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DrawList: fixed rendering issues on small and degenerate shapes.

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The "does stroke cover the whole shape" used to be overly pessimistic to stroking artifacts. This was due to the fringe, where the geometry would mess up before visually closing the shape.
Fixed the issue by adding max inner offest for the AddPolyline(), which limits the inner offset and also adjusts the texture coords.
Second part of the fix was to calculate the pass the max inner offset from the common shapes (circle, ngon, ellipse, rect).
While this does not fix all the ellipse rendering issues, it limits the issue a lot.
e.g. AddRect() w/ size=5, thickness=2 used to trigger AddRectFilled() fallback because threshold was pessimistic to prevent the AddPolyline() issues.
This commit is contained in:
Mikko Mononen
2026-07-31 11:45:41 +03:00
committed by ocornut
parent 04efdebb14
commit 30f70ac19c
2 changed files with 60 additions and 21 deletions
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76
imgui_draw.cpp
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@@ -948,7 +948,7 @@ static inline ImDrawFlags _GetStrokePos(ImDrawFlags flags, ImDrawFlags default_s
IM_MSVC_RUNTIME_CHECKS_RESTORE
void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32 col, float thickness, ImDrawFlags flags)
void ImDrawList::_AddPolyline(const ImVec2* points, const int points_count, ImU32 col, float thickness, ImDrawFlags flags, float max_inner_offset)
{
if (points_count < 2 || (col & IM_COL32_A_MASK) == 0)
return;
@@ -1050,6 +1050,16 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
uv2.x = uv0.x + (uv1.x - uv0.x) * ratio;
uv2.y = tex_uvs.z;
// Clamp inner offset and adjust texture coordinates to match the change.
// This is used by some of the convex shape rendering to avoid rendering artifacts when thickness is about to fill the whole shape.
if (thickness1 > max_inner_offset)
{
thickness1 = max_inner_offset;
const float s = (thickness0 + thickness1) / (thickness + fringe);
const float du = uv1.x - uv0.x;
uv1.x = uv0.x + du * s;
}
const float half_aa = _FringeScale * 0.5f; // Used for end caps, does not use "fringe" since end cap AA is not using the texture.
const float half_thickness = thickness * 0.5f;
const bool use_aa_ends = (flags & (ImDrawFlags_AALines | ImDrawFlags_AALineEnds)) == (ImDrawFlags_AALines | ImDrawFlags_AALineEnds);
@@ -2375,7 +2385,8 @@ void ImDrawList::AddRect(const ImVec2& p_min, const ImVec2& p_max, ImU32 col, fl
const float width = outer_max.x - outer_min.x;
const float height = outer_max.y - outer_min.y;
if (ImMin(width, height) < (thickness + _FringeScale) * 2.0f) IM_UNLIKELY
const float half_min_dim = ImMin(width, height) * 0.5f;
if (half_min_dim <= thickness) IM_UNLIKELY
{
// Rectangle has collapsed into filled rectangle.
AddRectFilled(outer_min, outer_max, col, outer_rounding, flags);
@@ -2448,7 +2459,8 @@ void ImDrawList::AddRect(const ImVec2& p_min, const ImVec2& p_max, ImU32 col, fl
if (!has_rounding || (flags & ImDrawFlags_RoundCornersMask_) == ImDrawFlags_RoundCornersNone)
{
const ImVec2 points[4] = { outer_min, ImVec2(outer_max.x, outer_min.y), outer_max, ImVec2(outer_min.x, outer_max.y) };
AddPolyline(points, 4, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | ImDrawFlags_StrokeInside | (flags & ~ImDrawFlags_StrokeMask_));
_AddPolyline(points, 4, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | ImDrawFlags_StrokeInside, half_min_dim);
_Path.Size = 0;
}
else
{
@@ -2468,7 +2480,9 @@ void ImDrawList::AddRect(const ImVec2& p_min, const ImVec2& p_max, ImU32 col, fl
PathArcToFast(ImVec2(outer_max.x - rounding_tr, outer_min.y + rounding_tr), rounding_tr, 9, 12);
PathArcToFast(ImVec2(outer_max.x - rounding_br, outer_max.y - rounding_br), rounding_br, 0, 3);
PathArcToFast(ImVec2(outer_min.x + rounding_bl, outer_max.y - rounding_bl), rounding_bl, 3, 6);
PathStroke(col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | ImDrawFlags_StrokeInside | (flags & ~ImDrawFlags_StrokeMask_));
_AddPolyline(_Path.Data, _Path.Size, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | ImDrawFlags_StrokeInside | (flags & ~ImDrawFlags_StrokeMask_), half_min_dim);
_Path.Size = 0;
}
}
@@ -2634,7 +2648,7 @@ void ImDrawList::AddQuad(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, c
flags = (flags & ~ImDrawFlags_StrokeMask_) | stroke_pos; // As AddPolyline() default is different
const ImVec2 points[4] = { p1, p2, p3, p4 };
AddPolyline(points, 4, col, thickness, flags | ImDrawFlags_Closed);
_AddPolyline(points, 4, col, thickness, flags | ImDrawFlags_Closed, FLT_MAX);
}
void ImDrawList::AddQuadFilled(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, const ImVec2& p4, ImU32 col)
@@ -2656,7 +2670,7 @@ void ImDrawList::AddTriangle(const ImVec2& p1, const ImVec2& p2, const ImVec2& p
flags = (flags & ~ImDrawFlags_StrokeMask_) | stroke_pos; // As AddPolyline() default is different
const ImVec2 points[3] = { p1, p2, p3 };
AddPolyline(points, 3, col, thickness, flags | ImDrawFlags_Closed);
_AddPolyline(points, 3, col, thickness, flags | ImDrawFlags_Closed, FLT_MAX);
}
void ImDrawList::AddTriangleFilled(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, ImU32 col)
@@ -2668,6 +2682,14 @@ void ImDrawList::AddTriangleFilled(const ImVec2& p1, const ImVec2& p2, const ImV
AddConvexPolyFilled(points, 3, col);
}
static float ApproxApothem(int num_segments)
{
// Calculates approximation (within 0.001%) distance from the center of the circumscribed circle to the edge of the polygon, cos(pi / n)
IM_ASSERT_PARANOID(num_segments >= 3);
const float u = 1.0f / num_segments;
return ((4.058712f * u * u) - 4.934802f) * u * u + 1.0f;
}
void ImDrawList::AddCircle(const ImVec2& center, float radius, ImU32 col, int num_segments, float thickness, ImDrawFlags flags)
{
if ((col & IM_COL32_A_MASK) == 0)
@@ -2691,7 +2713,8 @@ void ImDrawList::AddCircle(const ImVec2& center, float radius, ImU32 col, int nu
outer_radius = radius;
else if (stroke_pos == ImDrawFlags_StrokeOutside)
outer_radius = radius + thickness;
if (outer_radius < (thickness + _FringeScale)) IM_UNLIKELY
if (outer_radius <= thickness) IM_UNLIKELY
{
// The circle has collapsed into a filled circle.
