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SDL/src/video/SDL_stb.c

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/*
Simple DirectMedia Layer
Copyright (C) 1997-2025 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_stb_c.h"
#include "SDL_surface_c.h"
// We currently only support JPEG, but we could add other image formats if we wanted
#ifdef SDL_HAVE_STB
#define malloc SDL_malloc
#define realloc SDL_realloc
#define free SDL_free
#undef memcpy
#define memcpy SDL_memcpy
#undef memset
#define memset SDL_memset
#undef strcmp
#define strcmp SDL_strcmp
#undef strncmp
#define strncmp SDL_strncmp
#define strtol SDL_strtol
#define abs SDL_abs
#define pow SDL_pow
#define ldexp SDL_scalbn
#define STB_IMAGE_STATIC
#define STBI_NO_THREAD_LOCALS
#define STBI_FAILURE_USERMSG
#if defined(SDL_NEON_INTRINSICS)
#define STBI_NEON
#endif
#define STBI_ONLY_PNG
#define STBI_ONLY_JPEG
#define STBI_NO_GIF
#define STBI_NO_HDR
#define STBI_NO_LINEAR
#define STBI_NO_STDIO
#define STBI_ASSERT SDL_assert
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#undef memcpy
#define STB_IMAGE_WRITE_IMPLEMENTATION
#define STB_IMAGE_WRITE_STATIC
#define STBI_WRITE_NO_STDIO
#define STBIW_ASSERT SDL_assert
#include "stb_image_write.h"
#undef memset
#endif
#ifdef SDL_HAVE_STB
static bool SDL_ConvertPixels_MJPG_to_NV12(int width, int height, const void *src, int src_pitch, void *dst, int dst_pitch)
{
int w = 0, h = 0, format = 0;
stbi__context s;
stbi__start_mem(&s, src, src_pitch);
stbi__result_info ri;
SDL_zero(ri);
ri.bits_per_channel = 8;
ri.channel_order = STBI_ORDER_RGB;
ri.num_channels = 0;
stbi__nv12 nv12;
nv12.w = width;
nv12.h = height;
nv12.pitch = dst_pitch;
nv12.y = (stbi_uc *)dst;
nv12.uv = nv12.y + (nv12.h * nv12.pitch);
void *pixels = stbi__jpeg_load(&s, &w, &h, &format, 4, &nv12, &ri);
if (!pixels) {
return false;
}
return true;
}
#endif // SDL_HAVE_STB
bool SDL_ConvertPixels_STB(int width, int height,
SDL_PixelFormat src_format, SDL_Colorspace src_colorspace, SDL_PropertiesID src_properties, const void *src, int src_pitch,
SDL_PixelFormat dst_format, SDL_Colorspace dst_colorspace, SDL_PropertiesID dst_properties, void *dst, int dst_pitch)
{
#ifdef SDL_HAVE_STB
if (src_format == SDL_PIXELFORMAT_MJPG && dst_format == SDL_PIXELFORMAT_NV12) {
return SDL_ConvertPixels_MJPG_to_NV12(width, height, src, src_pitch, dst, dst_pitch);
}
bool result;
int w = 0, h = 0, format = 0;
int len = (src_format == SDL_PIXELFORMAT_MJPG) ? src_pitch : (height * src_pitch);
void *pixels = stbi_load_from_memory(src, len, &w, &h, &format, 4);
if (!pixels) {
return false;
}
if (w == width && h == height) {
result = SDL_ConvertPixelsAndColorspace(w, h, SDL_PIXELFORMAT_RGBA32, SDL_COLORSPACE_SRGB, 0, pixels, width * 4, dst_format, dst_colorspace, dst_properties, dst, dst_pitch);
} else {
result = SDL_SetError("Expected image size %dx%d, actual size %dx%d", width, height, w, h);
}
stbi_image_free(pixels);
return result;
#else
return SDL_SetError("SDL not built with STB image support");
#endif
}
#ifdef SDL_HAVE_STB
static int IMG_LoadSTB_IO_read(void *user, char *data, int size)
{
size_t amount = SDL_ReadIO((SDL_IOStream*)user, data, size);
return (int)amount;
