SDL/src/video/SDL_blit.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2026 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_sysvideo.h"
#include "SDL_surface_c.h"
#include "SDL_blit_auto.h"
#include "SDL_blit_copy.h"
#include "SDL_blit_slow.h"
#include "SDL_RLEaccel_c.h"
#include "SDL_pixels_c.h"

// The general purpose software blit routine
static bool SDLCALL SDL_SoftBlit(SDL_Surface *src, const SDL_Rect *srcrect,
                                SDL_Surface *dst, const SDL_Rect *dstrect)
{
    bool okay;
    int src_locked;
    int dst_locked;

    // Everything is okay at the beginning...
    okay = true;

    // Lock the destination if it's in hardware
    dst_locked = 0;
    if (SDL_MUSTLOCK(dst)) {
        if (!SDL_LockSurface(dst)) {
            okay = false;
        } else {
            dst_locked = 1;
        }
    }
    // Lock the source if it's in hardware
    src_locked = 0;
    if (SDL_MUSTLOCK(src)) {
        if (!SDL_LockSurface(src)) {
            okay = false;
        } else {
            src_locked = 1;
        }
    }

    // Set up source and destination buffer pointers, and BLIT!
    if (okay) {
        SDL_BlitFunc RunBlit;
        SDL_BlitInfo *info = &src->map.info;

        // Set up the blit information
        if (info->src_fmt->bits_per_pixel >= 8) {
            info->src = (Uint8 *)src->pixels +
                        srcrect->y * src->pitch +
                        srcrect->x * info->src_fmt->bytes_per_pixel;
        } else {
            info->src = (Uint8 *)src->pixels +
                        srcrect->y * src->pitch +
                        (srcrect->x * info->src_fmt->bits_per_pixel) / 8;
            info->leading_skip =
                        ((srcrect->x * info->src_fmt->bits_per_pixel) % 8) /
                        info->src_fmt->bits_per_pixel;
        }
        info->src_w = srcrect->w;
        info->src_h = srcrect->h;
        info->src_pitch = src->pitch;
        info->src_skip =
            info->src_pitch - info->src_w * info->src_fmt->bytes_per_pixel;
        info->dst = (Uint8 *)dst->pixels +
                    dstrect->y * dst->pitch +
                    dstrect->x * info->dst_fmt->bytes_per_pixel;
        info->dst_w = dstrect->w;
        info->dst_h = dstrect->h;
        info->dst_pitch = dst->pitch;
        info->dst_skip =
            info->dst_pitch - info->dst_w * info->dst_fmt->bytes_per_pixel;
        RunBlit = (SDL_BlitFunc)src->map.data;

        // Run the actual software blit
        RunBlit(info);
    }

    // We need to unlock the surfaces if they're locked
    if (dst_locked) {
        SDL_UnlockSurface(dst);
    }
    if (src_locked) {
        SDL_UnlockSurface(src);
    }
    // Blit is done!
    return okay;
}

#ifdef SDL_HAVE_BLIT_AUTO

#ifdef SDL_PLATFORM_MACOS
#include <sys/sysctl.h>

static bool SDL_UseAltivecPrefetch(void)
{
    const char key[] = "hw.l3cachesize";
    u_int64_t result = 0;
    size_t typeSize = sizeof(result);

    if (sysctlbyname(key, &result, &typeSize, NULL, 0) == 0 && result > 0) {
        return true;
    } else {
        return false;
    }
}
#else
static bool SDL_UseAltivecPrefetch(void)
{
    // Just guess G4
    return true;
}
#endif // SDL_PLATFORM_MACOS

static SDL_BlitFunc SDL_ChooseBlitFunc(SDL_PixelFormat src_format, SDL_PixelFormat dst_format, int flags,
                                       SDL_BlitFuncEntry *entries)
{
    int i, flagcheck = (flags & (SDL_COPY_MODULATE_MASK | SDL_COPY_BLEND_MASK | SDL_COPY_COLORKEY | SDL_COPY_NEAREST));
    static unsigned int features = 0x7fffffff;

    // Get the available CPU features
    if (features == 0x7fffffff) {
        features = SDL_CPU_ANY;
        if (SDL_HasMMX()) {
            features |= SDL_CPU_MMX;
        }
        if (SDL_HasSSE()) {
            features |= SDL_CPU_SSE;
        }
        if (SDL_HasSSE2()) {
            features |= SDL_CPU_SSE2;
        }
        if (SDL_HasAltiVec()) {
            if (SDL_UseAltivecPrefetch()) {
                features |= SDL_CPU_ALTIVEC_PREFETCH;
            } else {
                features |= SDL_CPU_ALTIVEC_NOPREFETCH;
            }
        }
    }

    for (i = 0; entries[i].func; ++i) {
        // Check for matching pixel formats
        if (src_format != entries[i].src_format) {
            continue;
        }
        if (dst_format != entries[i].dst_format) {
            continue;
        }

