src/video/SDL_surface.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_sysvideo.h"
#include "SDL_blit.h"
#include "SDL_RLEaccel_c.h"
#include "SDL_pixels_c.h"
#include "SDL_yuv_c.h"
#include "../render/SDL_sysrender.h"


/* Check to make sure we can safely check multiplication of surface w and pitch and it won't overflow size_t */
SDL_COMPILE_TIME_ASSERT(surface_size_assumptions,
    sizeof(int) == sizeof(Sint32) && sizeof(size_t) >= sizeof(Sint32));

/* Public routines */

/*
 * Calculate the pad-aligned scanline width of a surface
 */
static Sint64
SDL_CalculatePitch(Uint32 format, int width)
{
    Sint64 pitch;

    if (SDL_ISPIXELFORMAT_FOURCC(format) || SDL_BITSPERPIXEL(format) >= 8) {
        pitch = ((Sint64)width * SDL_BYTESPERPIXEL(format));
    } else {
        pitch = (((Sint64)width * SDL_BITSPERPIXEL(format)) + 7) / 8;
    }
    pitch = (pitch + 3) & ~3;   /* 4-byte aligning for speed */
    return pitch;
}

/*
 * Create an empty RGB surface of the appropriate depth using the given
 * enum SDL_PIXELFORMAT_* format
 */
SDL_Surface *
SDL_CreateRGBSurfaceWithFormat(Uint32 flags, int width, int height, int depth,
                               Uint32 format)
{
    Sint64 pitch;
    SDL_Surface *surface;

    /* The flags are no longer used, make the compiler happy */
    (void)flags;

    pitch = SDL_CalculatePitch(format, width);
    if (pitch < 0 || pitch > SDL_MAX_SINT32) {
        /* Overflow... */
        SDL_OutOfMemory();
        return NULL;
    }

    /* Allocate the surface */
    surface = (SDL_Surface *) SDL_calloc(1, sizeof(*surface));
    if (surface == NULL) {
        SDL_OutOfMemory();
        return NULL;
    }

    surface->format = SDL_AllocFormat(format);
    if (!surface->format) {
        SDL_FreeSurface(surface);
        return NULL;
    }
    surface->w = width;
    surface->h = height;
    surface->pitch = (int)pitch;
    SDL_SetClipRect(surface, NULL);

    if (SDL_ISPIXELFORMAT_INDEXED(surface->format->format)) {
        SDL_Palette *palette =
            SDL_AllocPalette((1 << surface->format->BitsPerPixel));
        if (!palette) {
            SDL_FreeSurface(surface);
            return NULL;
        }
        if (palette->ncolors == 2) {
            /* Create a black and white bitmap palette */
            palette->colors[0].r = 0xFF;
            palette->colors[0].g = 0xFF;
            palette->colors[0].b = 0xFF;
            palette->colors[1].r = 0x00;
            palette->colors[1].g = 0x00;
            palette->colors[1].b = 0x00;
        }
        SDL_SetSurfacePalette(surface, palette);
        SDL_FreePalette(palette);
    }

    /* Get the pixels */
    if (surface->w && surface->h) {
        /* Assumptions checked in surface_size_assumptions assert above */
        Sint64 size = ((Sint64)surface->h * surface->pitch);
        if (size < 0 || size > SDL_MAX_SINT32) {
            /* Overflow... */
            SDL_FreeSurface(surface);
            SDL_OutOfMemory();
            return NULL;
        }

        surface->pixels = SDL_SIMDAlloc((size_t)size);
        if (!surface->pixels) {
            SDL_FreeSurface(surface);
            SDL_OutOfMemory();
            return NULL;
        }
        surface->flags |= SDL_SIMD_ALIGNED;
        /* This is important for bitmaps */
        SDL_memset(surface->pixels, 0, surface->h * surface->pitch);
    }

    /* Allocate an empty mapping */
    surface->map = SDL_AllocBlitMap();
    if (!surface->map) {
        SDL_FreeSurface(surface);
        return NULL;
    }

    /* By default surface with an alpha mask are set up for blending */
    if (surface->format->Amask) {
        SDL_SetSurfaceBlendMode(surface, SDL_BLENDMODE_BLEND);
    }

    /* The surface is ready to go */
    surface->refcount = 1;
    return surface;
}

/*
 * Create an empty RGB surface of the appropriate depth
 */
SDL_Surface *
SDL_CreateRGBSurface(Uint32 flags,
                     int width, int height, int depth,
                     Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask)
{
    Uint32 format;

    /* Get the pixel format */
    format = SDL_MasksToPixelFormatEnum(depth, Rmask, Gmask, Bmask, Amask);
    if (format == SDL_PIXELFORMAT_UNKNOWN) {
        SDL_SetError("Unknown pixel format");
        return NULL;
    }

    return SDL_CreateRGBSurfaceWithFormat(flags, width, height, depth, format);
}

/*
 * Create an RGB surface from an existing memory buffer
 */
SDL_Surface *
SDL_CreateRGBSurfaceFrom(void *pixels,
                         int width, int height, int depth, int pitch,
                         Uint32 Rmask, Uint32 Gmask, Uint32 Bmask,
                         Uint32 Amask)
{
    SDL_Surface *surface;

    surface = SDL_CreateRGBSurface(0, 0, 0, depth, Rmask, Gmask, Bmask, Amask);
    if (surface != NULL) {
        surface->flags |= SDL_PREALLOC;
        surface->pixels = pixels;
        surface->w = width;
        surface->h = height;
        surface->pitch = pitch;
        SDL_SetClipRect(surface, NULL);
    }
    return surface;
}

