dbc_blit.h — single file public domain software blitter

An easy-to-use API to blit pixel rectangles (no scaling/rotation/shear support). Supports several blending modes. Should be cross-platform, but only x86 has an optimized SIMD implementation.

Repository also includes test/benchmark suite (check.c), a simple graphical demo (demo.c), and prebuilt DLLs for Windows (see test_dll.c for usage example).

Usage

In the style of STB libraries, dbc_blit.h acts as its own header, and expects you to select one file in which to create an implementation:

#define DBC_BLIT_IMPLEMENTATION // <-- only define in ONE file.
#include "dbc_blit.h"

The single exposed API function is:

void dbc_blit(
    int src_w, int src_h, int src_stride_in_bytes, const unsigned char *src_pixels,
    int dst_w, int dst_h, int dst_stride_in_bytes,       unsigned char *dst_pixels,
    int x, int y,
    const float *color, int mode);

• w, h, stride, pixel describe a rectangular pixel surface.
• x, y specify where src's (0,0) is placed on dst.
• color (optional) specifies color modulation (or colorkey, or alphatest threshold, depending on mode).
• mode is one of the following constants:

Mode	Description
DBCB_MODE_COPY	Straight copy
DBCB_MODE_ALPHA	Alpha-blending
DBCB_MODE_PMA	Premultiplied alpha (see also)
DBCB_MODE_GAMMA	Alpha-blending in sRGB
DBCB_MODE_PMG	Premultiplied alpha in sRGB
DBCB_MODE_COLORKEY8	8-bit with optional colorkey
DBCB_MODE_COLORKEY16	16-bit with optional colorkey
DBCB_MODE_5551	16-bit with 1-bit alpha channel
DBCB_MODE_MUL	Color multiplication
DBCB_MODE_MUG	Color multiplication in sRGB
DBCB_MODE_ALPHATEST	Alpha-test
DBCB_MODE_CPYG	Copy in sRGB (only matters with color modulation)

See documentation in dbc_blit.h for more details (including blending equations).

Speed

The performance depends on many factors, including the architecture (both CPU and memory), blending mode (sRGB modes may be about 10 times slower), and usage pattern (blitting a lot of small sprites at random coordinates may introduce cache misses). Broadly speaking, on a modern (as of 2022) x86 you should get fillrate of about 2 gigapixels per second in alpha-blending mode, single-threaded (dbc_blit.h does not use threading internally, but the API should be thread-safe, as long as there's no dst/dst or src/dst overlap). See table in dbc_blit.h for some more detailed timings.

Misc

Version 2.0.7.

Original developmnet thread: https://gamedev.ru/flame/forum/?id=218515 (in Russian).