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// SPDX-License-Identifier: BSD-3-Clause
// sdl_cap.c - LD_PRELOAD capture shim: records every frame GZDoom presents
// through SDL into an append-only file, so the host can harvest the guest's
// real rendered frames without any X/driver readback path.
//
// Hooks:
// SDL_RenderPresent(SDL_Renderer*) -> SDL_RenderReadPixels(ARGB8888)
// SDL_UpdateWindowSurface(SDL_Window*) -> SDL_GetWindowSurface pixels
// Both forward to the real SDL after capturing.
//
// File layout (little endian):
// [0] 8B magic "GZCAPV01" (+ 4088 B reserved zero)
// [4096] frame records:
// 4B "GZF2" | u32 w | u32 h | u32 stride | u32 bpp
// u64 ts_ns (CLOCK_MONOTONIC) | u64 seq | stride*h bytes (top-down)
// A trailing record with seq = 0xFFFFFFFFFFFFFFFF marks clean stop.
//
// Env: GZCAP (path, default /dev/shm/gzframes.bin), GZCAP_MAXF (0=unlimited)
#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#define ARGB8888 0x16362004u
typedef struct SDL_Renderer SDL_Renderer;
typedef struct SDL_Window SDL_Window;
typedef struct SDL_Surface {
uint32_t flags;
void *format;
int w, h;
int pitch;
void *pixels;
void *userdata;
int locked;
void *list_blitmap;
struct { int x, y, w, h; } clip_rect;
void *map;
int refcount;
} SDL_Surface;
static int (*real_RenderReadPixels)(SDL_Renderer *, const void *, uint32_t,
void *, int);
static int (*real_RenderPresent)(SDL_Renderer *);
static SDL_Surface *(*real_GetWindowSurface)(SDL_Window *);
static int (*real_UpdateWindowSurface)(SDL_Window *);
static int (*real_GetRendererOutputSize)(SDL_Renderer *, int *, int *);
static void (*real_GL_SwapWindow)(SDL_Window *);
static int (*real_GL_GetDrawableSize)(SDL_Window *, int *, int *);
static void (*real_glReadPixels)(int, int, int, int, unsigned, unsigned, void *);
static FILE *cap_fp;
static unsigned long long cap_count, cap_max = 0;
static int cap_stop;
__attribute__((constructor)) static void cap_init(void)
{
const char *p = getenv("GZCAP");
const char *m = getenv("GZCAP_MAXF");
char hdr[4096];
if (m)
cap_max = strtoull(m, NULL, 0);
if (!p)
p = "/dev/shm/gzframes.bin";
real_RenderReadPixels = dlsym(RTLD_NEXT, "SDL_RenderReadPixels");
real_RenderPresent = dlsym(RTLD_NEXT, "SDL_RenderPresent");
real_GetWindowSurface = dlsym(RTLD_NEXT, "SDL_GetWindowSurface");
real_UpdateWindowSurface = dlsym(RTLD_NEXT, "SDL_UpdateWindowSurface");
real_GetRendererOutputSize =
dlsym(RTLD_NEXT, "SDL_GetRendererOutputSize");
real_GL_SwapWindow = dlsym(RTLD_NEXT, "SDL_GL_SwapWindow");
real_GL_GetDrawableSize = dlsym(RTLD_NEXT, "SDL_GL_GetDrawableSize");
real_glReadPixels = dlsym(RTLD_NEXT, "glReadPixels");
if (!real_glReadPixels)
real_glReadPixels = dlsym(RTLD_DEFAULT, "glReadPixels");
if (!real_glReadPixels) {
void *h = dlopen("libGL.so.1", RTLD_NOW | RTLD_GLOBAL);
if (!h)
h = dlopen("libGLESv2.so.2", RTLD_NOW | RTLD_GLOBAL);
if (h)
real_glReadPixels = dlsym(h, "glReadPixels");
}
fprintf(stderr, "[gzcap] init path=%s present=%p updwin=%p swap=%p read=%p gros=%p\n",
p, (void *)real_RenderPresent, (void *)real_UpdateWindowSurface,
(void *)real_GL_SwapWindow, (void *)real_RenderReadPixels,
