encounter
/
SDL
mirror of https://github.com/encounter/SDL.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Added SDL_PremultiplyAlpha() to premultiply alpha on a block of SDL_PIXELFORMAT_ARGB8888 pixels

This commit is contained in:
Sam Lantinga 2021-11-21 12:18:10 -08:00
parent 49369142bd
commit c97b721868
9 changed files with 109 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
WhatsNew.txt
View File

@ -5,6 +5,9 @@ This is a list of major changes in SDL's version history.
2.0.18:
---------------------------------------------------------------------------
General:
* Added SDL_PremultiplyAlpha() to premultiply alpha on a block of SDL_PIXELFORMAT_ARGB8888 pixels
Linux:
* Added the hint SDL_HINT_LINUX_JOYSTICK_CLASSIC to control whether /dev/input/js* or /dev/input/event* are used as joystick devices
* Added the hint SDL_HINT_JOYSTICK_DEVICE to allow the user to specify devices that will be opened in addition to the normal joystick detection

28
include/SDL_surface.h
View File

@ -705,7 +705,7 @@ extern DECLSPEC SDL_Surface *SDLCALL SDL_ConvertSurfaceFormat
* \param height the height of the block to copy, in pixels
* \param src_format an SDL_PixelFormatEnum value of the `src` pixels format
* \param src a pointer to the source pixels
* \param src_pitch the pitch of the block to copy, in bytes
* \param src_pitch the pitch of the source pixels, in bytes
* \param dst_format an SDL_PixelFormatEnum value of the `dst` pixels format
* \param dst a pointer to be filled in with new pixel data
* \param dst_pitch the pitch of the destination pixels, in bytes
@ -720,6 +720,32 @@ extern DECLSPEC int SDLCALL SDL_ConvertPixels(int width, int height,
Uint32 dst_format,
void * dst, int dst_pitch);
/**
* Premultiply the alpha on a block of pixels.
*
* This is safe to use with src == dst, but not for other overlapping areas.
*
* This function is currently only implemented for SDL_PIXELFORMAT_ARGB8888.
*
* \param width the width of the block to convert, in pixels
* \param height the height of the block to convert, in pixels
* \param src_format an SDL_PixelFormatEnum value of the `src` pixels format
* \param src a pointer to the source pixels
* \param src_pitch the pitch of the source pixels, in bytes
* \param dst_format an SDL_PixelFormatEnum value of the `dst` pixels format
* \param dst a pointer to be filled in with premultiplied pixel data
* \param dst_pitch the pitch of the destination pixels, in bytes
* \returns 0 on success or a negative error code on failure; call
* SDL_GetError() for more information.
*
* \since This function is available since SDL 2.0.18.
*/
extern DECLSPEC int SDLCALL SDL_PremultiplyAlpha(int width, int height,
Uint32 src_format,
const void * src, int src_pitch,
Uint32 dst_format,
void * dst, int dst_pitch);
/**
* Perform a fast fill of a rectangle with a specific color.
*

1
src/dynapi/SDL_dynapi_overrides.h
View File

@ -854,3 +854,4 @@
#define SDL_GameControllerHasRumble SDL_GameControllerHasRumble_REAL
#define SDL_GameControllerHasRumbleTriggers SDL_GameControllerHasRumbleTriggers_REAL
#define SDL_hid_ble_scan SDL_hid_ble_scan_REAL
#define SDL_PremultiplyAlpha SDL_PremultiplyAlpha_REAL

1
src/dynapi/SDL_dynapi_procs.h
View File

@ -923,3 +923,4 @@ SDL_DYNAPI_PROC(SDL_bool,SDL_JoystickHasRumbleTriggers,(SDL_Joystick *a),(a),ret
SDL_DYNAPI_PROC(SDL_bool,SDL_GameControllerHasRumble,(SDL_GameController *a),(a),return)
SDL_DYNAPI_PROC(SDL_bool,SDL_GameControllerHasRumbleTriggers,(SDL_GameController *a),(a),return)
SDL_DYNAPI_PROC(void,SDL_hid_ble_scan,(SDL_bool a),(a),)
SDL_DYNAPI_PROC(int,SDL_PremultiplyAlpha,(int a, int b, Uint32 c, const void *d, int e, Uint32 f, void *g, int h),(a,b,c,d,e,f,g,h),return)