/*
 * Create an RGB surface from an existing memory buffer using the given given
 * enum SDL_PIXELFORMAT_* format
 */
SDL_Surface *
SDL_CreateRGBSurfaceWithFormatFrom(void *pixels,
                         int width, int height, int depth, int pitch,
                         Uint32 format)
{
    SDL_Surface *surface;

    surface = SDL_CreateRGBSurfaceWithFormat(0, 0, 0, depth, format);
    if (surface != NULL) {
        surface->flags |= SDL_PREALLOC;
        surface->pixels = pixels;
        surface->w = width;
        surface->h = height;
        surface->pitch = pitch;
        SDL_SetClipRect(surface, NULL);
    }
    return surface;
}

int
SDL_SetSurfacePalette(SDL_Surface * surface, SDL_Palette * palette)
{
    if (!surface) {
        return SDL_SetError("SDL_SetSurfacePalette() passed a NULL surface");
    }
    if (SDL_SetPixelFormatPalette(surface->format, palette) < 0) {
        return -1;
    }
    SDL_InvalidateMap(surface->map);

    return 0;
}

int
SDL_SetSurfaceRLE(SDL_Surface * surface, int flag)
{
    int flags;

    if (!surface) {
        return -1;
    }

    flags = surface->map->info.flags;
    if (flag) {
        surface->map->info.flags |= SDL_COPY_RLE_DESIRED;
    } else {
        surface->map->info.flags &= ~SDL_COPY_RLE_DESIRED;
    }
    if (surface->map->info.flags != flags) {
        SDL_InvalidateMap(surface->map);
    }
    return 0;
}

SDL_bool
SDL_HasSurfaceRLE(SDL_Surface * surface)
{
    if (!surface) {
        return SDL_FALSE;
    }

    if (!(surface->map->info.flags & SDL_COPY_RLE_DESIRED)) {
        return SDL_FALSE;
    }

    return SDL_TRUE;
}

int
SDL_SetColorKey(SDL_Surface * surface, int flag, Uint32 key)
{
    int flags;

    if (!surface) {
        return SDL_InvalidParamError("surface");
    }

    if (surface->format->palette && key >= ((Uint32) surface->format->palette->ncolors)) {
        return SDL_InvalidParamError("key");
    }

    if (flag & SDL_RLEACCEL) {
        SDL_SetSurfaceRLE(surface, 1);
    }

    flags = surface->map->info.flags;
    if (flag) {
        surface->map->info.flags |= SDL_COPY_COLORKEY;
        surface->map->info.colorkey = key;
    } else {
        surface->map->info.flags &= ~SDL_COPY_COLORKEY;
    }
    if (surface->map->info.flags != flags) {
        SDL_InvalidateMap(surface->map);
    }

    return 0;
}

SDL_bool
SDL_HasColorKey(SDL_Surface * surface)
{
    if (!surface) {
        return SDL_FALSE;
    }

    if (!(surface->map->info.flags & SDL_COPY_COLORKEY)) {
        return SDL_FALSE;
    }

    return SDL_TRUE;
}

int
SDL_GetColorKey(SDL_Surface * surface, Uint32 * key)
{
    if (!surface) {
        return SDL_InvalidParamError("surface");
    }

    if (!(surface->map->info.flags & SDL_COPY_COLORKEY)) {
        return SDL_SetError("Surface doesn't have a colorkey");
    }

    if (key) {
        *key = surface->map->info.colorkey;
    }
    return 0;
}

/* This is a fairly slow function to switch from colorkey to alpha
   NB: it doesn't handle bpp 1 or 3, because they have no alpha channel */
static void
SDL_ConvertColorkeyToAlpha(SDL_Surface * surface, SDL_bool ignore_alpha)
{
    int x, y, bpp;

    if (!surface) {
        return;
    }

    if (!(surface->map->info.flags & SDL_COPY_COLORKEY) ||
        !surface->format->Amask) {
        return;
    }

    bpp = surface->format->BytesPerPixel;

    SDL_LockSurface(surface);

    if (bpp == 2) {
        Uint16 *row, *spot;
        Uint16 ckey = (Uint16) surface->map->info.colorkey;
        Uint16 mask = (Uint16) (~surface->format->Amask);

        /* Ignore, or not, alpha in colorkey comparison */
        if (ignore_alpha) {
            ckey &= mask;
            row = (Uint16 *) surface->pixels;
            for (y = surface->h; y--;) {
                spot = row;
                for (x = surface->w; x--;) {
                    if ((*spot & mask) == ckey) {
                        *spot &= mask;
                    }
                    ++spot;
                }
                row += surface->pitch / 2;
            }
        } else {
            row = (Uint16 *) surface->pixels;
            for (y = surface->h; y--;) {
                spot = row;
                for (x = surface->w; x--;) {
                    if (*spot == ckey) {
                        *spot &= mask;
                    }
                    ++spot;
                }
                row += surface->pitch / 2;
            }
        }
    } else if (bpp == 4) {
        Uint32 *row, *spot;
        Uint32 ckey = surface->map->info.colorkey;
        Uint32 mask = ~surface->format->Amask;

        /* Ignore, or not, alpha in colorkey comparison */
        if (ignore_alpha) {
            ckey &= mask;
            row = (Uint32 *) surface->pixels;
            for (y = surface->h; y--;) {
                spot = row;
                for (x = surface->w; x--;) {
                    if ((*spot & mask) == ckey) {
                        *spot &= mask;
                    }
                    ++spot;
                }
                row += surface->pitch / 4;
            }
        } else {
            row = (Uint32 *) surface->pixels;
            for (y = surface->h; y--;) {
                spot = row;
                for (x = surface->w; x--;) {
                    if (*spot == ckey) {
                        *spot &= mask;
                    }
                    ++spot;
                }
                row += surface->pitch / 4;
            }
        }
    }

    SDL_UnlockSurface(surface);

    SDL_SetColorKey(surface, 0, 0);
    SDL_SetSurfaceBlendMode(surface, SDL_BLENDMODE_BLEND);
}

int
SDL_SetSurfaceColorMod(SDL_Surface * surface, Uint8 r, Uint8 g, Uint8 b)
{
    int flags;

    if (!surface) {
        return -1;
    }

    surface->map->info.r = r;
    surface->map->info.g = g;
    surface->map->info.b = b;

    flags = surface->map->info.flags;
    if (r != 0xFF || g != 0xFF || b != 0xFF) {
        surface->map->info.flags |= SDL_COPY_MODULATE_COLOR;
    } else {
        surface->map->info.flags &= ~SDL_COPY_MODULATE_COLOR;
    }
    if (surface->map->info.flags != flags) {
        SDL_InvalidateMap(surface->map);
    }
    return 0;
}


