SDL/src/video/SDL_blit_slow.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "../SDL_internal.h"

#include "SDL_video.h"
#include "SDL_blit.h"
#include "SDL_blit_slow.h"

/* The ONE TRUE BLITTER
 * This puppy has to handle all the unoptimized cases - yes, it's slow.
 */
void
SDL_Blit_Slow(SDL_BlitInfo * info)
{
    const int flags = info->flags;
    const Uint32 modulateR = info->r;
    const Uint32 modulateG = info->g;
    const Uint32 modulateB = info->b;
    const Uint32 modulateA = info->a;
    Uint32 srcpixel;
    Uint32 srcR, srcG, srcB, srcA;
    Uint32 dstpixel;
    Uint32 dstR, dstG, dstB, dstA;
    int srcy, srcx;
    int posy, posx;
    int incy, incx;
    SDL_PixelFormat *src_fmt = info->src_fmt;
    SDL_PixelFormat *dst_fmt = info->dst_fmt;
    int srcbpp = src_fmt->BytesPerPixel;
    int dstbpp = dst_fmt->BytesPerPixel;
    Uint32 rgbmask = ~src_fmt->Amask;
    Uint32 ckey = info->colorkey & rgbmask;

    srcy = 0;
    posy = 0;
    incy = (info->src_h << 16) / info->dst_h;
    incx = (info->src_w << 16) / info->dst_w;

    while (info->dst_h--) {
        Uint8 *src = 0;
        Uint8 *dst = info->dst;
        int n = info->dst_w;
        srcx = -1;
        posx = 0x10000L;
        while (posy >= 0x10000L) {
            ++srcy;
            posy -= 0x10000L;
        }
        while (n--) {
            if (posx >= 0x10000L) {
                while (posx >= 0x10000L) {
                    ++srcx;
                    posx -= 0x10000L;
                }
                src =
                    (info->src + (srcy * info->src_pitch) + (srcx * srcbpp));
            }
            if (src_fmt->Amask) {
                DISEMBLE_RGBA(src, srcbpp, src_fmt, srcpixel, srcR, srcG,
                              srcB, srcA);
            } else {
                DISEMBLE_RGB(src, srcbpp, src_fmt, srcpixel, srcR, srcG,
                             srcB);
                srcA = 0xFF;
            }
            if (flags & SDL_COPY_COLORKEY) {
                /* srcpixel isn't set for 24 bpp */
                if (srcbpp == 3) {
                    srcpixel = (srcR << src_fmt->Rshift) |
                        (srcG << src_fmt->Gshift) | (srcB << src_fmt->Bshift);
                }
                if ((srcpixel & rgbmask) == ckey) {
                    posx += incx;
                    dst += dstbpp;
                    continue;
                }
            }
            if (dst_fmt->Amask) {
                DISEMBLE_RGBA(dst, dstbpp, dst_fmt, dstpixel, dstR, dstG,
                              dstB, dstA);
            } else {
                DISEMBLE_RGB(dst, dstbpp, dst_fmt, dstpixel, dstR, dstG,
                             dstB);
                dstA = 0xFF;
            }

            if (flags & SDL_COPY_MODULATE_COLOR) {
                srcR = (srcR * modulateR) / 255;
                srcG = (srcG * modulateG) / 255;
                srcB = (srcB * modulateB) / 255;
            }
            if (flags & SDL_COPY_MODULATE_ALPHA) {
                srcA = (srcA * modulateA) / 255;
            }
            if (flags & (SDL_COPY_BLEND | SDL_COPY_ADD)) {
                /* This goes away if we ever use premultiplied alpha */
                if (srcA < 255) {
                    srcR = (srcR * srcA) / 255;
                    srcG = (srcG * srcA) / 255;
                    srcB = (srcB * srcA) / 255;
                }
            }
            switch (flags & (SDL_COPY_BLEND | SDL_COPY_ADD | SDL_COPY_MOD | SDL_COPY_MUL)) {
            case 0:
                dstR = srcR;
                dstG = srcG;
                dstB = srcB;
                dstA = srcA;
                break;
            case SDL_COPY_BLEND:
                dstR = srcR + ((255 - srcA) * dstR) / 255;
                dstG = srcG + ((255 - srcA) * dstG) / 255;
                dstB = srcB + ((255 - srcA) * dstB) / 255;
                dstA = srcA + ((255 - srcA) * dstA) / 255;
                break;
            case SDL_COPY_ADD:
                dstR = srcR + dstR;
                if (dstR > 255)
                    dstR = 255;
                dstG = srcG + dstG;
                if (dstG > 255)
                    dstG = 255;
                dstB = srcB + dstB;
                if (dstB > 255)
                    dstB = 255;
                break;
            case SDL_COPY_MOD:
                dstR = (srcR * dstR) / 255;
                dstG = (srcG * dstG) / 255;
                dstB = (srcB * dstB) / 255;
                break;
            case SDL_COPY_MUL:
                dstR = ((srcR * dstR) + (dstR * (255 - srcA))) / 255;
                if (dstR > 255)
                    dstR = 255;
                dstG = ((srcG * dstG) + (dstG * (255 - srcA))) / 255;
                if (dstG > 255)
                    dstG = 255;
                dstB = ((srcB * dstB) + (dstB * (255 - srcA))) / 255;
                if (dstB > 255)
                    dstB = 255;
                dstA = ((srcA * dstA) + (dstA * (255 - srcA))) / 255;
                if (dstA > 255)
                    dstA = 255;
                break;
            }
            if (dst_fmt->Amask) {
                ASSEMBLE_RGBA(dst, dstbpp, dst_fmt, dstR, dstG, dstB, dstA);
            } else {
                ASSEMBLE_RGB(dst, dstbpp, dst_fmt, dstR, dstG, dstB);
            }
            posx += incx;
            dst += dstbpp;
        }
        posy += incy;
        info->dst += info->dst_pitch;
    }
}

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