29
src/video/SDL_pixels.c
View File

@ -1227,33 +1227,4 @@ SDL_CalculateGammaRamp(float gamma, Uint16 * ramp)
}
}
/* Creates a copy of an ARGB8888-format surface's pixels with premultiplied alpha */
void
SDL_PremultiplySurfaceAlphaToARGB8888(SDL_Surface *src, Uint32 *dst)
{
Uint8 A, R, G, B;
int x, y;
if (SDL_MUSTLOCK(src))
SDL_LockSurface(src);
for (y = 0; y < src->h; ++y) {
Uint32 *src_px = (Uint32*)((Uint8 *)src->pixels + (y * src->pitch));
for (x = 0; x < src->w; ++x) {
/* Component bytes extraction. */
SDL_GetRGBA(*src_px++, src->format, &R, &G, &B, &A);
/* Alpha pre-multiplication of each component. */
R = ((Uint32)A * R) / 255;
G = ((Uint32)A * G) / 255;
B = ((Uint32)A * B) / 255;
/* ARGB8888 pixel recomposition. */
*dst++ = (((Uint32)A << 24) | ((Uint32)R << 16) | ((Uint32)G << 8) | (B << 0));
}
}
if (SDL_MUSTLOCK(src))
SDL_UnlockSurface(src);
}
/* vi: set ts=4 sw=4 expandtab: */

1
src/video/SDL_pixels_c.h
View File

@ -43,7 +43,6 @@ extern void SDL_InvalidateAllBlitMap(SDL_Surface *surface);
extern void SDL_DitherColors(SDL_Color * colors, int bpp);
extern Uint8 SDL_FindColor(SDL_Palette * pal, Uint8 r, Uint8 g, Uint8 b, Uint8 a);
extern void SDL_DetectPalette(SDL_Palette *pal, SDL_bool *is_opaque, SDL_bool *has_alpha_channel);
extern void SDL_PremultiplySurfaceAlphaToARGB8888(SDL_Surface *src, Uint32 *dst);
#endif /* SDL_pixels_c_h_ */

69
src/video/SDL_surface.c
View File

@ -1381,7 +1381,12 @@ int SDL_ConvertPixels(int width, int height,
void *nonconst_src = (void *) src;
int ret;
/* Check to make sure we are blitting somewhere, so we don't crash */
if (!src) {
return SDL_InvalidParamError("src");
}
if (!src_pitch) {
return SDL_InvalidParamError("src_pitch");
}
if (!dst) {
return SDL_InvalidParamError("dst");
}
@ -1440,6 +1445,68 @@ int SDL_ConvertPixels(int width, int height,
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.
*/

4
src/video/kmsdrm/SDL_kmsdrmmouse.c
View File

@ -278,7 +278,9 @@ KMSDRM_CreateCursor(SDL_Surface * surface, int hot_x, int hot_y)
like other backends do. Also, the GBM BO pixels have to be
alpha-premultiplied, but the SDL surface we receive has
straight-alpha pixels, so we always have to convert. */
SDL_PremultiplySurfaceAlphaToARGB8888(surface, curdata->buffer);
SDL_PremultiplyAlpha(surface->w, surface->h,
surface->format->format, surface->pixels, surface->pitch,
SDL_PIXELFORMAT_ARGB8888, curdata->buffer, surface->w * 4);
cursor->driverdata = curdata;

7
src/video/wayland/SDL_waylandmouse.c
View File

@ -280,7 +280,9 @@ Wayland_CreateCursor(SDL_Surface *surface, int hot_x, int hot_y)
}
/* Wayland requires premultiplied alpha for its surfaces. */
SDL_PremultiplySurfaceAlphaToARGB8888(surface, data->shm_data);
SDL_PremultiplyAlpha(surface->w, surface->h,
surface->format->format, surface->pixels, surface->pitch,
SDL_PIXELFORMAT_ARGB8888, data->shm_data, surface->w * 4);
data->surface = wl_compositor_create_surface(wd->compositor);
wl_surface_set_user_data(data->surface, NULL);
@ -447,4 +449,7 @@ Wayland_FiniMouse(SDL_VideoData *data)
}
SDL_free(data->cursor_themes);
}
#endif /* SDL_VIDEO_DRIVER_WAYLAND */
/* vi: set ts=4 sw=4 expandtab: */