This was originally to avoid duplicating clipping work in Maelstrom on a 486 computer. This has been confusing for users and computers are a little faster these days, so we'll make it work the way people expect.
This more closely matches the mental model of people using SDL, and locking a surface that isn't RLE encoded doesn't cause any issues.
Fixes https://github.com/libsdl-org/SDL/issues/5594
The function can now convert between pixels of different formats, and takes a parameter to control whether the premultiplication is done in sRGB or linear space.
Also added SDL_PremultiplySurfaceAlpha(), which can premultiply the pixels of a surface in-place.
Applying these changes to external code doesn't actually improve anything, and within the context of the other Get* functions for renderers and surfaces, these stand out as outliers, so I'm going to back this change out.
Currently, all SDL_Surfaces with an indexed pixel format have an
associated SDL_Palette. This palette either consists of entirely the
colour black, or -- in the special case of 1-bit surfaces, black and
white.
When an indexed surface is blitted to another indexed surface, a 'map'
is generated from the source surface's palette to the destination
surfaces palette, in order to preserve the look of the image if the
palettes differ.
However, in most cases, applications will want to blit the raw index
values, rather than translate to make the colours as similar as
possible. For instance, the destination surface's palette may have been
modified to fade the screen out.
This change allows an indexed surface to have no associated palette. If
either the source or destination surface of a blit do not have a
palette, then the raw indices are copied (assuming both have an indexed
format).
This mimics better what happens with most other APIs (such as
DirectDraw), where most users do not set a palette on any surface but
the screen, whose palette is implicitly used for the whole application.
SDL_Surface has been simplified and internal details are no longer in the public structure.
The `format` member of SDL_Surface is now an enumerated pixel format value. You can get the full details of the pixel format by calling `SDL_GetPixelFormatDetails(surface->format)`. You can get the palette associated with the surface by calling SDL_GetSurfacePalette(). You can get the clip rectangle by calling SDL_GetSurfaceClipRect().
SDL_PixelFormat has been renamed SDL_PixelFormatDetails and just describes the pixel format, it does not include a palette for indexed pixel types.
SDL_PixelFormatEnum has been renamed SDL_PixelFormat and is used instead of Uint32 for API functions that refer to pixel format by enumerated value.
SDL_MapRGB(), SDL_MapRGBA(), SDL_GetRGB(), and SDL_GetRGBA() take an optional palette parameter for indexed color lookups.
This better reflects how HDR content is actually used, e.g. most content is in the SDR range, with specular highlights and bright details beyond the SDR range, in the HDR headroom.
This more closely matches how HDR is handled on Apple platforms, as EDR.
This also greatly simplifies application code which no longer has to think about color scaling. SDR content is rendered at the appropriate brightness automatically, and HDR content is scaled to the correct range for the display HDR headroom.
These functions historically didn't set the error indicator on overflow.
Before commit 447b508a "error: SDL's allocators now call SDL_OutOfMemory
on error", their callers would call SDL_OutOfMemory() instead, which was
assumed to be close enough in meaning: "that's a silly amount of memory
that would overflow size_t" is similar to "that's more memory than
is available". Now that responsibility for calling SDL_OutOfMemory()
has been pushed down into SDL_calloc() and friends, the functions that
check for overflows might as well set more specific errors.
Signed-off-by: Simon McVittie <smcv@collabora.com>
