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Fixed bug 3359 - Software renderer does incorrect blending with SDL_RenderCopyEx

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Simon Hug

The software renderer produces incorrect results when blending textures at an angle with certain blend modes. It seems that there were some edge cases that weren't considered when the SW_RenderCopyEx function was last changed. Or another bug possibly covered up the problem. (More on that in another bug report.)

Most of the issues come from the fact that the rotating function sets a black colorkey. This is problematic because black is most likely appearing in the surface and the final blit will ignore these pixels. Unless a colorkey is already set (the software renderer currently never sets one), it's very hard to find a free color. Of course it could scan over the whole image until one is found, but that seems inefficient.

The following blend modes have issues when drawn at an angle.

NONE: The black pixels get ignored, making them essentially transparent. This breaks the 'dstRGBA = srcRGBA' definition of the NONE blend mode.

MOD: Again, the black pixels get ignored. This also breaks the 'dstRGB = dstRGB * srcRGB' definition of the MOD blend mode, where black pixels would make the destination black as well. A white colorkey will work though, with some preparations.

BLEND: There are some issues when blending a texture with a translucent RGBA target texture. I - uh - forgot what the problem here exactly is.

This patch fixes the issues mentioned above. It mainly changes the code so it tries to do things without the colorkey and removes the automatic format conversion part from the SDLgfx_rotateSurface function. Getting the format right is something the caller has to do now and the required code has been added to the SW_RenderCopyEx function.

There's a small change to the SW_CreateTexture function. RLE encoding a surface with an alpha mask can be a lossy process. Depending on how the user uses the RGBA channels, this may be undesired. The change that surfaces with an alpha mask don't get encoded makes the software renderer consistent with the other renderers.

The SW_RenderCopyEx function now does these steps: Lock the source surface if necessary. Create a clone of the source by using the pixel buffer directly. Check the format and set a flag if a conversion is necessary. Check if scaling or cropping is necessary and set the flag for that as well. Check if color and alpha modulation has to be done before the rotate. Check if the source is an opaque surface. If not, it creates a mask surface that is necessary for the NONE blend mode. If any of the flags were set, a new surface is created and the source will be converted, scaled, cropped, and modulated. The rest of the function stays somewhat the same. The mask also needs to be rotated of course and then there is the NONE blend mode...

It's surprisingly hard to get the pixel from a rotated surface to the destination buffer without affecting the pixel outside the rotated area. I found a way to do this with three blits which is pretty hard on the performance. Perhaps someone has an idea how to do this faster?

As mentioned above, the SDLgfx_rotateSurface now only takes 8-bit paletted or 32-bit with alpha mask surfaces. It additionally sets the new surfaces up for the MOD blend mode.

I shortly tested the 8-bit path of SDLgfx_rotateSurface and it seemed to work so far. This path is not used by the software renderer anyway.
This commit is contained in:
Sam Lantinga 2016-11-15 01:12:27 -08:00
parent f4d3ca201b
commit 4d4831c2ca
2 changed files with 231 additions and 179 deletions
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198
src/render/software/SDL_rotate.c
View file