int
SDL_GetSurfaceColorMod(SDL_Surface * surface, Uint8 * r, Uint8 * g, Uint8 * b)
{
    if (!surface) {
        return -1;
    }

    if (r) {
        *r = surface->map->info.r;
    }
    if (g) {
        *g = surface->map->info.g;
    }
    if (b) {
        *b = surface->map->info.b;
    }
    return 0;
}

int
SDL_SetSurfaceAlphaMod(SDL_Surface * surface, Uint8 alpha)
{
    int flags;

    if (!surface) {
        return -1;
    }

    surface->map->info.a = alpha;

    flags = surface->map->info.flags;
    if (alpha != 0xFF) {
        surface->map->info.flags |= SDL_COPY_MODULATE_ALPHA;
    } else {
        surface->map->info.flags &= ~SDL_COPY_MODULATE_ALPHA;
    }
    if (surface->map->info.flags != flags) {
        SDL_InvalidateMap(surface->map);
    }
    return 0;
}

int
SDL_GetSurfaceAlphaMod(SDL_Surface * surface, Uint8 * alpha)
{
    if (!surface) {
        return -1;
    }

    if (alpha) {
        *alpha = surface->map->info.a;
    }
    return 0;
}

int
SDL_SetSurfaceBlendMode(SDL_Surface * surface, SDL_BlendMode blendMode)
{
    int flags, status;

    if (!surface) {
        return -1;
    }

    status = 0;
    flags = surface->map->info.flags;
    surface->map->info.flags &=
        ~(SDL_COPY_BLEND | SDL_COPY_ADD | SDL_COPY_MOD | SDL_COPY_MUL);
    switch (blendMode) {
    case SDL_BLENDMODE_NONE:
        break;
    case SDL_BLENDMODE_BLEND:
        surface->map->info.flags |= SDL_COPY_BLEND;
        break;
    case SDL_BLENDMODE_ADD:
        surface->map->info.flags |= SDL_COPY_ADD;
        break;
    case SDL_BLENDMODE_MOD:
        surface->map->info.flags |= SDL_COPY_MOD;
        break;
    case SDL_BLENDMODE_MUL:
        surface->map->info.flags |= SDL_COPY_MUL;
        break;
    default:
        status = SDL_Unsupported();
        break;
    }

    if (surface->map->info.flags != flags) {
        SDL_InvalidateMap(surface->map);
    }

    return status;
}

int
SDL_GetSurfaceBlendMode(SDL_Surface * surface, SDL_BlendMode *blendMode)
{
    if (!surface) {
        return -1;
    }

    if (!blendMode) {
        return 0;
    }

    switch (surface->map->
            info.flags & (SDL_COPY_BLEND | SDL_COPY_ADD | SDL_COPY_MOD | SDL_COPY_MUL)) {
    case SDL_COPY_BLEND:
        *blendMode = SDL_BLENDMODE_BLEND;
        break;
    case SDL_COPY_ADD:
        *blendMode = SDL_BLENDMODE_ADD;
        break;
    case SDL_COPY_MOD:
        *blendMode = SDL_BLENDMODE_MOD;
        break;
    case SDL_COPY_MUL:
        *blendMode = SDL_BLENDMODE_MUL;
        break;
    default:
        *blendMode = SDL_BLENDMODE_NONE;
        break;
    }
    return 0;
}

SDL_bool
SDL_SetClipRect(SDL_Surface * surface, const SDL_Rect * rect)
{
    SDL_Rect full_rect;

    /* Don't do anything if there's no surface to act on */
    if (!surface) {
        return SDL_FALSE;
    }

    /* Set up the full surface rectangle */
    full_rect.x = 0;
    full_rect.y = 0;
    full_rect.w = surface->w;
    full_rect.h = surface->h;

    /* Set the clipping rectangle */
    if (!rect) {
        surface->clip_rect = full_rect;
        return SDL_TRUE;
    }
    return SDL_IntersectRect(rect, &full_rect, &surface->clip_rect);
}

void
SDL_GetClipRect(SDL_Surface * surface, SDL_Rect * rect)
{
    if (surface && rect) {
        *rect = surface->clip_rect;
    }
}

/*
 * Set up a blit between two surfaces -- split into three parts:
 * The upper part, SDL_UpperBlit(), performs clipping and rectangle
 * verification.  The lower part is a pointer to a low level
 * accelerated blitting function.
 *
 * These parts are separated out and each used internally by this
 * library in the optimimum places.  They are exported so that if
 * you know exactly what you are doing, you can optimize your code
 * by calling the one(s) you need.
 */
int
SDL_LowerBlit(SDL_Surface * src, SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
    /* Check to make sure the blit mapping is valid */
    if ((src->map->dst != dst) ||
        (dst->format->palette &&
         src->map->dst_palette_version != dst->format->palette->version) ||
        (src->format->palette &&
         src->map->src_palette_version != src->format->palette->version)) {
        if (SDL_MapSurface(src, dst) < 0) {
            return (-1);
        }
        /* just here for debugging */
/*         printf */
/*             ("src = 0x%08X src->flags = %08X src->map->info.flags = %08x\ndst = 0x%08X dst->flags = %08X dst->map->info.flags = %08X\nsrc->map->blit = 0x%08x\n", */
/*              src, dst->flags, src->map->info.flags, dst, dst->flags, */
/*              dst->map->info.flags, src->map->blit); */
    }
    return (src->map->blit(src, srcrect, dst, dstrect));
}


int
SDL_UpperBlit(SDL_Surface * src, const SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
    SDL_Rect fulldst;
    int srcx, srcy, w, h;

    /* Make sure the surfaces aren't locked */
    if (!src || !dst) {
        return SDL_SetError("SDL_UpperBlit: passed a NULL surface");
    }
    if (src->locked || dst->locked) {
        return SDL_SetError("Surfaces must not be locked during blit");
    }

    /* If the destination rectangle is NULL, use the entire dest surface */
    if (dstrect == NULL) {
        fulldst.x = fulldst.y = 0;
        fulldst.w = dst->w;
        fulldst.h = dst->h;
        dstrect = &fulldst;
    }

