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DrawList: fixed PathArcTo to not emit small segments.

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- Changed PathArcTo to select start/end sample in quatized multiples of arc fast sample count
- This is done in order to avoid small segments at the start and end of the path, which causes issues with line AA ends
- Renamed CalcArcStepAndCount to CalcCornerArcStepAndCount to make it more clear that it returns the values for 90 degree arc
This commit is contained in:
Mikko Mononen
2026-07-31 16:45:01 +03:00
committed by ocornut
parent d75d11cd2b
commit 65f176ef74
1 changed files with 19 additions and 10 deletions
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29
imgui_draw.cpp
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@@ -1517,7 +1517,7 @@ void ImDrawList::AddConvexPolyFilled(const ImVec2* points, const int points_coun
// Calculates arc step and step count for 90 degree arc. The calculated arc step will complete a 90 degree arc when stepped arc_step_count times.
IM_MSVC_RUNTIME_CHECKS_OFF
static void CalcArcStepAndCount(int segment_count, int& arc_step, int& arc_step_count)
static void CalcCornerArcStepAndCount(int segment_count, int& arc_step, int& arc_step_count)
{
arc_step = ImClamp(IM_DRAWLIST_ARCFAST_SAMPLE_MAX / segment_count, 1, IM_DRAWLIST_ARCFAST_TABLE_SIZE / 4);
arc_step_count = (IM_DRAWLIST_ARCFAST_TABLE_SIZE / 4) / arc_step;
@@ -1540,7 +1540,7 @@ void ImDrawList::_PathArcToFastEx(const ImVec2& center, float radius, int a_min_
// Calculate step size using the common function. No need to clamp, the step is already in range.
const int auto_seg_count = _CalcCircleAutoSegmentCount(radius);
int arc_step_count;
CalcArcStepAndCount(auto_seg_count, a_step, arc_step_count);
CalcCornerArcStepAndCount(auto_seg_count, a_step, arc_step_count);
}
else
{
@@ -1670,16 +1670,25 @@ void ImDrawList::PathArcTo(const ImVec2& center, float radius, float a_min, floa
// Automatic segment count
if (radius <= _Data->ArcFastRadiusCutoff)
{
{
const bool a_is_reverse = a_max < a_min;
// Calculate number of segments per circle.
// First we calculate the step count as usual, then match to the precomputed directions.
// This will give us the spacing between the samples (step), and how many segments to use in total for a full circle.
const int auto_seg_count = _CalcCircleAutoSegmentCount(radius);
int arc_step, arc_step_count;
CalcCornerArcStepAndCount(auto_seg_count, arc_step, arc_step_count);
const int arc_seg_count = arc_step_count * 4; // Seg count for full circle.
// We are going to use precomputed values for mid samples.
// Determine first and last sample in lookup table that belong to the arc.
const float a_min_sample_f = IM_DRAWLIST_ARCFAST_SAMPLE_MAX * a_min / (IM_PI * 2.0f);
const float a_max_sample_f = IM_DRAWLIST_ARCFAST_SAMPLE_MAX * a_max / (IM_PI * 2.0f);
// In first step we use the coarser segment count, and after rounding, convert back to the precomputed array index.
const float a_min_sample_f = arc_seg_count * a_min / (IM_PI * 2.0f);
const float a_max_sample_f = arc_seg_count * a_max / (IM_PI * 2.0f);
const int a_min_sample = a_is_reverse ? (int)ImFloor(a_min_sample_f) : (int)ImCeil(a_min_sample_f);
const int a_max_sample = a_is_reverse ? (int)ImCeil(a_max_sample_f) : (int)ImFloor(a_max_sample_f);
const int a_min_sample = (a_is_reverse ? (int)ImFloor(a_min_sample_f) : (int)ImCeil(a_min_sample_f)) * arc_step;
const int a_max_sample = (a_is_reverse ? (int)ImCeil(a_max_sample_f) : (int)ImFloor(a_max_sample_f)) * arc_step;
const int a_mid_samples = a_is_reverse ? ImMax(a_min_sample - a_max_sample, 0) : ImMax(a_max_sample - a_min_sample, 0);
const float a_min_segment_angle = a_min_sample * IM_PI * 2.0f / IM_DRAWLIST_ARCFAST_SAMPLE_MAX;
@@ -1691,7 +1700,7 @@ void ImDrawList::PathArcTo(const ImVec2& center, float radius, float a_min, floa
if (a_emit_start)
_Path.push_back(ImVec2(center.x + ImCos(a_min) * radius, center.y + ImSin(a_min) * radius));
if (a_mid_samples > 0)
_PathArcToFastEx(center, radius, a_min_sample, a_max_sample, 0);
_PathArcToFastEx(center, radius, a_min_sample, a_max_sample, arc_step);
if (a_emit_end)
_Path.push_back(ImVec2(center.x + ImCos(a_max) * radius, center.y + ImSin(a_max) * radius));
}
@@ -2237,7 +2246,7 @@ void ImDrawList::_AddRectTinyRounding(const ImVec2& p_min, const ImVec2& p_max,
const int auto_seg_count = _CalcCircleAutoSegmentCount(rounding);
int arc_step, arc_step_count;
CalcArcStepAndCount(auto_seg_count, arc_step, arc_step_count);
CalcCornerArcStepAndCount(auto_seg_count, arc_step, arc_step_count);
const int arc_point_count = arc_step_count + 1;
int vtx_count = (2 + arc_point_count) * 4 + 3;
@@ -4853,7 +4862,7 @@ static int InitCornerGeometry(float cx, float cy, float rounding, float circle_s
const int auto_seg_count = IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(rounding, circle_segment_max_error);
int arc_step, arc_step_count;
CalcArcStepAndCount(auto_seg_count, arc_step, arc_step_count);
CalcCornerArcStepAndCount(auto_seg_count, arc_step, arc_step_count);
const int arc_point_count = arc_step_count + 1;
// Build arc of points, with straight segments at each end.