}
static void IMG_LoadSTB_IO_skip(void *user, int n)
{
SDL_SeekIO((SDL_IOStream*)user, n, SDL_IO_SEEK_CUR);
}
static int IMG_LoadSTB_IO_eof(void *user)
{
SDL_IOStream *src = (SDL_IOStream*)user;
return SDL_GetIOStatus(src) == SDL_IO_STATUS_EOF;
}
static SDL_Surface *SDL_LoadSTB_IO(SDL_IOStream *src)
{
Sint64 start;
Uint8 magic[26];
int w, h, format;
stbi_uc *pixels;
stbi_io_callbacks rw_callbacks;
SDL_Surface *surface = NULL;
bool use_palette = false;
unsigned int palette_colors[256];
// src has already been validated
start = SDL_TellIO(src);
if (SDL_ReadIO(src, magic, sizeof(magic)) == sizeof(magic)) {
const Uint8 PNG_COLOR_INDEXED = 3;
if (magic[0] == 0x89 &&
magic[1] == 'P' &&
magic[2] == 'N' &&
magic[3] == 'G' &&
magic[12] == 'I' &&
magic[13] == 'H' &&
magic[14] == 'D' &&
magic[15] == 'R' &&
magic[25] == PNG_COLOR_INDEXED) {
use_palette = true;
}
}
SDL_SeekIO(src, start, SDL_IO_SEEK_SET);
/* Load the image data */
rw_callbacks.read = IMG_LoadSTB_IO_read;
rw_callbacks.skip = IMG_LoadSTB_IO_skip;
rw_callbacks.eof = IMG_LoadSTB_IO_eof;
w = h = format = 0; /* silence warning */
if (use_palette) {
/* Unused palette entries will be opaque white */
SDL_memset(palette_colors, 0xff, sizeof(palette_colors));
pixels = stbi_load_from_callbacks_with_palette(
&rw_callbacks,
src,
&w,
&h,
palette_colors,
SDL_arraysize(palette_colors)
);
} else {
pixels = stbi_load_from_callbacks(
&rw_callbacks,
src,
&w,
&h,
&format,
STBI_default
);
}
if (!pixels) {
SDL_SeekIO(src, start, SDL_IO_SEEK_SET);
return NULL;
}
if (use_palette) {
surface = SDL_CreateSurfaceFrom(
w,
h,
SDL_PIXELFORMAT_INDEX8,
pixels,
w
);
if (surface) {
bool has_colorkey = false;
int colorkey_index = -1;
bool has_alpha = false;
SDL_Palette *palette = SDL_CreateSurfacePalette(surface);
if (palette) {
int i;
Uint8 *palette_bytes = (Uint8 *)palette_colors;
for (i = 0; i < palette->ncolors; i++) {
palette->colors[i].r = *palette_bytes++;
palette->colors[i].g = *palette_bytes++;
palette->colors[i].b = *palette_bytes++;
palette->colors[i].a = *palette_bytes++;
if (palette->colors[i].a != SDL_ALPHA_OPAQUE) {
if (palette->colors[i].a == SDL_ALPHA_TRANSPARENT && !has_colorkey) {
has_colorkey = true;
colorkey_index = i;
} else {
/* Partial opacity or multiple colorkeys */
has_alpha = true;
}
}
}
}
if (has_alpha) {
SDL_SetSurfaceBlendMode(surface, SDL_BLENDMODE_BLEND);
} else if (has_colorkey) {
SDL_SetSurfaceColorKey(surface, true, colorkey_index);
}
/* FIXME: This sucks. It'd be better to allocate the surface first, then
* write directly to the pixel buffer:
* https://github.com/nothings/stb/issues/58
* -flibit
*/
surface->flags &= ~SDL_SURFACE_PREALLOCATED;
}
} else if (format == STBI_grey || format == STBI_rgb || format == STBI_rgb_alpha) {
surface = SDL_CreateSurfaceFrom(
w,
h,
(format == STBI_rgb_alpha) ? SDL_PIXELFORMAT_RGBA32 :
(format == STBI_rgb) ? SDL_PIXELFORMAT_RGB24 :
SDL_PIXELFORMAT_INDEX8,
pixels,
w * format
);
if (surface) {
/* Set a grayscale palette for gray images */
if (surface->format == SDL_PIXELFORMAT_INDEX8) {
SDL_Palette *palette = SDL_CreateSurfacePalette(surface);
if (palette) {
int i;
for (i = 0; i < palette->ncolors; i++) {
palette->colors[i].r = (Uint8)i;