    /* clip the source rectangle to the source surface */
    if (srcrect) {
        int maxw, maxh;

        srcx = srcrect->x;
        w = srcrect->w;
        if (srcx < 0) {
            w += srcx;
            dstrect->x -= srcx;
            srcx = 0;
        }
        maxw = src->w - srcx;
        if (maxw < w)
            w = maxw;

        srcy = srcrect->y;
        h = srcrect->h;
        if (srcy < 0) {
            h += srcy;
            dstrect->y -= srcy;
            srcy = 0;
        }
        maxh = src->h - srcy;
        if (maxh < h)
            h = maxh;

    } else {
        srcx = srcy = 0;
        w = src->w;
        h = src->h;
    }

    /* clip the destination rectangle against the clip rectangle */
    {
        SDL_Rect *clip = &dst->clip_rect;
        int dx, dy;

        dx = clip->x - dstrect->x;
        if (dx > 0) {
            w -= dx;
            dstrect->x += dx;
            srcx += dx;
        }
        dx = dstrect->x + w - clip->x - clip->w;
        if (dx > 0)
            w -= dx;

        dy = clip->y - dstrect->y;
        if (dy > 0) {
            h -= dy;
            dstrect->y += dy;
            srcy += dy;
        }
        dy = dstrect->y + h - clip->y - clip->h;
        if (dy > 0)
            h -= dy;
    }

    /* Switch back to a fast blit if we were previously stretching */
    if (src->map->info.flags & SDL_COPY_NEAREST) {
        src->map->info.flags &= ~SDL_COPY_NEAREST;
        SDL_InvalidateMap(src->map);
    }

    if (w > 0 && h > 0) {
        SDL_Rect sr;
        sr.x = srcx;
        sr.y = srcy;
        sr.w = dstrect->w = w;
        sr.h = dstrect->h = h;
        return SDL_LowerBlit(src, &sr, dst, dstrect);
    }
    dstrect->w = dstrect->h = 0;
    return 0;
}

int
SDL_UpperBlitScaled(SDL_Surface * src, const SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect)
{
    return SDL_PrivateUpperBlitScaled(src, srcrect, dst, dstrect, SDL_ScaleModeNearest);
}


int
SDL_PrivateUpperBlitScaled(SDL_Surface * src, const SDL_Rect * srcrect,
              SDL_Surface * dst, SDL_Rect * dstrect, SDL_ScaleMode scaleMode)
{
    double src_x0, src_y0, src_x1, src_y1;
    double dst_x0, dst_y0, dst_x1, dst_y1;
    SDL_Rect final_src, final_dst;
    double scaling_w, scaling_h;
    int src_w, src_h;
    int dst_w, dst_h;

    /* Make sure the surfaces aren't locked */
    if (!src || !dst) {
        return SDL_SetError("SDL_UpperBlitScaled: passed a NULL surface");
    }
    if (src->locked || dst->locked) {
        return SDL_SetError("Surfaces must not be locked during blit");
    }

    if (NULL == srcrect) {
        src_w = src->w;
        src_h = src->h;
    } else {
        src_w = srcrect->w;
        src_h = srcrect->h;
    }

    if (NULL == dstrect) {
        dst_w = dst->w;
        dst_h = dst->h;
    } else {
        dst_w = dstrect->w;
        dst_h = dstrect->h;
    }

    if (dst_w == src_w && dst_h == src_h) {
        /* No scaling, defer to regular blit */
        return SDL_BlitSurface(src, srcrect, dst, dstrect);
    }

    scaling_w = (double)dst_w / src_w;
    scaling_h = (double)dst_h / src_h;

    if (NULL == dstrect) {
        dst_x0 = 0;
        dst_y0 = 0;
        dst_x1 = dst_w;
        dst_y1 = dst_h;
    } else {
        dst_x0 = dstrect->x;
        dst_y0 = dstrect->y;
        dst_x1 = dst_x0 + dst_w;
        dst_y1 = dst_y0 + dst_h;
    }

    if (NULL == srcrect) {
        src_x0 = 0;
        src_y0 = 0;
        src_x1 = src_w;
        src_y1 = src_h;
    } else {
        src_x0 = srcrect->x;
        src_y0 = srcrect->y;
        src_x1 = src_x0 + src_w;
        src_y1 = src_y0 + src_h;

        /* Clip source rectangle to the source surface */

        if (src_x0 < 0) {
            dst_x0 -= src_x0 * scaling_w;
            src_x0 = 0;
        }

        if (src_x1 > src->w) {
            dst_x1 -= (src_x1 - src->w) * scaling_w;
            src_x1 = src->w;
        }

        if (src_y0 < 0) {
            dst_y0 -= src_y0 * scaling_h;
            src_y0 = 0;
        }

        if (src_y1 > src->h) {
            dst_y1 -= (src_y1 - src->h) * scaling_h;
            src_y1 = src->h;
        }
    }

    /* Clip destination rectangle to the clip rectangle */

    /* Translate to clip space for easier calculations */
    dst_x0 -= dst->clip_rect.x;
    dst_x1 -= dst->clip_rect.x;
    dst_y0 -= dst->clip_rect.y;
    dst_y1 -= dst->clip_rect.y;

    if (dst_x0 < 0) {
        src_x0 -= dst_x0 / scaling_w;
        dst_x0 = 0;
    }

    if (dst_x1 > dst->clip_rect.w) {
        src_x1 -= (dst_x1 - dst->clip_rect.w) / scaling_w;
        dst_x1 = dst->clip_rect.w;
    }

    if (dst_y0 < 0) {
        src_y0 -= dst_y0 / scaling_h;
        dst_y0 = 0;
    }

    if (dst_y1 > dst->clip_rect.h) {
        src_y1 -= (dst_y1 - dst->clip_rect.h) / scaling_h;
        dst_y1 = dst->clip_rect.h;
    }

    /* Translate back to surface coordinates */
    dst_x0 += dst->clip_rect.x;
    dst_x1 += dst->clip_rect.x;
    dst_y0 += dst->clip_rect.y;
    dst_y1 += dst->clip_rect.y;

    final_src.x = (int)SDL_round(src_x0);
    final_src.y = (int)SDL_round(src_y0);
    final_src.w = (int)SDL_round(src_x1 - src_x0);
    final_src.h = (int)SDL_round(src_y1 - src_y0);

    final_dst.x = (int)SDL_round(dst_x0);
    final_dst.y = (int)SDL_round(dst_y0);
    final_dst.w = (int)SDL_round(dst_x1 - dst_x0);
    final_dst.h = (int)SDL_round(dst_y1 - dst_y0);

