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SaveDestAlpha: clamp dest rectangle correctly.
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SDL blits only care about the destination x and y, ignoring the w and h,
and then we need to clamp on top of that anyhow, in case the x and y are
out of bounds.

Reference Issue #244.
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@icculus
icculus committed Oct 24, 2022
1 parent 219c358 commit 61e247d
Showing 1 changed file with 40 additions and 33 deletions.
73 changes: 40 additions & 33 deletions src/SDL12_compat.c
View file
Expand Up @@ -6232,7 +6232,7 @@ SDL_GetVideoSurface(void)
}

static int
SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, const SDL12_Rect *dstrect12, Uint8 **retval)
SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, SDL_Rect *dstrect20, Uint8 **retval)
{
/* The 1.2 docs say this:
* RGBA->RGBA:
Expand All @@ -6245,24 +6245,15 @@ SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, const SDL12_Rect *dstr
Uint8 *dstalpha = NULL;
const SDL_bool save_dstalpha = ((src12->flags & SDL12_SRCALPHA) && dst12->format->Amask && ((src12->format->alpha != 255) || src12->format->Amask)) ? SDL_TRUE : SDL_FALSE;

if (save_dstalpha) {
if (save_dstalpha && (dstrect20->w > 0) && (dstrect20->h > 0)) {
const Uint32 amask = dst12->format->Amask;
const Uint32 ashift = dst12->format->Ashift;
const Uint16 pitch = dst12->pitch;
SDL12_Rect fullrect;
Uint8 *dptr;
int x, y, w, h;

if (!dstrect12) {
fullrect.x = 0;
fullrect.y = 0;
fullrect.w = dst12->w;
fullrect.h = dst12->h;
dstrect12 = &fullrect;
}

w = dstrect12->w;
h = dstrect12->h;
w = dstrect20->w;
h = dstrect20->h;

dstalpha = (Uint8 *) SDL20_malloc(w * h);
if (!dstalpha) {
Expand All @@ -6273,7 +6264,7 @@ SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, const SDL12_Rect *dstr

if (dst12->format->BytesPerPixel == 2) {
const Uint16 *sptr = (const Uint16 *) dst12->pixels;
sptr += ((dst12->pitch / 2) * dstrect12->y) + dstrect12->x;
sptr += ((dst12->pitch / 2) * dstrect20->y) + dstrect20->x;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
*(dptr++) = (Uint8) ((sptr[x] & amask) >> ashift);
Expand All @@ -6282,7 +6273,7 @@ SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, const SDL12_Rect *dstr
}
} else if (dst12->format->BytesPerPixel == 4) {
const Uint32 *sptr = (const Uint32 *) dst12->pixels;
sptr += ((dst12->pitch / 4) * dstrect12->y) + dstrect12->x;
sptr += ((dst12->pitch / 4) * dstrect20->y) + dstrect20->x;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
*(dptr++) = (Uint8) ((sptr[x] & amask) >> ashift);
Expand All @@ -6299,30 +6290,21 @@ SaveDestAlpha(SDL12_Surface *src12, SDL12_Surface *dst12, const SDL12_Rect *dstr
}

static void
RestoreDestAlpha(SDL12_Surface *dst12, Uint8 *dstalpha, const SDL12_Rect *dstrect12)
RestoreDestAlpha(SDL12_Surface *dst12, Uint8 *dstalpha, const SDL_Rect *dstrect20)
{
if (dstalpha) {
const Uint8 *sptr = dstalpha;
const Uint32 amask = dst12->format->Amask;
const Uint32 ashift = dst12->format->Ashift;
const Uint16 pitch = dst12->pitch;
SDL12_Rect fullrect;
int x, y, w, h;

if (!dstrect12) {
fullrect.x = 0;
fullrect.y = 0;
fullrect.w = dst12->w;
fullrect.h = dst12->h;
dstrect12 = &fullrect;
}

w = dstrect12->w;
h = dstrect12->h;
w = dstrect20->w;
h = dstrect20->h;

