gfx_sprite.c File Reference

gfx_sprite_draw(): a run-length encoded image with 4-bit alpha, blended onto a canvas. See include/gfx_sprite.h. More...

#include "gfx_sprite.h"
#include "gfx_int.h"
#include "gfx_work.h"
#include <string.h>

Macros
#define	KEEP(a)
	The destination's weight under alpha a, in 32nds, rounded down: floor(32 x (15 - a) / 15).

Functions
static gfx_color_t	blend (gfx_color_t dst, gfx_color_t src, unsigned a)
	One partly covered pixel: src, premultiplied, over dst.
static gfx_color_t	rd16 (const uint8_t *p)
	A little-endian 16-bit value at p.
bool	gfx_sprite_draw (gfx_canvas_t *c, int x, int y, const gfx_sprite_t *sp)
	Blend sp onto c with its top-left corner at (x, y).

Variables
static const uint8_t	k_keep [16]
	KEEP() for every alpha, 0 to 15.

Detailed Description

gfx_sprite_draw(): a run-length encoded image with 4-bit alpha, blended onto a canvas. See include/gfx_sprite.h.

SPDX-License-Identifier: MIT

Macro Definition Documentation

KEEP

#define KEEP

(

a

)

Value:

((uint8_t)((32u * (15u - (a))) / 15u))

The destination's weight under alpha a, in 32nds, rounded down: floor(32 x (15 - a) / 15).

Function Documentation

blend()

gfx_color_t blend ( gfx_color_t dst, gfx_color_t src, unsigned a )

inlinestatic

One partly covered pixel: src, premultiplied, over dst.

The three channels are spread over a 32-bit word with room above each (green in bits 21 to 26, red 11 to 15, blue 0 to 4), scaled by one multiply and folded back. The weight is rounded down, so src plus the scaled dst stays within each channel and nothing carries.

Parameters

dst	the pixel under it
src	the sprite's pixel, premultiplied by its alpha
a	its alpha, 1 to 14 of 15

Returns

the blended pixel

gfx_sprite_draw()

bool gfx_sprite_draw	(	gfx_canvas_t *	c,
		int	x,
		int	y,
		const gfx_sprite_t *	sp )

Blend sp onto c with its top-left corner at (x, y).

Stops at the end of the table, or at a run that would cross the end of its row, so a short or damaged table draws less and reads nothing past its bytes.

Parameters

c	the canvas
x	the sprite's left edge on the canvas
y	its top edge
sp	the sprite, or NULL for none

Returns

true when the whole table was read, row by row, to its last byte; false for NULL, an empty sprite or a table that does not hold w x h pixels in exactly bytes

Variable Documentation

k_keep

const uint8_t k_keep[16]

static

Initial value:

                            = {
    KEEP(0),  KEEP(1),  KEEP(2),  KEEP(3),  KEEP(4),  KEEP(5),
    KEEP(6),  KEEP(7),  KEEP(8),  KEEP(9),  KEEP(10), KEEP(11),
    KEEP(12), KEEP(13), KEEP(14), KEEP(15),
}

KEEP() for every alpha, 0 to 15.