miloyip / line

2D Line Drawing Samples in C

2D Line Drawing Samples

This project contains C source code for drawing 2D lines by different techniques.

All samples output PNGs with svpng.

License: public domain.

Bresenham

The fundamental line drawing algorithm by Bresenham [1], based on rosetta code.

Sampling

Represent lines as capsule shapes, in order to support real-valued coordinates and variable width.

Anti-aliasing by super sampling

Simple anti-aliasing with 5x5 super sampling.

Anti-aliasing by signed distnace field

Using signed distnace field (SDF) of capsule shape to perform anti-aliasing with single sample per pixel.

SDF optimization with AABB

Use AABB of capsule to reduce the number of samples. Render shapes into the buffer individually with alpha blending.

Visual comparison

Performance comparison

$ make test
gcc -Wall -O3 -o line_bresenham line_bresenham.c
gcc -Wall -O3 -o line_sampling line_sampling.c
gcc -Wall -O3 -o line_supersampling line_supersampling.c
gcc -Wall -O3 -o line_sdf line_sdf.c
gcc -Wall -O3 -o line_sdfaabb line_sdfaabb.c
time ./line_bresenham
        0.03 real         0.02 user         0.00 sys
time ./line_sampling
        1.93 real         1.91 user         0.00 sys
time ./line_supersampling
       47.06 real        46.85 user         0.10 sys
time ./line_sdf
        2.00 real         1.98 user         0.00 sys
time ./line_sdfaabb
        0.03 real         0.03 user         0.00 sys

Final notes

1. These samples are only for illustrative purposes.
2. Line clipping are not performed.
3. The SDF AABB sample can be further optimized by tigther quaduraliteral bounds.

References

[1] Bresenham, Jack E. "Algorithm for computer control of a digital plotter." IBM Systems journal 4.1 (1965): 25-30.