if (dst12->format->BytesPerPixel == 2) {
Uint16 *dptr = (Uint16 *) dst12->pixels;
dptr += ((dst12->pitch / 2) * dstrect12->y) + dstrect12->x;
dptr += ((dst12->pitch / 2) * dstrect20->y) + dstrect20->x;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
dptr[x] = (Uint16) ((dptr[x] & ~amask) | ((((Uint16) *(sptr++)) << ashift) & amask));
Expand All @@ -6331,7 +6313,7 @@ RestoreDestAlpha(SDL12_Surface *dst12, Uint8 *dstalpha, const SDL12_Rect *dstrec
}
} else if (dst12->format->BytesPerPixel == 4) {
Uint32 *dptr = (Uint32 *) dst12->pixels;
dptr += ((dst12->pitch / 4) * dstrect12->y) + dstrect12->x;
dptr += ((dst12->pitch / 4) * dstrect20->y) + dstrect20->x;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
dptr[x] = (dptr[x] & ~amask) | ((((Uint32) *(sptr++)) << ashift) & amask);
Expand All @@ -6345,18 +6327,41 @@ RestoreDestAlpha(SDL12_Surface *dst12, Uint8 *dstalpha, const SDL12_Rect *dstrec
}
}

static void
PrepBlitDestRect(SDL_Rect *dstrect20, SDL12_Surface *dst12, const SDL12_Rect *dstrect12)
{
/* dstrect12 w and h is ignored, SDL 1.2 only cares about position. */
dstrect20->w = dst12->w;
dstrect20->h = dst12->h;

if (dstrect12) {
SDL_Rect fulldstrect20;
fulldstrect20.x = fulldstrect20.y = 0;
fulldstrect20.w = dst12->w;
fulldstrect20.h = dst12->h;
dstrect20->x = dstrect12->x;
dstrect20->y = dstrect12->y;
SDL20_IntersectRect(&fulldstrect20, dstrect20, dstrect20);
} else {
dstrect20->x = 0;
dstrect20->y = 0;
}
}

DECLSPEC12 int SDLCALL
SDL_UpperBlit(SDL12_Surface *src12, SDL12_Rect *srcrect12, SDL12_Surface *dst12, SDL12_Rect *dstrect12)
{
Uint8 *dstalpha;
SDL_Rect srcrect20, dstrect20;
int retval;

PrepBlitDestRect(&dstrect20, dst12, dstrect12);

if ((src12 == NULL) || (dst12 == NULL)) {
return SDL20_SetError("SDL_UpperBlit: passed a NULL surface");
} else if ((src12->pixels == NULL) || (dst12->pixels == NULL)) {
return SDL20_SetError("SDL_UpperBlit: passed a surface with NULL pixels");
} else if (SaveDestAlpha(src12, dst12, dstrect12, &dstalpha) < 0) {
} else if (SaveDestAlpha(src12, dst12, &dstrect20, &dstalpha) < 0) {
return -1;
}

Expand All @@ -6365,7 +6370,7 @@ SDL_UpperBlit(SDL12_Surface *src12, SDL12_Rect *srcrect12, SDL12_Surface *dst12,
dst12->surface20,
dstrect12 ? Rect12to20(dstrect12, &dstrect20) : NULL);

RestoreDestAlpha(dst12, dstalpha, dstrect12);
RestoreDestAlpha(dst12, dstalpha, &dstrect20);

if (dstrect12) {
Rect20to12(&dstrect20, dstrect12);
Expand All @@ -6381,7 +6386,9 @@ SDL_LowerBlit(SDL12_Surface *src12, SDL12_Rect *srcrect12, SDL12_Surface *dst12,
SDL_Rect srcrect20, dstrect20;
int retval;

if (SaveDestAlpha(src12, dst12, dstrect12, &dstalpha) < 0) {
PrepBlitDestRect(&dstrect20, dst12, dstrect12);

if (SaveDestAlpha(src12, dst12, &dstrect20, &dstalpha) < 0) {
return -1;
}

Expand All @@ -6390,7 +6397,7 @@ SDL_LowerBlit(SDL12_Surface *src12, SDL12_Rect *srcrect12, SDL12_Surface *dst12,
dst12->surface20,
dstrect12 ? Rect12to20(dstrect12, &dstrect20) : NULL);

RestoreDestAlpha(dst12, dstalpha, dstrect12);
RestoreDestAlpha(dst12, dstalpha, &dstrect20);

if (srcrect12) {
Rect20to12(&srcrect20, srcrect12);
Expand Down

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