Offscreen rendering to pixmap EGLSurface is odd
Submitted by Rinat
Assigned to mes..@..op.org
Description
When I render to a EGLSurface bound to an offscreen pixmap, then copy pixmap content to a window using XCopyArea, behaviour is odd.
Sample program below calls glClear() twice. First time it should make all pixmap red, second time — green. But when I run it on the integrated Intel adapter, it renders only red box. It seems all drawing commands after first glClear() are ignored.
My research have stopped at fb->_NumColorDrawBuffers becoming 0 in _mesa_drawbuffers(). Probably that was the immediate reason second glClear() was ignored.
#include <X11/Xlib.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <EGL/egl.h>
#include <GLES2/gl2.h>
Window wnd;
Window root_wnd;
Display *dpy;
Pixmap pixmap;
EGLDisplay egl_dpy;
EGLContext glc;
EGLSurface egl_surf;
void
handle_graphics_expose(XEvent *ev)
{
EGLBoolean ret;
ret = eglMakeCurrent(egl_dpy, egl_surf, egl_surf, glc);
if (!ret) {
printf("eglMakeCurrent failed\n");
exit(1);
}
printf("eglMakeCurrent ok\n");
glClearColor(1, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0, 1, 0, 1);
glClear(GL_COLOR_BUFFER_BIT);
glFinish();
eglWaitGL();
XCopyArea(dpy, pixmap, wnd, DefaultGC(dpy, 0),
0, 0, 400, 300, 10, 10);
XSync(dpy, False);
}
int
main(void)
{
dpy = XOpenDisplay(NULL);
root_wnd = DefaultRootWindow(dpy);
wnd = XCreateSimpleWindow(dpy, root_wnd, 0, 0, 400+20, 300+20, 0, 0, 0xa0a0f0);
printf("root_wnd = %p\n", (void *)root_wnd);
XSelectInput(dpy, wnd, ExposureMask);
XMapWindow(dpy, wnd);
XSync(dpy, False);
printf("wnd = %p\n", (void *)wnd);
egl_dpy = eglGetDisplay(dpy);
eglInitialize(egl_dpy, NULL, NULL);
int nconfigs = -1;
EGLConfig egl_config;
EGLint cfg_attrs[] = { EGL_ALPHA_SIZE, 0,
EGL_BLUE_SIZE, 8,
EGL_GREEN_SIZE, 8,
EGL_RED_SIZE, 8,
EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
EGL_SURFACE_TYPE, EGL_PIXMAP_BIT,
EGL_NONE };
eglChooseConfig(egl_dpy, cfg_attrs, &egl_config, 1, &nconfigs);
printf("nconfigs = %d\n", nconfigs);
printf("egl_config = %p\n", egl_config);
EGLint ctx_attrs[] = { EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE };
glc = eglCreateContext(egl_dpy, egl_config, EGL_NO_CONTEXT, ctx_attrs);
if (glc == EGL_NO_CONTEXT) {
printf("eglCreateContext returned EGL_NO_CONTEXT\n");
exit(1);
}
printf("context ok\n");
pixmap = XCreatePixmap(dpy, wnd, 400, 300, DefaultDepth(dpy, 0));
egl_surf = eglCreatePixmapSurface(egl_dpy, egl_config, pixmap, NULL);
if (egl_surf == EGL_NO_SURFACE) {
printf("eglCreatePixmapSurface returned EGL_NO_SURFACE\n");
exit(1);
}
printf("pixmap and surface ok\n");
// message loop
while (1) {
XEvent ev;
XNextEvent(dpy, &ev);
switch (ev.type) {
case GraphicsExpose:
case Expose:
handle_graphics_expose(&ev);
break;
default:
// do nothing
break;
}
}
eglTerminate(egl_dpy);
XFreePixmap(dpy, pixmap);
XDestroyWindow(dpy, wnd);
XCloseDisplay(dpy);
return 0;
}