From e5990afb6d147c822cb1a6c94c6183f082918535 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= Date: Sun, 23 Jun 2019 15:36:19 +0200 Subject: [PATCH] Add comment --- small3dlib.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/small3dlib.h b/small3dlib.h index fb68857..f0b7a38 100644 --- a/small3dlib.h +++ b/small3dlib.h @@ -1633,6 +1633,18 @@ typedef struct int16_t minorDiff; } S3L_BresenhamState; ///< State of drawing a line with Bresenham algorithm. +/** Serves to accelerate linear interpolation for performance-critical + code. Functions such as S3L_interpolate require division to compute each + interpolated value, while S3L_FastLerpState only requires a division for + the initiation and a shift for retrieving each interpolated value. + + S3L_FastLerpState stores a value and a step, both scaled (shifted by + S3L_FAST_LERP_QUALITY) to increase precision. The step is being added to the + value, which achieves the interpolation. This will only be useful for + interpolations in which we need to get the interpolated value in every step. + + BEWARE! Shifting a negative value is undefined, so handling shifting of + negative values has to be done cleverly. */ typedef struct { S3L_Unit valueScaled; @@ -1911,7 +1923,8 @@ void S3L_drawTriangle( s##SideFLS.valueScaled = 0;\ if (!down)\ {\ - s##SideFLS.valueScaled = S3L_FRACTIONS_PER_UNIT << S3L_FAST_LERP_QUALITY;\ + s##SideFLS.valueScaled =\ + S3L_FRACTIONS_PER_UNIT << S3L_FAST_LERP_QUALITY;\ s##SideFLS.stepScaled *= -1;\ }\ s##Inc = s##Dx >= 0 ? 1 : -1;\