agg_alpha_mask_u8.h

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//----------------------------------------------------------------------------
// Anti-Grain Geometry - Version 2.4
// Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
//
// Permission to copy, use, modify, sell and distribute this software 
// is granted provided this copyright notice appears in all copies. 
// This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.
//
//----------------------------------------------------------------------------
// Contact: [e-mail]
//          [e-mail]
//          http://www.antigrain.com
//----------------------------------------------------------------------------
//
// scanline_u8 class
//
//----------------------------------------------------------------------------
#ifndef AGG_ALPHA_MASK_U8_INCLUDED
#define AGG_ALPHA_MASK_U8_INCLUDED

#include <string.h>
#include "agg_basics.h"
#include "agg_rendering_buffer.h"

namespace agg
{
    //===================================================one_component_mask_u8
    struct one_component_mask_u8
    {
        static unsigned calculate(const int8u* p) { return *p; }
    };
    

    //=====================================================rgb_to_gray_mask_u8
    template<unsigned R, unsigned G, unsigned B>
    struct rgb_to_gray_mask_u8
    {
        static unsigned calculate(const int8u* p) 
        { 
            return (p[R]*77 + p[G]*150 + p[B]*29) >> 8; 
        }
    };

    //==========================================================alpha_mask_u8
    template<unsigned Step=1, unsigned Offset=0, class MaskF=one_component_mask_u8>
    class alpha_mask_u8
    {
    public:
        typedef int8u cover_type;
        typedef alpha_mask_u8<Step, Offset, MaskF> self_type;
        enum cover_scale_e
        { 
            cover_shift = 8,
            cover_none  = 0,
            cover_full  = 255
        };

        alpha_mask_u8() : m_rbuf(0) {}
        alpha_mask_u8(rendering_buffer& rbuf) : m_rbuf(&rbuf) {}

        void attach(rendering_buffer& rbuf) { m_rbuf = &rbuf; }

        MaskF& mask_function() { return m_mask_function; }
        const MaskF& mask_function() const { return m_mask_function; }

        
        //--------------------------------------------------------------------
        cover_type pixel(int x, int y) const
        {
            if(x >= 0 && y >= 0 && 
               x < (int)m_rbuf->width() && 
               y <= (int)m_rbuf->height())
            {
                return (cover_type)m_mask_function.calculate(
                                        m_rbuf->row_ptr(y) + x * Step + Offset);
            }
            return 0;
        }

        //--------------------------------------------------------------------
        cover_type combine_pixel(int x, int y, cover_type val) const
        {
            if(x >= 0 && y >= 0 && 
               x < (int)m_rbuf->width() && 
               y <= (int)m_rbuf->height())
            {
                return (cover_type)((cover_full + val * 
                                     m_mask_function.calculate(
                                        m_rbuf->row_ptr(y) + x * Step + Offset)) >> 
                                     cover_shift);
            }
            return 0;
        }


        //--------------------------------------------------------------------
        void fill_hspan(int x, int y, cover_type* dst, int num_pix) const
        {
            int xmax = m_rbuf->width() - 1;
            int ymax = m_rbuf->height() - 1;

            int count = num_pix;
            cover_type* covers = dst;

            if(y < 0 || y > ymax)
            {
                memset(dst, 0, num_pix * sizeof(cover_type));
                return;
            }

            if(x < 0)
            {
                count += x;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers, 0, -x * sizeof(cover_type));
                covers -= x;
                x = 0;
            }

            if(x + count > xmax)
            {
                int rest = x + count - xmax - 1;
                count -= rest;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers + count, 0, rest * sizeof(cover_type));
            }

            const int8u* mask = m_rbuf->row_ptr(y) + x * Step + Offset;
            do
            {
                *covers++ = (cover_type)m_mask_function.calculate(mask);
                mask += Step;
            }
            while(--count);
        }


        //--------------------------------------------------------------------
        void combine_hspan(int x, int y, cover_type* dst, int num_pix) const
        {
            int xmax = m_rbuf->width() - 1;
            int ymax = m_rbuf->height() - 1;

            int count = num_pix;
            cover_type* covers = dst;

            if(y < 0 || y > ymax)
            {
                memset(dst, 0, num_pix * sizeof(cover_type));
                return;
            }

            if(x < 0)
            {
                count += x;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers, 0, -x * sizeof(cover_type));
                covers -= x;
                x = 0;
            }

            if(x + count > xmax)
            {
                int rest = x + count - xmax - 1;
                count -= rest;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers + count, 0, rest * sizeof(cover_type));
            }

            const int8u* mask = m_rbuf->row_ptr(y) + x * Step + Offset;
            do
            {
                *covers = (cover_type)((cover_full + (*covers) * 
                                       m_mask_function.calculate(mask)) >> 
                                       cover_shift);
                ++covers;
                mask += Step;
            }
            while(--count);
        }

        //--------------------------------------------------------------------
        void fill_vspan(int x, int y, cover_type* dst, int num_pix) const
        {
            int xmax = m_rbuf->width() - 1;
            int ymax = m_rbuf->height() - 1;

            int count = num_pix;
            cover_type* covers = dst;

            if(x < 0 || x > xmax)
            {
                memset(dst, 0, num_pix * sizeof(cover_type));
                return;
            }

            if(y < 0)
            {
                count += y;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers, 0, -y * sizeof(cover_type));
                covers -= y;
                y = 0;
            }

            if(y + count > ymax)
            {
                int rest = y + count - ymax - 1;
                count -= rest;
                if(count <= 0) 
                {
                    memset(dst, 0, num_pix * sizeof(cover_type));
                    return;
                }
                memset(covers + count, 0, rest * sizeof(cover_type));
            }

            const int8u* mask = m_rbuf->row_ptr(y) + x * Step + Offset;
            do
            {
                *covers++ = (cover_type)m_mask_function.calculate(mask);
                mask += m_rbuf->stride();
            }
            while(--count);
        }

        //--------------------------------------------------------------------
        void combine_vspan(int x, int y, cover_type* dst, int num_pix) const
        {