        // Check flags
        if ((flagcheck & entries[i].flags) != flagcheck) {
            continue;
        }

        // Check CPU features
        if ((entries[i].cpu & features) != entries[i].cpu) {
            continue;
        }

        // We found the best one!
        return entries[i].func;
    }
    return NULL;
}
#endif // SDL_HAVE_BLIT_AUTO

// Figure out which of many blit routines to set up on a surface
bool SDL_CalculateBlit(SDL_Surface *surface, SDL_Surface *dst)
{
    SDL_BlitFunc blit = NULL;
    SDL_BlitMap *map = &surface->map;
    SDL_Colorspace src_colorspace = surface->colorspace;
    SDL_Colorspace dst_colorspace = dst->colorspace;

    // We don't currently support blitting to < 8 bpp surfaces
    if (SDL_BITSPERPIXEL(dst->format) < 8) {
        SDL_InvalidateMap(map);
        return SDL_SetError("Blit combination not supported");
    }

    // We should have cleared out RLE at this point
    SDL_assert(!(surface->internal_flags & SDL_INTERNAL_SURFACE_RLEACCEL));

    map->blit = SDL_SoftBlit;
    map->info.src_surface = surface;
    map->info.src_fmt = surface->fmt;
    map->info.src_pal = surface->palette;
    map->info.dst_surface = dst;
    map->info.dst_fmt = dst->fmt;
    map->info.dst_pal = dst->palette;

#ifdef SDL_HAVE_RLE
    // See if we can do RLE acceleration
    if (map->info.flags & SDL_COPY_RLE_DESIRED) {
        if (SDL_RLESurface(surface)) {
            return true;
        }
    }
#endif

    // Choose a standard blit function
    if (!blit) {
        if (src_colorspace != dst_colorspace ||
            SDL_BYTESPERPIXEL(surface->format) > 4 ||
            SDL_BYTESPERPIXEL(dst->format) > 4) {
            blit = SDL_Blit_Slow_Float;
        }
    }
    if (!blit) {
        if (map->identity && !(map->info.flags & ~SDL_COPY_RLE_DESIRED)) {
            blit = SDL_BlitCopy;
        } else if (SDL_ISPIXELFORMAT_10BIT(surface->format) ||
                   SDL_ISPIXELFORMAT_10BIT(dst->format)) {
            blit = SDL_Blit_Slow;
        }
#ifdef SDL_HAVE_BLIT_0
        else if (SDL_BITSPERPIXEL(surface->format) < 8 &&
                 SDL_ISPIXELFORMAT_INDEXED(surface->format)) {
            blit = SDL_CalculateBlit0(surface);
        }
#endif
#ifdef SDL_HAVE_BLIT_1
        else if (SDL_BYTESPERPIXEL(surface->format) == 1 &&
                 SDL_ISPIXELFORMAT_INDEXED(surface->format)) {
            blit = SDL_CalculateBlit1(surface);
        }
#endif
#ifdef SDL_HAVE_BLIT_A
        else if (map->info.flags & SDL_COPY_BLEND) {
            blit = SDL_CalculateBlitA(surface);
        }
#endif
#ifdef SDL_HAVE_BLIT_N
        else {
            blit = SDL_CalculateBlitN(surface);
        }
#endif
    }
#ifdef SDL_HAVE_BLIT_AUTO
    if (!blit) {
        SDL_PixelFormat src_format = surface->format;
        SDL_PixelFormat dst_format = dst->format;

        blit =
            SDL_ChooseBlitFunc(src_format, dst_format, map->info.flags,
                               SDL_GeneratedBlitFuncTable);
    }
#endif

#ifndef TEST_SLOW_BLIT
    if (!blit)
#endif
    {
        SDL_PixelFormat src_format = surface->format;
        SDL_PixelFormat dst_format = dst->format;

        if ((!SDL_ISPIXELFORMAT_INDEXED(src_format) ||
             (src_format == SDL_PIXELFORMAT_INDEX8 && surface->palette)) &&
            !SDL_ISPIXELFORMAT_FOURCC(src_format) &&
            (!SDL_ISPIXELFORMAT_INDEXED(dst_format) ||
             (dst_format == SDL_PIXELFORMAT_INDEX8 && dst->palette)) &&
            !SDL_ISPIXELFORMAT_FOURCC(dst_format)) {
            blit = SDL_Blit_Slow;
        }
    }
    map->data = (void *)blit;

    // Make sure we have a blit function
    if (!blit) {
        SDL_InvalidateMap(map);
        return SDL_SetError("Blit combination not supported");
    }

    return true;
}