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-rw-r--r--cairosdl-premultiply.c301
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diff --git a/cairosdl-premultiply.c b/cairosdl-premultiply.c
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-/*
- * Copyright (c) 2009 M Joonas Pihlaja
- * Copyright (c) 2009 Paul-Virak Khuong
- *
- * Permission is hereby granted, free of charge, to any person
- * obtaining a copy of this software and associated documentation
- * files (the "Software"), to deal in the Software without
- * restriction, including without limitation the rights to use,
- * copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the
- * Software is furnished to do so, subject to the following
- * conditions:
- *
- * The above copyright notice and this permission notice shall be
- * included in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
- * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
- * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
- * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
- * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
- * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
- * OTHER DEALINGS IN THE SOFTWARE.
- */
-/* A pixel premultiplier and an unpremultiplier using reciprocal
- * multiplication. It specialises constant runs and solid runs of
- * pixels with low overhead loops and uses only a 1KB table of
- * reciprocals.
- *
- * The unpremultiplier wa snarfed from
- * http://cgit.freedesktop.org/~joonas/unpremultiply
- *
- * See there for other faster or nonportable variations on
- * unpremultiply. This one is a good all rounder that doesn't take
- * that much data space. */
-#include <stddef.h>
-#include "cairosdl.h"
-
-/* Pixel format config for a 32 bit pixel with 8 bit components. Only
- * the location of alpha matters. Cairo uses ASHIFT 24. */
-#define ASHIFT CAIROSDL_ASHIFT
-#define RSHIFT ((24 + ASHIFT) % 32)
-#define GSHIFT ((16 + ASHIFT) % 32)
-#define BSHIFT (( 8 + ASHIFT) % 32)
-
-#define AMASK (255U << ASHIFT)
-#define RMASK (255U << RSHIFT)
-#define GMASK (255U << GSHIFT)
-#define BMASK (255U << BSHIFT)
-
-/* Set to 1 if the input can have superluminant pixels. Cairo doesn't
- * produce them. */
-#define DO_CLAMP_INPUT 0
-
-/* Shift x left by y bits. Supports negative y for right shifts. */
-#define SHIFT(x, y) ((y) < 0 ? (x) >> (-(y)) : (x) << (y))
-
-#define ceil_div(a,b) ((a) + (b)-1) / (b)
-
-/* The reciprocal_table[i] entries are defined by
- *
- * 0 when i = 0
- * 255 / i when i > 0
- *
- * represented in fixed point format with RECIPROCAL_BITS of
- * precision and errors rounded up. */
-#define RECIPROCAL_BITS 16
-static unsigned const reciprocal_table[256] = {
-# define R(i) ((i) ? ceil_div(255*(1<<RECIPROCAL_BITS), (i)) : 0)
-# define R1(i) R(i), R(i+1), R(i+2), R(i+3)
-# define R2(i) R1(i), R1(i+4), R1(i+8), R1(i+12)
-# define R3(i) R2(i), R2(i+16), R2(i+32), R2(i+48)
- R3(0), R3(64), R3(128), R3(192)
-};
-
-/* Transfer num_pixels premultiplied pixels from src[] to dst[] and
- * unpremultiply them. */
-static void
-unpremultiply_row(
- unsigned * dst,
- unsigned const * src,
- size_t num_pixels)
-{
- size_t i = 0;
- while (i < num_pixels) {
- /* We want to identify long runs of constant input pixels and
- * cache the unpremultiplied. */
- unsigned const_in, const_out;
-
- /* Diff is the or of all bitwise differences from const_in
- * during the probe period. If it is zero after the probe
- * period then every input pixel was identical in the
- * probe. */
- unsigned diff = 0;
-
- /* Accumulator for all alphas of the probe period pixels,
- * biased to make the sum zero if the */
- unsigned accu = -2*255;
-
- {
- unsigned rgba, a, r, g, b, recip;
- rgba = const_in = src[i];
- a = (rgba >> ASHIFT) & 255;
- accu += a;
- r = (rgba >> RSHIFT) & 255;
- g = (rgba >> GSHIFT) & 255;
- b = (rgba >> BSHIFT) & 255;
- recip = reciprocal_table[a];
-#if DO_CLAMP_INPUT
- r = r < a ? r : a;
- g = g < a ? g : a;
- b = b < a ? b : a;
-#endif
- r = SHIFT(r * recip, RSHIFT - RECIPROCAL_BITS);
- g = SHIFT(g * recip, GSHIFT - RECIPROCAL_BITS);
- b = SHIFT(b * recip, BSHIFT - RECIPROCAL_BITS);
- dst[i] = const_out =
- (r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