palette->colors[i].g = (Uint8)i;
palette->colors[i].b = (Uint8)i;
}
}
}
/* FIXME: This sucks. It'd be better to allocate the surface first, then
* write directly to the pixel buffer:
* https://github.com/nothings/stb/issues/58
* -flibit
*/
surface->flags &= ~SDL_SURFACE_PREALLOCATED;
}
} else if (format == STBI_grey_alpha) {
surface = SDL_CreateSurface(w, h, SDL_PIXELFORMAT_RGBA32);
if (surface) {
Uint8 *src_ptr = pixels;
Uint8 *dst = (Uint8 *)surface->pixels;
int skip = surface->pitch - (surface->w * 4);
int row, col;
for (row = 0; row < h; ++row) {
for (col = 0; col < w; ++col) {
Uint8 c = *src_ptr++;
Uint8 a = *src_ptr++;
*dst++ = c;
*dst++ = c;
*dst++ = c;
*dst++ = a;
}
dst += skip;
}
stbi_image_free(pixels);
}
} else {
SDL_SetError("Unknown image format: %d", format);
}
if (!surface) {
/* The error message should already be set */
stbi_image_free(pixels); /* calls SDL_free() */
SDL_SeekIO(src, start, SDL_IO_SEEK_SET);
}
return surface;
}
#endif // SDL_HAVE_STB
SDL_Surface *SDL_LoadPNG_IO(SDL_IOStream *src, bool closeio)
{
Sint64 start;
Uint8 magic[4];
bool is_PNG;
SDL_Surface *surface = NULL;
CHECK_PARAM(!src) {
SDL_InvalidParamError("src");
goto done;
}
start = SDL_TellIO(src);
is_PNG = false;
if (SDL_ReadIO(src, magic, sizeof(magic)) == sizeof(magic)) {
if (magic[0] == 0x89 &&
magic[1] == 'P' &&
magic[2] == 'N' &&
magic[3] == 'G') {
is_PNG = true;
}
}
SDL_SeekIO(src, start, SDL_IO_SEEK_SET);
if (!is_PNG) {
SDL_SetError("File is not a PNG file");
goto done;
}
#ifdef SDL_HAVE_STB
surface = SDL_LoadSTB_IO(src);
#else
SDL_SetError("SDL not built with STB image support");
#endif // SDL_HAVE_STB
done:
if (src && closeio) {
SDL_CloseIO(src);
}
return surface;
}
SDL_Surface *SDL_LoadPNG(const char *file)
{
SDL_IOStream *stream = SDL_IOFromFile(file, "rb");
if (!stream) {
return NULL;
}
return SDL_LoadPNG_IO(stream, true);
}
#ifdef SDL_HAVE_STB
static void SDL_STBWriteFunc(void *context, void *data, int size)
{
SDL_WriteIO(context, data, size);
}
#endif
bool SDL_SavePNG_IO(SDL_Surface *surface, SDL_IOStream *dst, bool closeio)
{
bool retval = false;
// Make sure we have somewhere to save
CHECK_PARAM(!SDL_SurfaceValid(surface)) {
SDL_InvalidParamError("surface");
goto done;
}
CHECK_PARAM(!dst) {
SDL_InvalidParamError("dst");
goto done;
}
#ifdef SDL_HAVE_STB
bool free_surface = false;
if (surface->format != SDL_PIXELFORMAT_RGBA32) {
surface = SDL_ConvertSurface(surface, SDL_PIXELFORMAT_RGBA32);
if (!surface) {
goto done;
}
free_surface = true;
}
if (stbi_write_png_to_func(SDL_STBWriteFunc, dst, surface->w, surface->h, 4, surface->pixels, surface->pitch)) {
retval = true;
} else {
SDL_SetError("Failed to write PNG");
}
if (free_surface) {
SDL_DestroySurface(surface);
}
#else
SDL_SetError("SDL not built with STB image support");
#endif
done:
if (dst && closeio) {
retval &= SDL_CloseIO(dst);
}
return retval;
}
bool SDL_SavePNG(SDL_Surface *surface, const char *file)
{
#ifdef SDL_HAVE_STB
SDL_IOStream *stream = SDL_IOFromFile(file, "wb");
if (!stream) {
return false;
}
return SDL_SavePNG_IO(surface, stream, true);
#else
return SDL_SetError("SDL not built with STB image support");
#endif
}
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