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Improve on automatic circle segment count calculation. (#3808) Amends

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ocornut
2021-02-17 13:06:26 +01:00
parent f107693d9b
commit fb15d8c858
5 changed files with 41 additions and 48 deletions
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29
imgui_internal.h
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@ -617,29 +617,20 @@ struct IMGUI_API ImChunkStream
//-----------------------------------------------------------------------------
// ImDrawList: Helper function to calculate a circle's segment count given its radius and a "maximum error" value.
//
// Estimation of number of circle segment based on error is derived using method described in
// this post (https://stackoverflow.com/a/2244088/15194693).
// Estimation of number of circle segment based on error is derived using method described in https://stackoverflow.com/a/2244088/15194693
// Number of segments (N) is calculated using equation:
//
// +- -+
// | pi |
// N = ceil | --------------------- | where r > 0, error <= r
// | acos(1 - error / r) |
// +- -+
//
// Note:
// Equation is significantly simpler that one in the post thanks for choosing segment
// that is perpendicular to X axis. Follow steps in the article from this starting condition
// and you will get this result.
// N = ceil ( pi / acos(1 - error / r) ) where r > 0, error <= r
// Our equation is significantly simpler that one in the post thanks for choosing segment that is
// perpendicular to X axis. Follow steps in the article from this starting condition and you will
// will get this result.
//
// Rendering circles with an odd number of segments, while mathematically correct will produce
// asymmetrical results on the raster grid. Therefore we're rounding N to next even number.
// (7 became 8, 11 became 12, but 8 will still be 8).
// asymmetrical results on the raster grid. Therefore we're rounding N to next even number (7->8, 8->8, 9->10 etc.)
//
#define IM_ROUNDUP_TO_EVEN(_V) ((((_V) + 1) / 2) * 2)
#define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN 4
#define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX 512
#define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(_RAD,_MAXERROR) ImClamp((((int)ImCeil(IM_PI / ImAcos(1 - ImMin((_MAXERROR), (_RAD)) / (_RAD))) + 1) / 2) * 2, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX)
#define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(_RAD,_MAXERROR) ImClamp(IM_ROUNDUP_TO_EVEN((int)ImCeil(IM_PI / ImAcos(1 - ImMin((_MAXERROR), (_RAD)) / (_RAD)))), IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX)
// ImDrawList: You may set this to higher values (e.g. 2 or 3) to increase tessellation of fast rounded corners path.
#ifndef IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER
@ -660,8 +651,8 @@ struct IMGUI_API ImDrawListSharedData
// [Internal] Lookup tables
ImVec2 ArcFastVtx[12 * IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER]; // FIXME: Bake rounded corners fill/borders in atlas
ImU8 CircleSegmentCounts[64]; // Precomputed segment count for given radius before we calculate it dynamically (to avoid calculation overhead)
const ImVec4* TexUvLines; // UV of anti-aliased lines in the atlas
ImU8 CircleSegmentCounts[64]; // Precomputed segment count for given radius before we calculate it dynamically (to avoid calculation overhead)
const ImVec4* TexUvLines; // UV of anti-aliased lines in the atlas
ImDrawListSharedData();
void SetCircleTessellationMaxError(float max_error);