    /* Clip again */
    {
        SDL_Rect tmp;
        tmp.x = 0;
        tmp.y = 0;
        tmp.w = src->w;
        tmp.h = src->h;
        SDL_IntersectRect(&tmp, &final_src, &final_src);
    }

    /* Clip again */
    SDL_IntersectRect(&dst->clip_rect, &final_dst, &final_dst);

    if (dstrect) {
        *dstrect = final_dst;
    }

    if (final_dst.w == 0 || final_dst.h == 0 ||
        final_src.w <= 0 || final_src.h <= 0) {
        /* No-op. */
        return 0;
    }

    return SDL_PrivateLowerBlitScaled(src, &final_src, dst, &final_dst, scaleMode);
}

/**
 *  This is a semi-private blit function and it performs low-level surface
 *  scaled blitting only.
 */
int
SDL_LowerBlitScaled(SDL_Surface * src, SDL_Rect * srcrect,
                SDL_Surface * dst, SDL_Rect * dstrect)
{
    return SDL_PrivateLowerBlitScaled(src, srcrect, dst, dstrect, SDL_ScaleModeNearest);
}

int
SDL_PrivateLowerBlitScaled(SDL_Surface * src, SDL_Rect * srcrect,
                SDL_Surface * dst, SDL_Rect * dstrect, SDL_ScaleMode scaleMode)
{
    static const Uint32 complex_copy_flags = (
        SDL_COPY_MODULATE_COLOR | SDL_COPY_MODULATE_ALPHA |
        SDL_COPY_BLEND | SDL_COPY_ADD | SDL_COPY_MOD | SDL_COPY_MUL |
        SDL_COPY_COLORKEY
    );

    if (srcrect->w > SDL_MAX_UINT16 || srcrect->h > SDL_MAX_UINT16 ||
        dstrect->w > SDL_MAX_UINT16 || dstrect->h > SDL_MAX_UINT16) {
        return SDL_SetError("Size too large for scaling");
    }

    if (!(src->map->info.flags & SDL_COPY_NEAREST)) {
        src->map->info.flags |= SDL_COPY_NEAREST;
        SDL_InvalidateMap(src->map);
    }

    if (scaleMode == SDL_ScaleModeNearest) {
        if ( !(src->map->info.flags & complex_copy_flags) &&
                src->format->format == dst->format->format &&
                !SDL_ISPIXELFORMAT_INDEXED(src->format->format) ) {
            return SDL_SoftStretch( src, srcrect, dst, dstrect );
        } else {
            return SDL_LowerBlit( src, srcrect, dst, dstrect );
        }
    } else {
        if ( !(src->map->info.flags & complex_copy_flags) &&
             src->format->format == dst->format->format &&
             !SDL_ISPIXELFORMAT_INDEXED(src->format->format) &&
             src->format->BytesPerPixel == 4 &&
             src->format->format != SDL_PIXELFORMAT_ARGB2101010) {
            /* fast path */
            return SDL_SoftStretchLinear(src, srcrect, dst, dstrect);
        } else {
            /* Use intermediate surface(s) */
            SDL_Surface *tmp1 = NULL;
            int ret;
            SDL_Rect srcrect2;
            int is_complex_copy_flags = (src->map->info.flags & complex_copy_flags);

            Uint32 flags;
            Uint8 r, g, b;
            Uint8 alpha;
            SDL_BlendMode blendMode;

            /* Save source infos */
            flags = src->flags;
            SDL_GetSurfaceColorMod(src, &r, &g, &b);
            SDL_GetSurfaceAlphaMod(src, &alpha);
            SDL_GetSurfaceBlendMode(src, &blendMode);
            srcrect2.x = srcrect->x;
            srcrect2.y = srcrect->y;
            srcrect2.w = srcrect->w;
            srcrect2.h = srcrect->h;

            /* Change source format if not appropriate for scaling */
            if (src->format->BytesPerPixel != 4 || src->format->format == SDL_PIXELFORMAT_ARGB2101010) {
                SDL_Rect tmprect;
                int fmt;
                tmprect.x = 0;
                tmprect.y = 0;
                tmprect.w = src->w;
                tmprect.h = src->h;
                if (dst->format->BytesPerPixel == 4 && dst->format->format != SDL_PIXELFORMAT_ARGB2101010) {
                    fmt = dst->format->format;
                } else {
                    fmt = SDL_PIXELFORMAT_ARGB8888;
                }
                tmp1 = SDL_CreateRGBSurfaceWithFormat(flags, src->w, src->h, 0, fmt);
                SDL_LowerBlit(src, srcrect, tmp1, &tmprect);


                srcrect2.x = 0;
                srcrect2.y = 0;
                SDL_SetSurfaceColorMod(tmp1, r, g, b);
                SDL_SetSurfaceAlphaMod(tmp1, alpha);
                SDL_SetSurfaceBlendMode(tmp1, blendMode);

                src = tmp1;
            }

            /* Intermediate scaling */
            if (is_complex_copy_flags || src->format->format != dst->format->format) {
                SDL_Rect tmprect;
                SDL_Surface *tmp2 = SDL_CreateRGBSurfaceWithFormat(flags, dstrect->w, dstrect->h, 0, src->format->format);
                SDL_SoftStretchLinear(src, &srcrect2, tmp2, NULL);

                SDL_SetSurfaceColorMod(tmp2, r, g, b);
                SDL_SetSurfaceAlphaMod(tmp2, alpha);
                SDL_SetSurfaceBlendMode(tmp2, blendMode);

                tmprect.x = 0;
                tmprect.y = 0;
                tmprect.w = dstrect->w;
                tmprect.h = dstrect->h;
                ret = SDL_LowerBlit(tmp2, &tmprect, dst, dstrect);
                SDL_FreeSurface(tmp2);
            } else {
                ret = SDL_SoftStretchLinear(src, &srcrect2, dst, dstrect);
            }

