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sham1/alpha-blend.c

Created May 8, 2023 20:54
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  1. sham1 created this gist May 8, 2023.
    49 changes: 49 additions & 0 deletions alpha-blend.c
    View file
    Original file line number Diff line number Diff line change
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    /*
    * Copyright (c) 2023 Jani Juhani Sinervo
    *
    * 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.
    */

    #include <stdint.h>

    void
    premul_argb_blend(uint8_t out[static restrict 4],
    const uint8_t a[const restrict 4],
    const uint8_t b[const restrict 4])
    {
    uint8_t blue_a = a[0];
    uint8_t green_a = a[1];
    uint8_t red_a = a[2];
    uint8_t alpha_a = a[3];

    uint8_t blue_b = b[0];
    uint8_t green_b = b[1];
    uint8_t red_b = b[2];
    uint8_t alpha_b = b[3];

    uint8_t blue_out = (255 * blue_a + 255 * blue_b - (blue_b * alpha_a))/255;
    uint8_t green_out = (255 * green_a + 255 * green_b - (green_b * alpha_a))/255;
    uint8_t red_out = (255 * red_a + 255 * red_b - (red_b * alpha_a))/255;
    uint8_t alpha_out = (255 * alpha_a + 255 * alpha_b - (alpha_b * alpha_a))/255;

    out[0] = blue_out;
    out[1] = green_out;
    out[2] = red_out;
    out[3] = alpha_out;
    }