@ -142,7 +142,7 @@ SDLgfx_rotozoomSurfaceSizeTrig(int width, int height, double angle,
cy = *cangle * y;
sx = *sangle * x;
sy = *sangle * y;
dstwidthhalf = MAX((int)
SDL_ceil(MAX(MAX(MAX(SDL_fabs(cx + sy), SDL_fabs(cx - sy)), SDL_fabs(-cx + sy)), SDL_fabs(-cx - sy))), 1);
dstheighthalf = MAX((int)
@ -390,10 +390,14 @@ transformSurfaceY(SDL_Surface * src, SDL_Surface * dst, int cx, int cy, int isin
/* !
\brief Rotates and zooms a surface with different horizontal and vertival scaling factors and optional anti-aliasing.
Rotates a 32bit or 8bit 'src' surface to newly created 'dst' surface.
Rotates a 32-bit or 8-bit 'src' surface to newly created 'dst' surface.
'angle' is the rotation in degrees, 'centerx' and 'centery' the rotation center. If 'smooth' is set
then the destination 32bit surface is anti-aliased. If the surface is not 8bit
or 32bit RGBA/ABGR it will be converted into a 32bit RGBA format on the fly.
then the destination 32-bit surface is anti-aliased. 8-bit surfaces must have a colorkey. 32-bit
surfaces must have a 8888 layout with red, green, blue and alpha masks (any ordering goes).
The blend mode of the 'src' surface has some effects on generation of the 'dst' surface: The NONE
mode will set the BLEND mode on the 'dst' surface. The MOD mode either generates a white 'dst'
surface and sets the colorkey or fills the it with the colorkey before copying the pixels.
When using the NONE and MOD modes, color and alpha modulation must be applied before using this function.
\param src The surface to rotozoom.
\param angle The angle to rotate in degrees.
@ -413,69 +417,47 @@ or 32bit RGBA/ABGR it will be converted into a 32bit RGBA format on the fly.
SDL_Surface *
SDLgfx_rotateSurface(SDL_Surface * src, double angle, int centerx, int centery, int smooth, int flipx, int flipy, int dstwidth, int dstheight, double cangle, double sangle)
{
SDL_Surface *rz_src;
SDL_Surface *rz_dst;
int is32bit, angle90;
int is8bit, angle90;
int i;
Uint8 r = 0, g = 0, b = 0, a = 0;
SDL_BlendMode blendmode;
Uint32 colorkey = 0;
int colorKeyAvailable = 0;
int colorKeyAvailable = SDL_FALSE;
double sangleinv, cangleinv;
/*
* Sanity check
*/
/* Sanity check */
if (src == NULL)
return (NULL);
return NULL;
if (src->flags & SDL_TRUE/* SDL_SRCCOLORKEY */) {
colorkey = _colorkey(src);
SDL_GetRGBA(colorkey, src->format, &r, &g, &b, &a);
colorKeyAvailable = 1;
if (SDL_GetColorKey(src, &colorkey) == 0) {
colorKeyAvailable = SDL_TRUE;
}
/*
* Determine if source surface is 32bit or 8bit
*/
is32bit = (src->format->BitsPerPixel == 32);
if ((is32bit) || (src->format->BitsPerPixel == 8)) {
/*
* Use source surface 'as is'
*/
rz_src = src;
} else {
rz_src = SDL_ConvertSurfaceFormat(src, SDL_PIXELFORMAT_ARGB32, src->flags);
if (rz_src == NULL) {
return NULL;
}
is32bit = 1;
}
/* This function requires a 32-bit surface or 8-bit surface with a colorkey */
is8bit = src->format->BitsPerPixel == 8 && colorKeyAvailable;
if (!(is8bit || (src->format->BitsPerPixel == 32 && src->format->Amask)))
return NULL;
/* Determine target size */
/* _rotozoomSurfaceSizeTrig(rz_src->w, rz_src->h, angle, &dstwidth, &dstheight, &cangle, &sangle); */
/*
* Calculate target factors from sin/cos and zoom
*/
/* Calculate target factors from sin/cos and zoom */
sangleinv = sangle*65536.0;
cangleinv = cangle*65536.0;
/*
* Alloc space to completely contain the rotated surface
*/
if (is32bit) {
/*
* Target surface is 32bit with source RGBA/ABGR ordering
*/
rz_dst =
SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight + GUARD_ROWS, 32,
rz_src->format->Rmask, rz_src->format->Gmask,
rz_src->format->Bmask, rz_src->format->Amask);
/* Alloc space to completely contain the rotated surface */
rz_dst = NULL;
if (is8bit) {
/* Target surface is 8 bit */
rz_dst = SDL_CreateRGBSurface(0, dstwidth, dstheight + GUARD_ROWS, 8, 0, 0, 0, 0);
if (rz_dst != NULL) {
for (i = 0; i < src->format->palette->ncolors; i++) {
rz_dst->format->palette->colors[i] = src->format->palette->colors[i];
}
rz_dst->format->palette->ncolors = src->format->palette->ncolors;
}
} else {
/*
* Target surface is 8bit
*/
rz_dst = SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight + GUARD_ROWS, 8, 0, 0, 0, 0);