            SDL_FreeSurface(tmp1);
            return ret;
        }
    }
}

/*
 * Lock a surface to directly access the pixels
 */
int
SDL_LockSurface(SDL_Surface * surface)
{
    if (!surface->locked) {
#if SDL_HAVE_RLE
        /* Perform the lock */
        if (surface->flags & SDL_RLEACCEL) {
            SDL_UnRLESurface(surface, 1);
            surface->flags |= SDL_RLEACCEL;     /* save accel'd state */
        }
#endif
    }

    /* Increment the surface lock count, for recursive locks */
    ++surface->locked;

    /* Ready to go.. */
    return (0);
}

/*
 * Unlock a previously locked surface
 */
void
SDL_UnlockSurface(SDL_Surface * surface)
{
    /* Only perform an unlock if we are locked */
    if (!surface->locked || (--surface->locked > 0)) {
        return;
    }

#if SDL_HAVE_RLE
    /* Update RLE encoded surface with new data */
    if ((surface->flags & SDL_RLEACCEL) == SDL_RLEACCEL) {
        surface->flags &= ~SDL_RLEACCEL;        /* stop lying */
        SDL_RLESurface(surface);
    }
#endif
}

/*
 * Creates a new surface identical to the existing surface
 */
SDL_Surface *
SDL_DuplicateSurface(SDL_Surface * surface)
{
    return SDL_ConvertSurface(surface, surface->format, surface->flags);
}

/*
 * Convert a surface into the specified pixel format.
 */
SDL_Surface *
SDL_ConvertSurface(SDL_Surface * surface, const SDL_PixelFormat * format,
                   Uint32 flags)
{
    SDL_Surface *convert;
    Uint32 copy_flags;
    SDL_Color copy_color;
    SDL_Rect bounds;
    int ret;
    SDL_bool palette_ck_transform = SDL_FALSE;
    int palette_ck_value = 0;
    SDL_bool palette_has_alpha = SDL_FALSE;
    Uint8 *palette_saved_alpha = NULL;
    int palette_saved_alpha_ncolors = 0;

    if (!surface) {
        SDL_InvalidParamError("surface");
        return NULL;
    }
    if (!format) {
        SDL_InvalidParamError("format");
        return NULL;
    }

    /* Check for empty destination palette! (results in empty image) */
    if (format->palette != NULL) {
        int i;
        for (i = 0; i < format->palette->ncolors; ++i) {
            if ((format->palette->colors[i].r != 0xFF) ||
                (format->palette->colors[i].g != 0xFF) ||
                (format->palette->colors[i].b != 0xFF))
                break;
        }
        if (i == format->palette->ncolors) {
            SDL_SetError("Empty destination palette");
            return (NULL);
        }
    }

    /* Create a new surface with the desired format */
    convert = SDL_CreateRGBSurface(flags, surface->w, surface->h,
                                   format->BitsPerPixel, format->Rmask,
                                   format->Gmask, format->Bmask,
                                   format->Amask);
    if (convert == NULL) {
        return (NULL);
    }

    /* Copy the palette if any */
    if (format->palette && convert->format->palette) {
        SDL_memcpy(convert->format->palette->colors,
                   format->palette->colors,
                   format->palette->ncolors * sizeof(SDL_Color));
        convert->format->palette->ncolors = format->palette->ncolors;
    }

    /* Save the original copy flags */
    copy_flags = surface->map->info.flags;
    copy_color.r = surface->map->info.r;
    copy_color.g = surface->map->info.g;
    copy_color.b = surface->map->info.b;
    copy_color.a = surface->map->info.a;
    surface->map->info.r = 0xFF;
    surface->map->info.g = 0xFF;
    surface->map->info.b = 0xFF;
    surface->map->info.a = 0xFF;
    surface->map->info.flags = (copy_flags & (SDL_COPY_RLE_COLORKEY | SDL_COPY_RLE_ALPHAKEY));
    SDL_InvalidateMap(surface->map);

    /* Copy over the image data */
    bounds.x = 0;
    bounds.y = 0;
    bounds.w = surface->w;
    bounds.h = surface->h;

    /* Source surface has a palette with no real alpha (0 or OPAQUE).
     * Destination format has alpha.
     * -> set alpha channel to be opaque */
    if (surface->format->palette && format->Amask) {
        SDL_bool set_opaque = SDL_FALSE;

        SDL_bool is_opaque, has_alpha_channel;
        SDL_DetectPalette(surface->format->palette, &is_opaque, &has_alpha_channel);

        if (is_opaque) {
            if (!has_alpha_channel) {
                set_opaque = SDL_TRUE;
            }
        } else {
            palette_has_alpha = SDL_TRUE;
        }

        /* Set opaque and backup palette alpha values */
        if (set_opaque) {
            int i;
            palette_saved_alpha_ncolors = surface->format->palette->ncolors;
            palette_saved_alpha = SDL_stack_alloc(Uint8, palette_saved_alpha_ncolors);
            for (i = 0; i < palette_saved_alpha_ncolors; i++) {
                palette_saved_alpha[i] = surface->format->palette->colors[i].a;
                surface->format->palette->colors[i].a = SDL_ALPHA_OPAQUE;
            }
        }
    }

    /* Transform colorkey to alpha. for cases where source palette has duplicate values, and colorkey is one of them */
    if (copy_flags & SDL_COPY_COLORKEY) {
        if (surface->format->palette && !format->palette) {
            palette_ck_transform = SDL_TRUE;
            palette_has_alpha = SDL_TRUE;
            palette_ck_value = surface->format->palette->colors[surface->map->info.colorkey].a;
            surface->format->palette->colors[surface->map->info.colorkey].a = SDL_ALPHA_TRANSPARENT;
        }
    }

    ret = SDL_LowerBlit(surface, &bounds, convert, &bounds);

    /* Restore colorkey alpha value */
    if (palette_ck_transform) {
        surface->format->palette->colors[surface->map->info.colorkey].a = palette_ck_value;
    }

    /* Restore palette alpha values */
    if (palette_saved_alpha) {
        int i;
        for (i = 0; i < palette_saved_alpha_ncolors; i++) {
            surface->format->palette->colors[i].a = palette_saved_alpha[i];
        }
        SDL_stack_free(palette_saved_alpha);
    }