AddCircleFilled(center, outer_radius, col, num_segments);
@@ -2715,7 +2738,15 @@ void ImDrawList::AddCircle(const ImVec2& center, float radius, ImU32 col, int nu
PathArcTo(center, radius, 0.0f, a_max, num_segments - 1);
}
PathStroke(col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos);
if (_Path.Size < 3)
return;
// Calculate distance to the edge of the polygon describing the circle.
// This will be used by _AddPolyline() to clamp the inner stroke expansion, to avoid creating rendering artifacts.
const float unit_apothem = ApproxApothem(_Path.Size);
const float edge_dist = radius * unit_apothem;
_AddPolyline(_Path.Data, _Path.Size, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos, edge_dist);
_Path.Size = 0;
}
void ImDrawList::AddCircleFilled(const ImVec2& center, float radius, ImU32 col, int num_segments)
@@ -2766,22 +2797,24 @@ void ImDrawList::AddNgon(const ImVec2& center, float radius, ImU32 col, int num_
}
radius = ImMax(0.01f, radius);
// Check overestimate first before testing details (+1.0f is intended, not FringeScale)
if (radius < (thickness * 2.0f + 1.0f))
{
const float unit_apothem = ImCos(IM_PI / (float)num_segments);
const float miter_thickness = thickness / unit_apothem;
// Calculate distance to the edge of the polygon describing the circle.
// This will be used by _AddPolyline() to clamp the inner stroke expansion, to avoid creating rendering artifacts.
const float unit_apothem = ApproxApothem(num_segments);
const float edge_dist = radius * unit_apothem;
// Check overestimate first before testing details.
if (radius < thickness * 2.0f)
{
float outer_radius = radius;
if (stroke_pos == ImDrawFlags_StrokeCenter)
outer_radius = radius + miter_thickness * 0.5f;
outer_radius = radius + thickness * 0.5f;
else if (stroke_pos == ImDrawFlags_StrokeCenterBiased)
outer_radius = radius + _CalculateCenterBiasedOffset(miter_thickness);
outer_radius = radius + _CalculateCenterBiasedOffset(thickness);
else if (stroke_pos == ImDrawFlags_StrokeInside)
outer_radius = radius;
else if (stroke_pos == ImDrawFlags_StrokeOutside)
outer_radius = radius + miter_thickness;
if (outer_radius < (miter_thickness + _FringeScale)) IM_UNLIKELY
outer_radius = radius + thickness;
if (outer_radius * unit_apothem <= thickness) IM_UNLIKELY
{
// The polygon has collapsed into a filled polygon.
AddNgonFilled(center, outer_radius, col, num_segments);
@@ -2792,7 +2825,8 @@ void ImDrawList::AddNgon(const ImVec2& center, float radius, ImU32 col, int num_
// Because we are filling a closed shape we remove 1 from the count of segments/points
const float a_max = (IM_PI * 2.0f) * ((float)num_segments - 1.0f) / (float)num_segments;
PathArcTo(center, radius, 0.0f, a_max, num_segments - 1);
PathStroke(col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos);
_AddPolyline(_Path.Data, _Path.Size, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos, edge_dist);
_Path.Size = 0;
}
// Guaranteed to honor 'num_segments'
@@ -2838,7 +2872,11 @@ void ImDrawList::AddEllipse(const ImVec2& center, const ImVec2& radius, ImU32 co
// Because we are filling a closed shape we remove 1 from the count of segments/points
const float a_max = IM_PI * 2.0f * ((float)num_segments - 1.0f) / (float)num_segments;
PathEllipticalArcTo(center, rad, rot, 0.0f, a_max, num_segments - 1);
PathStroke(col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos);
// Prevent the inside part of the stroke to be expanded too much to prevent some rendering artifacts.
const float max_inner_offset = ImMin(rad.x, rad.y);
_AddPolyline(_Path.Data, _Path.Size, col, thickness, ImDrawFlags_Closed | ImDrawFlags_MiterOnly | stroke_pos, max_inner_offset);
_Path.Size = 0;
}
void ImDrawList::AddEllipseFilled(const ImVec2& center, const ImVec2& radius, ImU32 col, float rot, int num_segments)