/* Target surface is 32 bit with source RGBA ordering */
rz_dst = SDL_CreateRGBSurface(0, dstwidth, dstheight + GUARD_ROWS, 32,
src->format->Rmask, src->format->Gmask,
src->format->Bmask, src->format->Amask);
}
/* Check target */
@ -485,17 +467,32 @@ SDLgfx_rotateSurface(SDL_Surface * src, double angle, int centerx, int centery,
/* Adjust for guard rows */
rz_dst->h = dstheight;
if (colorKeyAvailable == 1) {
colorkey = SDL_MapRGBA(rz_dst->format, r, g, b, a);
SDL_GetSurfaceBlendMode(src, &blendmode);
if (colorKeyAvailable == SDL_TRUE) {
/* If available, the colorkey will be used to discard the pixels that are outside of the rotated area. */
SDL_SetColorKey(rz_dst, SDL_TRUE, colorkey);
SDL_FillRect(rz_dst, NULL, colorkey);
} else if (blendmode == SDL_BLENDMODE_NONE) {
blendmode = SDL_BLENDMODE_BLEND;
} else if (blendmode == SDL_BLENDMODE_MOD) {
/* Without a colorkey, the target texture has to be white for the MOD blend mode so
* that the pixels outside the rotated area don't affect the destination surface.
*/
colorkey = SDL_MapRGBA(rz_dst->format, 255, 255, 255, 0);
SDL_FillRect(rz_dst, NULL, colorkey);
/* Setting a white colorkey for the destination surface makes the final blit discard
* all pixels outside of the rotated area. This doesn't interfere with anything because
* white pixels are already a no-op and the MOD blend mode does not interact with alpha.
*/
SDL_SetColorKey(rz_dst, SDL_TRUE, colorkey);
}
/*
* Lock source surface
*/
if (SDL_MUSTLOCK(rz_src)) {
SDL_LockSurface(rz_src);
SDL_SetSurfaceBlendMode(rz_dst, blendmode);
/* Lock source surface */
if (SDL_MUSTLOCK(src)) {
SDL_LockSurface(src);
}
/* check if the rotation is a multiple of 90 degrees so we can take a fast path and also somewhat reduce
@ -510,74 +507,29 @@ SDLgfx_rotateSurface(SDL_Surface * src, double angle, int centerx, int centery,
angle90 = -1;
}
/*
* Check which kind of surface we have
*/
if (is32bit) {
/*
* Call the 32bit transformation routine to do the rotation (using alpha)
*/
if (angle90 >= 0) {
transformSurfaceRGBA90(rz_src, rz_dst, angle90, flipx, flipy);
} else {
_transformSurfaceRGBA(rz_src, rz_dst, centerx, centery, (int) (sangleinv), (int) (cangleinv), flipx, flipy, smooth);
}
/*
* Turn on source-alpha support
*/
/* SDL_SetAlpha(rz_dst, SDL_SRCALPHA, 255); */
} else {
/*
* Copy palette and colorkey info
*/
for (i = 0; i < rz_src->format->palette->ncolors; i++) {
rz_dst->format->palette->colors[i] = rz_src->format->palette->colors[i];
}
rz_dst->format->palette->ncolors = rz_src->format->palette->ncolors;
/*
* Call the 8bit transformation routine to do the rotation
*/
if (is8bit) {
/* Call the 8-bit transformation routine to do the rotation */
if(angle90 >= 0) {
transformSurfaceY90(rz_src, rz_dst, angle90, flipx, flipy);
transformSurfaceY90(src, rz_dst, angle90, flipx, flipy);
} else {
transformSurfaceY(rz_src, rz_dst, centerx, centery, (int)(sangleinv), (int)(cangleinv), flipx, flipy);
transformSurfaceY(src, rz_dst, centerx, centery, (int)sangleinv, (int)cangleinv,
flipx, flipy);
}
} else {
/* Call the 32-bit transformation routine to do the rotation */
if (angle90 >= 0) {
transformSurfaceRGBA90(src, rz_dst, angle90, flipx, flipy);
} else {
_transformSurfaceRGBA(src, rz_dst, centerx, centery, (int)sangleinv, (int)cangleinv,
flipx, flipy, smooth);
}
}
if (colorKeyAvailable == 1) {
SDL_SetColorKey(rz_dst, /* SDL_SRCCOLORKEY */ SDL_TRUE | SDL_RLEACCEL, colorkey);
} else {
SDL_SetColorKey(rz_dst, SDL_FALSE, 0);
/* Unlock source surface */
if (SDL_MUSTLOCK(src)) {
SDL_UnlockSurface(src);
}
/* copy alpha mod, color mod, and blend mode */
{
SDL_BlendMode blendMode;
Uint8 alphaMod, cr, cg, cb;
SDL_GetSurfaceAlphaMod(src, &alphaMod);
SDL_GetSurfaceBlendMode(src, &blendMode);
SDL_GetSurfaceColorMod(src, &cr, &cg, &cb);
SDL_SetSurfaceAlphaMod(rz_dst, alphaMod);
SDL_SetSurfaceBlendMode(rz_dst, blendMode);
SDL_SetSurfaceColorMod(rz_dst, cr, cg, cb);
}
/*
* Unlock source surface
*/
if (SDL_MUSTLOCK(rz_src)) {
SDL_UnlockSurface(rz_src);
}
/*
* Cleanup temp surface
*/
if (rz_src != src) {
SDL_FreeSurface(rz_src);
}
/*
* Return destination surface
*/
return (rz_dst);
/* Return rotated surface */
return rz_dst;
}