    /* Clean up the original surface, and update converted surface */
    convert->map->info.r = copy_color.r;
    convert->map->info.g = copy_color.g;
    convert->map->info.b = copy_color.b;
    convert->map->info.a = copy_color.a;
    convert->map->info.flags =
        (copy_flags &
         ~(SDL_COPY_COLORKEY | SDL_COPY_BLEND
           | SDL_COPY_RLE_DESIRED | SDL_COPY_RLE_COLORKEY |
           SDL_COPY_RLE_ALPHAKEY));
    surface->map->info.r = copy_color.r;
    surface->map->info.g = copy_color.g;
    surface->map->info.b = copy_color.b;
    surface->map->info.a = copy_color.a;
    surface->map->info.flags = copy_flags;
    SDL_InvalidateMap(surface->map);

    /* SDL_LowerBlit failed, and so the conversion */
    if (ret < 0) {
        SDL_FreeSurface(convert);
        return NULL;
    }

    if (copy_flags & SDL_COPY_COLORKEY) {
        SDL_bool set_colorkey_by_color = SDL_FALSE;
        SDL_bool convert_colorkey = SDL_TRUE;

        if (surface->format->palette) {
            if (format->palette &&
                surface->format->palette->ncolors <= format->palette->ncolors &&
                (SDL_memcmp(surface->format->palette->colors, format->palette->colors,
                  surface->format->palette->ncolors * sizeof(SDL_Color)) == 0)) {
                /* The palette is identical, just set the same colorkey */
                SDL_SetColorKey(convert, 1, surface->map->info.colorkey);
            } else if (!format->palette) {
                if (format->Amask) {
                    /* No need to add the colorkey, transparency is in the alpha channel*/
                } else {
                    /* Only set the colorkey information */
                    set_colorkey_by_color = SDL_TRUE;
                    convert_colorkey = SDL_FALSE;
                }
            } else {
                set_colorkey_by_color = SDL_TRUE;
            }
        } else {
            set_colorkey_by_color = SDL_TRUE;
        }

        if (set_colorkey_by_color) {
            SDL_Surface *tmp;
            SDL_Surface *tmp2;
            int converted_colorkey = 0;

            /* Create a dummy surface to get the colorkey converted */
            tmp = SDL_CreateRGBSurface(0, 1, 1,
                                   surface->format->BitsPerPixel, surface->format->Rmask,
                                   surface->format->Gmask, surface->format->Bmask,
                                   surface->format->Amask);

            /* Share the palette, if any */
            if (surface->format->palette) {
                SDL_SetSurfacePalette(tmp, surface->format->palette);
            }

            SDL_FillRect(tmp, NULL, surface->map->info.colorkey);

            tmp->map->info.flags &= ~SDL_COPY_COLORKEY;

            /* Convertion of the colorkey */
            tmp2 = SDL_ConvertSurface(tmp, format, 0);

            /* Get the converted colorkey */
            SDL_memcpy(&converted_colorkey, tmp2->pixels, tmp2->format->BytesPerPixel);

            SDL_FreeSurface(tmp);
            SDL_FreeSurface(tmp2);

            /* Set the converted colorkey on the new surface */
            SDL_SetColorKey(convert, 1, converted_colorkey);

            /* This is needed when converting for 3D texture upload */
            if (convert_colorkey) {
                SDL_ConvertColorkeyToAlpha(convert, SDL_TRUE);
            }
        }
    }
    SDL_SetClipRect(convert, &surface->clip_rect);

    /* Enable alpha blending by default if the new surface has an
     * alpha channel or alpha modulation */
    if ((surface->format->Amask && format->Amask) ||
        (palette_has_alpha && format->Amask) ||
        (copy_flags & SDL_COPY_MODULATE_ALPHA)) {
        SDL_SetSurfaceBlendMode(convert, SDL_BLENDMODE_BLEND);
    }
    if ((copy_flags & SDL_COPY_RLE_DESIRED) || (flags & SDL_RLEACCEL)) {
        SDL_SetSurfaceRLE(convert, SDL_RLEACCEL);
    }

    /* We're ready to go! */
    return (convert);
}

SDL_Surface *
SDL_ConvertSurfaceFormat(SDL_Surface * surface, Uint32 pixel_format,
                         Uint32 flags)
{
    SDL_PixelFormat *fmt;
    SDL_Surface *convert = NULL;

    fmt = SDL_AllocFormat(pixel_format);
    if (fmt) {
        convert = SDL_ConvertSurface(surface, fmt, flags);
        SDL_FreeFormat(fmt);
    }
    return convert;
}

/*
 * Create a surface on the stack for quick blit operations
 */
static SDL_INLINE SDL_bool
SDL_CreateSurfaceOnStack(int width, int height, Uint32 pixel_format,
                         void * pixels, int pitch, SDL_Surface * surface,
                         SDL_PixelFormat * format, SDL_BlitMap * blitmap)
{
    if (SDL_ISPIXELFORMAT_INDEXED(pixel_format)) {
        SDL_SetError("Indexed pixel formats not supported");
        return SDL_FALSE;
    }
    if (SDL_InitFormat(format, pixel_format) < 0) {
        return SDL_FALSE;
    }

    SDL_zerop(surface);
    surface->flags = SDL_PREALLOC;
    surface->format = format;
    surface->pixels = pixels;
    surface->w = width;
    surface->h = height;
    surface->pitch = pitch;
    /* We don't actually need to set up the clip rect for our purposes */
    /* SDL_SetClipRect(surface, NULL); */

    /* Allocate an empty mapping */
    SDL_zerop(blitmap);
    blitmap->info.r = 0xFF;
    blitmap->info.g = 0xFF;
    blitmap->info.b = 0xFF;
    blitmap->info.a = 0xFF;
    surface->map = blitmap;

    /* The surface is ready to go */
    surface->refcount = 1;
    return SDL_TRUE;
}