- }
-
- if (i + 1 == num_pixels)
- return;
-
- {
- unsigned rgba, a, r, g, b, recip;
- rgba = src[i+1];
- a = (rgba >> ASHIFT) & 255;
- accu += a;
- r = (rgba >> RSHIFT) & 255;
- g = (rgba >> GSHIFT) & 255;
- b = (rgba >> BSHIFT) & 255;
- recip = reciprocal_table[a];
-#if DO_CLAMP_INPUT
- r = r < a ? r : a;
- g = g < a ? g : a;
- b = b < a ? b : a;
-#endif
- diff = rgba ^ const_in;
- r = SHIFT(r * recip, RSHIFT - RECIPROCAL_BITS);
- g = SHIFT(g * recip, GSHIFT - RECIPROCAL_BITS);
- b = SHIFT(b * recip, BSHIFT - RECIPROCAL_BITS);
- dst[i+1] =
- (r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
- }
-
- i += 2;
-
- /* Fall into special cases if we have special
- * circumstances. */
- if (0 != (accu & diff))
- continue;
-
- if (0 == accu) { /* a run of solid pixels. */
- unsigned in;
- while (AMASK == ((in = src[i]) & AMASK)) {
- dst[i++] = in;
- if (i == num_pixels) return;
- }
- } else if (0 == diff) { /* a run of constant pixels. */
- while (src[i] == const_in) {
- dst[i++] = const_out;
- if (i == num_pixels) return;
- }
- }
- }
-}
-
-/* Transfer num_pixels unpremultiplied pixels from src[] to dst[] and
- * premultiply them. */
-static void
-premultiply_row(
- unsigned * dst,
- unsigned const * src,
- size_t num_pixels)
-{
- size_t i = 0;
- while (i < num_pixels) {
- /* We want to identify long runs of constant input pixels and
- * cache the unpremultiplied. */
- unsigned const_in, const_out;
-
- /* Diff is the or of all bitwise differences from const_in
- * during the probe period. If it is zero after the probe
- * period then every input pixel was identical in the
- * probe. */
- unsigned diff = 0;
-
- /* Accumulator for all alphas of the probe period pixels,
- * biased to make the sum zero if the */
- unsigned accu = -2*255;
-
- {
- unsigned rgba, a, r, g, b;
- rgba = const_in = src[i];
- a = (rgba >> ASHIFT) & 255;
- accu += a;
- r = (rgba >> RSHIFT) & 255;
- g = (rgba >> GSHIFT) & 255;
- b = (rgba >> BSHIFT) & 255;
-
- r = SHIFT(r*a*257 + 32768, RSHIFT - 16);
- g = SHIFT(g*a*257 + 32768, GSHIFT - 16);
- b = SHIFT(b*a*257 + 32768, BSHIFT - 16);
- dst[i] = const_out =
- (r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
- }
-
- if (i + 1 == num_pixels)
- return;
-
- {
- unsigned rgba, a, r, g, b;
- rgba = src[i+1];
- a = (rgba >> ASHIFT) & 255;
- accu += a;
- r = (rgba >> RSHIFT) & 255;
- g = (rgba >> GSHIFT) & 255;
- b = (rgba >> BSHIFT) & 255;
- diff = rgba ^ const_in;
-
- r = SHIFT(r*a*257 + 32768, RSHIFT - 16);
- g = SHIFT(g*a*257 + 32768, GSHIFT - 16);
- b = SHIFT(b*a*257 + 32768, BSHIFT - 16);
- dst[i+1] =
- (r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
- }
-
- i += 2;
-
- /* Fall into special cases if we have special
- * circumstances. */
- if (0 != (accu & diff))
- continue;
-
- if (0 == accu) { /* a run of solid pixels. */
- unsigned in;
- while (AMASK == ((in = src[i]) & AMASK)) {
- dst[i++] = in;
- if (i == num_pixels) return;
- }
- } else if (0 == diff) { /* a run of constant pixels. */
- while (src[i] == const_in) {
- dst[i++] = const_out;
- if (i == num_pixels) return;
- }
- }
- }
-}
-
-void
-_cairosdl_blit_and_unpremultiply (
- void *target_buffer,
- size_t target_stride,
- void const *source_buffer,
- size_t source_stride,
- int width,
- int height)
-{
- unsigned char *target_bytes =
- (unsigned char *)target_buffer;
- unsigned char const *source_bytes =
- (unsigned char const *)source_buffer;
- if (width <= 0)
- return;
-
- while (height-- > 0) {
- unpremultiply_row ((unsigned *)target_bytes,
- (unsigned const *)source_bytes,
- width);
-
- target_bytes += target_stride;
- source_bytes += source_stride;
- }
-}
-
-void
-_cairosdl_blit_and_premultiply (
- void *target_buffer,
- size_t target_stride,
- void const *source_buffer,
- size_t source_stride,
- int width,
- int height)
-{
- unsigned char *target_bytes =
- (unsigned char *)target_buffer;
- unsigned char const *source_bytes =
- (unsigned char const *)source_buffer;
- if (width <= 0)
- return;
-
- while (height-- > 0) {
- premultiply_row ((unsigned *)target_bytes,
- (unsigned const *)source_bytes,
- width);
-
- target_bytes += target_stride;
- source_bytes += source_stride;
- }
-}
generated by cgit v1.2.1 (git 2.18.0) at 2022-05-19 06:36:23 +0000