(void *)real_GetRendererOutputSize, (void *)real_glReadPixels);
cap_fp = fopen(p, "wb");
if (!cap_fp)
return;
memset(hdr, 0, sizeof(hdr));
memcpy(hdr, "GZCAPV01", 8);
fwrite(hdr, 1, sizeof(hdr), cap_fp);
fflush(cap_fp);
}
static void cap_record(const void *px, int w, int h, int stride, int bpp)
{
struct timespec ts;
uint64_t tns, seq;
uint32_t rh[4];
char m[4] = { 'G', 'Z', 'F', '2' };
if (!cap_fp || cap_stop)
return;
if (cap_max && cap_count >= cap_max) {
uint64_t endseq = 0xFFFFFFFFFFFFFFFFull;
fwrite(m, 1, 4, cap_fp);
fwrite(&endseq, 8, 1, cap_fp);
fflush(cap_fp);
cap_stop = 1;
return;
}
clock_gettime(CLOCK_MONOTONIC, &ts);
tns = (uint64_t)ts.tv_sec * 1000000000ull + (uint64_t)ts.tv_nsec;
seq = cap_count;
rh[0] = (uint32_t)w;
rh[1] = (uint32_t)h;
rh[2] = (uint32_t)stride;
rh[3] = (uint32_t)bpp;
fwrite(m, 1, 4, cap_fp);
fwrite(rh, 4, 4, cap_fp);
fwrite(&tns, 8, 1, cap_fp);
fwrite(&seq, 8, 1, cap_fp);
fwrite(px, 1, (size_t)stride * h, cap_fp);
fflush(cap_fp);
cap_count++;
if ((cap_count & 31) == 0)
fprintf(stderr, "[gzcap] frames=%llu\n", cap_count);
}
int SDL_RenderPresent(SDL_Renderer *r)
{
static int hit;
if (!hit++)
fprintf(stderr, "[gzcap] hook RenderPresent\n");
if (cap_fp && !cap_stop && real_RenderReadPixels &&
real_GetRendererOutputSize) {
int w = 0, h = 0;
if (real_GetRendererOutputSize(r, &w, &h) == 0 && w > 0 && h > 0 &&
w <= 4096 && h <= 4096) {
static unsigned char *buf;
static size_t bufsz;
size_t need = (size_t)w * 4 * h;
if (bufsz < need) {
free(buf);
buf = malloc(need);
bufsz = buf ? need : 0;
}
if (buf && real_RenderReadPixels(r, NULL, ARGB8888, buf,
w * 4) == 0)
cap_record(buf, w, h, w * 4, 32);
}
}
if (real_RenderPresent)
return real_RenderPresent(r);
return 0;
}
int SDL_UpdateWindowSurface(SDL_Window *win)
{
static int hit;
if (!hit++)
fprintf(stderr, "[gzcap] hook UpdateWindowSurface\n");
if (cap_fp && !cap_stop && real_GetWindowSurface) {
SDL_Surface *s = real_GetWindowSurface(win);
if (s && s->pixels && s->w > 0 && s->h > 0 && s->pitch > 0 &&
s->w <= 4096 && s->h <= 4096)
cap_record(s->pixels, s->w, s->h, s->pitch, 32);
}
if (real_UpdateWindowSurface)
return real_UpdateWindowSurface(win);
return 0;
}
void SDL_GL_SwapWindow(SDL_Window *win)
{
static int hit;
static unsigned char *gbuf;
static size_t gbufsz;
if (!hit++)
fprintf(stderr, "[gzcap] hook GLSwapWindow\n");
if (cap_fp && !cap_stop && real_glReadPixels && real_GL_GetDrawableSize) {
int w = 0, h = 0;
if (real_GL_GetDrawableSize(win, &w, &h) == 0 && w > 0 && h > 0 &&
w <= 4096 && h <= 4096) {
size_t need = (size_t)w * 4 * h;
if (gbufsz < need) {
free(gbuf);
gbuf = malloc(need);
gbufsz = gbuf ? need : 0;
}
if (gbuf) {
real_glReadPixels(0, 0, w, h, 0x1908, 0x1401, gbuf);
/* GL rows are bottom-up: flip into a scratch record */
{
unsigned char *tmp = malloc(need);
int y;
if (tmp) {
for (y = 0; y < h; y++)
memcpy(tmp + (size_t)y * w * 4,
gbuf + (size_t)(h - 1 - y) * w * 4,
(size_t)w * 4);
cap_record(tmp, w, h, w * 4, 32);
free(tmp);
}
}
}
}
}
if (real_GL_SwapWindow)
real_GL_SwapWindow(win);
}
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