/*
 * Copy a block of pixels of one format to another format
 */
int SDL_ConvertPixels(int width, int height,
                      Uint32 src_format, const void * src, int src_pitch,
                      Uint32 dst_format, void * dst, int dst_pitch)
{
    SDL_Surface src_surface, dst_surface;
    SDL_PixelFormat src_fmt, dst_fmt;
    SDL_BlitMap src_blitmap, dst_blitmap;
    SDL_Rect rect;
    void *nonconst_src = (void *) src;
    int ret;

    if (!src) {
        return SDL_InvalidParamError("src");
    }
    if (!src_pitch) {
        return SDL_InvalidParamError("src_pitch");
    }
    if (!dst) {
        return SDL_InvalidParamError("dst");
    }
    if (!dst_pitch) {
        return SDL_InvalidParamError("dst_pitch");
    }

#if SDL_HAVE_YUV
    if (SDL_ISPIXELFORMAT_FOURCC(src_format) && SDL_ISPIXELFORMAT_FOURCC(dst_format)) {
        return SDL_ConvertPixels_YUV_to_YUV(width, height, src_format, src, src_pitch, dst_format, dst, dst_pitch);
    } else if (SDL_ISPIXELFORMAT_FOURCC(src_format)) {
        return SDL_ConvertPixels_YUV_to_RGB(width, height, src_format, src, src_pitch, dst_format, dst, dst_pitch);
    } else if (SDL_ISPIXELFORMAT_FOURCC(dst_format)) {
        return SDL_ConvertPixels_RGB_to_YUV(width, height, src_format, src, src_pitch, dst_format, dst, dst_pitch);
    }
#else
    if (SDL_ISPIXELFORMAT_FOURCC(src_format) || SDL_ISPIXELFORMAT_FOURCC(dst_format)) {
        SDL_SetError("SDL not built with YUV support");
        return -1;
    }
#endif

    /* Fast path for same format copy */
    if (src_format == dst_format) {
        int i;
        const int bpp = SDL_BYTESPERPIXEL(src_format);
        width *= bpp;
        for (i = height; i--;) {
            SDL_memcpy(dst, src, width);
            src = (const Uint8*)src + src_pitch;
            dst = (Uint8*)dst + dst_pitch;
        }
        return 0;
    }

    if (!SDL_CreateSurfaceOnStack(width, height, src_format, nonconst_src,
                                  src_pitch,
                                  &src_surface, &src_fmt, &src_blitmap)) {
        return -1;
    }
    if (!SDL_CreateSurfaceOnStack(width, height, dst_format, dst, dst_pitch,
                                  &dst_surface, &dst_fmt, &dst_blitmap)) {
        return -1;
    }

    /* Set up the rect and go! */
    rect.x = 0;
    rect.y = 0;
    rect.w = width;
    rect.h = height;
    ret = SDL_LowerBlit(&src_surface, &rect, &dst_surface, &rect);

    /* Free blitmap reference, after blitting between stack'ed surfaces */
    SDL_InvalidateMap(src_surface.map);

    return ret;
}

/*
 * Premultiply the alpha on a block of pixels
 *
 * This is currently only implemented for SDL_PIXELFORMAT_ARGB8888
 *
 * Here are some ideas for optimization:
 * https://github.com/Wizermil/premultiply_alpha/tree/master/premultiply_alpha
 * https://developer.arm.com/documentation/101964/0201/Pre-multiplied-alpha-channel-data
 */
int SDL_PremultiplyAlpha(int width, int height,
                         Uint32 src_format, const void * src, int src_pitch,
                         Uint32 dst_format, void * dst, int dst_pitch)
{
    int c;
    Uint32 srcpixel;
    Uint32 srcR, srcG, srcB, srcA;
    Uint32 dstpixel;
    Uint32 dstR, dstG, dstB, dstA;

    if (!src) {
        return SDL_InvalidParamError("src");
    }
    if (!src_pitch) {
        return SDL_InvalidParamError("src_pitch");
    }
    if (!dst) {
        return SDL_InvalidParamError("dst");
    }
    if (!dst_pitch) {
        return SDL_InvalidParamError("dst_pitch");
    }
    if (src_format != SDL_PIXELFORMAT_ARGB8888) {
        return SDL_InvalidParamError("src_format");
    }
    if (dst_format != SDL_PIXELFORMAT_ARGB8888) {
        return SDL_InvalidParamError("dst_format");
    }

    while (height--) {
        const Uint32 *src_px = (const Uint32 *)src;
        Uint32 *dst_px = (Uint32 *)dst;
        for (c = width; c; --c) {
            /* Component bytes extraction. */
            srcpixel = *src_px++;
            RGBA_FROM_ARGB8888(srcpixel, srcR, srcG, srcB, srcA);

            /* Alpha pre-multiplication of each component. */
            dstA = srcA;
            dstR = (srcA * srcR) / 255;
            dstG = (srcA * srcG) / 255;
            dstB = (srcA * srcB) / 255;

            /* ARGB8888 pixel recomposition. */
            ARGB8888_FROM_RGBA(dstpixel, dstR, dstG, dstB, dstA);
            *dst_px++ = dstpixel;
        }
        src = (const Uint8 *)src + src_pitch;
        dst = (Uint8 *)dst + dst_pitch;
    }
    return 0;
}

/*
 * Free a surface created by the above function.
 */
void
SDL_FreeSurface(SDL_Surface * surface)
{
    if (surface == NULL) {
        return;
    }
    if (surface->flags & SDL_DONTFREE) {
        return;
    }
    SDL_InvalidateMap(surface->map);

    SDL_InvalidateAllBlitMap(surface);

    if (--surface->refcount > 0) {
        return;
    }
    while (surface->locked > 0) {
        SDL_UnlockSurface(surface);
    }
#if SDL_HAVE_RLE
    if (surface->flags & SDL_RLEACCEL) {
        SDL_UnRLESurface(surface, 0);
    }
#endif
    if (surface->format) {
        SDL_SetSurfacePalette(surface, NULL);
        SDL_FreeFormat(surface->format);
        surface->format = NULL;
    }
    if (surface->flags & SDL_PREALLOC) {
        /* Don't free */
    } else if (surface->flags & SDL_SIMD_ALIGNED) {
        /* Free aligned */
        SDL_SIMDFree(surface->pixels);
    } else {
        /* Normal */
        SDL_free(surface->pixels);
    }
    if (surface->map) {
        SDL_FreeBlitMap(surface->map);
    }
    SDL_free(surface);
}

/* vi: set ts=4 sw=4 expandtab: */