sdlblendingfunctions.cpp

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/***************************************************************************
 *   Copyright (C) 2005-2019 by the FIFE team                              *
 *   http://www.fifengine.net                                              *
 *   This file is part of FIFE.                                            *
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 *   FIFE is free software; you can redistribute it and/or                 *
 *   modify it under the terms of the GNU Lesser General Public            *
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 *   version 2.1 of the License, or (at your option) any later version.    *
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 *   This library is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
 *   Lesser General Public License for more details.                       *
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 *   Free Software Foundation, Inc.,                                       *
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// Standard C++ library includes

// 3rd party library includes

// FIFE includes
// These includes are split up in two parts, separated by one empty line
// First block: files included from the FIFE root src directory
// Second block: files included from the same folder
#include "sdlblendingfunctions.h"

namespace FIFE {

    struct ColorRGB8 {
        uint8_t r, g, b;
    };

    struct ColorRGBA8 {
        uint8_t r, g, b, a;
    };

    void SDL_BlendRow_RGBA8_to_RGBA8( const uint8_t* src, uint8_t* dst, uint32_t alpha, int32_t n ) {
        const ColorRGBA8* srcColor = reinterpret_cast< const ColorRGBA8* >( src );
        ColorRGBA8* dstColor = reinterpret_cast< ColorRGBA8* >( dst );

        for( int32_t i = n; 0 < i; --i ) {
            uint32_t aMulA = alpha * srcColor->a;

            if( aMulA ) {
                uint32_t OneMin_aMulA = 65535 - aMulA;
                dstColor->r = ( aMulA * srcColor->r + OneMin_aMulA * dstColor->r ) >> 16;
                dstColor->g = ( aMulA * srcColor->g + OneMin_aMulA * dstColor->g ) >> 16;
                dstColor->b = ( aMulA * srcColor->b + OneMin_aMulA * dstColor->b ) >> 16;
                dstColor->a = 255;
            }
            ++dstColor;
            ++srcColor;
        }
    }

    void SDL_BlendRow_RGBA8_to_RGB8( const uint8_t* src, uint8_t* dst, uint32_t alpha, int32_t n ) {
        const ColorRGBA8* srcColor = reinterpret_cast< const ColorRGBA8* >( src );
        ColorRGB8* dstColor = reinterpret_cast< ColorRGB8* >( dst );

        for( int32_t i = n; 0 < i; --i ) {
            uint32_t aMulA = alpha * srcColor->a;
            if( aMulA ) {
                uint32_t OneMin_aMulA = 65535 - aMulA;
                dstColor->r = ( aMulA * srcColor->r + OneMin_aMulA * dstColor->r ) >> 16;
                dstColor->g = ( aMulA * srcColor->g + OneMin_aMulA * dstColor->g ) >> 16;
                dstColor->b = ( aMulA * srcColor->b + OneMin_aMulA * dstColor->b ) >> 16;
            }

            ++dstColor;
            ++srcColor;
        }
    }

    void SDL_BlendRow_RGBA8_to_RGB565( const uint8_t* src, uint8_t* dst, uint32_t alpha, int32_t n ) {
        const ColorRGBA8* srcColor = reinterpret_cast< const ColorRGBA8* >( src );
        uint16_t* dstColor = reinterpret_cast< uint16_t* >( dst );

        for( int32_t i = n; 0 < i; --i ) {
            uint32_t aMulA = ( alpha * srcColor->a ) >> 8;
            if( aMulA ) {
                uint32_t OneMin_aMulA = 255 - aMulA;
                uint32_t c = *dstColor;
                *dstColor = ( ( ( srcColor->b * aMulA ) +
                    ( ( ( c & 0xF800 ) >> 8 ) * OneMin_aMulA ) ) & 0xF800 ) |
                    ( ( ( ( srcColor->g * aMulA ) +
                    ( ( ( c & 0x07E0 ) >> 3 ) * OneMin_aMulA ) ) >> 5 ) & 0x07E0 ) |
                    ( ( ( ( srcColor->r * aMulA ) +
                    ( ( ( c & 0x001F ) << 3 ) * OneMin_aMulA ) ) >> 11 ) & 0x001F );
            }

            ++dstColor;
            ++srcColor;
        }
    }


    void SDL_BlendRow_RGBA4_to_RGB565( const uint8_t* src, uint8_t* dst, uint32_t alpha, int32_t n ) {
        const uint16_t* srcColor = reinterpret_cast< const uint16_t* >( src );
        uint16_t* dstColor = reinterpret_cast< uint16_t* >( dst );

        for( int32_t i = n; 0 < i; --i ) {
            uint32_t c1 = *dstColor;
            uint32_t c2 = *srcColor;

            uint32_t aMulA = c2 & 0xF;
            aMulA = ( alpha * aMulA ) / 15; 
            if( aMulA ) {
                uint32_t OneMin_aMulA = 255 - aMulA;
                uint32_t result;
                result = ( ( ( ( c2 & 0xF000 ) | 0x0800 ) * aMulA ) + ( ( c1 & 0xF800 ) * OneMin_aMulA ) ) & 0xF80000;
                result |= ( ( ( ( ( c2 & 0x0F00 ) >> 1 ) | 0x0040 ) * aMulA ) + ( ( c1 & 0x07E0 ) * OneMin_aMulA ) ) & 0x07E000;
                result |= ( ( ( ( ( c2 & 0x00F0 ) >> 3 ) | 0x0001 ) * aMulA ) + ( ( c1 & 0x001F ) * OneMin_aMulA ) ) & 0x001F00;
                *dstColor = static_cast< uint16_t >( result >> 8 );
            }

            ++dstColor;
            ++srcColor;
        }
    }

}