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// SPDX-License-Identifier: BSD-3-Clause
// gz_pbuf.c - LD_PRELOAD shim that gives an SDL2 GL client a GLX pbuffer
// context instead of a window context. The pbuffer path is proven on the
// emulated vGPU (gl_frames); the window drawable path wedges the X server.
// Build: gcc -shared -fPIC -O2 -o gz_pbuf.so gz_pbuf.c -lGL -lX11 -ldl
#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <GL/glx.h>
#include <GL/gl.h>
typedef struct SDL_Window SDL_Window;
static GLXContext g_ctx;
static GLXPbuffer g_pb;
static Display *g_dpy;
static int g_w, g_h;
static void *g_win;
static void *(*real_GetWindowSize)(SDL_Window *, int *, int *);
static int (*real_MakeCurrent)(SDL_Window *, void *);
static void (*real_SwapWindow)(SDL_Window *);
static void resolve(void)
{
if (!real_GetWindowSize)
real_GetWindowSize = dlsym(RTLD_NEXT, "SDL_GetWindowSize");
if (!real_MakeCurrent)
real_MakeCurrent = dlsym(RTLD_NEXT, "SDL_GL_MakeCurrent");
if (!real_SwapWindow)
real_SwapWindow = dlsym(RTLD_NEXT, "SDL_GL_SwapWindow");
}
static int make_pb(int w, int h)
{
static int attribs[] = {
GLX_DRAWABLE_TYPE, GLX_PBUFFER_BIT,
GLX_RENDER_TYPE, GLX_RGBA_BIT,
GLX_RED_SIZE, 8, GLX_GREEN_SIZE, 8, GLX_BLUE_SIZE, 8,
GLX_ALPHA_SIZE, 8,
GLX_DOUBLEBUFFER, False,
None
};
GLXFBConfig *fb;
int n = 0, scr;
if (!g_dpy)
g_dpy = XOpenDisplay(NULL);
if (!g_dpy)
return 0;
scr = DefaultScreen(g_dpy);
fb = glXChooseFBConfig(g_dpy, scr, attribs, &n);
if (!fb || n < 1)
return 0;
g_pb = glXCreatePbuffer(g_dpy, fb[0], (int[]){
GLX_PBUFFER_WIDTH, w, GLX_PBUFFER_HEIGHT, h, None });
if (!g_pb)
return 0;
g_ctx = glXCreateNewContext(g_dpy, fb[0], GLX_RGBA_TYPE, NULL, True);
if (!g_ctx) {
glXDestroyPbuffer(g_dpy, g_pb);
g_pb = 0;
return 0;
}
g_w = w;
g_h = h;
return 1;
}
void *SDL_GL_CreateContext(SDL_Window *win)
{
int w = 640, h = 480;
const char *ew, *eh;
resolve();
ew = getenv("GZPBUF_W"); eh = getenv("GZPBUF_H");
if (ew && eh) { w = atoi(ew); h = atoi(eh); }
else if (real_GetWindowSize) {
real_GetWindowSize(win, &w, &h);
if (w <= 0 || h <= 0) { w = 640; h = 480; }
}
if (!make_pb(w, h)) {
fprintf(stderr, "[gzpbuf] pbuffer create failed\n");
return NULL;
}
g_win = win;
glXMakeCurrent(g_dpy, g_pb, g_ctx);
fprintf(stderr, "[gzpbuf] pbuffer %dx%d ctx=%p\n", g_w, g_h, (void *)g_ctx);
return (void *)g_ctx;
}
int SDL_GL_MakeCurrent(SDL_Window *win, void *ctx)
{
resolve();
if (ctx && g_pb) {
glXMakeCurrent(g_dpy, g_pb, g_ctx);
return 0;
}
if (real_MakeCurrent)
return real_MakeCurrent(win, ctx);
return 0;
}
void SDL_GL_SwapWindow(SDL_Window *win)
{
(void)win;
glFinish();
}
void SDL_GL_GetDrawableSize(SDL_Window *win, int *w, int *h)
{
resolve();
if (g_w > 0 && g_h > 0) {
if (w) *w = g_w;
if (h) *h = g_h;
return;
}
if (real_GetWindowSize) {
real_GetWindowSize(win, w, h);
return;
}
if (w) *w = 640;
if (h) *h = 480;
}
void SDL_GL_GetWindowSize(SDL_Window *win, int *w, int *h)
{
SDL_GL_GetDrawableSize(win, w, h);
}
void *SDL_GL_GetCurrentContext(void)
{
return (void *)g_ctx;
}
SDL_Window *SDL_GL_GetCurrentWindow(void)
{
return (SDL_Window *)g_win;
}
void SDL_GL_DeleteContext(void *ctx)
{
if (g_ctx && (!ctx || ctx == (void *)g_ctx)) {
glXMakeCurrent(g_dpy, None, NULL);
glXDestroyContext(g_dpy, g_ctx);
if (g_pb)
glXDestroyPbuffer(g_dpy, g_pb);
g_ctx = NULL;
g_pb = 0;
}
}
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