
return text_size;
}

2
imgui_draw.cpp
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@@ -656,7 +656,7 @@ void ImDrawList::_OnChangedVtxOffset()
int ImDrawList::_CalcCircleAutoSegmentCount(float radius) const
{
// Automatic segment count
const int radius_idx = (int)(radius + 0.999999f); // ceil to never reduce accuracy
const int radius_idx = (int)(radius + 0.999f); // ceil to never reduce accuracy
if (radius_idx >= 0 && radius_idx < IM_COUNTOF(_Data->CircleSegmentCounts))
return _Data->CircleSegmentCounts[radius_idx]; // Use cached value
else

6
imgui_widgets.cpp
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@@ -1748,14 +1748,14 @@ void ImGui::SeparatorTextEx(ImGuiID id, const char* label, const char* label_end
const float separator_thickness = style.SeparatorTextBorderSize;
const ImVec2 min_size(label_size.x + extra_w + padding.x * 2.0f, ImMax(label_size.y + padding.y * 2.0f, separator_thickness));
const ImRect bb(pos, ImVec2(window->WorkRect.Max.x, pos.y + min_size.y));
const float text_baseline_y = ImTrunc((bb.GetHeight() - label_size.y) * style.SeparatorTextAlign.y + 0.99999f); //ImMax(padding.y, ImTrunc((style.SeparatorTextSize - label_size.y) * 0.5f));
const float text_baseline_y = ImTrunc((bb.GetHeight() - label_size.y) * style.SeparatorTextAlign.y + 0.999f); //ImMax(padding.y, ImTrunc((style.SeparatorTextSize - label_size.y) * 0.5f));
ItemSize(min_size, text_baseline_y);
if (!ItemAdd(bb, id))
return;
const float sep1_x1 = pos.x;
const float sep2_x2 = bb.Max.x;
const float seps_y = ImTrunc((bb.Min.y + bb.Max.y) * 0.5f + 0.99999f);
const float seps_y = ImTrunc((bb.Min.y + bb.Max.y) * 0.5f + 0.999f);
const float label_avail_w = ImMax(0.0f, sep2_x2 - sep1_x1 - padding.x * 2.0f);
const ImVec2 label_pos(pos.x + padding.x + ImMax(0.0f, (label_avail_w - label_size.x - extra_w) * style.SeparatorTextAlign.x), pos.y + text_baseline_y); // FIXME-ALIGN
@@ -8952,7 +8952,7 @@ int ImGui::PlotEx(ImGuiPlotType plot_type, const char* label, float (*values_get
// Tooltip on hover
if (hovered && inner_bb.Contains(g.IO.MousePos))
{
const float t = ImClamp((g.IO.MousePos.x - inner_bb.Min.x) / (inner_bb.Max.x - inner_bb.Min.x), 0.0f, 0.9999f);
const float t = ImClamp((g.IO.MousePos.x - inner_bb.Min.x) / (inner_bb.Max.x - inner_bb.Min.x), 0.0f, 0.999f);
const int v_idx = (int)(t * item_count);
IM_ASSERT(v_idx >= 0 && v_idx < values_count);